Abstract:
BACKGROUND: Alzheimer's disease (AD) is the major age-related form of dementia in which dysfunctional ubiquitin-proteasome system (UPS) and autophagy represent primary mechanisms leading to accumulation of misfolded proteins, dysfunction of astroglial cells, neuroinflammation and neurodegeneration. Alterations of the endoplasmic reticulum (ER)-mitochondria contact sites (MERCS), specifically the shortening of the distance between the organelles, was proposed as a key mechanism of cell dysfunction in AD. However, its link to the impairment of the proteolytic system in AD remains unexplored. METHODS: We used, as a model, hippocampal astrocytes from 3xTg-AD mice expressing either control plasmid or synthetic linkers stabilizing ER-mitochondrial interaction at 10 nm (10 nm-EML) or at 20 nm (20 nm-EML). Alternatively, astrocytes were treated with mitochondrial Ca(2+) uptake inhibitor benzethonium chloride or activator amorolfine. We used Western blot to assess protein expression and specific enzymatic activity tests for the analysis of proteasomal, autophagic and lysosomal activities. Single cell fluorescent Ca(2+) imaging, using 4mtD3cpv probe targeted to the mitochondrial matrix, was used to assess mitochondrial Ca(2+) uptake. RESULTS: Stabilization of MERCS at 20 nm (20 nm-MERCS), which promotes mitochondrial Ca(2+) uptake, rescued protein ubiquitination, UPS composition and activity. Immunoproteasome components beta2i and beta5i, upregulated in AD astrocytes, and INFgamma, a master-regulator of UPS remodelling in inflammatory conditions, were also rescued. Autophagic markers beclin 1, LC3II and p62, and lysosome-related marker cathepsin B, all upregulated in AD astrocytes, were significantly reduced, while autophagic flux was rescued, by stabilizing 20 nm-MERCS. Furthermore, stabilization of 20 nm-MERCS fully rescued previously reported deficit of mitochondrial Ca(2+) uptake. Strikingly, application of a mitochondrial Ca(2+) uptake positive modulator, amorolfine, partially rescued pathological remodelling of UPS and autophagy, suggesting that both mitochondrial Ca(2+)-related and Ca(2+)-unrelated mechanisms play a role in the beneficial effect of 20 nm-MERCS stabilization on protein dyshomeostasis. CONCLUSIONS: Our results suggest that disruption of ER-mitochondrial interaction is a key factor for AD-related dysregulation of protein degradation and provide a proof that stabilization of MERCS at a defined distance and/or pharmacological rescue of mitochondrial Ca(2+) uptake represent valuable strategies for the development of future anti-AD therapy.

Abstract:
Ataxia-telangiectasia (A-T) is a rare neurodegenerative disorder caused by the deficiency of the serine/threonine kinase ataxia telangiectasia mutated (ATM) protein, whose loss of function leads to altered cell cycle, apoptosis, oxidative stress balance and DNA repair after damage. The clinical manifestations are multisystemic, among them cerebellar degeneration and muscular ataxia. The molecular mechanism by which ATM loss leads to A-T is still uncertain and, currently only symptomatic treatments are available. In this study, we generated a functional skeletal muscle cell model that recapitulates A-T and highlights the role of ATM in calcium signalling and muscle contraction. To this aim, by using CRISPR/Cas9 technology, we knocked out the ATM protein in urine-derived stem cells (USCs) from healthy donors. The resulting USCs-ATM-KO maintained stemness but showed G2/S cell cycle progression and an inability to repair DNA after UV damage. Moreover, they showed increased cytosolic calcium release after ATP stimulation to the detriment of the mitochondria. The alterations of calcium homoeostasis were maintained after differentiation of USCs-ATM-KO into skeletal muscle cells (USC-SkMCs) and correlated with impaired cell contraction. Indeed, USC-SkMCs-ATM-KO contraction kinetics were dramatically accelerated compared to control cells. These results highlight the relevant function of ATM in skeletal muscle, which is not only dependent on a non-functional neuronal communication, paving the way for future studies on a muscular interpretation of A-T ataxia.

Abstract:
Alterations of endoplasmic reticulum (ER)-mitochondrial interaction have been associated with different pathological conditions, including neurodegenerative diseases, characterized by dysregulation of protein homeostasis. However, little is known about how enhanced ER-mitochondrial tethering affects cellular proteostatic machinery. Here, we transiently overexpressed synthetic ER-mitochondrial linkers (EMLs), stabilizing the ER-mitochondrial distance at

Abstract:
IP(3) receptor (IP(3)R)-mediated Ca(2+) transfer at the mitochondria-endoplasmic reticulum (ER) contact sites (MERCS) drives mitochondrial Ca(2+) uptake and oxidative metabolism and is linked to different pathologies, including Parkinson's disease (PD). The dependence of Ca(2+) transfer efficiency on the ER-mitochondria distance remains unexplored. Employing molecular rulers that stabilize ER-mitochondrial distances at 5 nm resolution, and using genetically encoded Ca(2+) indicators targeting the ER lumen and the sub-mitochondrial compartments, we now show that a distance of ~20 nm is optimal for Ca(2+) transfer and mitochondrial oxidative metabolism due to enrichment of IP(3)R at MERCS. In human iPSC-derived astrocytes from PD patients, 20 nm MERCS were specifically reduced, which correlated with a reduction of mitochondrial Ca(2+) uptake. Stabilization of the ER-mitochondrial interaction at 20 nm, but not at 10 nm, fully rescued mitochondrial Ca(2+) uptake in PD astrocytes. Our work determines with precision the optimal distance for Ca(2+) flux between ER and mitochondria and suggests a new paradigm for fine control over mitochondrial function.

Abstract:

Abstract:
BACKGROUND/OBJECTIVES: Methyltransferase EZH2-mediated H3K27me3 is involved in liver inflammation and fibrosis, but its role in hepatic metabolic derangements is not yet clearly defined. We investigated if a high-fat diet (HFD) induced early changes in EZH2 expression and H3K27 me3 in the liver of mice. METHODS: Five-week-old mice were fed an HFD or a low-fat diet (Control) for 2 weeks (2 W) or 8 weeks (8 W). Body weight was recorded weekly. Glycemia and oral glucose tolerance were assessed at baseline and after 2 W-8 W. Finally, livers were collected for further analysis. RESULTS: As expected, mice that received 8 W HFD showed an increase in body weight, glycemia, and liver steatosis and an impairment in glucose tolerance; no alterations were observed in 2 W HFD mice. Eight weeks of HFD caused hepatic EZH2 nuclear localization and increased H3 K27me3; surprisingly, the same alterations occurred in 2 W HFD mice livers, even before overweight onset. We demonstrated that selective EZH2 inhibition reduced H3K27me3 and counteracted lipid accumulation in HUH-7 cells upon palmitic acid treatment. CONCLUSIONS: In conclusion, we point to EZH2/H3K27me3 as an early epigenetic event occurring in fatty-acid-challenged livers both in vivo and in vitro, thus establishing EZH2 as a potential pharmacological target for metabolic derangements.

Abstract:
Alzheimer's disease (AD) represents an urgent yet unmet challenge for modern society, calling for exploration of innovative targets and therapeutic approaches. Astrocytes, main homeostatic cells in the CNS, represent promising cell-target. Our aim was to investigate if deletion of the regulatory CaNB1 subunit of calcineurin in astrocytes could mitigate AD-related memory deficits, neuropathology, and neuroinflammation. We have generated two, acute and chronic, AD mouse models with astrocytic CaNB1 ablation (ACN-KO). In the former, we evaluated the ability of beta-amyloid oligomers (AbetaOs) to impair memory and activate glial cells once injected in the cerebral ventricle of conditional ACN-KO mice. Next, we generated a tamoxifen-inducible astrocyte-specific CaNB1 knock-out in 3xTg-AD mice (indACNKO-AD). CaNB1 was deleted, by tamoxifen injection, in 11.7-month-old 3xTg-AD mice for 4.4 months. Spatial memory was evaluated using the Barnes maze; beta-amyloid plaques burden, neurofibrillary tangle deposition, reactive gliosis, and neuroinflammation were also assessed. The acute model showed that ICV injected AbetaOs in 2-month-old wild type mice impaired recognition memory and fostered a pro-inflammatory microglia phenotype, whereas in ACN-KO mice, AbetaOs were inactive. In indACNKO-AD mice, 4.4 months after CaNB1 depletion, we found preservation of spatial memory and cognitive flexibility, abolishment of amyloidosis, and reduction of neurofibrillary tangles, gliosis, and neuroinflammation. Our results suggest that ACN is crucial for the development of cognitive impairment, AD neuropathology, and neuroinflammation. Astrocyte-specific CaNB1 deletion is beneficial for both the abolishment of AbetaO-mediated detrimental effects and treatment of ongoing AD-related pathology, hence representing an intriguing target for AD therapy.

Abstract:
Tuberous Sclerosis Complex (TSC) is a multisystem genetic disorder characterized by the development of benign tumors in various organs, including the brain, and is often accompanied by epilepsy, neurodevelopmental comorbidities including intellectual disability and autism. A key hallmark of TSC is the hyperactivation of the mechanistic target of rapamycin (mTOR) signaling pathway, which induces alterations in cortical development and metabolic processes in astrocytes, among other cellular functions. These changes could modulate seizure susceptibility, contributing to the progression of epilepsy and its associated comorbidities. Epilepsy is characterized by dysregulation of calcium (Ca(2+)) channels and intracellular Ca(2+) dynamics. These factors contribute to hyperexcitability, disrupted synaptogenesis, and altered synchronization of neuronal networks, all of which contribute to seizure activity. This study investigates the intricate interplay between altered Ca(2+) dynamics, mTOR pathway dysregulation, and cellular metabolism in astrocytes. The transcriptional profile of TSC patients revealed significant alterations in pathways associated with cellular respiration, ER and mitochondria, and Ca(2+) regulation. TSC astrocytes exhibited lack of responsiveness to various stimuli, compromised oxygen consumption rate and reserve respiratory capacity underscoring their reduced capacity to react to environmental changes or cellular stress. Furthermore, our study revealed significant reduction of store operated calcium entry (SOCE) along with strong decrease of basal mitochondrial Ca(2+) concentration and Ca(2+) influx in TSC astrocytes. In addition, we observed alteration in mitochondrial membrane potential, characterized by increased depolarization in TSC astrocytes. Lastly, we provide initial evidence of structural abnormalities in mitochondria within TSC patient-derived astrocytes, suggesting a potential link between disrupted Ca(2+) signaling and mitochondrial dysfunction. Our findings underscore the complexity of the relationship between Ca(2+) signaling, mitochondria dynamics, apoptosis, and mTOR hyperactivation. Further exploration is required to shed light on the pathophysiology of TSC and on TSC associated neuropsychiatric disorders offering further potential avenues for therapeutic development.

Abstract:
Alzheimer's disease (AD) is characterized by complex etiology, long-lasting pathogenesis, and cell-type-specific alterations. Currently, there is no cure for AD, emphasizing the urgent need for a comprehensive understanding of cell-specific pathology. Astrocytes, principal homeostatic cells of the central nervous system, are key players in the pathogenesis of neurodegenerative diseases, including AD. Cellular models greatly facilitate the investigation of cell-specific pathological alterations and the dissection of molecular mechanisms and pathways. Tumor-derived and immortalized astrocytic cell lines, alongside the emerging technology of adult induced pluripotent stem cells, are widely used to study cellular dysfunction in AD. Surprisingly, no stable cell lines were available from genetic mouse AD models. Recently, we established immortalized hippocampal astroglial cell lines from amyloid-beta precursor protein/presenilin-1/Tau triple-transgenic (3xTg)-AD mice (denominated as wild type (WT)- and 3Tg-iAstro cells) using retrovirus-mediated transduction of simian virus 40 large T-antigen and propagation without clonal selection, thereby maintaining natural heterogeneity of primary cultures. Several groups have successfully used 3Tg-iAstro cells for single-cell and omics approaches to study astrocytic AD-related alterations of calcium signaling, mitochondrial dysfunctions, disproteostasis, altered homeostatic and signaling support to neurons, and blood-brain barrier models. Here we provide a comparative overview of the most used models to study astrocytes in vitro, such as primary culture, tumor-derived cell lines, immortalized astroglial cell lines, and induced pluripotent stem cell-derived astrocytes. We conclude that immortalized WT- and 3Tg-iAstro cells provide a non-competitive but complementary, low-cost, easy-to-handle, and versatile cellular model for dissection of astrocyte-specific AD-related alterations and preclinical drug discovery.

Abstract:
Protein misfolding is prominent in early cellular pathology of Alzheimer's disease (AD), implicating pathophysiological significance of endoplasmic reticulum stress/unfolded protein response (ER stress/UPR) and highlighting it as a target for drug development. Experimental data from animal AD models and observations on human specimens are, however, inconsistent. ER stress and associated UPR are readily observed in in vitro AD cellular models and in some AD model animals. In the human brain, components and markers of ER stress as well as UPR transducers are observed at Braak stages III-VI associated with severe neuropathology and neuronal death. The picture, however, is further complicated by the brain region- and cell type-specificity of the AD-related pathology. Terms 'disturbed' or 'non-canonical' ER stress/UPR were used to describe the discrepancies between experimental data and the classic ER stress/UPR cascade. Here we discuss possible 'disturbing' or 'interfering' factors which may modify ER stress/UPR in the early AD pathogenesis. We focus on the dysregulation of the ER Ca(2+) homeostasis, store-operated Ca(2+) entry, and the interaction between the ER and mitochondria. We suggest that a detailed study of the CNS cell type-specific alterations of Ca(2+) homeostasis in early AD may deepen our understanding of AD-related dysproteostasis.