The role of PGC-1 coactivators in aging skeletal muscle and heart

Progranulin promotes regulatory T cells plasticity by mitochondrial metabolism through AMPK/PGC-1α pathway in ARDS

As the aging population increases, the focus on elderly patients with acute respiratory distress syndrome (ARDS) is also increasing. In this article, we found progranulin (PGRN) differential expression in ARDS patients and healthy controls, even in young and old ARDS patients. Its expression strongly correlates with several cytokines in both young and elderly ARDS patients. PGRN has comparable therapeutic effects in young and elderly mice with lipopolysaccharide-induced acute lung injury, manifesting as lung injury, apoptosis, inflammation, and regulatory T cells (Tregs) differentiation. Considering that Tregs differentiation relies on metabolic reprogramming, we discovered that Tregs differentiation was mediated by mitochondrial function, especially in the aged population. Furthermore, we demonstrated that PGRN alleviated the mitochondrial damage during Tregs differentiation through the AMPK/PGC-1α pathway in T cells. Collectively, PGRN may regulate mitochondria function to promote Tregs differentiation through the AMPK/PGC-1α pathway to improve ARDS.

Cardiac arrhythmogenesis: roles of ion channels and their functional modification

Cardiac arrhythmias cause significant morbidity and mortality and pose a major public health problem. They arise from disruptions in the normally orderly propagation of cardiac electrophysiological activation and recovery through successive cardiomyocytes in the heart. They reflect abnormalities in automaticity, initiation, conduction, or recovery in cardiomyocyte excitation. The latter properties are dependent on surface membrane electrophysiological mechanisms underlying the cardiac action potential. Their disruption results from spatial or temporal instabilities and heterogeneities in the generation and propagation of cellular excitation. These arise from abnormal function in their underlying surface membrane, ion channels, and transporters, as well as the interactions between them. The latter, in turn, form common regulatory targets for the hierarchical network of diverse signaling mechanisms reviewed here. In addition to direct molecular-level pharmacological or physiological actions on these surface membrane biomolecules, accessory, adhesion, signal transduction, and cytoskeletal anchoring proteins modify both their properties and localization. At the cellular level of excitation-contraction coupling processes, Ca2+ homeostatic and phosphorylation processes affect channel activity and membrane excitability directly or through intermediate signaling. Systems-level autonomic cellular signaling exerts both acute channel and longer-term actions on channel expression. Further upstream intermediaries from metabolic changes modulate the channels both themselves and through modifying Ca2+ homeostasis. Finally, longer-term organ-level inflammatory and structural changes, such as fibrotic and hypertrophic remodeling, similarly can influence all these physiological processes with potential pro-arrhythmic consequences. These normal physiological processes may target either individual or groups of ionic channel species and alter with particular pathological conditions. They are also potentially alterable by direct pharmacological action, or effects on longer-term targets modifying protein or cofactor structure, expression, or localization. Their participating specific biomolecules, often clarified in experimental genetically modified models, thus constitute potential therapeutic targets. The insights clarified by the physiological and pharmacological framework outlined here provide a basis for a recent modernized drug classification. Together, they offer a translational framework for current drug understanding. This would facilitate future mechanistically directed therapeutic advances, for which a number of examples are considered here. The latter are potentially useful for treating cardiac, in particular arrhythmic, disease.

The potential of herbal drugs to treat heart failure: The roles of Sirt1/AMPK

Heart failure (HF) is a highly morbid syndrome that seriously affects the physical and mental health of patients and generates an enormous socio-economic burden. In addition to cardiac myocyte oxidative stress and apoptosis, which are considered mechanisms for the development of HF, alterations in cardiac energy metabolism and pathological autophagy also contribute to cardiac abnormalities and ultimately HF. Silent information regulator 1 (Sirt1) and adenosine monophosphate-activated protein kinase (AMPK) are nicotinamide adenine dinucleotide (NAD+)-dependent deacetylases and phosphorylated kinases, respectively. They play similar roles in regulating some pathological processes of the heart through regulating targets such as peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), protein 38 mitogen-activated protein kinase (p38 MAPK), peroxisome proliferator-activated receptors (PPARs), and mammalian target of rapamycin (mTOR). We summarized the synergistic effects of Sirt1 and AMPK in the heart, and listed the traditional Chinese medicine (TCM) that exhibit cardioprotective properties by modulating the Sirt1/AMPK pathway, to provide a basis for the development of Sirt1/AMPK activators or inhibitors for the treatment of HF and other cardiovascular diseases (CVDs).

The Molecular Mechanisms of Fuel Utilization during Exercise

Exercise is widely recognized for its positive impact on human health and well-being. The process of utilizing substrates in skeletal muscle during exercise is intricate and governed by complex mechanisms. Carbohydrates and lipids serve as the primary fuel sources for skeletal muscle during exercise. It is now understood that fuel selection during exercise is not solely determined by physical activity itself but is also influenced by the overall metabolic state of the body. The balance between lipid and carbohydrate utilization significantly affects exercise capacity, including endurance, fatigue, and overall performance. Therefore, comprehensively understanding the regulation of substrate utilization during exercise is of utmost importance. The aim of this review is to provide an extensive overview of the current knowledge regarding the pathways involved in the regulation of substrate utilization during exercise. By synthesizing existing research, we can gain a holistic perspective on the intricate relationship between exercise, metabolism, and fuel selection. This advanced understanding has the potential to drive advancements in the field of exercise science and contribute to the development of personalized exercise strategies for individuals looking to optimize their performance and overall health.

Cardiomyocyte electrophysiology and its modulation: current views and future prospects

Normal and abnormal cardiac rhythms are of key physiological and clinical interest. This introductory article begins from Sylvio Weidmann's key historic 1950s microelectrode measurements of cardiac electrophysiological activity and Singh & Vaughan Williams's classification of cardiotropic targets. It then proceeds to introduce the insights into cardiomyocyte function and its regulation that subsequently emerged and their therapeutic implications. We recapitulate the resulting view that surface membrane electrophysiological events underlying cardiac excitation and its initiation, conduction and recovery constitute the final common path for the cellular mechanisms that impinge upon this normal or abnormal cardiac electrophysiological activity. We then consider progress in the more recently characterized successive regulatory hierarchies involving Ca2+ homeostasis, excitation-contraction coupling and autonomic G-protein signalling and their often reciprocal interactions with the surface membrane events, and their circadian rhythms. Then follow accounts of longer-term upstream modulation processes involving altered channel expression, cardiomyocyte energetics and hypertrophic and fibrotic cardiac remodelling. Consideration of these developments introduces each of the articles in this Phil. Trans. B theme issue. The findings contained in these articles translate naturally into recent classifications of cardiac electrophysiological targets and drug actions, thereby encouraging future iterations of experimental cardiac electrophysiological discovery, and testing directed towards clinical management. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.

Mitochondrial transplantation as a possible therapeutic option for sarcopenia

With advancing age, the skeletal muscle phenotype is characterized by a progressive loss of mass, strength, and quality. This phenomenon, known as sarcopenia, has a negative impact on quality of life and increases the risk of morbidity and mortality in older adults. Accumulating evidence suggests that damaged and dysfunctional mitochondria play a critical role in the pathogenesis of sarcopenia. Lifestyle modifications, such as physical activity, exercise, and nutrition, as well as medical interventions with therapeutic agents, are effective in the management of sarcopenia and offer solutions to maintain and improve skeletal muscle health. Although a great deal of effort has been devoted to the identification of the best treatment option, these strategies are not sufficient to overcome sarcopenia. Recently, it has been reported that mitochondrial transplantation may be a possible therapeutic approach for the treatment of mitochondria-related pathological conditions such as ischemia, liver toxicity, kidney injury, cancer, and non-alcoholic fatty liver disease. Given the role of mitochondria in the function and metabolism of skeletal muscle, mitochondrial transplantation may be a possible option for the treatment of sarcopenia. In this review, we summarize the definition and characteristics of sarcopenia and molecular mechanisms associated with mitochondria that are known to contribute to sarcopenia. We also discuss mitochondrial transplantation as a possible option. Despite the progress made in the field of mitochondrial transplantation, further studies are needed to elucidate the role of mitochondrial transplantation in sarcopenia. KEY MESSAGES: Sarcopenia is the progressive loss of skeletal muscle mass, strength, and quality. Although the specific mechanisms that lead to sarcopenia are not fully understood, mitochondria have been identified as a key factor in the development of sarcopenia. Damaged and dysfunctional mitochondria initiate various cellular mediators and signaling pathways, which largely contribute to the age-related loss of skeletal muscle mass and strength. Mitochondrial transplantation has been reported to be a possible option for the treatment/prevention of several diseases. Mitochondrial transplantation may be a possible therapeutic option for improving skeletal muscle health and treating sarcopenia. Mitochondrial transplantation as a possible treatment option for sarcopenia.

Senescent Cells: A Therapeutic Target in Cardiovascular Diseases

Senescent cell accumulation has been observed in age-associated diseases including cardiovascular diseases. Senescent cells lack proliferative capacity and secrete senescence-associated secretory phenotype (SASP) factors that may cause or worsen many cardiovascular diseases. Therapies targeting senescent cells, especially senolytic drugs that selectively induce senescent cell removal, have been shown to delay, prevent, alleviate, or treat multiple age-associated diseases in preclinical models. Some senolytic clinical trials have already been completed or are underway for a number of diseases and geriatric syndromes. Understanding how cellular senescence affects the various cell types in the cardiovascular system, such as endothelial cells, vascular smooth muscle cells, fibroblasts, immune cells, progenitor cells, and cardiomyocytes, is important to facilitate translation of senotherapeutics into clinical interventions. This review highlights: (1) the characteristics of senescent cells and their involvement in cardiovascular diseases, focusing on the aforementioned cardiovascular cell types, (2) evidence about senolytic drugs and other senotherapeutics, and (3) the future path and clinical potential of senotherapeutics for cardiovascular diseases.

The Complex Interplay between Imbalanced Mitochondrial Dynamics and Metabolic Disorders in Type 2 Diabetes

Type 2 diabetes mellitus (T2DM) is a global burden, with an increasing number of people affected and increasing treatment costs. The advances in research and guidelines improve the management of blood glucose and related diseases, but T2DM and its complications are still a big challenge in clinical practice. T2DM is a metabolic disorder in which insulin signaling is impaired from reaching its effectors. Mitochondria are the "powerhouses" that not only generate the energy as adenosine triphosphate (ATP) using pyruvate supplied from glucose, free fatty acid (FFA), and amino acids (AA) but also regulate multiple cellular processes such as calcium homeostasis, redox balance, and apoptosis. Mitochondrial dysfunction leads to various diseases, including cardiovascular diseases, metabolic disorders, and cancer. The mitochondria are highly dynamic in adjusting their functions according to cellular conditions. The shape, morphology, distribution, and number of mitochondria reflect their function through various processes, collectively known as mitochondrial dynamics, including mitochondrial fusion, fission, biogenesis, transport, and mitophagy. These processes determine the overall mitochondrial health and vitality. More evidence supports the idea that dysregulated mitochondrial dynamics play essential roles in the pathophysiology of insulin resistance, obesity, and T2DM, as well as imbalanced mitochondrial dynamics found in T2DM. This review updates and discusses mitochondrial dynamics and the complex interactions between it and metabolic disorders.

Pleiotropic and multi-systemic actions of physical exercise on PGC-1α signaling during the aging process

Physical training is a potent therapeutic approach for improving mitochondrial health through peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) signaling pathways. However, comprehensive information regarding the physical training impact on PGC-1α in the different physiological systems with advancing age is not fully understood. This review sheds light on the frontier-of-knowledge data regarding the chronic effects of exercise on the PGC-1α signaling pathways in rodents and humans. We address the molecular mechanisms involved in the different tissues, clarifying the precise biological action of PGC-1α, restricted to the aged cell type. Distinct exercise protocols (short and long-term) and modalities (aerobic and resistance exercise) increase the transcriptional and translational PGC-1α levels in adipose tissue, brain, heart, liver, and skeletal muscle in animal models, suggesting that this versatile molecule induces pleiotropic responses. However, PGC-1α function in some human tissues (adipose tissue, heart, and brain) remains challenging for further investigations. PGC-1α is not a simple transcriptional coactivator but supports a biochemical environment of mitochondrial dynamics, controlling physiological processes (primary metabolism, tissue remodeling, autophagy, inflammation, and redox balance). Acting as an adaptive mechanism, the long-term effects of PGC-1α following exercise may reflect the energy demand to coordinate multiple organs and contribute to cellular longevity.

Resistance training prevents dynamics and mitochondrial respiratory dysfunction in vastus lateralis muscle of ovariectomized rats

To investigate whether ovariectomy affects mitochondrial respiratory function, gene expression of the biogenesis markers and mitochondrial dynamics of the vastus lateralis muscle, female Wistar rats divided into ovariectomized (OVX) and intact (INT) groups were kept sedentary (SED) or submitted to resistance training (RT) performed for thirteen weeks on a vertical ladder in which animals climbed with a workload apparatus. RT sessions were performed with four climbs with 65, 85, 95, and 100 % of the rat's previous maximum workload. Mitochondrial Respiratory Function data were obtained by High-resolution respirometry. Gene expression of FIS1, MFN1 and PGC1-α was evaluated by real-time PCR. There was a decrease on oxidative phosphorylation capacity in OVX-SED compared to other groups. Trained groups presented increase on oxidative phosphorylation capacity when compared to sedentary groups. For respiratory control ratio (RCR), OVX-SED presented lower values when compared to INT-SED and to trained groups. Trained groups presented RCR values higher compared to INT-SED. Exercise increased the values of FIS1, MFN1 and PGC1-α expression compared to OVX-SED. Our results demonstrated that in the absence of ovarian hormones, there is a great decrease in oxidative phosphorylation and electron transfer system capacities of sedentary animals. RT was able to increase the expression of genes related to mitochondrial dynamics markers, reversing the condition determined by ovariectomy.

Extracellular Vesicles and Cardiac Aging

Global population aging is a major challenge to health and socioeconomic policies. The prevalence of diseases progressively increases with aging, with cardiovascular disease being the major cause of mortality among elderly people. The allostatic overload imposed by the accumulation of cardiac senescent cells has been suggested to play a pivotal role in the aging-related deterioration of cardiovascular function. Senescent cells exhibit intrinsic disorders and release a senescence-associated secretory phenotype (SASP). Most of these SASP compounds and damaged molecules are released from senescent cells by extracellular vesicles (EVs). Once secreted, these EVs can be readily incorporated by recipient neighboring cells and elicit cellular damage or otherwise can promote extracellular matrix remodeling. This has been associated with the development of cardiac dysfunction, fibrosis, and vascular calcification, among others. The molecular signature of these EVs is highly variable and might provide important information for the development of aging-related biomarkers. Conversely, EVs released by the stem and progenitor cells can exert a rejuvenating effect, raising the possibility of future anti-aging therapies.

Keeping the beat against time: Mitochondrial fitness in the aging heart

The process of aging strongly correlates with maladaptive architectural, mechanical, and biochemical alterations that contribute to the decline in cardiac function. Consequently, aging is a major risk factor for the development of heart disease, the leading cause of death in the developed world. In this review, we will summarize the classic and recently uncovered pathological changes within the aged heart with an emphasis on the mitochondria. Specifically, we describe the metabolic changes that occur in the aging heart as well as the loss of mitochondrial fitness and function and how these factors contribute to the decline in cardiomyocyte number. In addition, we highlight recent pharmacological, genetic, or behavioral therapeutic intervention advancements that may alleviate age-related cardiac decline.

Gut microbiota in sarcopenia and heart failure

Sarcopenia is common in aging and in patients with heart failure (HF) who may experience worse outcomes. Patients with muscle wasting are more likely to experience falls and can have serious complications when undergoing cardiac procedures. While intensive nutritional support and exercise rehabilitation can help reverse some of these changes, they are often under-prescribed in a timely manner, and we have limited insights into who would benefit. Mechanistic links between gut microbial metabolites (GMM) have been identified and may contribute to adverse clinical outcomes in patients with cardio-renal diseases and aging. This review will examine the emerging evidence for the influence of the gut microbiome-derived metabolites and notable signaling pathways involved in both sarcopenia and HF, especially those linked to dietary intake and mitochondrial metabolism. This provides a unique opportunity to gain mechanistic and clinical insights into developing novel therapeutic strategies that target these GMM pathways or through tailored nutritional modulation to prevent progressive muscle wasting in elderly patients with heart failure.

HAX1-dependent control of mitochondrial proteostasis governs neutrophil granulocyte differentiation

The relevance of molecular mechanisms governing mitochondrial proteostasis to the differentiation and function of hematopoietic and immune cells is largely elusive. Through dissection of the network of proteins related to HCLS1-associated protein X-1, we defined a potentially novel functional CLPB/HAX1/(PRKD2)/HSP27 axis with critical importance for the differentiation of neutrophil granulocytes and, thus, elucidated molecular and metabolic mechanisms underlying congenital neutropenia in patients with HAX1 deficiency as well as bi- and monoallelic mutations in CLPB. As shown by stable isotope labeling by amino acids in cell culture (SILAC) proteomics, CLPB and HAX1 control the balance of mitochondrial protein synthesis and persistence crucial for proper mitochondrial function. Impaired mitochondrial protein dynamics are associated with decreased abundance of the serine-threonine kinase PRKD2 and HSP27 phosphorylated on serines 78 and 82. Cellular defects in HAX1^–/– cells can be functionally reconstituted by HSP27. Thus, mitochondrial proteostasis emerges as a critical molecular and metabolic mechanism governing the differentiation and function of neutrophil granulocytes.

Myokines and Resistance Training: A Narrative Review

In the last few years, the muscular system has gained attention due to the discovery of the muscle-secretome and its high potency for retaining or regaining health. These cytokines, described as myokines, released by the working muscle, are involved in anti-inflammatory, metabolic and immunological processes. These are able to influence human health in a positive way and are a target of research in metabolic diseases, cancer, neurological diseases, and other non-communicable diseases. Therefore, different types of exercise training were investigated in the last few years to find associations between exercise, myokines and their effects on human health. Particularly, resistance training turned out to be a powerful stimulus to enhance myokine release. As there are different types of resistance training, different myokines are stimulated, depending on the mode of training. This narrative review gives an overview about resistance training and how it can be utilized to stimulate myokine production in order to gain a certain health effect. Finally, the question of why resistance training is an important key regulator in human health will be discussed.

The Panax ginseng Berry Extract and Soluble Whey Protein Hydrolysate Mixture Ameliorates Sarcopenia-Related Muscular Deterioration in Aged Mice

Sarcopenia is prevalent as the aging population grows. Therefore, the need for supplements for the elderly is increasing. This study aimed to investigate the efficacy and mechanism of a Panax ginseng berry extract (GBE) and soluble whey protein hydrolysate (WPH) mixture on a sarcopenia-related muscular deterioration in aged mice. Ten-month-old male C57BL/6J mice were administered three different doses of the GBE + WPH mixture for 8 weeks; 700 mg/kg, 900 mg/kg, and 1100 mg/kg. Grip strength, serum inflammatory cytokines level, and mass of muscle tissues were estimated. The deteriorating function of aging muscle was investigated via protein or gene expression. Grip strength and mass of three muscle tissues were increased significantly in a dose-dependent manner, and increased anti-inflammatory cytokine alleviated systemic inflammatory state. The mixture resolved the imbalance of muscle protein turnover through activation of the PI3K/Akt pathway and increased gene expression of the muscle regeneration-related factors, while decreasing myostatin, which interferes with muscle protein synthesis and regeneration. Furthermore, we confirmed that increased mitochondria number in muscle with the improvement of mitochondrial biogenesis. These physiological changes were similar to the effects of exercise.

Hypoxia: Role of SIRT1 and the protective effect of resveratrol in ovarian function

Background

Ovarian function is closely related to the degree of vascular network development surrounding the ovary. Maternal aging‐related construction defects in this vascular network can cause ovarian hypoxia, which impedes oocyte nutrient supply, leading to physiological changes in the ovaries and oocytes. The anti‐aging gene Sirtuin 1 (SIRT1) senses and adapts to ambient stress and is associated with hypoxic environments and mitochondrial biogenesis.

Methods

The present study is a literature review focusing on investigations involving the changes in SIRT1 and mitochondrial expression during hypoxia and the cytoprotective effects of the SIRT1 activator, resveratrol.

Main findings

Hypoxia suppresses SIRT1 and mitochondrial expression. Resveratrol can reverse the hypoxia‐induced decrease in mitochondrial and SIRT1 activity. Resveratrol suppresses the production of hypoxia‐inducible factor‐1α and vascular endothelial growth factor proteins.

Conclusion

Resveratrol exhibits protective activity against hypoxic stress and may prevent hypoxia‐ or aging‐related mitochondrial dysfunction. Resveratrol treatment may be a potential option for infertility therapy.

Redox Signaling and Sarcopenia: Searching for the Primary Suspect

Sarcopenia, the age-related decline in muscle mass and function, derives from multiple etiological mechanisms. Accumulative research suggests that reactive oxygen species (ROS) generation plays a critical role in the development of this pathophysiological disorder. In this communication, we review the various signaling pathways that control muscle metabolic and functional integrity such as protein turnover, cell death and regeneration, inflammation, organismic damage, and metabolic functions. Although no single pathway can be identified as the most crucial factor that causes sarcopenia, age-associated dysregulation of redox signaling appears to underlie many deteriorations at physiological, subcellular, and molecular levels. Furthermore, discord of mitochondrial homeostasis with aging affects most observed problems and requires our attention. The search for the primary suspect of the fundamental mechanism for sarcopenia will likely take more intense research for the secret of this health hazard to the elderly to be unlocked.

Hypothalamus-skeletal muscle crosstalk during exercise and its role in metabolism modulation

Physical inactivity is a major public health problem that contributes to the development of several pathologies such as obesity, type 2 diabetes and cardiovascular diseases. Regular exercise mitigates the progression of these metabolic problems and contributes positively to memory and behavior. Therefore, public health agencies have incorporated exercise in the treatment of widespread disorders. The hypothalamus, specifically the ventromedial and the arcuate nuclei, responds to exercise activity and modulates energy metabolism through stimulation of the sympathetic nervous system and catecholamine secretion into the circulation. In addition, physical performance enhances cognitive functions and memory, mediated mostly by an increase in brain-derived neurotrophic factor levels in brain. During exercise training, skeletal muscle myofibers remodel their biochemical, morphological and physiological state. Moreover, skeletal muscle interacts with other organs by the release into the circulation of myokines, molecules that exhibit autocrine, paracrine and endocrine functions. Several studies have focused on the role of skeletal muscle and tissues in response to physical activity. However, how the hypothalamus could influence the skeletal muscle task in the context of exercise is less studied. Here, we review recent data about hypothalamus-skeletal muscle crosstalk in response to physical activity and focus on specific aspects such as the neuroendocrinological effects of exercise and the endocrine functions of skeletal muscle, to provide a perspective for future study directions.

Eight Weeks of High-Intensity Interval Static Strength Training Improves Skeletal Muscle Atrophy and Motor Function in Aged Rats via the PGC-1α/FNDC5/UCP1 Pathway

Background

Sarcopenia is a syndrome characterized by the loss of skeletal muscle mass and strength. Most studies have focused on dynamic resistance exercises for preventing muscular decline and maintaining the muscle strength of older individuals. However, this training mode is impractical for older people with osteoarthritis and a limited range of motion. The static strength training mode is more suitable for older people. Therefore, a determination of the effect and mechanism of static strength training on sarcopenia is critical.

Methods

In this study, we developed a training device designed to collect training data and evaluate the effects of static training on the upper limbs of rats. The expression of PGC-1α was locally blocked by injecting a siRNA at the midpoint of the biceps to determine whether PGC-1α signal transduction participates in the effects of high-intensity interval static training on muscle strength. Then, the rat’s motor capacity was measured after static strength training. Immunohistochemistry and Western blotting were applied to determine PGC-1α/FNDC5/UCP1 expression levels in the muscle and adipose tissue. The serum irisin level was also detected using an enzyme-linked immunosorbent assay (ELISA).

Results

Increased levels of serum irisin and local expression of FNDC5, PGC-1α, and UCP1 were observed in the biceps brachii and surrounding fatty tissue after static strength training. Static strength training showed an advantage in reducing body weight and white fat accumulation while increasing the muscle fiber volume, which resulted in a longer training time and shorter rest time.

Conclusion

Overall, these results indicated that high-intensity interval static training prevents skeletal muscle atrophy and improves the motor function of aged rats through the PGC-1α/FNDC5/UCP1 signaling pathway.

The mitochondrial DNA copy number of cumulus granulosa cells may be related to the maturity of oocyte cytoplasm

STUDY QUESTION

Is the mitochondrial DNA (mtDNA) copy number of cumulus granulosa cells (CGCs) related to the maturation of oocyte cytoplasm?

SUMMARY ANSWER

Compared with the mtDNA copy number of CGCs from germinal vesicles (GV), CGCs from Metaphase I (MI) oocytes appear to have a lower mtDNA copy number.

WHAT IS KNOWN ALREADY

The growth and development of CGCs and oocyte are synchronised. The interaction between CGCs and the oocyte provides the appropriate balance of energy, which is necessary for mammalian oocyte development. Moreover, in the oocyte-cumulus complex (OCC), mature oocytes with higher mtDNA copy numbers tend to have corresponding CGCs with higher mtDNA copy numbers.

STUDY DESIGN, SIZE, DURATION

This is a prospective study of 302 OCCs obtained from 70 women undergoing in vitro fertilisation with intracytoplasmic sperm injection (ICSI) at the Reproductive and Genetic Hospital of CITIC-Xiangya, between 24 February 2018 and 21 December 2019. The CGCs were divided into three groups (GV, MI and MII stages) based on the maturation status of their corresponding oocyte. The sample sizes (n = 302) of CGCs in the three stages were 63 (CGCGV), 70 (CGCMI) and 169 (CGCMII), respectively. Some of the samples (n = 257) was used to quantify the mtDNA copy number, while the rest (n = 45) were used to analyse the expression level of mitochondrial genes. Furthermore, we retrieved 82 immature oocytes from among the 257 OCCs used for mtDNA copy numbers, including 36 GV oocytes and 46 MI oocytes, for analysis of oocyte mtDNA.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We selected genes with high consistency of real-time PCR results to accurately measure the mtDNA copy number by testing the efficacy and the reproducibility in whole genome amplification (WGA) samples from a human embryonic stem cell line. The CGCs of each oocyte were individually isolated. The mtDNA copy number and gene expression of the CGCs were assessed using real-time PCR techniques. Mitochondrial DNA copy number of the corresponding immature oocytes was also evaluated.

MAIN RESULTS AND THE ROLE OF CHANCE

MT-ND1, MT-CO1 and β-globin genes were chosen for the assessment of mtDNA content, and mRNA expressions of MT-ND1, MT-CO1, PGC-1α and TFAM were also measured. The genome of 257 CGCs and 82 immature oocytes were amplified according to the multiple displacement amplification (MDA) protocol, and RNA was extracted from 45 CGCs. Compared with CGCGV, CGCMI had a significantly lower mtDNA copy number. In the MT-ND1 assay, the CGCGV: CGCMI was [270 ± 302]: [134 ± 201], P = 0.015. In the MT-CO1 assay, CGCGV: CGCMI was [205 ± 228]: [92 ± 112], P = 0.026. There was no statistical difference in mtDNA between CGCGV and CGCMII. In the MT-ND1 assay, CGCGV: CGCMII was [270 ± 302]: [175 ± 223], P = 0.074. In the MT-CO1 assay, CGCGV: CGCMII was [205 ± 228]: [119 ± 192], P = 0.077. No statistical difference of mtDNA copy number was observed between CGCMI and CGCMII. In the MT-ND1 assay, CGCMI: CGCMII was [134 ± 201]: [175 ± 223], P = 0.422. In the MT-CO1 assay, CGCMI: CGCMII was [92 ± 112]: [119 ± 192], P = 0.478. To verify the reliability of the above results, we further analysed the mtDNA copy number of CGCs of 14 patients with GV, MI and MII oocytes, and the results showed that the mtDNA copy number of CGCMI may be lower. The mtDNA copy number of CGCGV and CGCMI was statistically different in the MT-ND1 assay where CGCGV: CGCMI was [249 ± 173]: [118 ± 113], P = 0.016, but in the MT-CO1 assay, CGCGV: CGCMI was [208 ± 199]: [83 ± 98], P = 0.109. There was no significant difference in mtDNA between CGCGV and CGCMII. In the MT-ND1 assay, CGCGV: CGCMII was [249 ± 173]: [185 ± 200], P = 0.096. In the MT-CO1 assay, CGCGV: CGCMII was [208 ± 199]: [114 ± 139], P = 0.096. There was also no significant difference in mtDNA between CGCMI and CGCMII. In the MT-ND1 assay, CGCMI: CGCMII was [118 ± 113]: [185 ± 200], P = 0.198. In the MT-CO1 assay, CGCMI: CGCMII was [83 ± 98]: [114 ± 139], P = 0.470. Moreover, there were no statistical differences in the expression levels of MT-ND1, MT-CO1, PGC-1α and TFAM between CGCGV, CGCMI and CGCMII (P > 0.05).

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Due to the ethical issues, the study did not quantify the mtDNA content of MII oocytes. Thus, whether the change in mtDNA copy number in CGCs is related to the different developmental stages of oocytes has not been further confirmed. Moreover, the sample size was relatively small.

WIDER IMPLICATIONS OF THE FINDINGS

The mtDNA copy number of CGCs decreases from the GV phase to the MI phase and stays steady from the MI to MII stage. At different stages of oocyte maturation, the mtDNA of CGCs may undergo self-degradation and replication to meet the energy requirements of the corresponding oocyte and the maturation of the oocyte cytoplasm.

STUDY FUNDING/COMPETING INTEREST(S)

Funding was provided by the National Key R&D Program of China (Grant 2018YFC1003100, to L.H.), the science and technology major project of the Ministry of Science and Technology of Hunan Province, China (grant 2017SK1030, to G.L.), the National Natural Science Foundation of China (grant 81873478, to L.H.), and Merck Serono China Research Fund for Fertility Experts (to L.H.). There is no conflict of interest.

Benchside to the bedside of frailty and cardiovascular aging: Main shared cellular and molecular mechanisms

Due to the impact that frailty and cardiac aging have on society and health systems, the mechanisms surrounding these conditions must be known. If the frailty and cardiovascular complications are due to numerous controllable factors or not, different strategies must be considered to improve the elderly patient's prognosis and improve their quality of life. This review aimed to investigate the main shared mechanisms of cardiac aging and frailty. MEDLINE-PubMed, Cohrane and EMBASE databases were searched to perform this review. The mesh-terms used for this search was frailty, cardiovascular disease, cardiovascular aging, or heart failure (HF). Frailty frequently coexists with heart conditions since they share predisposing pathophysiological alterations, the aging process, and elevated comorbidity burden, contributing to fast functional decline and sarcopenia. Mitochondrial dysfunctions and decreased protein synthesis lead to protein degradation, denervation, atrophy, impairment in the fatty acid oxidation, resulting in cardiomyopathy. The homeostasis of muscle metabolism deteriorates with aging, leading to a reduction in muscle quality and quantity. The installation of a low-grade and chronic inflammatory process adds to an impairment in glucose, protein and lipid metabolism, endothelial dysfunction, cardiovascular conditions, sarcopenia, and HF. The exacerbated rise in inflammatory biomarkers and impaired insulin resistance leads to worsening of the patient's general condition. The good news is that frailty is a dynamic syndrome, fluctuating between different states of seriousness but still has potential for reversibility based on physical activity, cognitive training, nutrition intervention, and a plethora of other approaches that can be performed by a multi-disciplinary team.

The β3 Adrenergic Receptor Agonist CL316243 Ameliorates the Metabolic Abnormalities of High-Fat Diet-Fed Rats by Activating AMPK/PGC-1α Signaling in Skeletal Muscle

PURPOSE

Skeletal muscle has a major influence on whole-body metabolic homeostasis. In the present study, we aimed to determine the metabolic effects of the β3 adrenergic receptor agonist CL316243 (CL) in the skeletal muscle of high-fat diet-fed rats.

METHODS

Sprague-Dawley rats were randomly allocated to three groups, which were fed a control diet (C) or a high-fat diet (HF), and half of the latter were administered 1 mg/kg CL by gavage once weekly (HF+CL), for 12 weeks. At the end of this period, the serum lipid profile and glucose tolerance of the rats were evaluated. In addition, the phosphorylation and protein and mRNA expression of AMP-activated protein kinase (AMPK), peroxisome proliferator-activated receptor γ coactivator (PGC)-1α, and carnitine palmitoyl transferase (CPT)-1b in skeletal muscle were measured by Western blot analysis and qPCR. The direct effects of CL on the phosphorylation (p-) and expression of AMPK, PGC-1α, and CPT-1b were also evaluated by Western blotting and immunofluorescence in L6 myotubes.

RESULTS

CL administration ameliorated the abnormal lipid profile and glucose tolerance of the high-fat diet-fed rats. In addition, the expression of p-AMPK, PGC-1α, and CPT-1b in the soleus muscle was significantly increased by CL. CL (1 µM) also increased the protein expression of p-AMPK, PGC-1α, and CPT-1b in L6 myotubes. However, the effect of CL on PGC-1α protein expression was blocked by the AMPK antagonist compound C, which suggests that CL increases PGC-1α protein expression via AMPK.

CONCLUSION

Activation of the β3 adrenergic receptor in skeletal muscle ameliorates the metabolic abnormalities of high-fat diet-fed rats, at least in part via activation of the AMPK/PGC-1α pathway.

Nutrients and Pathways that Regulate Health Span and Life Span

Both life span and health span are influenced by genetic, environmental and lifestyle factors. With the genetic influence on human life span estimated to be about 20–25%, epigenetic changes play an important role in modulating individual health status and aging. Thus, a main part of life expectance and healthy aging is determined by dietary habits and nutritional factors. Excessive or restricted food consumption have direct effects on health status. Moreover, some dietary interventions including a reduced intake of dietary calories without malnutrition, or a restriction of specific dietary component may promote health benefits and decrease the incidence of aging-related comorbidities, thus representing intriguing potential approaches to improve healthy aging. However, the relationship between nutrition, health and aging is still not fully understood as well as the mechanisms by which nutrients and nutritional status may affect health span and longevity in model organisms. The broad effect of different nutritional conditions on health span and longevity occurs through multiple mechanisms that involve evolutionary conserved nutrient-sensing pathways in tissues and organs. These pathways interacting each other include the evolutionary conserved key regulators mammalian target of rapamycin, AMP-activated protein kinase, insulin/insulin-like growth factor 1 pathway and sirtuins. In this review we provide a summary of the main molecular mechanisms by which different nutritional conditions, i.e., specific nutrient abundance or restriction, may affect health span and life span.

MBNL1-Associated Mitochondrial Dysfunction and Apoptosis in C2C12 Myotubes and Mouse Skeletal Muscle

We explored the interrelationship between a tissue-specific alternative splicing factor muscleblind-like 1 (MBNL1) and peroxisome proliferator-activated receptor-γ coactivator 1-α (PGC-1α), B-cell lymphoma 2 (Bcl-2) or Bcl-2-associated X protein (Bax) in C2C12 myotubes and mouse skeletal muscle to investigate a possible physiological role of MBNL1 in mitochondrial-associated apoptosis of skeletal muscle. Expression level of PGC-1α and mitochondrial membrane potential evaluated by the fluorescence ratio of JC-1 aggregate to monomer in C2C12 myotubes were suppressed by knockdown of MBNL1. Conversely, the ratio of Bax to Bcl-2 as well as the apoptotic index in C2C12 myotubes was increased by MBNL1 knockdown. In plantaris muscle, on the other hand, not only the minimum muscle fiber diameter but also the expression level of MBNL1 and PGC-1α in of 100-week-old mice were significantly lower than that of 10-week-old mice. Furthermore, the ratio of Bax to Bcl-2 in mouse plantaris muscle was increased by aging. These results suggest that MBNL1 may play a key role in aging-associated muscle atrophy accompanied with mitochondrial dysfunction and apoptosis via mediating PGC-1α expression in skeletal muscle.

Physical Exercise and Myokines: Relationships with Sarcopenia and Cardiovascular Complications

Skeletal muscle is capable of secreting different factors in order to communicate with other tissues. These mediators, the myokines, show potentially far-reaching effects on non-muscle tissues and can provide a molecular interaction between muscle and body physiology. Sarcopenia is a chronic degenerative neuromuscular disease closely related to cardiomyopathy and chronic heart failure, which influences the production and release of myokines. Our objective was to explore the relationship between myokines, sarcopenia, and cardiovascular diseases (CVD). The autocrine, paracrine, and endocrine actions of myokines include regulation of energy expenditure, insulin sensitivity, lipolysis, free fatty acid oxidation, adipocyte browning, glycogenolysis, glycogenesis, and general metabolism. A sedentary lifestyle accelerates the aging process and is a risk factor for developing sarcopenia, metabolic syndrome, and CVD. Increased adipose tissue resulting from the decrease in muscle mass in patients with sarcopenia may also be involved in the pathology of CVD. Myokines are protagonists in the complex condition of sarcopenia, which is associated with adverse clinical outcomes in patients with CVD. The discovery of new pathways and the link between myokines and CVD remain a cornerstone toward multifaceted interventions and perhaps the minimization of the damage resulting from muscle loss induced by factors such as atherosclerosis.

l-Citrulline supplementation improves glucose and exercise tolerance in obese male mice

NEW FINDINGS

What is the central question of the study? Does the action of l-citrulline, which has been shown to augment performance in animals and athletes, possibly via increasing mitochondrial function, translate to obese animals, and does this improve glycaemia? What is the main finding and its importance? Chronic supplementation with l-citrulline improves not only exercise capacity, but also glycaemia in obese mice, which would be beneficial as obese individuals are at increased risk for type 2 diabetes. However, l-citrulline supplementation also caused a mild impairment in insulin signalling and insulin tolerance in obese mice. ABSTRACT: l-Citrulline is an organic α-amino acid that has been shown to have a number of salutary actions on whole-body physiology, including reducing muscle wasting and augmenting exercise and muscle performance. The latter has been suggested to arise from elevations in mitochondrial function. Because enhancing mitochondrial function has been proposed as a novel strategy to mitigate insulin resistance, our goal was to determine whether supplementation with l-citrulline could also improve glycaemia in an experimental mouse model of obesity. We hypothesized that l-citrulline treatment would improve glycaemia in obese mice, and this would be associated with elevations in skeletal muscle mitochondrial function. Ten-week-old C57BL/6J mice were fed either a low-fat (10% kcal from lard) or a high-fat (60% kcal from lard) diet, while receiving drinking water supplemented with either vehicle or l-citrulline (0.6 g l^-1 ) for 15 weeks. Glucose homeostasis was assessed via glucose/insulin tolerance testing, while in vivo metabolism was assessed via indirect calorimetry, and forced exercise treadmill testing was utilized to assess endurance. As expected, obese mice supplemented with l-citrulline exhibited an increase in exercise capacity, which was associated with an improvement in glucose tolerance. Consistent with augmented mitochondrial function, we observed an increase in whole body oxygen consumption rates in obese mice supplemented with l-citrulline. Surprisingly, l-citrulline supplementation worsened insulin tolerance and reduced insulin signalling in obese mice. Taken together, although l-citrulline supplementation improves both glucose tolerance and exercise capacity in obese mice, caution must be applied with its broad use as a nutraceutical due to a potential deterioration of insulin sensitivity.

Cardiomyocyte Senescence and Cellular Communications Within Myocardial Microenvironments

Cardiovascular diseases have become the leading cause of human death. Aging is an independent risk factor for cardiovascular diseases. Cardiac aging is associated with maladaptation of cellular metabolism, dysfunction (or senescence) of cardiomyocytes, a decrease in angiogenesis, and an increase in tissue scarring (fibrosis). These events eventually lead to cardiac remodeling and failure. Senescent cardiomyocytes show the hallmarks of DNA damage, endoplasmic reticulum stress, mitochondria dysfunction, contractile dysfunction, hypertrophic growth, and senescence-associated secreting phenotype (SASP). Metabolism within cardiomyocytes is essential not only to fuel the pump function of the heart but also to maintain the functional homeostasis and participate in the senescence of cardiomyocytes. The senescence of cardiomyocyte is also regulated by the non-myocytes (endothelial cells, fibroblasts, and immune cells) in the local microenvironment. On the other hand, the senescent cardiomyocytes alter their phenotypes and subsequently affect the non-myocytes in the local microenvironment and contribute to cardiac aging and pathological remodeling. In this review, we first summarized the hallmarks of the senescence of cardiomyocytes. Then, we discussed the metabolic switch within senescent cardiomyocytes and provided a discussion of the cellular communications between dysfunctional cardiomyocytes and non-myocytes in the local microenvironment. We also addressed the functions of metabolic regulators within non-myocytes in modulating myocardial microenvironment. Finally, we pointed out some interesting and important questions that are needed to be addressed by further studies.

Constitutive PGC-1α overexpression in skeletal muscle does not protect from age-dependent decline in neurogenesis

Aerobic exercise prevents age-dependent decline in cognition and hippocampal neurogenesis. The transcription factor peroxisome proliferator-activated receptor gamma co-activator 1-alpha (PGC-1α) mediates many of the exercise-induced benefits in skeletal muscle, including the release of factors into the circulation with neurotrophic effects. We use a transgenic mouse model with muscle-specific overexpression of PGC-1α to study the contribution of chronic muscle activation on exercise-induced effects on hippocampal neurogenesis in aging. Young and old transgenic and wild type animals of both sexes displayed a robust age-related reduction in newborn BrdU⁺-cells, immature neurons (DCX⁺-cells) and new mature BrdU⁺/NeuN⁺-neurons in the dentate gyrus. No differences were detected between genotypes or sexes. Analysis of serum proteins showed a tendency towards increased levels of myokines and reduced levels of pro-inflammatory cytokines for transgenic animals, but only musclin was found to be significantly up-regulated in transgenic animals. We conclude that constitutive muscular overexpression of PGC-1α, despite potent systemic changes, is insufficient for mimicking exercise-induced effects on hippocampal neurogenesis in aging. Continued studies are required to investigate the complex molecular mechanisms by which circulating signals could mediate exercise-induced effects on the central nervous system in disease and aging, with the aim of discovering new therapeutic possibilities for patients.

New opportunities: Drosophila as a model system for exercise research

Because of the growing rates of obesity in much of the world, exercise as a treatment option for obesity and as part of a healthy lifestyle is of great interest to the general public, health policy makers, and scientists alike. Despite the long history of exercise promotion and exercise research, there are still significant gaps in our understanding of how exercise impacts individuals and what role genetics plays in determining an individual’s response to exercise. Model organisms are positioned uniquely to help address these questions because of the challenges associated with carrying out large-scale, well-controlled studies in humans. The fruit fly model system, Drosophila melanogaster, has joined the models used for exercise research only recently but already has made significant contributions to the field. In this review, we highlight the opportunities for exercise research in Drosophila. We review the resources available to researchers interested in using Drosophila for exercise research, focusing on the existing systems to induce exercise in Drosophila, to measure the amount of exercise performed, and to assess physical fitness. We illustrate the potential of the Drosophila system by drawing attention to pioneering studies in Drosophila exercise research and emphasize the unique opportunities this model system represents.

Antiapoptotic and mitochondrial biogenetic effects of exercise training on ovariectomized hypertensive rat hearts

This study was to investigate the effects of exercise training on antiapoptotic pathways and mitochondrial biogenesis in ovariectomized hypertensive rats. Histopathological analysis, TUNEL assay, and Western blotting were performed on the excised hearts from female spontaneously hypertensive rats (SHR), which were divided into a sham-operated sedentary hypertensive (SHR-S), a sedentary hypertensive ovariectomized (SHR-O), and hypertensive ovariectomized rats that underwent treadmill exercise training (SHR-OT; 60 min/day, 5 days/wk) for 8 wk, along with normotensive Wistar Kyoto rats (WKY). When compared with the WKY group, the SHR-S group exhibited decreased protein levels of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) and mitochondrial OPA-1 (mitochondrial biogenesis) and decreased further in the SHR-O group. The protein levels of p-PI3K, p-Akt, Bcl-2, Bcl-xL (prosurvival pathways), and the protein levels of PGC-1α and mitochondrial OPA1 (mitochondrial biogenesis) were increased in the SHR-OT group, but estrogen receptor (ER)α and ERβ were not changed when compared with the SHR-O group. The protein levels of t-Bid, Bad, Bax, cytosolic cytochrome c, activated caspase 9, and activated caspase 3 (mitochondria-dependent apoptotic pathways), as well as Fas ligand, TNF-α, Fas receptors, Fas-associated death domain, activated caspase 8 (Fas receptor-dependent apoptotic pathways) were decreased in the SHR-OT group, when compared with the SHR-O group. Exercise training protection on the coexistence of hypertension and ovariectomy-induced cardiac mitochondria-dependent and Fas receptor-dependent apoptotic pathways by enhancing the Bcl2-related and mitochondrial biogenetic prosurvival pathways might provide a new therapeutic effect on cardiac protection in oophorectomized early postmenopausal hypertensive women. NEW & NOTEWORTHY Widely dispersed cardiac apoptosis was found in the coexistence of hypertension and ovariectomy. Exercise training on a treadmill could prevent ovariectomized hypertension-induced widely dispersed cardiac apoptosis via mitochondria-dependent apoptotic pathway (t-Bid, Bad, Bax, cytosolic cytochrome c, activated caspase 9, and activated caspase 3) and Fas receptor-dependent apoptotic pathway (Fas ligand, tumor necrosis factor-α, Fas receptors, Fas-associated death domain, activated caspase 8, and activated caspase 3) through enhancing the Bcl2-related (p-PI3K, p-Akt, Bcl-2, Bcl-xL) and mitochondrial biogenetic (PGC-1α and mitochondrial optic atrophy 1) prosurvival pathways.

Reduced cardiomyocyte Na+ current in the age-dependent murine Pgc-1β-/- model of ventricular arrhythmia

Peroxisome proliferator-activated receptor-γ coactivator-1 deficient (Pgc-1β-/- ) murine hearts model the increased, age-dependent, ventricular arrhythmic risks attributed to clinical conditions associated with mitochondrial energetic dysfunction. These were accompanied by compromised action potential (AP) upstroke rates and impaired conduction velocities potentially producing arrhythmic substrate. We tested a hypothesis implicating compromised Na+ current in these electrophysiological phenotypes by applying loose patch-clamp techniques in intact young and aged, wild-type (WT) and Pgc-1β-/- , ventricular cardiomyocyte preparations for the first time. This allowed conservation of their in vivo extracellular and intracellular conditions. Depolarising steps elicited typical voltage-dependent activating and inactivating inward Na+ currents with peak amplitudes increasing or decreasing with their respective activating or preceding inactivating voltage steps. Two-way analysis of variance associated Pgc-1β-/- genotype with independent reductions in maximum peak ventricular Na+ currents from -36.63 ± 2.14 (n = 20) and -35.43 ± 1.96 (n = 18; young and aged WT, respectively), to -29.06 ± 1.65 (n = 23) and -27.93 ± 1.63 (n = 20; young and aged Pgc-1β-/- , respectively) pA/μm2 (p < 0.0001), without independent effects of, or interactions with age. Voltages at half-maximal current V*, and steepness factors k in plots of voltage dependences of both Na+ current activation and inactivation, and time constants for its postrepolarisation recovery from inactivation, remained indistinguishable through all experimental groups. So were the activation and rectification properties of delayed outward (K+ ) currents, demonstrated from tail currents reflecting current recoveries from respective varying or constant voltage steps. These current-voltage properties directly implicate decreases specifically in maximum available Na+ current with unchanged voltage dependences and unaltered K+ current properties, in proarrhythmic reductions in AP conduction velocity in Pgc-1β-/- ventricles.

The Shape of Mitochondrial Dysfunction in Down Syndrome

Oxidative stress (OS) and mitochondrial dysfunction (MD) have been extensively studied and defined as therapeutic targets in Down syndrome (DS). Though originally associated to individual genes located in supernumerary chromosome 21, OS and MD metabolic compromises appear to be linked to whole genome functionally defined transcriptional fingerprints that further exacerbate the contribution of critical genes in DS-AD pathology. As the main ROS generator, mitochondrial complex double-membrane organization, tightly regulated fission/fusion dynamics, and involvement in critical pathways, makes it particularly vulnerable to functional alterations. Consequently, mitochondrial network morphology depends on its metabolic state and has been used as an indicator of cellular homeostasis. Initial qualitative categorization, suitable for sparse arranged fragments analysis, were proven to be ineffective to measure network connectivity and replaced by innovative tools that involve the transformation of raw images to linear skeletons. These manipulations allowed the development of a new generation of structural parameters, such as mean degree value (MDV). Alterations in DS mitochondrial networks include increased frequency of aberrant morphologies, shorter mitochondrial fragments, and significantly lower mitochondrial network connectivity. Similar structural and functional mitochondrial defects are common to other neurodegenerative diseases, such as Parkinson disease and Prion disease, and to a progeroid syndrome like HGPS. Therapeutic interventions aimed to either increase mitochondrial biogenesis or diminish OS using mitochondrial-targeted antioxidants, successfully restored mitochondrial activity and structural organization, confirming the strong correlation between network form and function.

Parkin overexpression protects from ageing-related loss of muscle mass and strength

KEY POINTS

Recent evidence suggests that impaired mitophagy, a process in charge of removing damaged/dysfunctional mitochondria and in part regulated by Parkin, could contribute to the ageing-related loss of muscle mass and function. In the present study, we show that Parkin overexpression attenuates ageing-related loss of muscle mass and strength and unexpectedly causes hypertrophy in adult skeletal muscles. We also show that Parkin overexpression leads to increases in mitochondrial content and enzymatic activities. Finally, our results show that Parkin overexpression protects from ageing-related increases in markers of oxidative stress, fibrosis and apoptosis. Our findings place Parkin as a potential therapeutic target to attenuate sarcopenia and improve skeletal muscle health and performance.

ABSTRACT

The ageing-related loss of muscle mass and strength, a process called sarcopenia, is one of the most deleterious hallmarks of ageing. Solid experimental evidence indicates that mitochondrial dysfunctions accumulate with ageing and are critical in the sarcopenic process. Recent findings suggest that mitophagy, the process in charge of the removal of damaged/dysfunctional mitochondria, is altered in aged muscle. Impaired mitophagy represents an attractive mechanism that could contribute to the accumulation of mitochondrial dysfunctions and sarcopenia. To test this hypothesis, we investigated the impact of Parkin overexpression in skeletal muscles of young and old mice. Parkin was overexpressed for 4 months in muscles of young (3 months) and late middle-aged (18 months) mice using i.m. injections of adeno-associated viruses. We show that Parkin overexpression increased muscle mass, fibre size and mitochondrial enzyme activities in both young and old muscles. In old mice, Parkin overexpression increased muscle strength, peroxisome proliferator‐activated receptor gamma coactivator 1‐alpha (PGC‐1α) and mitochondrial density. Parkin overexpression also attenuated the ageing-related increase in 4-hydroxynonenal content (a marker of oxidative stress) and type I collagen content (a marker of fibrosis), as well as the number of terminal deoxynucleotidyl transferase dUTP nick-end labelling-positive myonuclei (a marker of apoptosis). Overall, our results indicate that Parkin overexpression attenuates sarcopenia and unexpectedly causes hypertrophy in adult muscles. They also show that Parkin overexpression leads to increases in mitochondrial content and enzymatic activities. Finally, our results show that Parkin overexpression protects against oxidative stress, fibrosis and apoptosis. These findings highlight that Parkin may be an attractive therapeutic target with respect to attenuating sarcopenia and improving skeletal muscle health and performance.

Resveratrol and/or exercise training counteract aging-associated decline of physical endurance in aged mice; targeting mitochondrial biogenesis and function

Mitochondrial dysfunction and decreased mitochondrial content are hallmarks of aging that leads to decreased physical endurance. Our aim was to explore the anti-aging effect of resveratrol (RSVT) supplementation, a polyphenol, and/or exercise training, started at an older age, on improving physical activity, therefore, help in frailty avoidance and promotion of healthy aging in elderly. Eighteen-month-old aged mice received RSVT (15 mg/kg/day) and/or exercise trained for 4 weeks showed significant longer time to exhaustion with decreased blood lactate and free fatty acids levels associated with improved oxidative stress evidenced by decreased gastrocnemius muscle lipid peroxidation and increased antioxidant enzymes activities, catalase and superoxide dismutase, when compared to aged mice control group. These changes were accompanied by over-expression of skeletal muscle peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) mRNA, the master regulator of mitochondrial biogenesis, and increased muscle citrate synthase activity, a marker for mitochondrial function. These findings may provide evidence for improved physical endurance by RSVT supplementation or exercise training with better results of their combination, even at an older age, through increasing mitochondrial biogenesis and function. Increased muscle PGC-1α mRNA expression and citrate synthase enzyme activity in addition to improved aging-associated oxidative damage were among the mechanisms involved in this protection.

Ventricular pro-arrhythmic phenotype, arrhythmic substrate, ageing and mitochondrial dysfunction in peroxisome proliferator activated receptor-γ coactivator-1β deficient (Pgc-1β-/-) murine hearts

INTRODUCTION

Ageing and age-related bioenergetic conditions including obesity, diabetes mellitus and heart failure constitute clinical ventricular arrhythmic risk factors.

MATERIALS AND METHODS

Pro-arrhythmic properties in electrocardiographic and intracellular recordings were compared in young and aged, peroxisome proliferator-activated receptor-γ coactivator-1β knockout (Pgc-1β-/-) and wild type (WT), Langendorff-perfused murine hearts, during regular and programmed stimulation (PES), comparing results by two-way ANOVA.

RESULTS AND DISCUSSION

Young and aged Pgc-1β-/- showed higher frequencies and durations of arrhythmic episodes through wider PES coupling-interval ranges than WT. Both young and old, regularly-paced, Pgc-1β-/- hearts showed slowed maximum action potential (AP) upstrokes, (dV/dt)max (∼157 vs. 120-130 V s-1), prolonged AP latencies (by ∼20%) and shortened refractory periods (∼58 vs. 51 ms) but similar AP durations (∼50 ms at 90% recovery) compared to WT. However, Pgc-1β-/- genotype and age each influenced extrasystolic AP latencies during PES. Young and aged WT ventricles displayed distinct, but Pgc-1β-/- ventricles displayed similar dependences of AP latency upon (dV/dt)max resembling aged WT. They also independently increased myocardial fibrosis. AP wavelengths combining activation and recovery terms paralleled contrasting arrhythmic incidences in Pgc-1β-/- and WT hearts. Mitochondrial dysfunction thus causes pro-arrhythmic Pgc-1β-/- phenotypes by altering AP conduction through reducing (dV/dt)max and causing age-dependent fibrotic change.

Overexpression of PGC-1α in aging muscle enhances a subset of young-like molecular patterns

PGC‐1α is a transcriptional co‐activator known as the master regulator of mitochondrial biogenesis. Its control of metabolism has been suggested to exert critical influence in the aging process. We have aged mice overexpressing PGC‐1α in skeletal muscle to determine whether the transcriptional changes reflected a pattern of expression observed in younger muscle. Analyses of muscle proteins showed that Pax7 and several autophagy markers were increased. In general, the steady‐state levels of several muscle proteins resembled that of muscle from young mice. Age‐related mtDNA deletion levels were not increased by the PGC‐1α‐associated increase in mitochondrial biogenesis. Accordingly, age‐related changes in the neuromuscular junction were minimized by PGC‐1α overexpression. RNA‐Seq showed that several genes overexpressed in the aged PGC‐1α transgenic are expressed at higher levels in young when compared to aged skeletal muscle. As expected, there was increased expression of genes associated with energy metabolism but also of pathways associated with muscle integrity and regeneration. We also found that PGC‐1α overexpression had a mild but significant effect on longevity. Taken together, overexpression of PGC‐1α in aged muscle led to molecular changes that resemble the patterns observed in skeletal muscle from younger mice.

Mild aerobic training with blood flow restriction increases the hypertrophy index and MuSK in both slow and fast muscles of old rats: Role of PGC-1α

AIMS

Existing evidence emphasize the role of mitochondrial dysfunction in sarcopenia which is revealed as loss of skeletal muscle mass and neuromuscular junction remodeling. We assessed the effect of low-intensity aerobic training along with blood flow restriction on muscle hypertrophy index, muscle-specific kinase (MuSK), a pivotal protein of the neuromuscular junction and Peroxisome proliferator-activated receptor gamma co-activator 1-alpha (PGC-1α) in aged male rats.

MAIN METHODS

Animals groups were control (CTL), sham (Sh), leg blood flow restriction (BFR), exercise (Ex), sham + exercise (Sh + Ex), and BFR plus exercise (BFR + Ex) groups. The exercise groups were trained with low intensity exercise for 10 weeks. 48 h after the last training session, animals were sacrificed under anesthesia. Soleus and EDL muscles were isolated, hypertrophy index was estimated and MuSK and PGC-1α were measured by western blot method.

KEY FINDINGS

Hypertrophy index enhanced in soleus and Extensor digitorum longus (EDL) muscles of BFR + Ex group (P < 0.01 versus CTL and Sh groups, and P < 0.001 versus other groups). The MuSK protein of soleus and EDL muscles increased in BFR + Ex group (P < 0.01 and P < 0.001, respectively) in comparison with CTL and Sh groups. In BFR + Ex group, the PGC-1α protein increased in both soleus and EDL (P < 0.001 compared to other groups). Also the PGC-1α of soleus muscle was higher in Ex and Sh + Ex groups versus CTL and Sh groups (P < 0.05).

SIGNIFICANCE

Findings suggest that low endurance exercise plus BFR improves the MuSK and hypertrophy index of both slow and fast muscles of elderly rats probably through the rise of PGC-1α expression.

Moderate Modulation of Cardiac PGC-1α Expression Partially Affects Age-Associated Transcriptional Remodeling of the Heart

Aging is associated with a decline in cardiac function due to a decreased myocardial reserve. This adverse cardiac remodeling comprises of a variety of changes, including a reduction in mitochondrial function and a decline in the expression of the peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), a central regulator of mitochondrial biogenesis and metabolic adaptation in the myocardium. To study the etiological involvement of PGC-1α in cardiac aging, we used mouse models mimicking the modest down- and upregulation of this coactivator in the old and the exercised heart, respectively. Young mice with reduced cardiac expression of PGC-1α recapitulated part of the age-related impairment in mitochondrial gene expression, but otherwise did not aggravate the aging process. Inversely however, moderate overexpression of PGC-1α counteracts numerous key age-related remodeling changes, e.g., by improving blood pressure, age-associated apoptosis, and collagen accumulation, as well as in the expression of many, but not all cardiac genes involved in mitochondrial biogenesis, dynamics, metabolism, calcium handling and contractility. Thus, while the reduction of PGC-1α in the heart is insufficient to cause an aging phenotype, moderate overexpression reduces pathological remodeling of older hearts and could thereby contribute to the beneficial effects of exercise on cardiac function in aging.

Effects of exercise in a cold environment on transcriptional control of PGC-1α

Peroxisome proliferator-activated receptor-α coactivator-1α (PGC-1α) mRNA is increased with both exercise and exposure to cold temperature. However, transcriptional control has yet to be examined during exercise in the cold. Additionally, the need for environmental cold exposure after exercise may not be a practical recovery modality. The purpose of this study was to determine mitochondrial-related gene expression and transcriptional control of PGC-1α following exercise in a cold compared with room temperature environment. Eleven recreationally trained males completed two 1-h cycling bouts in a cold (7°C) or room temperature (20°C) environment, followed by 3 h of supine recovery in standard room conditions. Muscle biopsies were taken from the vastus lateralis preexercise, postexercise, and after a 3-h recovery. Gene expression and transcription factor binding to the PGC-1α promoter were analyzed. PGC-1α mRNA increased from preexercise to 3 h of recovery, but there was no difference between trials. Estrogen-related receptor-α (ERRα), myocyte enhancer factor-2 (MEF2A), and nuclear respiratory factor-1 (NRF-1) mRNA were lower in cold than at room temperature. Forkhead box class-O (FOXO1) and cAMP response element-binding protein (CREB) binding to the PGC-1α promoter were increased postexercise and at 3 h of recovery. MEF2A binding increased postexercise, and activating transcription factor 2 (ATF2) binding increased at 3 h of recovery. These data indicate no difference in PGC-1α mRNA or transcriptional control after exercise in cold versus room temperature and 3 h of recovery. However, the observed reductions in the mRNA of select transcription factors downstream of PGC-1α indicate a potential influence of exercise in the cold on the transcriptional response related to mitochondrial biogenesis.

PGC-1α-Derived Peptide Influences Energy in Normal Human Dermal Fibroblasts

Mitochondrial energy metabolism declines during aging. PGC-1α is a transcription coactivator that plays a key role in the regulation of energetic metabolism and mitochondrial biogenesis in the cells. The aim of this study was to compare the PPARGC1A gene expression level in normal human dermal fibroblasts (NHDF) derived from young and old donors. A PGC-1α-derived peptide was then synthetized and its ability to affect the PPARGC1A gene expression and mitochondrial function was tested. We assessed changes in PPARGC1A gene expression using quantitative RT-PCR. The effect of the PGC-1α-derived peptide on energy production was determined using an ATP bioluminescent assay kit. We also studied changes in mitochondrial membrane potential using JC-1 fluorescent dye and the level of reactive oxygen species (ROS) using DCFH-DA dye in NHDF cells after UVA/B irradiation alone and in combination with a peptide treatment. The PPARGC1A gene expression decreased in an aged human dermal fibroblast. The PGC-1α-derived peptide was synthetized and increased the PPARGC1A gene expression and ATP levels in cells. Furthermore, the mitochondrial membrane potential in UVA/B irradiated cells treated with the tested PGC-1α-derived peptide was increased compared to irradiated controls. Moreover, the ROS levels in UVA/B irradiated cells treated with the PGC-1α-derived peptide decreased. On the basis of our results, PGC-1α emerges as an interesting target to combat decreasing energetic metabolism in aging skin cells. Indeed, the PGC-1α-derived peptide increasing the PPARGC1A gene expression improved the mitochondrial function and increased energy production in the cells.

Adipose triglyceride lipase decrement affects skeletal muscle homeostasis during aging through FAs-PPARα-PGC-1α antioxidant response

During aging skeletal muscle shows an accumulation of oxidative damage as well as intramyocellular lipid droplets (IMLDs). However, although the impact of these modifications on muscle tissue physiology is well established, the direct effectors critical for their occurrence are poorly understood. Here we show that during aging the main lipase of triacylglycerols, ATGL, significantly declines in gastrocnemius and its downregulation in C2C12 myoblast leads to the accumulation of lipid droplets. Indeed, we observed an increase of oxidative damage to proteins in terms of carbonylation, S-nitrosylation and ubiquitination that is dependent on a defective antioxidant cell response mediated by ATGL-PPARα-PGC-1α. Overall our findings describe a pivotal role for ATGL in the antioxidant/anti-inflammatory response of muscle cells highlighting this lipase as a therapeutic target for fighting the progressive decline in skeletal muscle mass and strength.

Impaired regeneration in calpain-3 null muscle is associated with perturbations in mTORC1 signaling and defective mitochondrial biogenesis

Background

Previous studies in patients with limb-girdle muscular dystrophy type 2A (LGMD2A) have suggested that calpain-3 (CAPN3) mutations result in aberrant regeneration in muscle.

Methods

To gain insight into pathogenesis of aberrant muscle regeneration in LGMD2A, we used a paradigm of cardiotoxin (CTX)-induced cycles of muscle necrosis and regeneration in the CAPN3-KO mice to simulate the early features of the dystrophic process in LGMD2A. The temporal evolution of the regeneration process was followed by assessing the oxidative state, size, and the number of metabolic fiber types at 4 and 12 weeks after last CTX injection. Muscles isolated at these time points were further investigated for the key regulators of the pathways involved in various cellular processes such as protein synthesis, cellular energy status, metabolism, and cell stress to include Akt/mTORC1 signaling, mitochondrial biogenesis, and AMPK signaling. TGF-β and microRNA (miR-1, miR-206, miR-133a) regulation were also assessed. Additional studies included in vitro assays for quantifying fusion index of myoblasts from CAPN3-KO mice and development of an in vivo gene therapy paradigm for restoration of impaired regeneration using the adeno-associated virus vector carrying CAPN3 gene in the muscle.

Results

At 4 and 12 weeks after last CTX injection, we found impaired regeneration in CAPN3-KO muscle characterized by excessive numbers of small lobulated fibers belonging to oxidative metabolic type (slow twitch) and increased connective tissue. TGF-β transcription levels in the regenerating CAPN3-KO muscles were significantly increased along with microRNA dysregulation compared to wild type (WT), and the attenuated radial growth of muscle fibers was accompanied by perturbed Akt/mTORC1 signaling, uncoupled from protein synthesis, through activation of AMPK pathway, thought to be triggered by energy shortage in the CAPN3-KO muscle. This was associated with failure to increase mitochondria content, PGC-1α, and ATP5D transcripts in the regenerating CAPN3-KO muscles compared to WT. In vitro studies showed defective myotube fusion in CAPN3-KO myoblast cultures. Replacement of CAPN3 by gene therapy in vivo increased the fiber size and decreased the number of small oxidative fibers.

Conclusion

Our findings provide insights into understanding of the impaired radial growth phase of regeneration in calpainopathy.

Electronic supplementary material

The online version of this article (10.1186/s13395-017-0146-6) contains supplementary material, which is available to authorized users.

Cardiomyocyte ionic currents in intact young and aged murine Pgc-1β-/- atrial preparations

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Energetically-deficient Pgc-1β−/− murine atria show age-dependent arrhythmia.

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Voltage clamp studies investigated their underlying membrane current changes.

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Pgc-1β−/− atria showed reduced inward Na⁺ currents with normal voltage-dependences.

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Outward repolarising K+ currents retained normal activation and rectification.

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A resulting slowed action potential conduction explains the arrhythmic phenotype.

Introduction

Recent studies reported that energetically deficient murine Pgc-1β^−/− hearts replicate age-dependent atrial arrhythmic phenotypes associated with their corresponding clinical conditions, implicating action potential (AP) conduction slowing consequent upon reduced AP upstroke rates.

Materials and methods

We tested a hypothesis implicating Na⁺ current alterations as a mechanism underlying these electrophysiological phenotypes. We applied loose patch-clamp techniques to intact young and aged, WT and Pgc-1β^−/−, atrial cardiomyocyte preparations preserving their in vivo extracellular and intracellular conditions.

Results and discussion

Depolarising steps activated typical voltage-dependent activating and inactivating inward (Na⁺) currents whose amplitude increased or decreased with the amplitudes of the activating, or preceding inactivating, steps. Maximum values of peak Na⁺ current were independently influenced by genotype but not age or interacting effects of genotype and age on two-way ANOVA. Neither genotype, nor age, whether independently or interactively, influenced voltages at half-maximal current, or steepness factors, for current activation and inactivation, or time constants for recovery from inactivation following repolarisation. In contrast, delayed outward (K⁺) currents showed similar activation and rectification properties through all experimental groups. These findings directly demonstrate and implicate reduced Na⁺ in contrast to unchanged K⁺ current, as a mechanism for slowed conduction causing atrial arrhythmogenicity in Pgc-1β^−/− hearts.