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INTRODUCTION: Neuroinflammation is a major contributor to the progression of frontotemporal dementia (FTD). Galectin‐3 (Gal‐3), a microglial activation regulator, holds promise as a therapeutic target and potential biomarker. Our study aimed to investigate Gal‐3 levels in patients with FTD and assess its diagnostic potential. METHODS: We examined Gal‐3 levels in brain, serum, and cerebrospinal fluid (CSF) samples of patients with FTD and controls. Multiple linear regressions between Gal‐3 levels and other FTD markers were explored. RESULTS: Gal‐3 levels were increased significantly in patients with FTD, mainly across brain tissue and CSF, compared to controls. Remarkably, Gal‐3 levels were higher in cases with tau pathology than TAR‐DNA Binding Protein 43 (TDP‐43) pathology. Only MAPT mutation carriers displayed increased Gal‐3 levels in CSF samples, which correlated with total tau and 14‐3‐3. DISCUSSION: Our findings underscore the potential of Gal‐3 as a diagnostic marker for FTD, particularly in MAPT cases, and highlights the relation of Gal‐3 with neuronal injury markers. [ABSTRACT FROM AUTHOR]

Background: Microglia, the brain‐resident myeloid cells, play a major role in the immune responses of the nervous system and in the pathogenesis of Alzheimer's disease (AD). However, the presence of peripheral myeloid cells in the AD brains, and their contribution to disease progression, remain to be demonstrated. Method: Cellular (immunostainings and image analysis) and molecular (qPCR and western blots) approaches have been carried out in post‐mortem hippocampal samples from patients with AD (Braak V‐VI) and age‐matched controls without neurological symptoms (Braak II). Results: Our study provides evidence that circulating monocytes infiltrate the AD brains. Our findings showed that a high proportion of demented individuals was associated with up‐regulation of genes rarely expressed by microglial cells and abundant in monocytes‐derived cells (MDC), among which stands the scavenger receptor Cd163. These Cd163‐positive MDC invaded the brain parenchyma, acquired a microglial‐like morphology, and were located in close proximity to blood vessels. These cells infiltrated the nearby amyloid plaques contributing to plaque‐associated myeloid cell heterogeneity. Besides, control individuals with high amyloid pathology, showed no signs of MDC brain infiltration or plaque invasion. The MDC infiltration was associated with the progression and severity of AD pathology. Conclusion: These results reveal the co‐existence of distinct myeloid populations associated with amyloid plaques during disease progression, as well their region‐specific contribution to neuroimmune protection. The recruitment of monocytes could be a consequence rather than the cause of the severity of the disease. Whether monocyte infiltration is beneficial or detrimental to AD pathology remains to be fully elucidated. These findings open the opportunity to design targeted therapies, not only to microglia, but also to peripheral immune cell population to modulate amyloid pathology and provide a better understanding of the immunological mechanisms underlying AD progression. Supported by ISCiii grants(PI21‐0915 (to AG),PI21‐00914 (to JV) co‐financed by FEDER funds from European Union, by Junta de Andalucia grants P18‐RT‐2233 (to AG) and US‐1262734 (to JV) co‐financed by Programa Operativo FEDER 2014‐2020, and by grant PPIT.UMA.B1‐2019‐07 (to ESM). [ABSTRACT FROM AUTHOR]

Neuronal loss is the best neuropathological substrate that correlates with cortical atrophy and dementia in Alzheimer's disease (AD). Defective GABAergic neuronal functions may lead to cortical network hyperactivity and aberrant neuronal oscillations and in consequence, generate a detrimental alteration in memory processes. In this study, using immunohistochemical and stereological approaches, we report that the two major and non‐overlapping groups of inhibitory interneurons (SOM‐cells and PV‐cells) displayed distinct vulnerability in the perirhinal cortex of APP/PS1 mice and AD patients. SOM‐positive neurons were notably sensitive and exhibited a dramatic decrease in the perirhinal cortex of 6‐month‐old transgenic mice (57% and 61% in areas 36 and 35, respectively) and, most importantly, in AD patients (91% in Braak V–VI cases). In addition, this interneuron degenerative process seems to occur in parallel, and closely related, with the progression of the amyloid pathology. However, the population expressing PV was unaffected in APP/PS1 mice while in AD brains suffered a pronounced and significant loss (69%). As a key component of cortico‐hippocampal networks, the perirhinal cortex plays an important role in memory processes, especially in familiarity‐based memory recognition. Therefore, disrupted functional connectivity of this cortical region, as a result of the early SOM and PV neurodegeneration, might contribute to the altered brain rhythms and cognitive failures observed in the initial clinical phase of AD patients. Finally, these findings highlight the failure of amyloidogenic AD models to fully recapitulate the selective neuronal degeneration occurring in humans. [ABSTRACT FROM AUTHOR]

Background: Alzheimer's disease (AD) is characterized by presenting a complex pathology, not fully resolved yet. This fact, together with the lack of reliable models, has impeded the development of effective therapies. Recently, several studies have shown that functional glial cell defects have a key role in the pathology of AD. However, this glial dysfunction, currently, cannot be correctly modeled using the available animal models, so we hypothesized that cells derived from Alzheimer's patients can serve as a better platform for studying the disease. In this sense, human pluripotent stem cells (hPSC) allow the generation of different types of neural cells, which can be used for disease modeling, identification of new targets and drugs development. Method: We have a collection of hiPSCs derived from patients with sporadic forms of AD stratified based on APOE genotype. We have differentiated these cells towards neural cells and mature them to neurons or astrocytes using a serum‐free approach, to assess intrinsic differences between those derived from AD patients or healthy controls. Result: We have implemented a serum‐free approach and generated neural precursors and astrocytes from all the lines tested. We observe differences at the phenotypic level and a reduced capacity to differentiate towards neural lineage in those lines derived from APOE4 carriers. Conclusion: Our preliminary data suggest intrinsic differences in the neural differentiation capacity between cell lines derived from APOE4 or APOE3 carrier subjects. Further experiments would contribute to elucidate novel pathogenic pathways associated with neurodegeneration and susceptible of therapeutic modulation, likely contributing to the development of new effective drugs against AD. Acknowledgments: This study was supported by Instituto de Salud Carlos III (ISCiii) of Spain, co‐financed by FEDER funds from European Union, through grants PI21/00915 (to AG) and PI21/00914 (to JV); by Junta de Andalucia through Consejería de Economía y Conocimiento grants UMA20‐FEDERJA‐048 (to JAGL), PY18‐RT‐2233 (to AG) and US‐1262734 (to JV) co‐financed by Programa Operativo FEDER 2014‐2020, University of Malaga (B1‐2020_04) to JAGL and Programa Operativo de Empleo Juvenil SNGJ4‐11 to LCP. [ABSTRACT FROM AUTHOR]

Aims Here, we tested the hypothesis that glial responses via the production of cytokines such as transforming growth factor-beta 1 ( TGFβ1) and tumour necrosis factor alpha ( TNFα), which play important roles in neurodegenerative diseases, are correlated with the severity of congenital hydrocephalus in the hyh mouse model. We also searched for evidence of this association in human cases of primary hydrocephalus. Methods Hyh mice, which exhibit either severe or compensated long-lasting forms of hydrocephalus, were examined and compared with wild-type mice. TGFβ1, TNFα and TNFα R1 mRNA levels were quantified using real-time PCR. TNFα and TNFα R1 were immunolocalized in the brain tissues of hyh mice and four hydrocephalic human foetuses relative to astroglial and microglial reactions. Results The TGFβ1 mRNA levels were not significantly different between hyh mice exhibiting severe or compensated hydrocephalus and normal mice. In contrast, severely hydrocephalic mice exhibited four- and two-fold increases in the mean levels of TNFα and TNFα R1, respectively, compared with normal mice. In the hyh mouse, TNFα and TNFα R1 immunoreactivity was preferentially detected in astrocytes that form a particular periventricular reaction characteristic of hydrocephalus. However, these proteins were rarely detected in microglia, which did not appear to be activated. TNFα immunoreactivity was also detected in the glial reaction in the small group of human foetuses exhibiting hydrocephalus that were examined. Conclusions In the hyh mouse model of congenital hydrocephalus, TNFα and TNFα R1 appear to be associated with the severity of the disease, probably mediating the astrocyte reaction, neurodegenerative processes and ischaemia. [ABSTRACT FROM AUTHOR]

Dysfunctions of the ubiquitin proteasome system (UPS) have been proposed to be involved in the aetiology and/or progression of several age-related neurodegenerative disorders. However, the mechanisms linking proteasome dysfunction to cell degeneration are poorly understood. We examined in young and aged rat hippocampus the activation of the unfolded protein response (UPR) under cellular stress induced by proteasome inhibition. Lactacystin injection blocked proteasome activity in young and aged animals in a similar extent and increased the amount of ubiquitinated proteins. Young animals activated the three UPR arms, IRE1α, ATF6α and PERK, whereas aged rats failed to induce the IRE1α and ATF6α pathways. In consequence, aged animals did not induce the expression of pro-survival factors (chaperones, Bcl-XL and Bcl-2), displayed a more sustained expression of pro-apoptotic markers (CHOP, Bax, Bak and JKN), an increased caspase-3 processing. At the cellular level, proteasome inhibition induced neuronal damage in young and aged animals as assayed using Fluorojade-B staining. However, degenerating neurons were evident as soon as 24 h postinjection in aged rats, but it was delayed up to 3 days in young animals. Our findings show evidence supporting age-related dysfunctions in the UPR activation as a potential mechanism linking protein accumulation to cell degeneration. An imbalance between pro-survival and pro-apoptotic proteins, because of noncanonical activation of the UPR in aged rats, would increase the susceptibility to cell degeneration. These findings add a new molecular vision that might be relevant in the aetiology of several age-related neurodegenerative disorders. [ABSTRACT FROM AUTHOR]

Alterations in the proteasome activity in the CNS have been described during aging. However, a detailed study of all proteasome subunits is actually lacking. We have analyzed, in vivo, the age-related modifications in the molecular composition of hippocampal proteasomes. We found that the immunoproteasome/proteasome ratio was increased in aged hippocampus. The processing of the low-molecular-mass protein (LMP)7/β5i subunit, practically absent in young hippocampus, was increased in aged animals. Among the potential factors underlying these modifications we evaluated the neuroinflammation and the transcription factor Zif268. Lipopolysaccharide (LPS)-induced neuroinflammation in young rats, up-regulated the expression of immunoproteasome subunits and increased the processing of the LMP7/β5i protein. Moreover, the hydrophobicity of cellular peptides, analyzed by liquid chromatography, increased in both, young LPS-injected animals and aged rats, suggesting that immunoproteasomes including the LMP7/β5i subunit could, at least in part, account for this modification. Also, the mRNA expression of the transcription factor Zif268, which down-regulates the immunoproteasome subunit LMP7/β5i by binding to sequences within the promoter regions, was decreased in both, aged hippocampus and young LPS-injected animals. Finally, we found that spatial memory training in young animals, a situation in which the expression of Zif268 is increased, modified the mRNA expression of the constitutive and catalytic subunits in an opposite manner. Based on present data, we propose that the age-related increases in the content of hippocampal immunoproteasome is mostly because of neuroinflammatory processes associated to aging. [ABSTRACT FROM AUTHOR]

Increased neuroinflammatory reaction is frequently observed during normal brain aging. However, a direct link between neuroinflammation and neurodegeneration during aging has not yet been clearly shown. Here, we have characterized the age-related hippocampal inflammatory processes and the potential relation with hippocampal neurodegeneration. The mRNA expression of the pro-inflammatory cytokines IL-1β and tumor necrosis factor-α (TNF-α), and the iNOs enzyme was significantly increased in aged hippocampus. Accordingly, numerous activated microglial cells were observed in aged rats. These cells were differentially distributed along the hippocampus, being more frequently located in the hilus and the CA3 area. The mRNA expression of somatostatin, a neuropeptide expressed by some GABAergic interneurons, and the number of somatostatin-immunopositive cells decreased in aged rats. However, the number of hippocampal parvalbumin-containing GABAergic interneurons was preserved. Interestingly, in aged rats, the mRNA expression of somatostatin and IL-1β was inversely correlated and, the decrease in the number of somatostatin-immunopositive cells was higher in the hilus of dentate gyrus than in the CA1 region. Finally, intraperitoneal chronic lipopolysaccharide (LPS) injection in young animals mimicked the age-related hippocampal inflammation as well as the decrease of somatostatin mRNA expression. Present results strongly support the neuroinflammation as a potential factor involved in the age-related degeneration of somatostatin GABAergic cells. [ABSTRACT FROM AUTHOR]

Abstract We previously reported that the pharmacological properties of the hippocampal GABA[sub A] receptor and the expression of several subunits are modified during normal ageing. However, correlation between these post-synaptic modifications and pre-synaptic deficits were not determined. To address this issue, we have analysed the mRNA levels of several GABAergic molecular markers in young and old rat hippocampus, including glutamic acid decarboxylase enzymes, parvalbumin, calretinin, somatostatin, neuropeptide Y and vasoactive intestinal peptide (VIP). There was a differential age-related decrease in these interneuronal mRNAs that was inversely correlated with up-regulation of the α1 GABA receptor subunit. Somatostatin and neuropeptide Y mRNAs were most frequently affected (75% of the animals), then calretinin and VIP mRNAs (50% of the animals), and parvalbumin mRNA (25% of the animals) in the aged hippocampus. This selective vulnerability was well correlated at the protein/cellular level as analysed by immunocytochemistry. Somatostatin interneurones, which mostly innervate principal cell distal dendrites, were more vulnerable than calretinin interneurones, which target other interneurones. Parvalbumin interneurones, which mostly innervate perisomatic domains of principal cells, were preserved. This age-dependent differential reduction of specific hippocampal inteneuronal subpopulations might produce functional alterations in the GABAergic tone which might be compensated, at the post-synaptic level, by up-regulation of the expression of the α1 GABA[sub A] receptor subunit. [ABSTRACT FROM AUTHOR]

Background: Alzheimer's disease (AD) is characterized by presenting a complex pathology, not fully resolved yet. This fact, together with the lack of reliable models, has impeded the development of effective therapies. Recently, several studies have shown that functional glial cell defects have a key role in the pathology of AD. However, this glial dysfunction, currently, cannot be correctly modeled using the available animal models, so we hypothesized that cells derived from Alzheimer's patients can serve as a better platform for studying the disease. In this sense, human pluripotent stem cells (hPSC) allow the generation of different types of neural cells, which can be used for disease modeling, identification of new targets and drugs development. Method: We have a collection of hiPSCs derived from patients with sporadic forms of AD. We have differentiated these cells towards neural lineage to obtain neurons and astrocytes. For the generation of oligodendrocytes (OLs), we have developed a fast and robust protocol to generate mature OLs in just 22 days. Result: We have generated neural precursors from all the lines tested. In the case of OLs, the cells generated resemble primary OLs and can myelinate neurons in vivo and in vitro using a screening compatible platform. This platform is being transferred for the generation of the other glial cells. Conclusion: This methodology can be used to elucidate the pathogenic pathways associated with neurodegeneration and to identify new therapeutic targets susceptible to modulation, contributing to the development of new effective drugs against AD. Acknowledgments: J.A.G.L has been supported by a contract of doctor reincorporation plan from the I Plan Propio of the University of Malaga (Spain) and by CIBERNED. The work was supported by Instituto de Salud Carlos III (ISCiii) of Spain, co‐financed by FEDER funds from European Union (grant PI18/01557 to A.G., grant P18/1556 to JV), by Junta de Andalucia co‐financed by FEDER funds grant UMA18‐FEDERJA‐211 (to AG), by Consejeria de Salud of Junta de Andalucia (grant PI‐0276‐2018 to J.A.G.L.) and by CIBERNED. [ABSTRACT FROM AUTHOR]

Background: The accumulation of amyloid beta (Aβ), giving rise to soluble toxic oligomers and insoluble amyloid plaques, is one of the main hallmarks of Alzheimer's disease (AD). Aβ pathology triggers an inflammatory response mediated by activated astroglia and microglia. However, the specific role of the latter in the progression of AD and their relationship with plaques are not fully understood yet. Here we have analyzed, at cellular and subcellular levels, the progression of amyloid pathology and the associated activated microglia in the hippocampus of the model APP750SL/PS1M146L. Method: Immunohistochemistry for light and electron microscopy were performed in hippocampal samples from 4‐ to 18‐month‐old APP750SL/PS1M146L mice. Quantifications were done by image analysis and stereology. Result: There is an age‐dependent increase in the amyloid burden and plaques grow, increasing both the size of the core and the halo, in the hippocampus of APP/PS1 model. Besides, a correlation exists between the size of plaques and the number of neuritic dystrophies surrounding them. Amyloid plaques are surrounded by activated microglia, showing a transcriptomic DAM profile. Microglial processes intertwine with the amyloid fibrils, acting as a barrier that isolates plaques and phagocytose Aβ, which might be toxic for these cells. Therefore, microglia surrounding amyloid plaques show ultrastructural signs of dysfunction, which might lead to a worsening of amyloid pathology and neurodegeneration. Conclusion: Microglia surrounding amyloid plaques suffer a degenerative process with the progression of the pathology, which might affect their functions of phagocytosis/isolation/compaction of amyloid plaques. This could contribute to the progression of AD, with the plaques releasing highly toxic soluble Aβ oligomers to the brain parenchyma. Therefore, restoring microglial function or renewing this population might be a promising therapeutic approach for AD. Supported by: Instituto de Salud Carlos III, co‐financed by FEDER funds from European Union, projects PI18/01557 (to AG) and PI18/01556 (to JV), by CIBERNED (to AG and JV), and by Junta de Andalucia project UMA18‐FEDERJA211 (to AG). [ABSTRACT FROM AUTHOR]

Background: The neuroinflammatory process involving particularly microglial cells, constitutes a hallmark of Alzheimer´s disease (AD) and has been postulated as a critical factor in the disease progression since the identification of several genetic risk factors related to microglial functions. However, the microglial phenotypes in the human pathology have not been determined yet. In this sense, we have previously reported a limited activation and microglial degeneration in the hippocampus of AD patients in contrast to the proinflammatory response long observed in amyloidogenic models. Here, we have further examined the functional/phenotypic profile displayed by microglial cells (activation/degeneration) in two different and vulnerable brain areas of AD patients (frontal cortex and hippocampus). Method: Cellular (immunohistochemistry and image analysis) and molecular (qPCR and western blots) approaches have been carried out in samples from non‐demented controls (Braak II) and AD cases (Braak V‐VI). Result: Microglial cells from frontal cortex of AD patients showed a generalized and exacerbate activation similar to that observed in APP/PS1 mice. These strongly activated microglial cells, predominantly located surrounding amyloid plaques, could drive the AD pathology and, in consequence, could be implicated in the pathology progression. These findings in the frontal cortex were highly in contrast to the attenuated activation and degenerative morphology showed by microglial cells in the hippocampus of the same AD patients. Conclusion: Regional differences in the microglial response exhibit the heterogeneity and complexity of the microglial phenotypes and suggest different functional states of these glial cells in a region‐specific manner. All together, these data need to be considered for better understand the immunological mechanisms underlying AD progression. Modulating brain inflammatory responses might be a promising avenue to prevent cognitive dysfunction in AD patients. Supported by PI18/01557 (AG) and PI18/01556 (JV) grants from ISCiii of Spain and Junta de Andalucia UMA18‐FEDERJA211 (to AG), all co‐financed by FEDER funds from European Union. [ABSTRACT FROM AUTHOR]