Epigenetic inheritance of proteostasis and ageing

A neurodegenerative cellular stress response linked to dark microglia and toxic lipid secretion

The brain's primary immune cells, microglia, are a leading causal cell type in Alzheimer's disease (AD). Yet, the mechanisms by which microglia can drive neurodegeneration remain unresolved. Here, we discover that a conserved stress signaling pathway, the integrated stress response (ISR), characterizes a microglia subset with neurodegenerative outcomes. Autonomous activation of ISR in microglia is sufficient to induce early features of the ultrastructurally distinct "dark microglia" linked to pathological synapse loss. In AD models, microglial ISR activation exacerbates neurodegenerative pathologies and synapse loss while its inhibition ameliorates them. Mechanistically, we present evidence that ISR activation promotes the secretion of toxic lipids by microglia, impairing neuron homeostasis and survival in vitro. Accordingly, pharmacological inhibition of ISR or lipid synthesis mitigates synapse loss in AD models. Our results demonstrate that microglial ISR activation represents a neurodegenerative phenotype, which may be sustained, at least in part, by the secretion of toxic lipids.

Proteostasis Decline and Redox Imbalance in Age-Related Diseases: The Therapeutic Potential of NRF2

Nuclear factor erythroid 2-related factor 2 (NRF2) is a master regulator of cellular homeostasis, overseeing the expression of a wide array of genes involved in cytoprotective processes such as antioxidant and proteostasis control, mitochondrial function, inflammation, and the metabolism of lipids and glucose. The accumulation of misfolded proteins triggers the release, stabilization, and nuclear translocation of NRF2, which in turn enhances the expression of critical components of both the proteasomal and lysosomal degradation pathways. This process facilitates the clearance of toxic protein aggregates, thereby actively maintaining cellular proteostasis. As we age, the efficiency of the NRF2 pathway declines due to several factors including increased activity of its repressors, impaired NRF2-mediated antioxidant and cytoprotective gene expression, and potential epigenetic changes, though the precise mechanisms remain unclear. This leads to diminished antioxidant defenses, increased oxidative damage, and exacerbated metabolic dysregulation and inflammation-key contributors to age-related diseases. Given NRF2's role in mitigating proteotoxic stress, the pharmacological modulation of NRF2 has emerged as a promising therapeutic strategy, even in aged preclinical models. By inducing NRF2, it is possible to mitigate the damaging effects of oxidative stress, metabolic dysfunction, and inflammation, thus reducing protein misfolding. The review highlights NRF2's therapeutic implications for neurodegenerative diseases and cardiovascular conditions, emphasizing its role in improving proteostasis and redox homeostasis Additionally, it summarizes current research into NRF2 as a therapeutic target, offering hope for innovative treatments to counteract the effects of aging and associated diseases.

Transgenerational inheritance of adrenal steroidogenesis inhibition induced by prenatal dexamethasone exposure and its intrauterine mechanism

BACKGROUND

Adrenal gland is the synthesis and secretion organ of glucocorticoid, which is crucial to fetal development and postnatal fate. Recently, we found that prenatal dexamethasone exposure (PDE) could cause adrenal dysfunction in offspring rats, but its multigenerational genetic effects and related mechanisms have not been reported.

METHODS

The PDE rat model was established, and female filial generation 1 (F1) rats mate with wild males to produce the F2, the same way for the F3. Three generation rats were sacrificed for the related detection. SW-13 cells were used to clarify the epigenetic molecular mechanism.

RESULTS

This study confirmed that PDE could activate fetal adrenal glucocorticoid receptor (GR). The activated GR, on the one hand, up-regulated Let-7b (in human cells) to inhibit steroidogenic acute regulatory protein (StAR) expression directly; on the other hand, down-regulated CCCTC binding factor (CTCF) and up-regulated DNA methyltransferase 3a/3b (Dnmt3a/3b), resulting in H19 hypermethylation and low expression. The decreased interaction of H19 and let-7 can further inhibit adrenal steroidogenesis. Additionally, oocytes transmitted the expression change of H19/let-7c axis to the next generation rats. Due to its genetic stability, F2 generation oocytes indirectly exposed to dexamethasone also inhibited H19 expression, which could be inherited to the F3 generation.

CONCLUSIONS

This cascade effect of CTCF/H19/Let-7c ultimately resulted in the transgenerational inheritance of adrenal steroidogenesis inhibition of PDE offspring. This study deepens the understanding of the intrauterine origin of adrenal developmental toxicity, and it will provide evidence for the systematic analysis of the transgenerational inheritance effect of acquired traits induced by PDE. Video Abstract.

Necrostatin-1S mitigates type-2 diabetes-associated cognitive decrement and lipotoxicity-induced neuro-microglia changes through p-RIPK-RIPK3-p-MLKL axis

Type-2 diabetes mellitus (T2DM) is associated with neuroinflammation and cognitive decrement. Necroptosis programmed necrosis is emerging as the major contributing factor to central changes. It is best characterized by the upregulation of p-RIPK(Receptor Interacting Kinase), p-RIPK3, and the phosphorylated-MLKL (mixed-lineage kinase domain-like protein). The present study aims to evaluate the neuroprotective effect of Necrostatin (Nec-1S), a p-RIPK inhibitor, on cognitive changes in the experimental T2DM model in C57BL/6 mice and lipotoxicity-induced neuro-microglia changes in neuro2A and BV2 cells. Further, the study also explores whether Nec-1S would restore mitochondrial and autophago-lysosomal function.T2DM was developed in mice by feeding them a high-fat diet (HFD) for 16 weeks and injecting a single dose of streptozotocin (100 mg/kg, i.p) on the 12^th week. Nec-1S was administered for 3 weeks at (10 mg/kg, i.p) once every 3 days. Lipotoxicity was induced in neuro2A, and BV2 cells using 200 µM palmitate/bovine serum albumin conjugate. Nec-1S (50 µM), and GSK-872(10 µM) were further used to explore their relative effect. The neurobehavioral performance was assessed using mazes and task-assisted performance tests. To decipher the hypothesis plasma parameters, western blot, immunofluorescence, microscopy, and quantitative reverse transcription-PCR studies were carried out. The Nec-1S treatment restored cognitive performance and reduced the p-RIPK-p-RIPK3-p-MLKL mediated neuro-microglia changes in the brain and in cells as well, under lipotoxic stress. Nec-1S reduced tau, and amyloid oligomer load. Moreover, Nec-1S restored mitochondrial function and autophago-lysosome clearance. The findings highlight the central impact of metabolic syndrome and how Nes-1S, by acting as a multifaceted agent, improved central functioning.

Proteostasis in Parkinson's disease: Recent development and possible implication in diagnosis and therapeutics

The protein dyshomeostasis is identified as the hallmark of many age-related neurodegenerative disorders including Parkinson's disease (PD). The diseased brain shows the deposition of Lewy bodies composed of α-synuclein protein aggregates. Functional proteostasis is characterized by the well-coordinated signaling network constituting unfolded protein response (UPR), the ubiquitin-proteasome system (UPS), and the autophagy-lysosome pathway (ALP). These networks ensure proper synthesis, folding, confirmation, and degradation of protein i.e., α-synuclein protein in PD. The proper functioning the of intricately woven proteostasis network is quite resilient to sustain under the influence of stressors. The synuclein protein turnover is hugely influenced by the autosomal dominant, recessive, and X-linked mutational changes of a gene involved in UPR, UPS, and ALP. The methylation, acetylation-related epigenetic modifications of DNA and histone proteins along with microRNA-mediated transcriptional changes also lead to extensive proteostasis dysregulation. The result of defective proteostasis is the deposition of many proteins which start appearing in the biofluids and can be identified as potential biomarkers for early diagnosis of PD. The therapeutic intervention targeted at different strata of proteostasis machinery holds great possibilities for delaying the age-related accumulation of pathological hallmarks.

C. elegans as an Animal Model to Study the Intersection of DNA Repair, Aging and Neurodegeneration

Since its introduction as a genetic model organism, Caenorhabditis elegans has yielded insights into the causes of aging. In addition, it has provided a molecular understanding of mechanisms of neurodegeneration, one of the devastating effects of aging. However, C. elegans has been less popular as an animal model to investigate DNA repair and genomic instability, which is a major hallmark of aging and also a cause of many rare neurological disorders. This article provides an overview of DNA repair pathways in C. elegans and the impact of DNA repair on aging hallmarks, such as mitochondrial dysfunction, telomere maintenance, and autophagy. In addition, we discuss how the combination of biological characteristics, new technical tools, and the potential of following precise phenotypic assays through a natural life-course make C. elegans an ideal model organism to study how DNA repair impact neurodegeneration in models of common age-related neurodegenerative diseases.

The pathogenesis of amyotrophic lateral sclerosis: Mitochondrial dysfunction, protein misfolding and epigenetics

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease with multiple complex mechanisms involved. Among them, mitochondrial dysfunction plays an important role in ALS. Multiple studies have shown that mitochondria are closely associated with reactive oxygen species production and oxidative stress and exhibit different functional states in different genetic backgrounds. In this review we explored the roles of Ca²⁺, autophagy, mitochondrial quality control in the regulation of mitochondrial homeostasis and their relationship with ALS. In addition, we also summarized and analyzed the roles of protein misfolding and abnormal aggregation in the pathogenesis of ALS. Moreover, we also discussed how epigenetic mechanisms such as DNA methylation and protein post-translational modification affect initiation and progression of ALS. Nevertheless, existing events still cannot fully explain the pathogenesis of ALS at present, more studies are required to explore pathological mechanisms of ALS.

Mechanisms Through Which Some Mitochondria-Generated Metabolites Act as Second Messengers That Are Essential Contributors to the Aging Process in Eukaryotes Across Phyla

Recent studies have revealed that some low-molecular weight molecules produced in mitochondria are essential contributing factors to aging and aging-associated pathologies in evolutionarily distant eukaryotes. These molecules are intermediates or products of certain metabolic reactions that are activated in mitochondria in response to specific changes in the nutrient, stress, proliferation, or age status of the cell. After being released from mitochondria, these metabolites directly or indirectly change activities of a distinct set of protein sensors that reside in various cellular locations outside of mitochondria. Because these protein sensors control the efficiencies of some pro- or anti-aging cellular processes, such changes in their activities allow to create a pro- or anti-aging cellular pattern. Thus, mitochondria can function as signaling platforms that respond to certain changes in cell stress and physiology by remodeling their metabolism and releasing a specific set of metabolites known as "mitobolites." These mitobolites then define the pace of cellular and organismal aging because they regulate some longevity-defining processes taking place outside of mitochondria. In this review, we discuss recent progress in understanding mechanisms underlying the ability of mitochondria to function as such signaling platforms in aging and aging-associated diseases.

Developmental programming of aging trajectory

There is accumulating evidence that aging phenotype and longevity may be developmentally programmed. Main mechanisms linking developmental conditions to later-life health outcomes include persistent changes in epigenetic regulation, (re)programming of major endocrine axes such as growth hormone/insulin-like growth factor axis and hypothalamic-pituitary-adrenal axis and also early-life immune maturation. Recently, evidence has also been generated on the role of telomere biology in developmental programming of aging trajectory. In addition, persisting changes of intestinal microbiota appears to be crucially involved in these processes. In this review, experimental and epidemiological evidence on the role of early-life conditions in programming of aging phenotypes are presented and mechanisms potentially underlying these associations are discussed.

Epigenetics of Subcellular Structure Functioning in the Origin of Risk or Resilience to Comorbidity of Neuropsychiatric and Cardiometabolic Disorders

Mechanisms controlling mitochondrial function, protein folding in the endoplasmic reticulum (ER) and nuclear processes such as telomere length and DNA repair may be subject to epigenetic cues that relate the genomic expression and environmental exposures in early stages of life. They may also be involved in the comorbid appearance of cardiometabolic (CMD) and neuropsychiatric disorders (NPD) during adulthood. Mitochondrial function and protein folding in the endoplasmic reticulum are associated with oxidative stress and elevated intracellular calcium levels and may also underlie the vulnerability for comorbid CMD and NPD. Mitochondria provide key metabolites such as nicotinamide adenine dinucleotide (NAD+), ATP, α-ketoglutarate and acetyl coenzyme A that are required for many transcriptional and epigenetic processes. They are also a source of free radicals. On the other hand, epigenetic markers in nuclear DNA determine mitochondrial biogenesis. The ER is the subcellular organelle in which secretory proteins are folded. Many environmental factors stop the ability of cells to properly fold proteins and modify post-translationally secretory and transmembrane proteins leading to endoplasmic reticulum stress and oxidative stress. ER functioning may be epigenetically determined. Chronic ER stress is emerging as a key contributor to a growing list of human diseases, including CMD and NPD. Telomere loss causes chromosomal fusion, activation of the control of DNA damage-responses, unstable genome and altered stem cell function, which may underlie the comorbidity of CMD and NPD. The length of telomeres is related to oxidative stress and may be epigenetically programmed. Pathways involved in DNA repair may be epigenetically programmed and may contribute to diseases. In this paper, we describe subcellular mechanisms that are determined by epigenetic markers and their possible relation to the development of increased susceptibility to develop CMD and NPD.

Non-genomic transmission of longevity between generations: potential mechanisms and evidence across species

Accumulating animal and human data indicate that environmental exposures experienced during sensitive developmental periods may strongly influence risk of adult disease. Moreover, the effects triggered by developmental environmental cues can be transgenerationally transmitted, potentially affecting offspring health outcomes. Increasing evidence suggests a central role of epigenetic mechanisms (heritable alterations in gene expression occurring without changes in underlying DNA sequence) in mediating these effects. This review summarizes the findings from animal models, including worms, insects, and rodents, and also from human studies, indicating that lifespan and longevity-associated characteristics can be transmitted across generations via non-genetic factors.

Transgenerational epigenetics: Integrating soma to germline communication with gametic inheritance

Evidence supporting germline mediated epigenetic inheritance of environmentally induced traits has increasingly emerged over the past several years. Although the mechanisms underlying this inheritance remain unclear, recent findings suggest that parental gamete-borne epigenetic factors, particularly RNAs, affect post-fertilization and developmental gene regulation, ultimately leading to phenotypic appearance in the offspring. Complex processes involving gene expression and epigenetic regulation are considered to perpetuate across generations. In addition to transfer of germline factors, epigenetic inheritance via gametes also requires a mechanism whereby the information pertaining to the induced traits is communicated from soma to germline. Despite violating a century-old view in biology, this communication seems to play a role in transmission of environmental effects across generations. Circulating RNAs, especially those associated with extracellular vesicles like exosomes, are emerging as promising candidates that can transmit gene regulatory information in this direction. Cumulatively, these new observations provide a basis to integrate epigenetic inheritance. With significant implications in health, disease and ageing, the latter appears poised to revolutionize biology.

Empirical Validation of a Hypothesis of the Hormetic Selective Forces Driving the Evolution of Longevity Regulation Mechanisms

Exogenously added lithocholic bile acid and some other bile acids slow down yeast chronological aging by eliciting a hormetic stress response and altering mitochondrial functionality. Unlike animals, yeast cells do not synthesize bile acids. We therefore hypothesized that bile acids released into an ecosystem by animals may act as interspecies chemical signals that generate selective pressure for the evolution of longevity regulation mechanisms in yeast within this ecosystem. To empirically verify our hypothesis, in this study we carried out a three-step process for the selection of long-lived yeast species by a long-term exposure to exogenous lithocholic bile acid. Such experimental evolution yielded 20 long-lived mutants, three of which were capable of sustaining their considerably prolonged chronological lifespans after numerous passages in medium without lithocholic acid. The extended longevity of each of the three long-lived yeast species was a dominant polygenic trait caused by mutations in more than two nuclear genes. Each of the three mutants displayed considerable alterations to the age-related chronology of mitochondrial respiration and showed enhanced resistance to chronic oxidative, thermal, and osmotic stresses. Our findings empirically validate the hypothesis suggesting that hormetic selective forces can drive the evolution of longevity regulation mechanisms within an ecosystem.