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Glucose metabolism disturbances may result in diabetes-associated cognitive decline (DACI). Methionine restriction (MR) diet has emerged as a potential dietary strategy for managing glucose homeostasis. However, the effects and underlying mechanisms of MR on DACI have not been fully elucidated. Here, we found that a 13-week MR (0.17 % methionine, w/w) intervention starting at 8 weeks of age improved peripheral insulin sensitivity in male db/db mice, a model for type 2 diabetes. Notably, MR significantly improved working as well as long-term memory in db/db mice, accompanied by increased PSD-95 level and reduced neuroinflammatory factors, malondialdehyde (MDA), and 8-hydroxy-2′-deoxyguanosine (8-OHdG). We speculate that this effect may be mediated by MR activating hepatic fibroblast growth factor 21 (FGF21) and the brain FGFR1/AMPK/GLUT4 signaling pathway to enhance brain glucose metabolism. To further delineate the mechanism, we used intracerebroventricular injection of adeno-associated virus to specifically knock down FGFR1 in the brain to verify the role of FGFR1 in MR-mediated DACI. It was found that the positive effects of MR on DACI were offset, reflected in decreased cognitive function, impaired synaptic plasticity, upregulated neuroinflammation, and balanced enzymes regulating reactive oxygen species (Sod1, Sod2, Nox4). Of note, the FGFR1/AMPK/GLUT4 signaling pathway and brain glucose metabolism were inhibited. In summary, our study demonstrated that MR increased peripheral insulin sensitivity, activated brain FGFR1/AMPK/GLUT4 signaling through FGF21, maintained normal glucose metabolism and redox balance in the brain, and thereby alleviated DACI. These results provide new insights into the effects of MR diet on cognitive dysfunction caused by impaired brain energy metabolism.

Abstract Background Diabetes-associated cognitive impairment (DACI) poses a significant challenge to the self-management of diabetes, markedly elevating the risk of adverse complications. A burgeoning body of evidence implicates microglia as a central player in the pathogenesis of DACI. Methods We utilized proteomics to identify potential biomarkers in high glucose (HG)-treated microglia, followed by gene knockdown techniques for mechanistic validation in vitro and in vivo. Results Our proteomic analysis identified a significant upregulation of AKAP8L in HG-treated microglia, with concurrent dysregulation of autophagy and inflammation markers, making AKAP8L a novel biomarker of interest. Notably, the accumulation of AKAP8L was specific to HG-treated microglia, with no observed changes in co-cultured astrocytes or neurons, a pattern that was mirrored in streptozotocin (STZ)-induced diabetic mice. Further studies through co-immunoprecipitation and proximity ligation assay indicated that the elevated AKAP8L in HG-treated microglial cells interacts with the mTORC1. In the STZ mouse model, we demonstrated that both AKAP8L knockdown and rapamycin treatment significantly enhanced cognitive function, as evidenced by improved performance in the Morris water maze, and reduced microglial activation. Moreover, these interventions effectively suppressed mTORC1 signaling, normalized autophagic flux, mitigated neuroinflammation, and decreased pyroptosis. Conclusions Our findings highlight the critical role of AKAP8L in the development of DACI. By interacting with mTORC1, AKAP8L appears to obstruct autophagic processes and initiate a cascade of neuroinflammatory responses. The identification of AKAP8L as a key mediator in DACI opens up new avenues for potential therapeutic interventions.

Background: Diabetes-associated cognitive impairment (DACI) poses a significant challenge to the self-management of diabetes, markedly elevating the risk of adverse complications. A burgeoning body of evidence implicates microglia as a central player in the pathogenesis of DACI. Methods: We utilized proteomics to identify potential biomarkers in high glucose (HG)-treated microglia, followed by gene knockdown techniques for mechanistic validation in vitro and in vivo. Results: Our proteomic analysis identified a significant upregulation of AKAP8L in HG-treated microglia, with concurrent dysregulation of autophagy and inflammation markers, making AKAP8L a novel biomarker of interest. Notably, the accumulation of AKAP8L was specific to HG-treated microglia, with no observed changes in co-cultured astrocytes or neurons, a pattern that was mirrored in streptozotocin (STZ)-induced diabetic mice. Further studies through co-immunoprecipitation and proximity ligation assay indicated that the elevated AKAP8L in HG-treated microglial cells interacts with the mTORC1. In the STZ mouse model, we demonstrated that both AKAP8L knockdown and rapamycin treatment significantly enhanced cognitive function, as evidenced by improved performance in the Morris water maze, and reduced microglial activation. Moreover, these interventions effectively suppressed mTORC1 signaling, normalized autophagic flux, mitigated neuroinflammation, and decreased pyroptosis. Conclusions: Our findings highlight the critical role of AKAP8L in the development of DACI. By interacting with mTORC1, AKAP8L appears to obstruct autophagic processes and initiate a cascade of neuroinflammatory responses. The identification of AKAP8L as a key mediator in DACI opens up new avenues for potential therapeutic interventions. [ABSTRACT FROM AUTHOR]

• DM induces cholesterol buildup and worsens microglial responses. • SCAP overexpression in DM mice is linked to DACI. • Loss of microglial SCAP improves cognition in DM mice. • SCAP-NLRP3 axis is key for microglial inflammatory response regulation. Hyperglycemia-induced pathological microglial responses and subsequent neuronal damage are notable characteristics of diabetes-associated cognitive impairment (DACI). Cholesterol accumulation in the brain is a prevalent consequence of diabetes mellitus (DM), exacerbating pathological microglial responses. Regarding disordered glucose and lipid metabolism, the Sterol Regulatory Element-Binding Protein (SREBP) cleavage-activating protein (SCAP), a cholesterol sensor, exhibits increased expression and abnormal translocation from the endoplasmic reticulum to the Golgi, amplifying the inflammatory response. Therefore, we hypothesized that overexpression of microglia-SCAP and cholesterol accumulation in DM mice could induce pathological microglial responses associated with DACI. Our type 2 DM mice model presented an abnormal increase in microglial SCAP expression. The functional loss of microglia-specific SCAP in DM mice improved cognitive impairment, neuronal synaptic plasticity deficits, and abnormal microglial responses. Mechanistically, the accumulated SCAP directly bound to and enhanced the activation of the microglial-specific inflammatory amplifier, NLRP3 inflammasome, in Golgi, thereby increasing pathological microglial responses and promoting neuronal damage. These findings indicate an important regulatory axis of microglial responses from SCAP to the NLRP3 inflammasome pathway in microglia. These underscore the crosstalk between cholesterol disorders and pathological microglial responses, offering a promising avenue for pharmaceutical interventions in DACI. [ABSTRACT FROM AUTHOR]

Qingsen Ran,1 He Tian,1 Jian Lin,1 Han Wang,2 Bo Wang,1 Zhixin Chen,1 Da Song,1 Chunzhu Gong1 1Department of Science and Education, Shenzhen Pingle Orthopedic Hospital (Shenzhen Pingshan Traditional Chinese Medicine Hospital), Shenzhen, Guangzhou Province, 518118, People’s Republic of China; 2Department of Gastroenterology, Affiliated Hospital of Changchun University of Chinese Medicine, Changchun, Jilin Province, 130021, People’s Republic of ChinaCorrespondence: Chunzhu Gong, Email gczq_82@126.comAbstract: The progression of diabetes frequently results in a myriad of neurological disorders, including ischemic stroke, depression, blood-brain barrier impairment, and cognitive dysfunction. Notably, diabetes-associated cognitive impairment, a prevalent comorbidity during the course of diabetes, progressively affects patients’ cognitive abilities and may reciprocally influence diabetes management, thereby severely impacting patients’ quality of life. Extracellular vesicles, particularly nanoscale exosomes, have garnered considerable attention in recent years. These exosomes carry and transfer various functional molecules, such as proteins, lipids, and diverse non-coding RNAs, serving as novel regulators and communicators in intercellular interactions. Of particular interest, mesenchymal stem cell-derived exosomes (MSC-Exos) have been reported to traverse the blood-brain barrier and ameliorate intracerebral pathologies. This review elucidates the role of MSC-Exos in diabetes-related cognitive impairment, with a focus on their applications as biomarkers, modulation of neuronal regeneration and synaptic plasticity, anti-inflammatory properties, antioxidative effects, and their involvement in regulating the functionality of β-amyloid proteins during the course of cognitive impairment. The immense therapeutic potential of MSC-Exos in the treatment of diabetes-induced cognitive dysfunction is emphasized.Keywords: diabetes-associated cognitive impairment, mesenchymal stem cell-derived exosomes, blood-brain barrier, neuronal regeneration, synaptic plasticity

Background: Diabetes-associated cognitive impairment (DACI) is a common complication of diabetes, and studies have shown that DACI is more severe in postmenopausal patients with diabetes. Forsythoside B (FTS·B) can inhibit inflammation and reduce synaptic dysfunction, which can improve cognitive function. However, it has not been confirmed whether FTS·B has a reversing or retarding effect on postmenopausal diabetic encephalopathy. Methods: Seven days after bilateral ovariectomy (OVX) or sham surgery, adult female C57 mice (n = 15/group) received intraperitoneal injection of streptozotocin (60 mg/kg/day/L) and citrate buffer for 5 consecutive days to induce diabetes mellitus (DM). Fourteen days later, ovariectomized diabetic mice were given intraperitoneal injection of FTS·B (100, 150 mg/kg/day/L) and subcutaneous injection of 17β-estradiol (1 mg/kg) for 8 weeks [OVX + DM + low-FTS·B group (L-F), OVX + DM + high-FTS·B group (HF), and OVX + DM + 17β-estradiol (ER)]. In addition, the following control groups were defined: Sham, OVX, DM, and OVX + DM (O + D). Fasting plasma glucose, body weight and blood insulin levels were determined in each group of mice. Next, their cognitive function was tested through behavioral experiments. Hematoxylin & eosin (H&E) and Nissl staining were used to detect the morphological changes in the hippocampus. The aggregation of amyloid beta (Aβ) and the hyperaggregation of p-tau were assessed by immunohistochemistry. Interleukin-1β (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), brain-derived neurotrophic factor (BDNF), postsynaptic density-95 (PSD-95), synaptophysin, and synapsin-1 expression in the hippocampus was detected by real-time polymerase chain reaction (RT-PCR) and western blot analysis. Results: FTS·B can decrease fasting glucose and blood insulin level. Behavioral results showed that cognitive decline was the most severe in the O + D group, and the ER, L-F, and H-F groups revised the cognitive decline. Compared to the O + D group, more normal morphology, which has obvious nucleoli and clear nuclear membrane, was observed by H&E and Nissl staining in the ER, L-F, and H-F groups. FTS·B alleviated DACI by reducing the aggregation of Aβ and the hyperaggregation of p-tau in the hippocampus. Moreover, the protein and mRNA expression showed that FTS·B not only inhibited inflammation by decreasing IL-1β, IL-6, and TNF-α but also modulated synaptic plasticity by increasing BDNF, PSD-95, synaptophysin, and synapsin-1. Conclusion: These results suggest that FTS·B may be a novel therapeutic target for postmenopausal diabetic encephalopathy treatment. [ABSTRACT FROM AUTHOR]

Sarsasapogenin (Sar), a natural steroidal compound, shows neuroprotection, cognition‐enhancement, antiinflammation, antithrombosis effects, and so on. However, whether Sar has ameliorative effects on diabetes‐associated cognitive impairment remains unknown. In this study, we found that Sar ameliorated diabetes‐associated memory impairment in streptozotocin‐induced diabetic rats, evidenced by increased numbers of crossing platform and percentage of time spent in the target quadrant in Morris water maze tests, and suppressed the nucleotide‐binding domain and leucine‐rich repeat containing protein 1 (NLRP1) inflammasome in hippocampus and cerebral cortex. Furthermore, Sar inhibited advanced glycation end‐products and its receptor (AGEs/RAGE) axis and suppressed up‐regulation of thrombin receptor protease‐activated receptor 1 (PAR‐1) in cerebral cortex. On the other hand, Sar mitigated high glucose‐induced neuronal damages, NLRP1 inflammasome activation, and PAR‐1 up‐regulation in high glucose‐cultured SH‐SY5Y cells, but did not affect thrombin activity. Moreover, the effects of Sar were similar to those of a selective PAR‐1 antagonist vorapaxar. Further studies indicated that activation of the NLRP1 inflammasome and NF‐κB mediated the effect of PAR‐1 up‐regulation in high glucose condition by using PAR‐1 knockdown assay. In summary, this study demonstrated that Sar prevented memory impairment caused by diabetes, which was achieved through suppressing neuroinflammation from activated NLRP1 inflammasome and NF‐κB regulated by cerebral PAR‐1. Highlights: Sarsasapogenin ameliorated memory impairment caused by diabetes in rats.Sarsasapogenin mitigated neuronal damages and neuroinflammation by down‐regulating cerebral PAR‐1.The NLRP1 inflammasome and NF‐κB signaling mediated the pro‐inflammatory effects of PAR‐1.Sarsasapogenin was a pleiotropic neuroprotective agent and memory enhancer in diabetic rodents. [ABSTRACT FROM AUTHOR]