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Tsukushi is a newly identified hepatokine. Recent studies have shown that it relates to diabetes, lipid metabolism and fibrosis, but there is currently no investigation about whether Tsukushi is associated with diabetic kidney disease. Therefore, this study aimed to investigate the relationship between Tsukushi and diabetic kidney disease by characterizing Tsukushi levels in healthy subjects and type 2 diabetes with urinary albumin-creatinine ratio. Methods: Serum Tsukushi level was quantified by enzyme-linked immunosorbent assay in 167 normoalbuminuria, 80 microalbuminuria, and 31 macroalbuminuria patients with type 2 diabetes as compared with 53 healthy subjects. The correlation analysis was used to investigate the relationship between urinary albumin-creatinine ratio or Tsukushi level and other metabolic parameters. Multiple linear regression and logistic regression analysis were used to analyze the independent factors for urinary albumin-creatinine ratio and estimated glomerular filtration rate. Results: The Tsukushi level in the macroalbuminuria group was significantly higher than that in the normoalbuminuria or the microalbuminuria group. Multiple linear regression showed that the significantly independent factors for UACR included high Tsukushi quartile, systolic blood pressure, creatinine, homeostasis model assessment of insulin resistance, low 2-h post-oral glucose tolerance test c-peptide and female. Logistic regression demonstrated that the odds ratio of Tsukushi for glomerular filtration rate ≤ 90(mL/min/1.73m2) was 1.636 (95% CI 1.091– 2.452, P=0.017). Conclusion: The circulating Tsukushi increased in type 2 diabetes patients with albuminuria and was associated with urinary albumin-creatinine ratio, implying that Tsukushi may be involved in the pathogenesis of diabetic kidney disease, which deserves future studies. [ABSTRACT FROM AUTHOR]

Background and Aims: Tsukushi (TSK) is a recently identified hepatokine, and we aimed to investigate the association between systemic TSK and the severity of nonalcoholic fatty liver disease (NAFLD) in subjects with and without type 2 diabetes mellitus (DM). Methods: Three hundred ninety-three DM and 289 without DM individuals were recruited for transient elastography assessment to determine liver steatosis and fibrosis. Serum TSK was measured by ELISA. The presence of NAFLD was defined as controlled attenuation parameter ≥ 248 dB/m. Results: NAFLD was present in 276 (70.2%) and 129 (44.6%) subjects with and without DM respectively, and they had higher serum TSK levels than those without NAFLD [DM group: 91.0 ng/mL (61.7-133.8) vs 82.5 (60.9-118.5), P < .01 respectively; without DM group: 97.1 ng/mL (69.3-148.6) vs 80.8 (53.4-111.6) respectively, P < .01]. Univariate analysis showed that serum TSK significantly correlated with the degree of steatosis and fibrosis both in subjects with and without DM. On multivariable regression analysis, only liver stiffness and estimated glomerular filtration rate were significant determinants of TSK level, and the relationship was independent of diabetes and serum adiponectin. Out of 405 subjects with NAFLD, 49 had either advanced fibrosis or cirrhosis. The area under receiver operating characteristic curve of serum TSK to indicate advanced fibrosis or cirrhosis was 0.70 (95% CI .62-.77), which was significantly better than that of fibrosis-4 index, 0.64 (95% CI .55-.72), P < .05. Conclusion: Serum TSK levels were increased in subjects with NAFLD and reflected the severity of liver fibrosis. Background and Aims: Tsukushi (TSK) is a recently identified hepatokine, and we aimed to investigate the association between systemic TSK and the severity of nonalcoholic fatty liver disease (NAFLD) in subjects with and without type 2 diabetes mellitus (DM). Methods: Three hundred ninety-three DM and 289 without DM individuals were recruited for transient elastography assessment to determine liver steatosis and fibrosis. Serum TSK was measured by ELISA. The presence of NAFLD was defined as controlled attenuation parameter ≥ 248 dB/m. Results: NAFLD was present in 276 (70.2%) and 129 (44.6%) subjects with and without DM respectively, and they had higher serum TSK levels than those without NAFLD [DM group: 91.0 ng/mL (61.7-133.8) vs 82.5 (60.9-118.5), P < .01 respectively; without DM group: 97.1 ng/mL (69.3-148.6) vs 80.8 (53.4-111.6) respectively, P < .01]. Univariate analysis showed that serum TSK significantly correlated with the degree of steatosis and fibrosis both in subjects with and without DM. On multivariable regression analysis, only liver stiffness and estimated glomerular filtration rate were significant determinants of TSK level, and the relationship was independent of diabetes and serum adiponectin. Out of 405 subjects with NAFLD, 49 had either advanced fibrosis or cirrhosis. The area under receiver operating characteristic curve of serum TSK to indicate advanced fibrosis or cirrhosis was 0.70 (95% CI .62-.77), which was significantly better than that of fibrosis-4 index, 0.64 (95% CI .55-.72), P < .05. Conclusion: Serum TSK levels were increased in subjects with NAFLD and reflected the severity of liver fibrosis. [ABSTRACT FROM AUTHOR]

Purpose: Tsukushi (TSK), a novel hepatokine, has recently been pointed out to play an important role in energy homeostasis and glycolipid metabolism. However, there are no clinical studies on the association of TSK with metabolic syndrome (MetS), the typical constellation of metabolic disorders. This study was conducted to explore the relationship between TSK and MetS as well as each of its metabolic component clinically. Methods: We analyzed in this cross-sectional study serum TSK levels by ELISA in 392 participants, including 90 non-MetS and 302 MetS, to compare TSK in two groups and in different numbers of metabolic components. The odds ratios (OR) of TSK quartile in MetS and each metabolic component were computed by multivariate logistic regression analysis. Results: TSK was substantially higher in MetS than in non-MetS subjects (P < 0.001). TSK increased with the concomitant increase of the number of metabolic components (P for <0.001). Logistic regression analyses demonstrated that the OR of MetS was 2.74 for the highest versus the lowest quartile of TSK (P < 0.001) after adjusting for age, gender, smoking status, alcohol consumption and medication use. Additionally, TSK was associated with the OR of poor HDL-C and elevated fasting glucose (P < 0.05). Conclusion: Circulating TSK was higher in MetS patients and linked with MetS risk, suggesting that TSK may play a role in the genesis of MetS and be a potential therapeutic target for MetS. Future study should investigate the connection between TSK levels and MetS pathogenesis. [ABSTRACT FROM AUTHOR]

Tsukushi (TSK), a leucine-rich peptidoglycan in the extracellular compartment, mediates multiple signaling pathways that are critical for development and metabolism. TSK regulates signaling pathways that eventually control cellular communication, proliferation, and cell fate determination. Research on TSK has become more sophisticated in recent years, illustrating its involvement in the physiology and pathophysiology of neural, genetic, and metabolic diseases. In a recent study, we showed that TSK therapy reversed the pathophysiological abnormalities of the hydrocephalic (a neurological disorder) brain in mice. This review summarizes the roles of TSK in key signaling processes in the mammalian development, disorders, and evaluating its possible therapeutic and diagnostic potential. [ABSTRACT FROM AUTHOR]

Tsukushi (TSK) proteoglycan dysfunction leads to hydrocephalus, a condition defined by excessive fluid collection in the ventricles and lateral ventricular enlargement. TSK injections into the LV at birth are effective at rescuing the lateral ventricle (LV). TSK regulates the activation of the Wnt signaling to facilitate the proper expansion of the LV and maintain the fate of the neural stem cell lineage. However, the molecular mechanism by which TSK acts on neural stem/progenitor cells (NSCs) during LV development is unknown. We demonstrated that TSK is crucial for the splicing and development-associated gene regulation of GFAP-expressing subventricular zone (SVZ) NSCs. We isolated GFAP-expressing NSCs from the SVZ of wild-type (GFAPGFP/+/TSK+/+) and TSK knock-out (GFAPGFP/+/TSK−/−) mice on postnatal day 3 and compared their transcriptome and splicing profiles. TSK deficiency in NSCs resulted in genome-wide missplicing (alteration in exon usage) and transcriptional dysregulation affecting the post-transcriptional regulatory processes (including splicing, cell cycle, and circadian rhythm) and developmental signaling networks specific to the cell (including Wnt, Sonic Hedgehog, and mTOR signaling). Furthermore, TSK deficiency prominently affected the splicing of genes encoding RNA and DNA binding proteins in the nervous SVZ and non-nervous muscle tissues. These results suggested that TSK is involved in the maintenance of correct splicing and gene regulation in GFAP-expressing NSCs, thereby protecting cell fate and LV development. Hence, our study provides a critical insight on hydrocephalus development.

Tsukushi (TSK) is a member of the small leucine-rich proteoglycan family that controls developmental processes and organogenesis. TSK was also identified as a new hepatokine, which is mainly expressed in the liver, and is secreted by hepatocytes, to regulate energy and glycolipid metabolism in response to nonalcoholic fatty liver disease. However, the role of plasma TSK, especially its role in the general population, has not been fully addressed. We investigated the associations between plasma TSK concentration and several metabolic markers, including fibroblast growth factor 21 (FGF21), a hepatokine, and adiponectin, an adipokine, in 253 subjects (men/women: 114/139) with no medication in the Tanno–Sobetsu Study, which employed a population-based cohort. There was no significant sex difference in plasma TSK concentration, and the level was positively correlated with the fatty liver index (FLI) (r = 0.131, p = 0.038), levels of insulin (r = 0.295, p < 0.001) and levels of FGF21 (r = 0.290, p < 0.001), and was negatively correlated with the total cholesterol level (r = −0.124, p = 0.049). There was no significant correlation between the TSK level and body mass index, waist circumference, adiponectin, high-density lipoprotein cholesterol or total bile acids. The multivariable regression analysis showed that high levels of insulin and FGF21 and a low level of total cholesterol were independent determinants of plasma TSK concentration, after adjustment for age, sex and FLI. In conclusion, plasma TSK concentration is independently associated with high levels of insulin and FGF21, a hepatokine, and a low level of total cholesterol, but not with adiposity and adiponectin, in a general population of subjects who have not taken any medications. [ABSTRACT FROM AUTHOR]

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Tsukushi is a small, leucine-rich repeat proteoglycan that interacts with and regulates essential cellular signaling cascades in the chick retina and murine subventricular zone, hippocampus, dermal hair follicles, and the cochlea. However, its function in the vestibules of the inner ear remains unknown. Here, we investigated the function of Tsukushi in the vestibules and found that Tsukushi deficiency in mice resulted in defects in posterior semicircular canal formation in the vestibules, but did not lead to vestibular hair cell loss. Furthermore, Tsukushi accumulated in the non-prosensory and prosensory regions during the embryonic and postnatal developmental stages. The downregulation of Tsukushi altered the expression of key genes driving vestibule differentiation in the non-prosensory regions. Our results indicate that Tsukushi interacts with Wnt2b, bone morphogenetic protein 4, fibroblast growth factor 10, and netrin 1, thereby controlling semicircular canal formation. Therefore, Tsukushi may be an essential component of the molecular pathways regulating vestibular development. [ABSTRACT FROM AUTHOR]

Abstract Tsukushi (TSK)—a small, secreted, leucine-rich-repeat proteoglycan—interacts with and regulates essential cellular signaling cascades. However, its functions in the mouse inner ear are unknown. In this study, measurement of auditory brainstem responses, fluorescence microscopy, and scanning electron microscopy revealed that TSK deficiency in mice resulted in the formation of abnormal stereocilia in the inner hair cells and hearing loss but not in the loss of these cells. TSK accumulated in nonprosensory regions during early embryonic stages and in both nonprosensory and prosensory regions in late embryonic stages. In adult mice, TSK was localized in the organ of Corti, spiral ganglion cells, and the stria vascularis. Moreover, loss of TSK caused dynamic changes in the expression of key genes that drive the differentiation of the inner hair cells in prosensory regions. Finally, our results revealed that TSK interacted with Sox2 and BMP4 to control stereocilia formation in the inner hair cells. Hence, TSK appears to be an essential component of the molecular pathways that regulate inner ear development.

Tsukushi (TSK) is a member of the small leucine-rich proteoglycan family that controls developmental processes and organogenesis. TSK was also identified as a new hepatokine, which is mainly expressed in the liver, and is secreted by hepatocytes, to regulate energy and glycolipid metabolism in response to nonalcoholic fatty liver disease. However, the role of plasma TSK, especially its role in the general population, has not been fully addressed. We investigated the associations between plasma TSK concentration and several metabolic markers, including fibroblast growth factor 21 (FGF21), a hepatokine, and adiponectin, an adipokine, in 253 subjects (men/women: 114/139) with no medication in the Tanno–Sobetsu Study, which employed a population-based cohort. There was no significant sex difference in plasma TSK concentration, and the level was positively correlated with the fatty liver index (FLI) (r = 0.131, p = 0.038), levels of insulin (r = 0.295, p < 0.001) and levels of FGF21 (r = 0.290, p < 0.001), and was negatively correlated with the total cholesterol level (r = −0.124, p = 0.049). There was no significant correlation between the TSK level and body mass index, waist circumference, adiponectin, high-density lipoprotein cholesterol or total bile acids. The multivariable regression analysis showed that high levels of insulin and FGF21 and a low level of total cholesterol were independent determinants of plasma TSK concentration, after adjustment for age, sex and FLI. In conclusion, plasma TSK concentration is independently associated with high levels of insulin and FGF21, a hepatokine, and a low level of total cholesterol, but not with adiposity and adiponectin, in a general population of subjects who have not taken any medications.

Background: Tsukushi (TSK) is a secreted hepatokine recently identified as playing an important role in modulating glucose and lipid metabolism, and systemic energy homeostasis. However, information is not available regarding the association between circulating TSK and hyperthyroidism in humans.Methods: We measured serum TSK levels in 180 patients with hyperthyroidism and 82 healthy controls recruited from the clinic. Of them, 46 hyperthyroid patients received thionamide treatment for 3 months.Results: Hyperthyroid patients had higher levels of circulating TSK than healthy controls [186.67 (133.63–280.59) ng/ml vs. 97.27 (77.87–146.96) ng/ml, P < 0.001]. Subjects with higher level of serum free triiodothyronine (T3) and free thyroxine (T4) had higher levels of circulating TSK. In addition, serum TSK levels markedly declined with the improvement of thyroid function after thionamide treatment. In multivariable linear regression analyses, circulating TSK concentrations were significantly associated with serum free T3, free T4, thyroid stimulating hormone, thyrotropin receptor antibody, total cholesterol, low-density lipoprotein cholesterol (LDL-cholesterol), high-density lipoprotein cholesterol (HDL-cholesterol), and basal metabolic rate (all P < 0.01), adjusting for age, gender, smoking, and body mass index (BMI). Importantly, circulating TSK was significantly associated with risks of hyperthyroidism in multivariable logistic regression analyses, adjusting for age, gender, smoking, BMI, fasting glucose, LDL-cholesterol, and insulin resistance (HOMA-IR) [OR (95% CI), 1.012(1.005–1.019), P = 0.001].Conclusion: These findings indicate that circulating TSK concentrations are independently associated with hyperthyroidism, suggesting that circulating TSK may be a predictive factor of hyperthyroidism and can be used for therapeutic monitoring.

Background: Tsukushi (TSK) is a secreted hepatokine recently identified as playing an important role in modulating glucose and lipid metabolism, and systemic energy homeostasis. However, information is not available regarding the association between circulating TSK and hyperthyroidism in humans. Methods: We measured serum TSK levels in 180 patients with hyperthyroidism and 82 healthy controls recruited from the clinic. Of them, 46 hyperthyroid patients received thionamide treatment for 3 months. Results: Hyperthyroid patients had higher levels of circulating TSK than healthy controls [186.67 (133.63–280.59) ng/ml vs. 97.27 (77.87–146.96) ng/ml, P < 0.001]. Subjects with higher level of serum free triiodothyronine (T3) and free thyroxine (T4) had higher levels of circulating TSK. In addition, serum TSK levels markedly declined with the improvement of thyroid function after thionamide treatment. In multivariable linear regression analyses, circulating TSK concentrations were significantly associated with serum free T3, free T4, thyroid stimulating hormone, thyrotropin receptor antibody, total cholesterol, low-density lipoprotein cholesterol (LDL-cholesterol), high-density lipoprotein cholesterol (HDL-cholesterol), and basal metabolic rate (all P < 0.01), adjusting for age, gender, smoking, and body mass index (BMI). Importantly, circulating TSK was significantly associated with risks of hyperthyroidism in multivariable logistic regression analyses, adjusting for age, gender, smoking, BMI, fasting glucose, LDL-cholesterol, and insulin resistance (HOMA-IR) [OR (95% CI), 1.012(1.005–1.019), P = 0.001]. Conclusion: These findings indicate that circulating TSK concentrations are independently associated with hyperthyroidism, suggesting that circulating TSK may be a predictive factor of hyperthyroidism and can be used for therapeutic monitoring. [ABSTRACT FROM AUTHOR]

Tsukushi (TSK)—a small, secreted, leucine-rich-repeat proteoglycan—interacts with and regulates essential cellular signaling cascades. However, its functions in the mouse inner ear are unknown. In this study, measurement of auditory brainstem responses, fluorescence microscopy, and scanning electron microscopy revealed that TSK deficiency in mice resulted in the formation of abnormal stereocilia in the inner hair cells and hearing loss but not in the loss of these cells. TSK accumulated in nonprosensory regions during early embryonic stages and in both nonprosensory and prosensory regions in late embryonic stages. In adult mice, TSK was localized in the organ of Corti, spiral ganglion cells, and the stria vascularis. Moreover, loss of TSK caused dynamic changes in the expression of key genes that drive the differentiation of the inner hair cells in prosensory regions. Finally, our results revealed that TSK interacted with Sox2 and BMP4 to control stereocilia formation in the inner hair cells. Hence, TSK appears to be an essential component of the molecular pathways that regulate inner ear development. [ABSTRACT FROM AUTHOR]

Introduction: Endochondral ossification is one of a key process for bone maturation. Tsukushi (TSK) is a novel member of the secreted small leucine-rich repeat proteoglycan (SLRP) family. SLRPs localize to skeletal regions and play significant roles during whole phases of bone development. Although prior evidence suggests that TSK may be involved in the regulation of bone formation, its role in skeletal development has not yet been elucidated. Methods: In the present study, we examined TSK's function during bone growth by comparing skeletal growth of TSK deficient (TSK−/−) mice and wild type (WT) mice. And an in vitro experiment using siRNA transfection of a chondrogenic cell line was performed. Results: TSK−/− mice exhibited decreased weight and short stature at 3 weeks of age due to decreased longitudinal bone growth coupled with low bone mass. Furthermore, an in vitro experiment using siRNA transfection into a chondrogenic cell line revealed that decreased TSK expression induced down-regulation of key chondrogenic marker gene expression and up-regulation of mid-to-late chondrogenic markers gene expression. Conclusions: Our results reveal that TSK regulates bone elongation and bone mass by modulating growth plate chondrocyte function and consequently, overall body size.

Hepatokines are proteins secreted by the liver that impact the functions of the liver and various tissues through autocrine, paracrine, and endocrine signaling. Recently, Tsukushi (TSK) was identified as a new hepatokine that is induced by obesity and cold exposure. It was proposed that TSK controls sympathetic innervation and thermogenesis in brown adipose tissue (BAT) and that loss of TSK protects against diet-induced obesity and improves glucose homeostasis. Here we report the impact of deleting and/or overexpressing TSK on BAT thermogenic capacity, body weight regulation, and glucose homeostasis. We measured the expression of thermogenic genes and markers of BAT innervation and activation in TSK-null and TSK-overexpressing mice. Body weight, body temperature, and parameters of glucose homeostasis were also assessed in the context of TSK loss and overexpression. The loss of TSK did not affect the thermogenic activation of BAT. We found that TSK-null mice were not protected against the development of obesity and did not show improvement in glucose tolerance. The overexpression of TSK also failed to modulate thermogenesis, body weight gain, and glucose homeostasis in mice. TSK is not a significant regulator of BAT thermogenesis and is unlikely to represent an effective target to prevent obesity and improve glucose homeostasis. • Loss of TSK does not affect brown fat thermogenic capacity. • Loss of TSK does not protect mice against the development of obesity. • Loss of TSK does not improve glucose homeostasis. • Overexpression of TSK does not affect thermogenesis, body weight gain and glucose homeostasis. [ABSTRACT FROM AUTHOR]

Background and Aims: Tsukushi (TSK) is a recently identified hepatokine, and we aimed to investigate the association between systemic TSK and the severity of nonalcoholic fatty liver disease (NAFLD) in subjects with and without type 2 diabetes mellitus (DM)., Methods: Three hundred ninety-three DM and 289 without DM individuals were recruited for transient elastography assessment to determine liver steatosis and fibrosis. Serum TSK was measured by ELISA. The presence of NAFLD was defined as controlled attenuation parameter ≥ 248 dB/m., Results: NAFLD was present in 276 (70.2%) and 129 (44.6%) subjects with and without DM respectively, and they had higher serum TSK levels than those without NAFLD [DM group: 91.0 ng/mL (61.7-133.8) vs 82.5 (60.9-118.5), P < .01 respectively; without DM group: 97.1 ng/mL (69.3-148.6) vs 80.8 (53.4-111.6) respectively, P < .01]. Univariate analysis showed that serum TSK significantly correlated with the degree of steatosis and fibrosis both in subjects with and without DM. On multivariable regression analysis, only liver stiffness and estimated glomerular filtration rate were significant determinants of TSK level, and the relationship was independent of diabetes and serum adiponectin. Out of 405 subjects with NAFLD, 49 had either advanced fibrosis or cirrhosis. The area under receiver operating characteristic curve of serum TSK to indicate advanced fibrosis or cirrhosis was 0.70 (95% CI .62-.77), which was significantly better than that of fibrosis-4 index, 0.64 (95% CI .55-.72), P < .05., Conclusion: Serum TSK levels were increased in subjects with NAFLD and reflected the severity of liver fibrosis., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

• TSK was found to be highly expressed in lung cancer tissues and cell lines. • TSK regulates epithelial-mesenchymal transition and proliferation in lung cancer cells. • TSK may be a key coordinator of multiple pathways and important structural elements in the lung cancer microenvironment. Tsukushi (TSK), a member of the small leucine-rich repeat proteoglycan (SLRP) family, plays multifunctional roles by interacting with signaling molecules during development. However, the role of TSK in cancer remains unknown. The aim of the present study was to investigate the biological significance of TSK in lung cancer. Immunohistochemistry of lung cancer tissues and reverse transcription polymerase chain reaction (PCR) of lung cancer cell lines were carried out to detect TSK. Then, RNA sequence analysis, Gene Ontology analysis, quantitative real-time PCR, western blotting, cell counting assay, invasion assays, and xenograft studies were done in a human lung adenocarcinoma cell line, H1975 with modification of TSK expression levels, in order to investigate its biological roles, in particular epithelial–mesenchymal transition (EMT) and proliferation. TSK was found to be highly expressed in lung cancer tissues and cell lines. Modification of TSK expression levels in H1975 resulted in changes in molecules related to EMT, including cadherin-1, snail family transcriptional repressor 1, snail family transcriptional repressor 2, and vimentin. The results of cell counting and xenograft assays showed that TSK promotes cell proliferation. In lung cancer cells, TSK is expressed more highly than the other SLRPs family members, and regulates the EMT and proliferation. Thus, TSK may be a key coordinator of multiple pathways and an important structural element in the lung cancer microenvironment. [ABSTRACT FROM AUTHOR]

Extracellular molecules coordinate the multiple signaling pathways spatiotemporally to exchange information between cells during development. Understanding the regulation of these signal molecule-dependent pathways elucidates the mechanism of intercellular crosstalks. CCN2/CTGF is one of the CCN family members that binds BMP2, fibronectin, aggrecan, FGFR2 - regulating cartilage and bone formation, angiogenesis, wound repair etc. Tsukushi (TSK), which belongs to the Small Leucine-Rich Proteoglycan (SLRP) family, binds nodal/Vg1/TGF-β1, BMP4/chordin, Delta, FGF8, Frizzled4, and is involved in the early body formation, bone growth, wound healing, retinal stem cell regulation etc. These two secreted molecules are expressed in similar tissues and involved in several biological events by functioning as extracellular signaling modulators. Here, we examine the molecular interaction between CCN2 and TSK biochemically. Co-precipitation assay and Surface Plasmon Resonance measurement showed their direct binding with the Kd value 15.3 nM. Further, the Solid-phase Binding Assay indicated that TSK binds to IGFBP and CT domains of CCN2. Our data suggest that CCN2 and TSK exert their function together in the body formation. [ABSTRACT FROM AUTHOR]

Tsukushi (TSK) is a small signaling molecule which takes part in different developmental processes of multiple vertebrate organisms. The diverse activity of TSK depends on its ability to bind various intermediate molecules from different major signaling pathways. Interactions of TSK with BMP, FGF, TGF-β and Wnt pathways have already been confirmed. In this review, we will introduce the latest information regarding the involvement of TSK in developmental events. We suggest a fine tuning role for TSK in multiple signaling cascades. Also, we recommend further studies on the developmental role of TSK to fully reveal its potential. [ABSTRACT FROM AUTHOR]

During somitogenesis, segmentation of the body axis occurs by epithelial somites budding off from the rostral end of the unsegmented presomitic mesoderm (PSM), and its molecular regulation is achieved by a molecular oscillator and signaling molecules. Tsukushi (TSK) is a unique secreted protein and involved in diverse biological cascades in vertebrate embryos by modulating several signaling pathways at the extracellular region. However, the involvement of TSK in somitogenesis remains unknown. In this study, we investigated the detailed expression patterns of TSK at different developmental stages of a chick embryo. Chick-TSK (C-TSK) is expressed in the PSM and shows an oscillation pattern with three phases. The oscillation pattern of C-TSK in the PSM is similar to that of c-Notch1 and c-hairy1, but not to c-Delta1. Our in vitro data showed that Notch signaling is necessary for the normal expression of C-TSK and that expression of C-TSK is an intrinsic property of the anterior PSM. These data suggest that TSK plays a role in chick somitogenesis. [ABSTRACT FROM AUTHOR]

During the wound-healing process, macrophages, fibroblasts, and myofibroblasts play a leading role in shifting from the inflammation phase to the proliferation phase, although little is known about the cell differentiation and molecular control mechanisms underlying these processes. Previously, we reported that Tsukushi (TSK), a member of the small leucine-rich repeat proteoglycan family, functions as a key extracellular coordinator of multiple signalling networks. In this study, we investigated the contribution of TSK to wound healing. Analysis of wound tissue in heterozygous TSK-lacZ knock-in mice revealed a pattern of sequential TSK expression from macrophages to myofibroblasts. Quantitative PCR and in vitro cell induction experiments showed that TSK controls macrophage function and myofibroblast differentiation by inhibiting TGF-β1 secreted from macrophages. Our results suggest TSK facilitates wound healing by maintaining inflammatory cell quiescence. [ABSTRACT FROM AUTHOR]

Tsukushi (TSK) proteoglycan dysfunction leads to hydrocephalus, a condition defined by excessive fluid collection in the ventricles and lateral ventricular enlargement. TSK injections into the LV at birth are effective at rescuing the lateral ventricle (LV). TSK regulates the activation of the Wnt signaling to facilitate the proper expansion of the LV and maintain the fate of the neural stem cell lineage. However, the molecular mechanism by which TSK acts on neural stem/progenitor cells (NSCs) during LV development is unknown. We demonstrated that TSK is crucial for the splicing and development-associated gene regulation of GFAP-expressing subventricular zone (SVZ) NSCs. We isolated GFAP-expressing NSCs from the SVZ of wild-type (GFAP GFP/+ /TSK +/+ ) and TSK knock-out (GFAP GFP/+ /TSK -/- ) mice on postnatal day 3 and compared their transcriptome and splicing profiles. TSK deficiency in NSCs resulted in genome-wide missplicing (alteration in exon usage) and transcriptional dysregulation affecting the post-transcriptional regulatory processes (including splicing, cell cycle, and circadian rhythm) and developmental signaling networks specific to the cell (including Wnt, Sonic Hedgehog, and mTOR signaling). Furthermore, TSK deficiency prominently affected the splicing of genes encoding RNA and DNA binding proteins in the nervous SVZ and non-nervous muscle tissues. These results suggested that TSK is involved in the maintenance of correct splicing and gene regulation in GFAP-expressing NSCs, thereby protecting cell fate and LV development. Hence, our study provides a critical insight on hydrocephalus development., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Istiaq, Umemoto, Ito, Suda, Shimamura and Ohta.)

Abstract: We have shown that draxin is a repulsive axon guidance molecule for a variety of neuron classes and that genetic deletion of draxin in mice results in the absence of all forebrain commissures. Moreover, we also identified a secreted molecule, Tsukushi (TSK), that belongs to the small leucine-rich proteoglycan family (SLRP) and inhibits signaling molecules, such as BMP and Wnt. TSK knockout mice show malformation of the corpus callosum (CC) and agenesis of the anterior commissure (AC), suggesting the importance of TSK function in forebrain commissure formation. There is a possibility that the combined function of these two proteins is essential for the formation of these commissures. In this study, we investigate this possibility by generating draxin/TSK doubly heterozygous mice and comparing their forebrain commissure phenotypes with those of singly heterozygous mice. We found that, although draxin and TSK did not interact directly, their genetic interaction was evident from the significantly higher prevalence of CC malformation and agenesis of the AC in the draxin/TSK doubly heterozygous mice. Importantly, in this study, we demonstrated a new function of TSK in guiding anterior olfactory neuronal (AON) and cortical axons. TSK bound to and provided growth inhibitory signals dose-dependently to AON and cortical axons in outgrowth assay. TSK also induced growth cone collapse when applied acutely to these cultured neurons. Furthermore, TSK and draxin had additive effects in inhibiting cortical and AON neurite outgrowth. Thus, based on a combination of genetic analyses and in vitro experiments, we propose that the combined guidance activities of draxin and TSK regulate forebrain commissure formation. [Copyright &y& Elsevier]

Abstract: The hair follicle contains stem/progenitor cells that supply progeny for skin development and the hair cycle. Several signaling molecules belonging to the Wnt, BMP, shh, and transforming growth factor β (TGF-β) signaling cascades are involved in the normal hair follicle cycle. However, the systemic mechanism of how these humoral factors are controlled remains largely unknown. Previously, we reported that Tsukushi (TSK), a member of the small leucine-rich repeat proteoglycan family, functions extracellularly as a key coordinator of multiple signaling networks. Here, we show that TSK is expressed at the restricted areas of hair follicle during the morphogenesis and the hair cycle. Targeted disruption of the TSK gene causes the hair cycle to be delayed with low levels of TGF-β1 and phosphorylated Smad2/3 (pSmad2/3) expression. Biochemical analysis indicates that TSK directly binds to TGF-β1. Our data suggest that TSK controls the hair cycle by regulating TGF-β1 signaling. [Copyright &y& Elsevier]

The small leucine-rich repeat proteoglycan ( SLRPs) family of proteins currently consists of five classes, based on their structural composition and chromosomal location. As biologically active components of the extracellular matrix ( ECM), SLRPs were known to bind to various collagens, having a role in regulating fibril assembly, organization and degradation. More recently, as a function of their diverse proteins cores and glycosaminoglycan side chains, SLRPs have been shown to be able to bind various cell surface receptors, growth factors, cytokines and other ECM components resulting in the ability to influence various cellular functions. Their involvement in several signaling pathways such as Wnt, transforming growth factor-β and epidermal growth factor receptor also highlights their role as matricellular proteins. SLRP family members are expressed during neural development and in adult neural tissues, including ocular tissues. This review focuses on describing SLRP family members involvement in neural development with a brief summary of their role in non-neural ocular tissues and in response to neural injury. [ABSTRACT FROM AUTHOR]

Abstract: The anterior commissure (AC) is one of the important commissure projections in the brain that conveys information from one side of the nervous system to the other. During development, the axons from the anterior AC (aAC) and the posterior AC (pAC) course in the same dorsoventral plane and converge into a common fascicle for midline crossing. Previously, we reported that Tsukushi (TSK), a member of the secreted small leucine rich repeat proteoglycan family, functions as a key coordinator of multiple pathways outside of cells through the regulation of an extracellular signaling network. Here, we show evidence that TSK is critical for the formation of the AC. In mice lacking TSK, the aAC and the pAC axons fail to cross the midline, leading to an almost total absence of the AC in adult mice. DiI labeling indicated that the aAC axons grew out from the anterior olfactory nucleus and migrated along normal pathways but never crossed the midline. Therefore, we have uncovered a crucial role for TSK for AC formation in the mouse brain. [ABSTRACT FROM AUTHOR]

We acquire information from the outside world through our eyes which contain the retina, the photosensitive component of the central nervous system. Once the adult mammalian retina is damaged, the retinal neuronal death causes a severe loss of visual function. It has been believed that the adult mammalian retina had no regenerative capacity. However, the identification of neuronal progenitor cells in the retina sheds some light on cellular therapies for damaged retinal regeneration. In this review, we highlight three potential stem/progenitor cells in the eye, the ciliary body epithelium cells, the iris pigmented epithelium cells, and Müller glia. In order to make them prime candidates for the possible treatment of retinal diseases, it is important to understand their basic characters. In addition, we discuss the key signaling molecules that function extracellularly and determine whether neuronal progenitors remain quiescent, proliferate, or differentiate. Finally, we introduce a secreted protein, Tsukushi, which is a possible candidate as a niche molecule for retinal stem/progenitor cells. [ABSTRACT FROM AUTHOR]

Aims: Tsukushi, a newly identified hepatokine, has been recently characterized as a potent modifier in lipid metabolism and energy homeostasis, but the role of Tsukushi in diabetes remains almost unknown. We detected for the first time the serum Tsukushi levels in newly diagnosed type 2 diabetes, exploring the relationship between Tsukushi and various metabolic parameters.Methods: A total of 172 participants were recruited, including 86 patients with newly diagnosed type 2 diabetes and 86 subjects with normal glucose tolerance according to oral glucose tolerance test. Serum Tsukushi was measured by ELISA. The insulin resistance, pancreas β-cell function and insulin sensitivity were determined by homeostasis model assessment (HOMA-IR, HOMA-β), Stumvoll insulin sensitivity index (ISIstumvoll) and Stumvoll metabolic clearance rate (MCRstumvoll).Results: Serum Tsukushi was significantly higher in type 2 diabetes than in normal glucose tolerance [1.22(0.86,1.74) vs 0.8(0.5,1.38) ng/mL; P < 0.001]. Multiple regression analysis showed that BMI, 2-h post-OGTT glucose and TC were independently related factors influencing Tsukushi. Logistic regression analyses demonstrated that Tsukushi was associated with higher risk of type 2 diabetes independently.Conclusions: Circulating Tsukushi levels significantly increase in patients with type 2 diabetes, which suggest that Tsukushi may play a role in type 2 diabetes pathogenesis. [ABSTRACT FROM AUTHOR]

Retinal diseases such as age-related macular degeneration (AMD), retinopathy of prematurity (ROP), and diabetic retinopathy (DR) are the leading causes of visual impairment worldwide. There is a critical need to understand the structural and cellular components that play a vital role in the pathophysiology of retinal diseases. One potential component is the family of structural proteins called small leucine-rich proteoglycans (SLRPs). SLRPs are crucial in many fundamental biological processes involved in the maintenance of retinal homeostasis. They are present within the extracellular matrix (ECM) of connective and vascular tissues and contribute to tissue organization and modulation of cell growth. They play a vital role in cell–matrix interactions in many upstream signaling pathways involved in fibrillogenesis and angiogenesis. In this comprehensive review, we describe the expression patterns and function of SLRPs in the retina, including Biglycan and Decorin from class I; Fibromodulin, Lumican, and a Proline/arginine-rich end leucine-rich repeat protein (PRELP) from class II; Opticin and Osteoglycin/Mimecan from class III; and Chondroadherin (CHAD), Tsukushi and Nyctalopin from class IV. [ABSTRACT FROM AUTHOR]

• Hepatic TSK expression is reduced six months after LAGB which is mainly driven by weight loss. • Hepatic TSK expression directly correlates with weight loss and indirectly correlates with histological severity of liver disease. • TSK might reflect a promising target for treating obesity and NAFLD. Obesity has emerged as a substantial global healthcare issue that is frequently associated with insulin resistance and non-alcoholic fatty liver disease (NAFLD). Tsukushi (TSK), a liver-derived molecule, was recently identified as a major driver of NAFLD. Laparoscopic adjustable gastric banding (LAGB) has proven effective in reducing body weight and improving NAFLD. We therefore aimed to investigate the relation between LAGB-induced weight loss and TSK expression. Twenty-six obese patients undergoing LAGB were included in the study and metabolic parameters were assessed before (t0) and six months after LAGB (t6). The expression of TSK in liver and subcutaneous adipose tissue (AT) specimens was determined at both time points. To unravel regulatory mechanisms of TSK expression, human peripheral blood mononuclear cells (PBMCs) were stimulated with pro-inflammatory cytokines and TSK mRNA levels were analyzed by quantitative polymerase chain reaction. LAGB induced pronounced weight loss which was paralleled by amelioration of metabolic disturbances and histologically defined NAFLD. While hepatic TSK expression was markedly decreased after LAGB, adipose tissue TSK expression remained comparable to baseline. The decline in hepatic TSK expression after LAGB positively correlated with weight loss and the reduction in BMI, and negatively correlated with NAFLD activity score (NAS). In human PBMCs, pro-inflammatory cytokines such as IL-1β and TNFα induced the expression of TSK. In conclusion, LAGB-induced weight loss reduces hepatic TSK expression. Inhibiting TSK might represent a promising target for treating NAFLD in the future. [ABSTRACT FROM AUTHOR]

Introduction: Endochondral ossification is one of a key process for bone maturation. Tsukushi (TSK) is a novel member of the secreted small leucine-rich repeat proteoglycan (SLRP) family. SLRPs localize to skeletal regions and play significant roles during whole phases of bone development. Although prior evidence suggests that TSK may be involved in the regulation of bone formation, its role in skeletal development has not yet been elucidated., Methods: In the present study, we examined TSK's function during bone growth by comparing skeletal growth of TSK deficient (TSK-/-) mice and wild type (WT) mice. And an in vitro experiment using siRNA transfection of a chondrogenic cell line was performed., Results: TSK-/- mice exhibited decreased weight and short stature at 3 weeks of age due to decreased longitudinal bone growth coupled with low bone mass. Furthermore, an in vitro experiment using siRNA transfection into a chondrogenic cell line revealed that decreased TSK expression induced down-regulation of key chondrogenic marker gene expression and up-regulation of mid-to-late chondrogenic markers gene expression., Conclusions: Our results reveal that TSK regulates bone elongation and bone mass by modulating growth plate chondrocyte function and consequently, overall body size.

Three classes of signaling molecule, VG1, WNT and BMP, play crucial roles in axis formation in the chick embryo. Although VG1 and WNT signals have a pivotal function in inducing the primitive streak and Hensen's node in the embryo midline, their action is complemented by that of BMP antagonists that protect the prospective axial tissue from the inhibitory influence of BMPs secreted from the periphery. We have previously reported that a secreted factor, chick Tsukushi (TSK), is expressed in the primitive streak and Hensen's node, where it works as a BMP antagonist. Here, we describe a new crucial function for TSK in promoting formation of the primitive streak and Hensen's node by positively regulating VG1 activity. We provide evidence that TSK directly binds VG1 in vitro, and that TSK and VG1 functionally interact in axis formation, as shown by biological assays performed in chick and Xenopus embryos. Furthermore, we show that alternative splicing of TSK RNA leads to the formation of two isoforms (TSKA, originally designated as TSK, and TSKB) that differ in their C-terminal region. Biochemical and biological assays indicate that TSKB is a much weaker BMP antagonist than TSKA, although both isoforms efficiently interact with VG1. Remarkably, although both TSKA and TSKB are expressed throughout the early extending primitive streak, their expression patterns diverge during gastrulation. TSKA expression concentrates in Hensen's node, a well-known source of anti-BMP signals, whereas TSKB accumulates in the middle primitive streak (MPS), a region known to work as a node-inducing center where VG1 expression is also specifically localized. Loss-of-function experiments demonstrate that TSKB, but not TSKA, function is required in the MPS for induction of Hensen's node. Taken together, these results indicate that TSK isoforms play a crucial role in chick axis formation by locally modulating VG1 and BMP activities during gastrulation. [ABSTRACT FROM AUTHOR]