Epigenetic modifiers promote mitochondrial biogenesis and oxidative metabolism leading to enhanced differentiation of neuroprogenitor cells

Emerging Functional Connections Between Metabolism and Epigenetic Remodeling in Neural Differentiation

Stem cells possess extraordinary capacities for self-renewal and differentiation, making them highly valuable in regenerative medicine. Among these, neural stem cells (NSCs) play a fundamental role in neural development and repair processes. NSC characteristics and fate are intricately regulated by the microenvironment and intracellular signaling. Interestingly, metabolism plays a pivotal role in orchestrating the epigenome dynamics during neural differentiation, facilitating the transition from undifferentiated NSC to specialized neuronal and glial cell types. This intricate interplay between metabolism and the epigenome is essential for precisely regulating gene expression patterns and ensuring proper neural development. This review highlights the mechanisms behind metabolic regulation of NSC fate and their connections with epigenetic regulation to shape transcriptional programs of stemness and neural differentiation. A comprehensive understanding of these molecular gears appears fundamental for translational applications in regenerative medicine and personalized therapies for neurological conditions.

Sodium butyrate ameliorates high glucose-suppressed neuronal mitophagy by restoring PRKN expression via inhibiting the RELA-HDAC8 complex

Damaged mitochondria accumulation in diabetes is one of the main features that contribute to increased incidence of cognitive impairment by inducing apoptosis. Butyrate is a major metabolite produced by microbiota that has neuroprotective effects by regulating mitochondrial function. However, detailed mechanisms underlying how butyrate can regulate neuronal mitophagy remain unclear. Here, we examined the regulatory effects of sodium butyrate (NaB) on high glucose-induced mitophagy dysregulation, neuronal apoptosis, and cognitive impairment and its underlying mechanisms in human-induced pluripotent stem cell-derived neurons, SH-SY5Ys, and streptozotocin (STZ)-induced diabetic mice. In our results, diabetic mice showed gut-microbiota dysbiosis, especially a decreased number of butyrate-producing bacteria and reduced NaB plasma concentration. NaB ameliorated high glucose-induced neuronal mitochondrial dysfunction by recovering PRKN/Parkin-mediated mitophagy. High glucose-induced reactive oxygen species (ROS) and -inhibited PRKAA/AMPKα stimulated the RELA/p65-HDAC8 complex, which downregulated PRKN protein expression by binding to the PRKN promoter region. NaB restored PRKN expression by blocking RELA nuclear translocation and directly inhibiting HDAC8 in the nucleus. In addition, HDAC8 overexpression inhibited the positive effect of NaB on high glucose-induced mitophagy dysfunction and neuronal apoptosis. Oral administration of NaB improved cognitive impairment in diabetic mice by restoring mitophagy in the hippocampus. Taken together, NaB ameliorates neuronal mitophagy through PRKN restoration by inhibiting RELA-HDAC8 complexes, suggesting that NaB is an important substance for protecting neuronal apoptosis in diabetes-associated cognitive impairment.

Emerging Neuroprotective Strategies: Unraveling the Potential of HDAC Inhibitors in Traumatic Brain Injury Management

Traumatic brain injury (TBI) is a significant global health problem, leading to high rates of mortality and disability. It occurs when an external force damages the brain, causing immediate harm and triggering further pathological processes that exacerbate the condition. Despite its widespread impact, the underlying mechanisms of TBI remain poorly understood, and there are no specific pharmacological treatments available. This creates an urgent need for new, effective neuroprotective drugs and strategies tailored to the diverse needs of TBI patients. In the realm of gene expression regulation, chromatin acetylation plays a pivotal role. This process is controlled by two classes of enzymes: histone acetyltransferase (HAT) and histone deacetylase (HDAC). These enzymes modify lysine residues on histone proteins, thereby determining the acetylation status of chromatin. HDACs, in particular, are involved in the epigenetic regulation of gene expression in TBI. Recent research has highlighted the potential of HDAC inhibitors (HDACIs) as promising neuroprotective agents. These compounds have shown encouraging results in animal models of various neurodegenerative diseases. HDACIs offer multiple avenues for TBI management: they mitigate the neuroinflammatory response, alleviate oxidative stress, inhibit neuronal apoptosis, and promote neurogenesis and axonal regeneration. Additionally, they reduce glial activation, which is associated with TBI-induced neuroinflammation. This review aims to provide a comprehensive overview of the roles and mechanisms of HDACs in TBI and to evaluate the therapeutic potential of HDACIs. By summarizing current knowledge and emphasizing the neuroregenerative capabilities of HDACIs, this review seeks to advance TBI management and contribute to the development of targeted treatments.

Dysfunctional Postnatal Mitochondrial Energy Metabolism in a Patient with Neurodevelopmental Defects Caused by Intrauterine Growth Restriction Due to Idiopathic Placental Insufficiency

We report the case of a four-year-old male patient with a complex medical history born prematurely as the result of intrauterine growth restriction due to placental insufficiency. His clinical manifestations included severe neurodevelopmental deficits, global developmental delay, Pierre-Robin sequence, and intractable epilepsy with both generalized and focal features. The proband's low levels of citrulline and lactic acidosis provoked by administration of Depakoke were evocative of a mitochondrial etiology. The proband's genotype-phenotype correlation remained undefined in the absence of nuclear and mitochondrial pathogenic variants detected by deep sequencing of both genomes. However, live-cell mitochondrial metabolic investigations provided evidence of a deficient oxidative-phosphorylation pathway responsible for adenosine triphosphate (ATP) synthesis, leading to chronic energy crisis in the proband. In addition, our metabolic analysis revealed metabolic plasticity in favor of glycolysis for ATP synthesis. Our mitochondrial morphometric analysis by transmission electron microscopy confirmed the suspected mitochondrial etiology, as the proband's mitochondria exhibited an immature morphology with poorly developed and rare cristae. Thus, our results support the concept that suboptimal levels of intrauterine oxygen and nutrients alter fetal mitochondrial metabolic reprogramming toward oxidative phosphorylation (OXPHOS) leading to a deficient postnatal mitochondrial energy metabolism. In conclusion, our collective studies shed light on the long-term postnatal mitochondrial pathophysiology caused by intrauterine growth restriction due to idiopathic placental insufficiency and its negative impact on the energy-demanding development of the fetal and postnatal brain.

Histone H3 Acetylation Is Involved in Retinoid Acid-Induced Neural Differentiation through Increasing Mitochondrial Function

Histone acetylation and mitochondrial function contribute importantly to neural differentiation, which is critically associated with neurodevelopmental disorders such as Down Syndrome (DS). However, whether and how histone acetylation regulates mitochondrial function and further affects neural differentiation has not been well described. In this study, when treated with retinoid acid (RA), the human neuroblastoma SH-SY5Y cell line was used as a neural differentiation model. We found that the acetylation of histone H3, especially H3 lysine 14 acetylation (H3K14ac), and mitochondrial function, including biogenesis and electron transport chain, were enhanced during neural differentiation. Specific inhibition of histone acetyltransferases (HATs) induced neural differentiation deficits, accompanied by downregulation of mitochondrial function. Furthermore, RA receptors (RARs) interacting with HATs were involved in the increased H3K14ac and the enhanced mitochondrial function during the neural differentiation process. Finally, receptor-interacting protein 140 (RIP140), a co-repressor of RARs, was also involved in regulating histone acetylation. RIP140 overexpression inhibited histone acetylation and mediated negative feedback on target genes which are involved in RA signaling. These findings evidenced that when interacting with RARs which had been negatively regulated by RIP140, RA promoted neural differentiation by promoting H3K14ac and enhanced mitochondrial function. This provides a molecular foundation for further investigations into abnormal neural development.

Reciprocal Regulation of Peroxisome Biogenesis and Myogenic Factors Is Critical for Myogenesis

Mitochondria (MITO) and peroxisomes (PEXO) are the major organelles involved in the oxidative metabolism of cells, but detailed examination of their dynamics and functional adaptations during skeletal muscle (SKM) development (myogenesis) is still lacking. In this study, we found that during myogenesis, MITO DNA, ROS level, and redox ratio increased in myotubes, but the membrane potential (Δψm) and ATP content reduced, implying that the MITO efficiency might reduce during myogenesis. The PEXO number and density both increased during myogenesis, which probably resulted from the accumulation and increased biogenesis of PEXO. The expression of PEXO biogenesis factors was induced during myogenesis in vitro and in utero, and their promoters were also activated by MyoD. Knockdown of the biogenesis factors Pex3 repressed not only the PEXO density and functions but also the levels of MITO genes and functions, suggesting a close coupling between PEXO biogenesis and MITO functions. Surprisingly, Pex3 knockdown by the CRISPRi system repressed myogenic differentiation, indicating critical involvement of PEXO biogenesis in myogenesis. Taken together, these observations suggest that the dynamics and functions of both MITO and PEXO are coupled with each other and with the metabolic changes that occur during myogenesis, and these metabolic couplings are critical to myogenesis.

Epidrugs in the Therapy of Central Nervous System Disorders: A Way to Drive on?

The polygenic nature of neurological and psychiatric syndromes and the significant impact of environmental factors on the underlying developmental, homeostatic, and neuroplastic mechanisms suggest that an efficient therapy for these disorders should be a complex one. Pharmacological interventions with drugs selectively influencing the epigenetic landscape (epidrugs) allow one to hit multiple targets, therefore, assumably addressing a wide spectrum of genetic and environmental mechanisms of central nervous system (CNS) disorders. The aim of this review is to understand what fundamental pathological mechanisms would be optimal to target with epidrugs in the treatment of neurological or psychiatric complications. To date, the use of histone deacetylases and DNA methyltransferase inhibitors (HDACis and DNMTis) in the clinic is focused on the treatment of neoplasms (mainly of a glial origin) and is based on the cytostatic and cytotoxic actions of these compounds. Preclinical data show that besides this activity, inhibitors of histone deacetylases, DNA methyltransferases, bromodomains, and ten-eleven translocation (TET) proteins impact the expression of neuroimmune inflammation mediators (cytokines and pro-apoptotic factors), neurotrophins (brain-derived neurotropic factor (BDNF) and nerve growth factor (NGF)), ion channels, ionotropic receptors, as well as pathoproteins (β-amyloid, tau protein, and α-synuclein). Based on this profile of activities, epidrugs may be favorable as a treatment for neurodegenerative diseases. For the treatment of neurodevelopmental disorders, drug addiction, as well as anxiety disorders, depression, schizophrenia, and epilepsy, contemporary epidrugs still require further development concerning a tuning of pharmacological effects, reduction in toxicity, and development of efficient treatment protocols. A promising strategy to further clarify the potential targets of epidrugs as therapeutic means to cure neurological and psychiatric syndromes is the profiling of the epigenetic mechanisms, which have evolved upon actions of complex physiological lifestyle factors, such as diet and physical exercise, and which are effective in the management of neurodegenerative diseases and dementia.

The Crosstalk between Microbiome and Mitochondrial Homeostasis in Neurodegeneration

Mitochondria are highly dynamic organelles that serve as the primary cellular energy-generating system. Apart from ATP production, they are essential for many biological processes, including calcium homeostasis, lipid biogenesis, ROS regulation and programmed cell death, which collectively render them invaluable for neuronal integrity and function. Emerging evidence indicates that mitochondrial dysfunction and altered mitochondrial dynamics are crucial hallmarks of a wide variety of neurodevelopmental and neurodegenerative conditions. At the same time, the gut microbiome has been implicated in the pathogenesis of several neurodegenerative disorders due to the bidirectional communication between the gut and the central nervous system, known as the gut-brain axis. Here we summarize new insights into the complex interplay between mitochondria, gut microbiota and neurodegeneration, and we refer to animal models that could elucidate the underlying mechanisms, as well as novel interventions to tackle age-related neurodegenerative conditions, based on this intricate network.

Exogenous Players in Mitochondria-Related CNS Disorders: Viral Pathogens and Unbalanced Microbiota in the Gut-Brain Axis

Billions of years of co-evolution has made mitochondria central to the eukaryotic cell and organism life playing the role of cellular power plants, as indeed they are involved in most, if not all, important regulatory pathways. Neurological disorders depending on impaired mitochondrial function or homeostasis can be caused by the misregulation of "endogenous players", such as nuclear or cytoplasmic regulators, which have been treated elsewhere. In this review, we focus on how exogenous agents, i.e., viral pathogens, or unbalanced microbiota in the gut-brain axis can also endanger mitochondrial dynamics in the central nervous system (CNS). Neurotropic viruses such as Herpes, Rabies, West-Nile, and Polioviruses seem to hijack neuronal transport networks, commandeering the proteins that mitochondria typically use to move along neurites. However, several neurological complications are also associated to infections by pandemic viruses, such as Influenza A virus and SARS-CoV-2 coronavirus, representing a relevant risk associated to seasonal flu, coronavirus disease-19 (COVID-19) and "Long-COVID". Emerging evidence is depicting the gut microbiota as a source of signals, transmitted via sensory neurons innervating the gut, able to influence brain structure and function, including cognitive functions. Therefore, the direct connection between intestinal microbiota and mitochondrial functions might concur with the onset, progression, and severity of CNS diseases.

Rectal administration of butyrate ameliorates pulmonary fibrosis in mice through induction of hepatocyte growth factor in the colon via the HDAC-PPARγ pathway

Butyrate, given by oral administration or in drinking water, has been shown to improve experimental pulmonary fibrosis (PF) in mice despite of very low bioavailability. The pharmacokinetic-pharmacodynamics disconnection attracts us to explore its anti-PF mechanism in view of the intestinal expression of anti-PF factors. In bleomycin-induced PF in mice, rectal administration of butyrate (500 mg/kg) exhibited a significant anti-PF effect, with a maximum plasma concentration largely lower than the minimum effective concentration (1 mM) at which butyrate inhibited the expression of pro-inflammatory factors by lung epithelial cells and the production of extracellular matrix by lung fibroblasts. The rectal administration of butyrate significantly upregulated the mRNA expression of hepatocyte growth factor (HGF) in the colons of PF mice, but showed no significant effect on the mRNA expression of HGF in the small intestines, lungs and livers. In colon epithelial cells, the monocarboxylate transporter inhibitor α-cyano-4-hydroxycinnamic acid (CHC) abrogated butyrate-induced expression of HGF, indicating that butyrate functions through entering into cells. Butyrate showed no significant effect on the histone acetylation in the promoter region of HGF, suggesting that it promotes HGF expression not by directly affecting the histone deacetylation of HGF but by other pathways. GW9662, the inhibitor of PPARγ, significantly attenuated the effect of butyrate to promote the mRNA expression of HGF. Butyrate was able to enhance the acetylation of PPARγ, and a targeted mutation of lysine at the position 240 (K240) of PPARγ markedly diminished the induction of butyrate on HGF expression, suggesting that butyrate promoted HGF expression in colon epithelial cells by upregulating PPARγ K240 acetylation. In summary, rectal administration of butyrate promotes the expression of HGF in colonic epithelial cells through upregulating PPARγ acetylation via inhibition of HDAC activity. The findings of the present study provide a reasonable explanation for the anti-PF action mode of butyrate based on the 'lung-gut axis', and found that intestine-derived butyrate and HGF may be involved in the modulation of the occurrence and progression of PF.

Metabolic-epigenetic nexus in regulation of stem cell fate

Stem cell fate determination is one of the central questions in stem cell biology, and although its regulation has been studied at genomic and proteomic levels, a variety of biological activities in cells occur at the metabolic level. Metabolomics studies have established the metabolome during stem cell differentiation and have revealed the role of metabolites in stem cell fate determination. While metabolism is considered to play a biological regulatory role as an energy source, recent studies have suggested the nexus between metabolism and epigenetics because several metabolites function as cofactors and substrates in epigenetic mechanisms, including histone modification, DNA methylation, and microRNAs. Additionally, the epigenetic modification is sensitive to the dynamic metabolites and consequently leads to changes in transcription. The nexus between metabolism and epigenetics proposes a novel stem cell-based therapeutic strategy through manipulating metabolites. In the present review, we summarize the possible nexus between metabolic and epigenetic regulation in stem cell fate determination, and discuss the potential preventive and therapeutic strategies via targeting metabolites.

Mitochondrial function in spinal cord injury and regeneration

Many people around the world suffer from some form of paralysis caused by spinal cord injury (SCI), which has an impact on quality and life expectancy. The spinal cord is part of the central nervous system (CNS), which in mammals is unable to regenerate, and to date, there is a lack of full functional recovery therapies for SCI. These injuries start with a rapid and mechanical insult, followed by a secondary phase leading progressively to greater damage. This secondary phase can be potentially modifiable through targeted therapies. The growing literature, derived from mammalian and regenerative model studies, supports a leading role for mitochondria in every cellular response after SCI: mitochondrial dysfunction is the common event of different triggers leading to cell death, cellular metabolism regulates the immune response, mitochondrial number and localization correlate with axon regenerative capacity, while mitochondrial abundance and substrate utilization regulate neural stem progenitor cells self-renewal and differentiation. Herein, we present a comprehensive review of the cellular responses during the secondary phase of SCI, the mitochondrial contribution to each of them, as well as evidence of mitochondrial involvement in spinal cord regeneration, suggesting that a more in-depth study of mitochondrial function and regulation is needed to identify potential targets for SCI therapeutic intervention.

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.

Sodium butyrate attenuates rotenone-induced toxicity by activation of autophagy through epigenetically regulating PGC-1α expression in PC12 cells

Short-chain fatty acids (SCFAs) are considered the key molecular link between gut microbiota and pathogenesis of Parkinson's disease (PD). However, the role of SCFAs in PD pathogenesis is controversial. Autophagy is important for the degradation of α-synuclein, which is critical to the development of PD. However, whether SCFAs can regulate autophagy in PD remains unknown. We aimed to investigate the role of SCFAs and explore the potential mechanisms in rat dopaminergic PC12 cells treated with rotenone. Expression levels of α-synuclein, peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) and microtubule-associated protein 1 light chain 3 beta (LC3B)-II were detected by Western blot. Histone acetylation levels at PGC-1α promoter region were measured using chromatin immunoprecipitation-quantitative polymerase chain reaction (ChIP-qPCR). Among the three SCFAs, sodium butyrate (NaB) protected against rotenone-induced toxicity. NaB activated autophagy pathway and reduced rotenone-induced α-synuclein expression through the activation of autophagy. Notably, NaB activated autophagy pathway through upregulating PGC-1α expression. More importantly, NaB promoted the levels of histone 3 lysine 9 acetylation (H3K9Ac) and histone 3 lysine 27 acetylation (H3K27Ac) at PGC-1α promoter region, indicating that NaB promotes PGC-1α expression via histone acetylation modification. In conclusion, NaB can protect against rotenone-induced toxicity through activation of the autophagy pathway by upregulating PGC-1α expression via epigenetic modification.

Histone deacetylase in neuropathology

Neuroepigenetics, a new branch of epigenetics, plays an important role in the regulation of gene expression. Neuroepigenetics is associated with holistic neuronal function and helps in formation and maintenance of memory and learning processes. This includes neurodevelopment and neurodegenerative defects in which histone modification enzymes appear to play a crucial role. These modifications, carried out by acetyltransferases and deacetylases, regulate biologic and cellular processes such as apoptosis and autophagy, inflammatory response, mitochondrial dysfunction, cell-cycle progression and oxidative stress. Alterations in acetylation status of histone as well as non-histone substrates lead to transcriptional deregulation. Histone deacetylase decreases acetylation status and causes transcriptional repression of regulatory genes involved in neural plasticity, synaptogenesis, synaptic and neural plasticity, cognition and memory, and neural differentiation. Transcriptional deactivation in the brain results in development of neurodevelopmental and neurodegenerative disorders. Mounting evidence implicates histone deacetylase inhibitors as potential therapeutic targets to combat neurologic disorders. Recent studies have targeted naturally-occurring biomolecules and micro-RNAs to improve cognitive defects and memory. Multi-target drug ligands targeting HDAC have been developed and used in cell-culture and animal-models of neurologic disorders to ameliorate synaptic and cognitive dysfunction. Herein, we focus on the implications of histone deacetylase enzymes in neuropathology, their regulation of brain function and plausible involvement in the pathogenesis of neurologic defects.

Adenosine A2A receptor null chondrocyte transcriptome resembles that of human osteoarthritic chondrocytes

Adenosine signaling plays a critical role in the maintenance of articular cartilage and may serve as a novel therapeutic for osteoarthritis (OA), a highly prevalent and morbid disease without effective therapeutics in the current market. Mice lacking adenosine A2A receptors (A2AR) develop spontaneous OA by 16 weeks of age, a finding relevant to human OA since loss of adenosine signaling due to diminished adenosine production (NT5E deficiency) also leads to development of OA in mice and humans. To better understand the mechanism by which A2AR and adenosine generation protect from OA development, we examined differential gene expression in neonatal chondrocytes from WT and A2AR null mice. Analysis of differentially expressed genes was analyzed by KEGG pathway analysis, and oPOSSUM and the flatiron database were used to identify transcription factor binding enrichment, and tissue-specific network analyses and patterns were compared to gene expression patterns in chondrocytes from patients with OA. There was a differential expression of 2211 genes (padj<0.05). Pathway enrichment analysis revealed that pro-inflammatory changes, increased metalloprotease, reduced matrix organization, and homeostasis are upregulated in A2AR null chondrocytes. Moreover, stress responses, including autophagy and HIF-1 signaling, seem to be important drivers of OA and bear marked resemblance to the human OA transcriptome. Although A2AR null mice are born with grossly intact articular cartilage, we identify here the molecular foundations for early-onset OA in these mice, further establishing their role as models for human disease and the potential use of adenosine as a treatment for human disease.

Mitochondrial quality control: Epigenetic signatures and therapeutic strategies

Mitochondria are semi-autonomous organelle staging a crucial role in cellular stress response, energy metabolism and cell survival. Maintaining mitochondrial quality control is very important for its homeostasis. Pathological conditions such as oxidative stress and neurodegeneration, disrupt this quality control, and involvement of genetic and epigenetic materials in this disruption have been reported. These regulatory factors trigger mitochondrial imbalance, as seen in many neurodegenerative diseases like Alzheimer's disease, Parkinson's disease, Amyotrophic lateral sclerosis, and Huntington's disease. The dynamic regulatory pathways i.e. mitophagy, biogenesis, permeability pore transitioning, fusion-fission are affected as a consequence and have been reviewed in this article. Moreover, several epigenetic mechanisms such as DNA methylation and histone modulation participating in such neurological disorders have also been discussed. Apart from it, therapeutic approaches targeting mitochondrial quality control have been tremendously explored showing ameliorative effects for these diseases, and have been discussed here with a novel perspective.

Cystatin B-deficiency triggers ectopic histone H3 tail cleavage during neurogenesis

Cystatin B (CSTB) acts as an inhibitor of cysteine proteases of the cathepsin family and loss-of-function mutations result in human brain diseases with a genotype-phenotype correlation. In the most severe case, CSTB-deficiency disrupts brain development, and yet the molecular basis of this mechanism is missing. Here, we establish CSTB as a regulator of chromatin structure during neural stem cell renewal and differentiation. Murine neural precursor cells (NPCs) undergo transient proteolytic cleavage of the N-terminal histone H3 tail by cathepsins B and L upon induction of differentiation into neurons and glia. In contrast, CSTB-deficiency triggers premature H3 tail cleavage in undifferentiated self-renewing NPCs and sustained H3 tail proteolysis in differentiating neural cells. This leads to significant transcriptional changes in NPCs, particularly of nuclear-encoded mitochondrial genes. In turn, these transcriptional alterations impair the enhanced mitochondrial respiration that is induced upon neural stem cell differentiation. Collectively, our findings reveal the basis of epigenetic regulation in the molecular pathogenesis of CSTB deficiency.

The role of mitophagy in the regulation of mitochondrial energetic status in neurons

Mitochondria are the main cellular energy powerhouses and supply most of the energy in the form of ATP to fuel essential neuronal functions through oxidative phosphorylation (OXPHOS). In Alzheimer disease (AD), metabolic and mitochondrial disruptions are an early feature preceding any histopathological and clinical manifestations. Mitochondrial malfunction is also linked to synaptic defects in early AD. Mitophagy serves as a key cellular quality control mechanism involving sequestration of damaged mitochondria within autophagosomes and their subsequent degradation in lysosomes. However, it remains largely unknown whether mitophagy is involved in the regulation of energy metabolism in neurons, and if so, whether metabolic deficiency in AD is attributed to mitophagy dysfunction. Here we reveal that mitophagy is broadly activated in metabolically enhanced neurons upon OXPHOS stimulation, which sustains high energetic activity by increasing mitochondrial turnover and hence facilitating mitochondrial maintenance. Unexpectedly, in AD-related mutant HsAPP Tg mouse brains, early stimulation of OXPHOS activity fails to correct energy deficits but exacerbates synapse loss as a consequence of mitophagy failure. Excitingly, lysosomal enhancement in AD neurons restores impaired metabolic function by promoting elimination of damaged mitochondria, protecting against synaptic damage in AD mouse brains. Taken together, we propose a new mechanism by which mitophagy controls bioenergetic status in neurons, furthering our understanding of the direct impact of mitophagy defects on AD-linked metabolic deficits and shedding light on the development of novel therapeutic strategies to treat AD by the early stimulation of mitochondrial metabolism combined with elevation of lysosomal proteolytic activity.

Selenium supplementation inhibits IGF-1 signaling and confers methionine restriction-like healthspan benefits to mice

Methionine restriction (MR) dramatically extends the healthspan of several organisms. Methionine-restricted rodents have less age-related pathology and increased longevity as compared with controls, and recent studies suggest that humans might benefit similarly. Mechanistically, it is likely that the decreased IGF-1 signaling that results from MR underlies the benefits of this regimen. Thus, we hypothesized that interventions that decrease IGF-1 signaling would also produce MR-like healthspan benefits. Selenium supplementation inhibits IGF-1 signaling in rats and has been studied for its putative healthspan benefits. Indeed, we show that feeding mice a diet supplemented with sodium selenite results in an MR-like phenotype, marked by protection against diet-induced obesity, as well as altered plasma levels of IGF-1, FGF-21, adiponectin, and leptin. Selenomethionine supplementation results in a similar, albeit less robust response, and also extends budding yeast lifespan. Our results indicate that selenium supplementation is sufficient to produce MR-like healthspan benefits for yeast and mammals.

Epigenetic Regulation of Mitochondrial Quality Control Genes in Multiple Myeloma: A Sequenom MassARRAY Pilot Investigation on HMCLs

The mitochondrial quality control network includes several epigenetically-regulated genes involved in mitochondrial dynamics, mitophagy, and mitochondrial biogenesis under physiologic conditions. Dysregulated expression of such genes has been reported in various disease contexts, including cancer. However, their expression pattern and the possible underlying epigenetic modifications remain to be defined within plasma cell (PC) dyscrasias. Herein, we compared the mRNA expression of mitochondrial quality control genes from multiple myeloma, plasma cell leukemia patients and human myeloma cell lines (HMCLs) with healthy plasma cells; moreover, by applying the Sequenom MassARRAY EpiTYPER technology, we performed a pilot investigation of their CpG methylation status in HMCLs. Overall, the results provided indicate dysregulated expression of several mitochondrial network’s genes, and alteration of the CpG methylation profile, underscoring novel potential myeloma biomarkers deserving in-depth functional investigation in the future.

Diet-dependent gut microbiota impacts on adult neurogenesis through mitochondrial stress modulation

The influence of dietary factors on brain health and mental function is becoming increasingly recognized. Similarly, mounting evidence supports a role for gut microbiota in modulating central nervous system function and behaviour. Still, the molecular mechanisms responsible for the impact of diet and associated microbiome in adult neurodegeneration are still largely unclear. In this study, we aimed to investigate whether and how changes in diet-associated microbiome and its metabolites impact on adult neurogenesis. Mice were fed a high-fat, choline-deficient diet, developing obesity and several features of the metabolic syndrome, including non-alcoholic steatohepatitis. Strikingly, our results showed, for the first time, that animals fed with this specific diet display premature increased neurogenesis, possibly exhausting the available neural stem cell pool for long-term neurogenesis processes. The high-fat, choline-deficient diet further induced neuroinflammation, oxidative stress, synaptic loss and cell death in different regions of the brain. Notably, this diet-favoured gut dysbiosis in the small intestine and cecum, up-regulating metabolic pathways of short-chain fatty acids, such as propionate and butyrate and significantly increasing propionate levels in the liver. By dissecting the effect of these two specific short-chain fatty acids in vitro, we were able to show that propionate and butyrate enhance mitochondrial biogenesis and promote early neurogenic differentiation of neural stem cells through reactive oxygen species- and extracellular signal-regulated kinases 1/2-dependent mechanism. More importantly, neurogenic niches of high-fat, choline-deficient-fed mice showed increased expression of mitochondrial biogenesis markers, and decreased mitochondrial reactive oxygen species scavengers, corroborating the involvement of this mitochondrial stress-dependent pathway in mediating changes of adult neurogenesis by diet. Altogether, our results highlight a mitochondria-dependent pathway as a novel mediator of the gut microbiota–brain axis upon dietary influences.

Maternally inherited mitochondrial respiratory disorders: from pathogenetic principles to therapeutic implications

Maternally inherited mitochondrial respiratory disorders are rare, progressive, and multi-systemic diseases that remain intractable, with no effective therapeutic interventions. Patients share a defective oxidative phosphorylation pathway responsible for mitochondrial ATP synthesis, in most cases due to pathogenic mitochondrial variants transmitted from mother to child or to a rare de novo mutation or large-scale deletion of the mitochondrial genome. The clinical diagnosis of these mitochondrial diseases is difficult due to exceptionally high clinical variability, while their genetic diagnosis has improved with the advent of next-generation sequencing. The mechanisms regulating the penetrance of the mitochondrial variants remain unresolved with the patient's nuclear background, epigenomic regulation, heteroplasmy, mitochondrial haplogroups, and environmental factors thought to act as rheostats. The lack of animal models mimicking the phenotypic manifestations of these disorders has hampered efforts toward curative therapies. Patient-derived cellular paradigms provide alternative models for elucidating the pathogenic mechanisms and screening pharmacological small molecules to enhance mitochondrial function. Recent progress has been made in designing promising approaches to curtail the negative impact of dysfunctional mitochondria and alleviate clinical symptoms: 1) boosting mitochondrial biogenesis; 2) shifting heteroplasmy; 3) reprogramming metabolism; and 4) administering hypoxia-based treatment. Here, we discuss their varying efficacies and limitations and provide an outlook on their therapeutic potential and clinical application.

Regulation of Adult Neurogenesis in Mammalian Brain

Adult neurogenesis is a multistage process by which neurons are generated and integrated into existing neuronal circuits. In the adult brain, neurogenesis is mainly localized in two specialized niches, the subgranular zone (SGZ) of the dentate gyrus and the subventricular zone (SVZ) adjacent to the lateral ventricles. Neurogenesis plays a fundamental role in postnatal brain, where it is required for neuronal plasticity. Moreover, perturbation of adult neurogenesis contributes to several human diseases, including cognitive impairment and neurodegenerative diseases. The interplay between extrinsic and intrinsic factors is fundamental in regulating neurogenesis. Over the past decades, several studies on intrinsic pathways, including transcription factors, have highlighted their fundamental role in regulating every stage of neurogenesis. However, it is likely that transcriptional regulation is part of a more sophisticated regulatory network, which includes epigenetic modifications, non-coding RNAs and metabolic pathways. Here, we review recent findings that advance our knowledge in epigenetic, transcriptional and metabolic regulation of adult neurogenesis in the SGZ of the hippocampus, with a special attention to the p53-family of transcription factors.

Role of metformin in epigenetic regulation of placental mitochondrial biogenesis in maternal diabetes

Adverse maternal environments, such as diabetes and obesity, impair placental mitochondrial function, which affects fetal development and offspring long-term health. The underlying mechanisms and effective interventions to abrogate such effect remain unclear. Our previous studies demonstrated impaired mitochondrial biogenesis in male human placenta of diabetic mothers. In the present studies, epigenetic marks possibly related to mitochondrial biogenesis in placentae of women with diabetes (n = 23) and controls (n = 23) were analyzed. Effects of metformin were examined in human placental explants from a subgroup of diabetic women and in a mouse model of maternal high fat diet feeding. We found that maternal diabetes was associated with epigenetic regulation of mitochondrial biogenesis in human placenta in a fetal sex-dependent manner, including decreased histone acetylation (H3K27 acetylation) and increased promoter methylation of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α). In male placenta, the levels of H3K27 acetylation and PGC-1α promoter methylation correlated significantly with the activity of AMP-activated protein kinase (AMPK). Metformin treatment on male diabetic placental explant activated AMPK and stimulated PGC-1α expression, concomitant with increased H3K27 acetylation and decreased PGC-1α promoter methylation. In vivo, we show that maternal metformin treatment along with maternal high fat diet significantly increased mouse placental abundance of PGC-1α expression and downstream mitochondrial transcription factor A (TFAM) and inhibited maternal high fat diet-impaired placental efficiency and glucose tolerance in offspring. Together, these findings suggest the capability of metformin to stimulate placental mitochondrial biogenesis and inhibit the aberrant epigenetic alterations occurring in maternal diabetes during pregnancy, conferring protective effects on offspring.

Uridine Prevents Negative Effects of OXPHOS Xenobiotics on Dopaminergic Neuronal Differentiation

Neuronal differentiation appears to be dependent on oxidative phosphorylation capacity. Several drugs inhibit oxidative phosphorylation and might be detrimental for neuronal differentiation. Some pregnant women take these medications during their first weeks of gestation when fetal nervous system is being developed. These treatments might have later negative consequences on the offspring's health. To analyze a potential negative effect of three widely used medications, we studied in vitro dopaminergic neuronal differentiation of cells exposed to pharmacologic concentrations of azidothymidine for acquired immune deficiency syndrome; linezolid for multidrug-resistant tuberculosis; and atovaquone for malaria. We also analyzed the dopaminergic neuronal differentiation in brains of fetuses from pregnant mice exposed to linezolid. The drugs reduced the in vitro oxidative phosphorylation capacity and dopaminergic neuronal differentiation. This differentiation process does not appear to be affected in the prenatally exposed fetus brain. Nevertheless, the global DNA methylation in fetal brain was significantly altered, perhaps linking an early exposure to a negative effect in older life. Uridine was able to prevent the negative effects on in vitro dopaminergic neuronal differentiation and on in vivo global DNA methylation. Uridine could be used as a protective agent against oxidative phosphorylation-inhibiting pharmaceuticals provided during pregnancy when dopaminergic neuronal differentiation is taking place.

Exosomes from human urine-derived stem cells enhanced neurogenesis via miR-26a/HDAC6 axis after ischaemic stroke

Endogenous neurogenesis holds promise for brain repair and long‐term functional recovery after ischaemic stroke. However, the effects of exosomes from human urine‐derived stem cells (USC‐Exos) in neurogenesis remain unclear. This study aimed to investigate whether USC‐Exos enhanced neurogenesis and promoted functional recovery in brain ischaemia. By using an experimental stroke rat model, we found that intravenous injection of USC‐Exos enhanced neurogenesis and alleviated neurological deficits in post‐ischaemic stroke rats. We used neural stem cells (NSCs) subjected to oxygen‐glucose deprivation/reoxygenation (OGD/R) as an in vitro model of ischaemic stroke. The in vitro results suggested that USC‐Exos promoted both proliferation and neuronal differentiation of NSCs after OGD/R. Notably, a further mechanism study revealed that the pro‐neurogenesis effects of USC‐Exos may be partially attributed to histone deacetylase 6 (HDAC6) inhibition via the transfer of exosomal microRNA‐26a (miR‐26a). Taken together, this study indicates that USC‐Exos can be used as a novel promising strategy for brain ischaemia, which highlights the application of USC‐Exos.

The effects of histone deacetylase inhibitors on the attentional set-shifting task performance of alcohol-dependent rats

OBJECTIVES

Alcohol dependence causes extensive damage to the central nervous system, resulting in impaired brain structure and behavioral changes. Moreover, histone deacetylase (HDAC) inhibitors restrain the activity of HDAC and cause increased histone acetylation, which may be related to alcohol dependence.

METHODS

Ethanol dependence was modelled in animals by persistent alcohol exposure and tested in the conditioned place preference (CPP) paradigm. To induce CPP, the alcohol-treated rats were given orally gradient concentration (3%, 6%, and 9% v/v) alcohol administration for 20 consecutive days. The sodium butyrate (NaB)-treated rats were injected daily. Cognitive flexibility was evaluated using an attentional set-shifting task (ASST) in which the rats performed a series of seven consecutive discriminations after the final CPP paradigm.

RESULTS

Ethanol administration induced alcohol dependence behaviors, with more time spent in the ethanol-paired compartment. Compared with the CPP scores of the control group, the scores of the ethanol- and NaB-treated groups were significantly higher. In the ASST, alcohol-treated rats had significantly increased number of trials to reach criteria (TTC) in most phases, higher error rate, and lower cognitive levels compared to the control group. Moreover, the present findings demonstrated that NaB combined with ethanol caused cognitive deficits as the result of an increased number of TTC during the ASST.

CONCLUSIONS

The attentional/cognitive flexibility of the prefrontal cortex of alcohol-dependent rats was damaged and the NaB administration procedure itself did not produce cognitive deficits, but instead exacerbated cognitive impairment in alcohol-dependent rats.

The nuclear background influences the penetrance of the near-homoplasmic m.1630 A > G MELAS variant in a symptomatic proband and asymptomatic mother

In this study, we report the metabolic consequences of the m.1630 A > G variant in fibroblasts from the symptomatic proband affected with the mitochondrial encephalomyopathy lactic acidosis and stroke-like episode Syndrome and her asymptomatic mother. By long-range PCR followed by massively parallel sequencing of the mitochondrial genome, we accurately measured heteroplasmy in fibroblasts from the proband (89.6%) and her mother (94.8%). Using complementary experimental approaches, we show a functional correlation between manifestation of clinical symptoms and bioenergetic potential. Our mitochondrial morphometric analysis reveals a link between defects of mitochondrial cristae ultrastructure and symptomatic status. Despite near-homoplasmic level of the m.1630A > G variant, the mother's fibroblasts have a normal OXPHOS metabolism, which stands in contrast to the severely impaired OXPHOS response of the proband's fibroblasts. The proband's fibroblasts also exhibit glycolysis at near constitutive levels resulting in a stunted compensatory glycolytic response to offset the severe OXPHOS defect. Whole exome sequencing reveals the presence of a heterozygous nonsense VARS2 variant (p.R334X) exclusively in the proband, which removes two thirds of the VARS2 protein containing key domains interacting with the mt-tRNA^val and may play a role in modulating the penetrance of the m.1630A > G variant despite similar near homoplasmic levels. Our transmission electron microscopy study also shows unexpected ultrastructural changes of chromatin suggestive of differential epigenomic regulation between the proband and her mother that may explain the differential OXPHOS response between the proband and her mother. Future study will decipher by which molecular mechanisms the nuclear background influences the penetrance of the m.1630 A > G variant causing MELAS.