MOTS-c is an exercise-induced mitochondrial-encoded regulator of age-dependent physical decline and muscle homeostasis

Endurance training enhances skeletal muscle mitochondrial respiration by promoting MOTS-c secretion

The mitochondrial open reading frame of 12S rRNA-c (MOTS-c) is a biologically active mitochondria-derived peptide. However, the relationship between MOTS-c, skeletal muscle mitochondrial function, and endurance exercise adaptations is unknown. Here, we tested indices such as maximal oxygen uptake and serum MOTS-c levels in marathon runners and sedentary subjects. In addition, we tested aerobic exercise capacity, skeletal muscle mitochondrial respiration rate, and serum MOTS-c levels in mice subjected to long-term endurance training groups and sedentary groups. Our results indicated a close association between serum MOTS-c levels and aerobic exercise capacity. Circulating MOTS-c levels are expected to be an important indicator for predicting aerobic exercise capacity and assessing body fat status, endurance training load, and physical function. More importantly, we found that endurance training may enhance the mitochondrial respiratory function of skeletal muscle by promoting the secretion of MOTS-c and activating the AMPK/PGC-1α pathway.

MOTS-c relieves hepatocellular carcinoma resistance to TRAIL-induced apoptosis under hypoxic conditions by activating MEF2A

BACKGROUND

Mitochondrial ORF of the 12S rRNA type-c (MOTS-c) as an AMPK agonist can regulate the expression of adaptive nuclear genes to promote cell homeostasis. However, the investigation of MOTS-c in hepatocellular carcinoma (HCC) is insufficient. This study aims to reveal the role of MOTS-c on HCC cell apoptosis.

METHODS

Huh7 and HCCLM3 cells were incubated with MOTS-c under a hypoxic condition. MOTS-c levels were quantified by enzyme-linked immunosorbent assay in the peripheral blood of HCC patients and healthy controls. Cell viability was detected by 3-(4,5-Dimethylthazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Cell apoptosis was investigated by flow cytometry and Tunel assay. Protein expression was detected by western blotting or immunohistochemistry assay. Dual-luciferase reporter assay and chromatin immunoprecipitation assay were performed to identify the association among myocyte enhancer factor 2A (MEF2A), death receptor 4 (DR4) and DR5. A tumor-bearing nude mouse model was conducted to assess the effect of MOTS-c on HCC tumor formation in vivo.

RESULTS

MOTS-c levels in the peripheral blood of HCC patients were significantly lower compared to healthy individuals. MOTS-c promoted HCC cell apoptosis under hypoxia conditions. Hypoxia stimulation decreased the protein expression of MEF2A, DR4, DR5, fas-associating via death domain (FADD) and caspase-8, while these effects were attenuated after MOTS-c treatment. MOTS-c induced TRAIL-induced apoptosis of HCC cells by activating MEF2A through the phosphorylation of AMPK under hypoxia treatment. In addition, MEF2A transcriptionally up-regulated DR4 and DR5. MOTS-c activated MEF2A to regulate DR4 and DR5 expression, further mediating TRAIL-induced apoptosis. Further, MOTS-c treatment relieved hypoxia-induced tumor growth in vivo.

CONCLUSION

MOTS-c relieved hypoxia-induced HCC cell resistance to TRAIL-caused apoptosis by activating MEF2A.

Mitochondrial-derived microproteins: from discovery to function

Given the uniqueness of the mitochondria, and the fact that they have their own genome, mitochondrial-derived microproteins (MDPs) are similar to, but different from, nuclear-encoded microproteins. The discovery of an increasing number of microproteins from this organelle and the importance of mitochondria to cellular and organismal health make it a priority to study this novel class of proteins in search of possible therapeutic targets and cures. In this review, we discuss the history of MDP discovery, describe the function of each MDP, and conclude with future goals and techniques to help discover more MDPs.

MOTS-c modulates skeletal muscle function by directly binding and activating CK2

MOTS-c is a mitochondrial microprotein that improves metabolism. Here, we demonstrate CK2 is a direct and functional target of MOTS-c. MOTS-c directly binds to CK2 and activates it in cell-free systems. MOTS-c administration to mice prevented skeletal muscle atrophy and enhanced muscle glucose uptake, which were blunted by suppressing CK2 activity. Interestingly, the effects of MOTS-c are tissue-specific. Systemically administered MOTS-c binds to CK2 in fat and muscle, yet stimulates CK2 activity in muscle while suppressing it in fat by differentially modifying CK2-interacting proteins. Notably, a naturally occurring MOTS-c variant, K14Q MOTS-c, has reduced binding to CK2 and does not activate it or elicit its effects. Male K14Q MOTS-c carriers exhibited a higher risk of sarcopenia and type 2 diabetes (T2D) in an age- and physical-activity-dependent manner, whereas females had an age-specific reduced risk of T2D. Altogether, these findings provide evidence that CK2 is required for MOTS-c effects.

The Human Mitochondrial Genome Encodes for an Interferon-Responsive Host Defense Peptide

The mitochondrial DNA (mtDNA) can trigger immune responses and directly entrap pathogens, but it is not known to encode for active immune factors. The immune system is traditionally thought to be exclusively nuclear-encoded. Here, we report the identification of a mitochondrial-encoded host defense peptide (HDP) that presumably derives from the primordial proto-mitochondrial bacteria. We demonstrate that MOTS-c (mitochondrial open reading frame from the twelve S rRNA type-c) is a mitochondrial-encoded amphipathic and cationic peptide with direct antibacterial and immunomodulatory functions, consistent with the peptide chemistry and functions of known HDPs. MOTS-c targeted E. coli and methicillin-resistant S. aureus (MRSA), in part, by targeting their membranes using its hydrophobic and cationic domains. In monocytes, IFNγ, LPS, and differentiation signals each induced the expression of endogenous MOTS-c. Notably, MOTS-c translocated to the nucleus to regulate gene expression during monocyte differentiation and programmed them into macrophages with unique transcriptomic signatures related to antigen presentation and IFN signaling. MOTS-c-programmed macrophages exhibited enhanced bacterial clearance and shifted metabolism. Our findings support MOTS-c as a first-in-class mitochondrial-encoded HDP and indicates that our immune system is not only encoded by the nuclear genome, but also by the co-evolved mitochondrial genome.

Mitochondrial-Derived Peptide MOTS-c Suppresses Ovarian Cancer Progression by Attenuating USP7-Mediated LARS1 Deubiquitination

Mitochondrial-nuclear communication plays a vital role in maintaining cellular homeostasis. MOTS-c, a short peptide derived from the 12S rRNA of mitochondrial DNA, has been suggested as a retrograde mitochondrial signal. Although recent clinical studies have suggested a possible link between MOTS-c and human cancer, the role of MOTS-c in tumorigenesis has yet to be investigated. Here, MOTS-c levels are found to be reduced in both serum and tumor tissues from ovarian cancer (OC) patients, which are associated with poor patients' prognosis. Exogenous MOTS-c inhibits the proliferation, migration and invasion of OC cells, and induces cell cycle arrest and apoptosis. Mechanistically, MOTS-c interacts with LARS1 and promotes its ubiquitination and proteasomal degradation. In addition, USP7 was identified as a deubiquitinase of LARS1, and MOTS-c can attenuates USP7-mediated LARS1 deubiquitination by competing with USP7 for binding to LARS1. Besides, LARS1 was found to be increased and play an important oncogenic function in OC. More importantly, MOTS-c displays a marked anti-tumor effect on OC growth without systemic toxicity in vivo. In conclusion, this study reveals a crucial role of MOTS-c in OC and provides a possibility for MOTS-c as a therapeutic target for the treatment of this manlignacy.

The Relationship Between MOTS-c K14Q Polymorphism and Sarcopenia, Blood Lipids, and Mental Health in Older Korean Adults

Background/objectives: An East Asian-specific 1382A>C polymorphism in the mitochondrial open reading frame of the 12S rRNA type-c results in an amino acid substitution from Lys (K) to Gln (Q) at the 14th amino acid residue. This study investigated the association between m.1382A>C polymorphism and sarcopenia, blood lipids, and mental health in older Korean adults. Methods: The study included 683 community-dwelling Korean adults (345 men and 338 women) aged 65 years and older. The m.1382A>C polymorphism was genotyped with a 7500 real-time PCR system. Handgrip strength (HGS) was measured, and appendicular skeletal muscle (ASM) mass was calculated. Demographics, blood lipids, falling risk, nutritional intake, cognition function, and depression were additionally measured. Results: Men carrying the C allele had significantly higher ASM (21.6 ± 3.0 vs. 19.5 ± 2.2 kg, p = 0.018), ASM/height2 (7.76 ± 0.76 vs. 7.14 ± 0.62 kg/m2, p = 0.012), lean mass (53.3 ± 6.2 vs. 46.5 ± 4.0 kg, p < 0.001), left HGS (33.3 ± 5.0 vs. 28.9 ± 4.0 kg, p = 0.010), and right HGS (35.6 ± 5.3 vs. 30.9 ± 4.3 kg, p = 0.009) than men carrying the A allele. The genotype differences in ASM (p = 0.017), ASM/height2 (p = 0.011), lean mass (p < 0.001), left HGS (p = 0.010), and right HGS (p = 0.009) remained significant even after adjusting for all measured covariates. By contrast, no significant differences in other measured parameters were found between women carrying the A and C alleles. Conclusions: Our study findings indicate that the m.1382A>C polymorphism may be used as a genetic biomarker of age-related sarcopenia in older Korean men.

Unraveling aging from transcriptomics

Research into aging constitutes a pivotal endeavor aimed at elucidating the underlying biological mechanisms governing aging and age-associated diseases, as well as promoting healthy longevity. Recent advances in transcriptomic technologies, such as bulk RNA sequencing (RNA-seq), single-cell transcriptomics, and spatial transcriptomics, have revolutionized our ability to study aging at unprecedented resolution and scale. These technologies present novel opportunities for the discovery of biomarkers, elucidation of molecular pathways, and development of targeted therapeutic strategies for age-related disorders. This review surveys recent breakthroughs in different types of transcripts on aging, such as mRNA, long noncoding (lnc)RNA, tRNA, and miRNA, highlighting key findings and discussing their potential implications for future studies in this field.

Mitochondrial Function and Dysfunction in White Adipocytes and Therapeutic Implications

For a long time, white adipocytes were thought to function as lipid storages due to the sizeable unilocular lipid droplet that occupies most of their space. However, recent discoveries have highlighted the critical role of white adipocytes in maintaining energy homeostasis and contributing to obesity and related metabolic diseases. These physiological and pathological functions depend heavily on the mitochondria that reside in white adipocytes. This article aims to provide an up-to-date overview of the recent research on the function and dysfunction of white adipocyte mitochondria. After briefly summarizing the fundamental aspects of mitochondrial biology, the article describes the protective role of functional mitochondria in white adipocyte and white adipose tissue health and various roles of dysfunctional mitochondria in unhealthy white adipocytes and obesity. Finally, the article emphasizes the importance of enhancing mitochondrial quantity and quality as a therapeutic avenue to correct mitochondrial dysfunction, promote white adipocyte browning, and ultimately improve obesity and its associated metabolic diseases. © 2024 American Physiological Society. Compr Physiol 14:5581-5640, 2024.

Mitochondrial-derived peptides in cardiovascular disease: Novel insights and therapeutic opportunities

BACKGROUND

Mitochondria-derived peptides (MDPs) represent a recently discovered family of peptides encoded by short open reading frames (ORFs) found within mitochondrial genes. This group includes notable members including humanin (HN), mitochondrial ORF of the 12S rDNA type-c (MOTS-c), and small humanin-like peptides 1-6 (SHLP1-6). MDPs assume pivotal roles in the regulation of diverse cellular processes, encompassing apoptosis, inflammation, and oxidative stress, which are all essential for sustaining cellular viability and normal physiological functions. Their emerging significance extends beyond this, prompting a deeper exploration into their multifaceted roles and potential applications.

AIM OF REVIEW

This review aims to comprehensively explore the biogenesis, various types, and diverse functions of MDPs. It seeks to elucidate the central roles and underlying mechanisms by which MDPs participate in the onset and development of cardiovascular diseases (CVDs), bridging the connections between cell apoptosis, inflammation, and oxidative stress. Furthermore, the review highlights recent advancements in clinical research related to the utilization of MDPs in CVD diagnosis and treatment.

KEY SCIENTIFIC CONCEPTS OF REVIEW

MDPs levels are diminished with aging and in the presence of CVDs, rendering them potential new indicators for the diagnosis of CVDs. Also, MDPs may represent a novel and promising strategy for CVD therapy. In this review, we delve into the biogenesis, various types, and diverse functions of MDPs. We aim to shed light on the pivotal roles and the underlying mechanisms through which MDPs contribute to the onset and advancement of CVDs connecting cell apoptosis, inflammation, and oxidative stress. We also provide insights into the current advancements in clinical research related to the utilization of MDPs in the treatment of CVDs. This review may provide valuable information with MDPs for CVD diagnosis and treatment.

Exercise Alleviates Cardiovascular Diseases by Improving Mitochondrial Homeostasis

Engaging in regular exercise and physical activity contributes to delaying the onset of cardiovascular diseases (CVDs). However, the physiological mechanisms underlying the benefits of regular exercise or physical activity in CVDs remain unclear. The disruption of mitochondrial homeostasis is implicated in the pathological process of CVDs. Exercise training effectively delays the onset and progression of CVDs by significantly ameliorating the disruption of mitochondrial homeostasis. This includes improving mitochondrial biogenesis, increasing mitochondrial fusion, decreasing mitochondrial fission, promoting mitophagy, and mitigating mitochondrial morphology and function. This review provides a comprehensive overview of the benefits of physical exercise in the context of CVDs, establishing a connection between the disruption of mitochondrial homeostasis and the onset of these conditions. Through a detailed examination of the underlying molecular mechanisms within mitochondria, the study illuminates how exercise can provide innovative perspectives for future therapies for CVDs.

Adipose thermogenic mechanisms by cold, exercise and intermittent fasting: Similarities, disparities and the application in treatment

Given its nonnegligible role in metabolic homeostasis, adipose tissue has been the target for treating metabolic disorders such as obesity, diabetes and cardiovascular diseases. Besides its lipolytic function, adipose thermogenesis has gained increased interest due to the irreplaceable contribution to dissipating energy to restore equilibrium, and its therapeutic effects have been testified in various animal models. In this review, we will brief about the canonical cold-stimulated adipose thermogenic mechanisms, elucidate on the exercise- and intermittent fasting-induced adipose thermogenic mechanisms, with a focus on the similarities and disparities among these signaling pathways, in an effort to uncover the overlapped and specific targets that may yield potent therapeutic efficacy synergistically in improving metabolic health.

Temporal expression of mitochondrial life cycle markers during acute and chronic overload of rat plantaris muscles

Skeletal muscle hypertrophy is generally associated with a fast-to-slow phenotypic adaptation in both human and rodent models. Paradoxically, this phenotypic shift is not paralleled by a concomitant increase in mitochondrial content and aerobic markers that would be expected to accompany a slow muscle phenotype. To understand the temporal response of the mitochondrial life cycle (i.e., biogenesis, oxidative phosphorylation, fission/fusion, and mitophagy/autophagy) to hypertrophic stimuli, in this study, we used the functional overload (FO) model in adult female rats and examined the plantaris muscle responses at 1 and 10 weeks. As expected, the absolute plantaris muscle mass increased by ∼12 and 26% at 1 and 10 weeks following the FO procedure, respectively. Myosin heavy-chain isoform types I and IIa significantly increased by 116% and 17%, respectively, in 10-week FO plantaris muscles. Although there was a general increase in protein markers associated with mitochondrial biogenesis in acute FO muscles, this response was unexpectedly sustained under 10-week FO conditions after muscle hypertrophy begins to plateau. Furthermore, the early increase in mito/autophagy markers observed under acute FO conditions was normalized by 10 weeks, suggesting a cellular environment favoring mitochondrial biogenesis to accommodate the aerobic demands of the plantaris muscle. We also observed a significant increase in the expression of mitochondrial-, but not nuclear-, encoded oxidative phosphorylation (OXPHOS) proteins and peptides (i.e., humanin and MOTS-c) under chronic, but not acute, FO conditions. Taken together, the temporal response of markers related to the mitochondrial life cycle indicates a pattern of promoting biogenesis and mitochondrial protein expression to support the energy demands and/or enhanced neural recruitment of chronically overloaded skeletal muscle.

Mitochondria-encoded peptide MOTS-c participates in plasma membrane repair by facilitating the translocation of TRIM72 to membrane

Rationale: An impairment of plasma membrane repair has been implicated in various diseases such as muscular dystrophy and ischemia/reperfusion injury. MOTS-c, a short peptide encoded by mitochondria, has been shown to pass through the plasma membrane into the bloodstream. This study determined whether this biological behavior was involved in membrane repair and its underlying mechanism. Methods and Results: In human participants, the level of MOTS-c was positively correlated with the abundance of mitochondria, and the membrane repair molecule TRIM72. In contrast to high-intensity eccentric exercise, moderate-intensity exercise improved sarcolemma integrity and physical performance, accompanied by an increase of mitochondria beneath the damaged sarcolemma and secretion of MOTS-c. Furthermore, moderate-intensity exercise increased the interaction between MOTS-c and TRIM72, and MOTS-c facilitated the trafficking of TRIM72 to the sarcolemma. In vitro studies demonstrated that MOTS-c attenuated membrane damage induced by hypotonic solution, which could be blocked by siRNA-TRIM72, but not AMPK inhibitor. Co-immunoprecipitation study showed that MOTS-c interacted with TRIM72 C-terminus, but not N-terminus. The dynamic membrane repair assay revealed that MOTS-c boosted the trafficking of TRIM72 to the injured membrane. However, MOTS-c itself had negligible effects on membrane repair, which was recapitulated in TRIM72-/- mice. Unexpectedly, MOTS-c still increased the fusion of vesicles with the membrane in TRIM72-/- mice, and dot blot analysis revealed an interaction between MOTS-c and phosphatidylinositol (4,5) bisphosphate [PtdIns (4,5) P2]. Finally, MOTS-c blunted ischemia/reperfusion-induced membrane disruption, and preserved heart function. Conclusions: MOTS-c/TRIM72-mediated membrane integrity improvement participates in mitochondria-triggered membrane repair. An interaction between MOTS-c and plasma lipid contributes to the fusion of vesicles with membrane. Our data provide a novel therapeutic strategy for rescuing organ function by facilitating membrane repair with MOTS-c.

Combined physical exercise re-synchronizes expression of Bmal1 and REV-ERBα and up-regulates apoptosis and metabolism in the prostate during aging

BACKGROUND

Aging increases the prevalence of prostate cancer. The circadian clock coordinates metabolism, cell cycle, and tumor suppressor p53. Although physical exercise has several effects on preventing prostate diseases, its effect on regulating genes and proteins of the circadian rhythm of the prostate needs to be better evaluated. The present study verified expression of REV-ERBα (Nr1d1), Bmal1, apoptosis, tumor suppressors, energetic metabolism markers, and androgen receptors in the prostatic microenvironment in 18-month-old mice submitted to combined physical training.

METHODS

C57BL/6 J mice were divided into 2 groups: 6 months-old (n = 10) and 18 months-old, (n = 20). The 18-month-old animals were divided into 2 subgroups: sedentary (n = 10, 18 m Sed) and submitted to combined physical training (n = 10, 18 m TR). Combined physical training protocol was performed by running on the treadmill (40-60 % of incremental load test) and climbing strength training (40-50 % of maximum repetition test), consisting of 5×/week (3 days aerobic and 2 days strength) for 3 weeks. The prostate was prepared for Western blot and RT-qPCR analysis, and the plasm was prepared for the biochemistry analysis.

RESULTS

Combined physical exercise during aging led to increased levels of Bmal1 and decreased levels of REV-ERBα in the prostate. These results were accompanied by a reduction in the AMPK/SIRT1/PGC-1α proteins and an increase in the PI3K/AKT and p53/PTEN/caspase 3 pathways, promoting apoptotic potential.

CONCLUSION

These findings suggest that strength and aerobic physical exercise may be preventive in the development of preneoplastic molecular alterations and age-related features by re-synchronizes Bmal1 and REV-ERBα in prostatic tissues.

Expression Patterns of MOTS-c in Adrenal Tumors: Results from a Preliminary Study

Adrenal tumors, such as adrenocortical carcinoma (ACC), adrenocortical adenoma (ACA), and pheochromocytoma (PCC) are complex diseases with unclear causes and treatments. Mitochondria and mitochondrial-derived peptides (MDPs) are crucial for cancer cell survival. The primary aim of this study was to analyze samples from different adrenal diseases, adrenocortical carcinoma, adrenocortical adenoma, and pheochromocytoma, and compare them with normal adrenal tissue to determine whether the expression levels of the mitochondrial open reading frame of the 12S rRNA type-c (MOTS-c) gene and protein vary between different types of adrenal tumors compared to healthy controls using qPCR, ELISA, and IHC methods. Results showed decreased MOTS-c mRNA expression in all adrenal tumors compared to controls, while serum MOTS-c protein levels increased in ACA and PCC but not in ACC. The local distribution of MOTS-c protein in adrenal tissue was reduced in all tumors. Notably, MOTS-c protein expression declined with ACC progression (stages III and IV) but was unrelated to patient age or sex. Tumor size and testosterone levels positively correlated with MOTS-c mRNA but negatively with serum MOTS-c protein. Additionally, serum MOTS-c protein correlated positively with glucose, total cholesterol, HDL, LDL, and SHGB levels. These findings suggest disrupted expression of MOTS-c in the spectrum of adrenal diseases, which might be caused by mechanisms involving increased mitochondrial dysfunction and structural changes in the tissue associated with disease progression. This study provides a detailed examination of MOTS-c mRNA and protein in adrenal tumors, indicating the potential role of MDPs in tumor biology and progression.

The Mitochondrial-Derived Peptide MOTS-c May Refine Mortality and Cardiovascular Risk Prediction in Chronic Hemodialysis Patients: A Multicenter Cohort Study

INTRODUCTION

Uremic patients exhibit remarkably increased rates of mortality and cardiovascular (CV) events, but risk prediction in this setting remains difficult. Systemic mitochondrial dysfunction is pervasive in end-stage kidney disease and may contribute to CV complications. We tested the clinical significance of circulating MOTS-c, a small mitochondrial-derived peptide, as a biomarker for improving mortality and CV risk prediction in hemodialysis (HD) patients.

METHODS

We conducted a prospective, observational, multicenter study on 94 prevalent HD patients. The study endpoint was a composite of all-cause mortality and non-fatal CV events. The diagnostic and prognostic capacities of predictive models based on cohort-related risk factors were tested before and after the inclusion of MOTS-c.

RESULTS

MOTS-c levels were higher in HD patients than in controls (p < 0.001) and even more elevated (p = 0.01) in the 53 individuals experiencing the combined endpoint during follow-up (median duration: 26.5 months). MOTS-c was independently associated with the endpoint at either multivariate logistic (OR 1.020; 95% CI: 1.011-1.109; p = 0.03) or Cox regression analyses (HR 1.004; 95% CI: 1.000-1.025; p = 0.05) and the addition of this biomarker to prognostic models including the other cohort-related risk predictors (age, left ventricular mass, evidence of diastolic dysfunction, diabetes, pulse pressure) significantly improved the calibration, risk variability explanation, discrimination (receiver operating characteristic area under the curve from 0.727 to 0.743; C-index from 0.658 to 0.700), and particularly, the overall reclassification capacity (NRI 15.87%; p = 0.01).

CONCLUSIONS

In HD patients, the mitochondrial-derived peptide MOTS-c may impart significant information to refine CV risk prediction, beyond cohort-related risk factors. Future investigations are needed to generalize these findings in larger and more heterogeneous cohorts.

A novel protein CYTB-187AA encoded by the mitochondrial gene CYTB modulates mammalian early development

The mitochondrial genome transcribes 13 mRNAs coding for well-known proteins essential for oxidative phosphorylation. We demonstrate here that cytochrome b (CYTB), the only mitochondrial-DNA-encoded transcript among complex III, also encodes an unrecognized 187-amino-acid-long protein, CYTB-187AA, using the standard genetic code of cytosolic ribosomes rather than the mitochondrial genetic code. After validating the existence of this mtDNA-encoded protein arising from cytosolic translation (mPACT) using mass spectrometry and antibodies, we show that CYTB-187AA is mainly localized in the mitochondrial matrix and promotes the pluripotent state in primed-to-naive transition by interacting with solute carrier family 25 member 3 (SLC25A3) to modulate ATP production. We further generated a transgenic knockin mouse model of CYTB-187AA silencing and found that reduction of CYTB-187AA impairs females' fertility by decreasing the number of ovarian follicles. For the first time, we uncovered the novel mPACT pattern of a mitochondrial mRNA and demonstrated the physiological function of this 14th protein encoded by mtDNA.

An 8-Week study on the effects of high and Moderate-Intensity interval exercises on mitochondrial MOTS-C changes and their relation to metabolic markers in male diabetic sand rats

Mitochondrial dysfunction is a significant feature of type 2 diabetes. MOTS-C, a peptide derived from mitochondria, has positive effects on metabolism and exercise capacity. This study explored the impact of high and moderate-intensity interval exercises on mitochondrial MOTS-C alterations and their correlation with metabolic markers in male diabetic sand rats. Thirty male sand rats were divided into six groups: control, MIIT, DM + HIIT, DM + MIIT, DM, and HIIT (5 rats each). Diabetes was induced using a high-fat diet (HFD) combined with streptozotocin (STZ). The Wistar sand rats in exercise groups underwent 8 weeks of interval training of varying intensities. Post sample collection, protein expressions of PCG-1a, AMPK, and GLUT4 were assessed through Western blot analysis, while MOTS-C protein expression was determined using ELISA. Both exercise intensity and diabetes significantly affected the levels of PCG-1a, MOTS-C, GLUT4 proteins, and insulin resistance (p < 0.001). The combined effect of diabetes status and exercise intensity on these levels was also significant (p < 0.001). However, the diabetes effect varied when comparing high-intensity to moderate-intensity exercise. The moderate-intensity exercise group with diabetes showed higher levels of PCG-1a, MOTS-C, and GLUT4 proteins and reduced insulin resistance levels (p < 0.001). Exercise intensity (p = 0.022) and diabetes (p = 0.008) significantly influenced AMPK protein levels. The interplay between diabetes status and exercise intensity on AMPK protein levels was noteworthy, with the moderate-intensity diabetes group exhibiting higher AMPK levels than the high-intensity diabetes group (p < 0.001). In conclusion, exercise elevates the levels of PCG-1a, MOTS-C, GLUT4, and AMPK proteins, regulating insulin resistance in diabetic sand rats. Given the AMPK-MOTS-C mitochondrial pathway's mechanisms, interval exercises might enhance the metabolic rates and general health of diabetic rodents.

The Mitochondrial-Derived Peptide MOTS-c Alleviates Radiation Pneumonitis via an Nrf2-Dependent Mechanism

Radiation pneumonitis (RP) is a prevalent and fatal complication of thoracic radiotherapy due to the lack of effective treatment options. RP primarily arises from mitochondrial injury in lung epithelial cells. The mitochondrial-derived peptide MOTS-c has demonstrated protective effects against various diseases by mitigating mitochondrial injury. C57BL/6 mice were exposed to 20 Gy of lung irradiation (IR) and received daily intraperitoneal injections of MOTS-c for 2 weeks. MOTS-c significantly ameliorated lung tissue damage, inflammation, and oxidative stress caused by radiation. Meanwhile, MOTS-c reversed the apoptosis and mitochondrial damage of alveolar epithelial cells in RP mice. Furthermore, MOTS-c significantly inhibited oxidative stress and mitochondrial damage in MLE-12 cells and primary mouse lung epithelial cells. Mechanistically, MOTS-c increased the nuclear factor erythroid 2-related factor (Nrf2) level and promoted its nuclear translocation. Notably, Nrf2 deficiency abolished the protective function of MOTS-c in mice with RP. In conclusion, MOTS-c alleviates RP by protecting mitochondrial function through an Nrf2-dependent mechanism, indicating that MOTS-c may be a novel potential protective agent against RP.

Inhibition of Crif1 protects fatty acid-induced POMC neuron-like cell-line damage by increasing CPT-1 function

Hypothalamic proopiomelanocortin (POMC) neurons are sensors of signals that reflect the energy stored in the body. Inducing mild stress in proopiomelanocortin neurons protects them from the damage promoted by the consumption of a high-fat diet, mitigating the development of obesity; however, the cellular mechanisms behind these effects are unknown. Here, we induced mild stress in a proopiomelanocortin neuron cell line by inhibiting Crif1. In proopiomelanocortin neurons exposed to high levels of palmitate, the partial inhibition of Crif1 reverted the defects in mitochondrial respiration and ATP production; this was accompanied by improved mitochondrial fusion/fission cycling. Furthermore, the partial inhibition of Crif1 resulted in increased reactive oxygen species production, increased fatty acid oxidation, and reduced dependency on glucose for mitochondrial respiration. These changes were dependent on the activity of CPT-1. Thus, we identified a CPT-1-dependent metabolic shift toward greater utilization of fatty acids as substrates for respiration as the mechanism behind the protective effect of mild stress against palmitate-induced damage of proopiomelanocortin neurons.NEW & NOTEWORTHY Saturated fats can damage hypothalamic neurons resulting in positive energy balance, and this is mitigated by mild cellular stress; however, the mechanisms behind this protective effect are unknown. Using a proopiomelanocortin cell line, we show that under exposure to a high concentration of palmitate, the partial inhibition of the mitochondrial protein Crif1 results in protection due to a metabolic shift warranted by the increased expression and activity of the mitochondrial fatty acid transporter CPT-1.

Socialized mitochondria: mitonuclear crosstalk in stress

Traditionally, mitochondria are considered sites of energy production. However, recent studies have suggested that mitochondria are signaling organelles that are involved in intracellular interactions with other organelles. Remarkably, stressed mitochondria appear to induce a beneficial response that restores mitochondrial function and cellular homeostasis. These mitochondrial stress-centered signaling pathways have been rapidly elucidated in multiple organisms. In this review, we examine current perspectives on how mitochondria communicate with the rest of the cell, highlighting mitochondria-to-nucleus (mitonuclear) communication under various stresses. Our understanding of mitochondria as signaling organelles may provide new insights into disease susceptibility and lifespan extension.

WDR23 mediates NRF2 proteostasis and cytoprotective capacity in the hippocampus

Pathogenic brain aging and neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease are characterized by chronic neuroinflammation and the accumulation of dysfunctional or misfolded proteins that lead to progressive neuronal cell death. Here we demonstrate that a murine model with global loss of the CUL4-DDB1 substrate receptor WDR23 (Wdr23KO) results in changes in multiple age-related hippocampal-dependent behaviors. The behavioral differences observed in Wdr23KO animals accompany the stabilization of the NRF2/NFE2L2 protein, an increase in RNA transcripts regulated by this cytoprotective transcription factor, and an increase in the steady state level of antioxidant defense proteins. Taken together, these findings reveal a role for WDR23-proteostasis in mediating cytoprotective capacity in the hippocampus and reveal the potential for targeting WDR23-NRF2 signaling interactions for development of therapies for neurodegenerative disorders.

Central MOTS-c infusion affects reproductive hormones in obese and non-obese rats

MOTS-c, a mitochondrial-derived peptide, acts as a systemic hormone and MOTS-c level is inversely correlated with markers of obesity. Obesity is a risk factor for male reproductive physiology and is expressed as an important cause of infertility. In this study, we aimed to determine the effects of MOTS-c, which has been proven in the hypothalamus and testicles, on the actors involved in the reproductive axis. In the study, 80 male Wistar-Albino rats were divided into two main groups, obese and non-obese (n = 40). Rats in the first main group were fed with fatty diet feed and obesity was induced. The second main group was fed with normal diet feed. Each main group was divided into 4 subgroups (Control, Sham, 10 and 100 µM MOTS-c). The lateral ventricles of the animals in the treatment groups were infused with 10 and 100 µM MOTS-c (solvent in Sham group) for 14 days. At the end of the experiment, hypothalamic Gonadotropin-Releasing Hormone (GnRH) gene expression level, serum testosterone, Luteinizing hormone (LH) and Follicle stimulating hormone (FSH) levels were determined. MOTS-c infusion caused an increase in GnRH mRNA, protein expression levels and serum testosterone, LH and FSH levels in obese and non-obese rats (p < 0.05). MOTS-c administration more significantly upregulated hormone levels in non-obese rats (p < 0.05). MOTS-c administration increases these hormones, suggesting that MOTS-c may stimulate the reproductive axis. Our results reveal that MOTS-c plays a role in the central regulation of reproduction, as well as causes increased LH, FSH and testosterone release.

Mitochondrial-derived microprotein MOTS-c attenuates immobilization-induced skeletal muscle atrophy by suppressing lipid infiltration

Mitochondrial open reading frame of the 12S ribosomal RNA type-c (MOTS-c), a mitochondrial microprotein, has been described as a novel regulator of glucose and lipid metabolism. In addition to its role as a metabolic regulator, MOTS-c prevents skeletal muscle atrophy in high fat-fed mice. Here, we examined the preventive effect of MOTS-c on skeletal muscle mass, using an immobilization-induced muscle atrophy model, and explored its underlying mechanisms. Male C57BL/6J mice (10 wk old) were randomly assigned to one of the three experimental groups: nonimmobilization control group (sterilized water injection), immobilization control group (sterilized water injection), and immobilization and MOTS-c-treated group (15 mg/kg/day MOTS-c injection). We used casting tape for the immobilization experiment. After 8 days of the experimental period, skeletal muscle samples were collected and used for Western blotting, RNA sequencing, and lipid and collagen assays. Immobilization reduced ∼15% of muscle mass, whereas MOTS-c treatment attenuated muscle loss, with only a 5% reduction. MOTS-c treatment also normalized phospho-AKT, phospho-FOXO1, and phospho-FOXO3a expression levels and reduced circulating inflammatory cytokines, such as interleukin-1b (IL-1β), interleukin-6 (IL-6), chemokine C-X-C motif ligand 1 (CXCL1), and monocyte chemoattractant protein 1 (MCP-1), in immobilized mice. Unbiased RNA sequencing and its downstream analyses demonstrated that MOTS-c modified adipogenesis-modulating gene expression within the peroxisome proliferator-activated receptor (PPAR) pathway. Supporting this observation, muscle fatty acid levels were lower in the MOTS-c-treated group than in the casted control mice. These results suggest that MOTS-c treatment inhibits skeletal muscle lipid infiltration by regulating adipogenesis-related genes and prevents immobilization-induced muscle atrophy.NEW & NOTEWORTHY MOTS-c, a mitochondrial microprotein, attenuates immobilization-induced skeletal muscle atrophy. MOTS-c treatment improves systemic inflammation and skeletal muscle AKT/FOXOs signaling pathways. Furthermore, unbiased RNA sequencing and subsequent assays revealed that MOTS-c prevents lipid infiltration in skeletal muscle. Since lipid accumulation is one of the common pathologies among other skeletal muscle atrophies induced by aging, obesity, cancer cachexia, and denervation, MOTS-c treatment could be effective in other muscle atrophy models as well.

Small peptides: could they have a big role in metabolism and the response to exercise?

Exercise is a powerful non-pharmacological intervention for the treatment and prevention of numerous chronic diseases. Contracting skeletal muscles provoke widespread perturbations in numerous cells, tissues and organs, which stimulate multiple integrated adaptations that ultimately contribute to the many health benefits associated with regular exercise. Despite much research, the molecular mechanisms driving such changes are not completely resolved. Technological advancements beginning in the early 1960s have opened new avenues to explore the mechanisms responsible for the many beneficial adaptations to exercise. This has led to increased research into the role of small peptides (<100 amino acids) and mitochondrially derived peptides in metabolism and disease, including those coded within small open reading frames (sORFs; coding sequences that encode small peptides). Recently, it has been hypothesized that sORF-encoded mitochondrially derived peptides and other small peptides play significant roles as exercise-sensitive peptides in exercise-induced physiological adaptation. In this review, we highlight the discovery of mitochondrially derived peptides and newly discovered small peptides involved in metabolism, with a specific emphasis on their functions in exercise-induced adaptations and the prevention of metabolic diseases. In light of the few studies available, we also present data on how both single exercise sessions and exercise training affect expression of sORF-encoded mitochondrially derived peptides. Finally, we outline numerous research questions that await investigation regarding the roles of mitochondrially derived peptides in metabolism and prevention of various diseases, in addition to their roles in exercise-induced physiological adaptations, for future studies.

Beneficial Effects of Low-Grade Mitochondrial Stress on Metabolic Diseases and Aging

Mitochondria function as platforms for bioenergetics, nutrient metabolism, intracellular signaling, innate immunity regulators, and modulators of stem cell activity. Thus, the decline in mitochondrial functions causes or correlates with diabetes mellitus and many aging-related diseases. Upon stress or damage, the mitochondria elicit a series of adaptive responses to overcome stress and restore their structural integrity and functional homeostasis. These adaptive responses to low-level or transient mitochondrial stress promote health and resilience to upcoming stress. Beneficial effects of low-grade mitochondrial stress, termed mitohormesis, have been observed in various organisms, including mammals. Accumulated evidence indicates that treatments boosting mitohormesis have therapeutic potential in various human diseases accompanied by mitochondrial stress. Here, we review multiple cellular signaling pathways and interorgan communication mechanisms through which mitochondrial stress leads to advantageous outcomes. We also discuss the relevance of mitohormesis in obesity, diabetes, metabolic liver disease, aging, and exercise.

Mitochondrial-derived peptides: Antidiabetic functions and evolutionary perspectives

Mitochondrial-derived peptides (MDPs) are a novel class of bioactive microproteins encoded by short open-reading frames (sORF) in mitochondrial DNA (mtDNA). Currently, three types of MDPs have been identified: Humanin (HN), MOTS-c (Mitochondrial ORF within Twelve S rRNA type-c), and SHLP1-6 (small Humanin-like peptide, 1 to 6). The 12 S ribosomal RNA (MT-RNR1) gene harbors the sequence for MOTS-c, whereas HN and SHLP1-6 are encoded by the 16 S ribosomal RNA (MT-RNR2) gene. Special genetic codes are used in mtDNA as compared to nuclear DNA: (i) ATA and ATT are used as start codons in addition to the standard start codon ATG; (ii) AGA and AGG are used as stop codons instead of coding for arginine; (iii) the standard stop codon UGA is used to code for tryptophan. While HN, SHLP6, and MOTS-c are encoded by the H (heavy owing to high guanine + thymine base composition)-strand of the mtDNA, SHLP1-5 are encoded by the L (light owing to less guanine + thymine base composition)-strand. MDPs attenuate disease pathology including Type 1 diabetes (T1D), Type 2 diabetes (T2D), gestational diabetes, Alzheimer's disease (AD), cardiovascular diseases, prostate cancer, and macular degeneration. The current review will focus on the MDP regulation of T2D, T1D, and gestational diabetes along with an emphasis on the evolutionary pressures for conservation of the amino acid sequences of MDPs.

The mitochondrial genome-encoded peptide MOTS-c interacts with Bcl-2 to alleviate nonalcoholic steatohepatitis progression

Nonalcoholic steatohepatitis (NASH) is a metabolism-associated fatty liver disease with accumulated mitochondrial stress, and targeting mitochondrial function is a potential therapy. The mitochondrial genome-encoded bioactive peptide MOTS-c plays broad physiological roles, but its effectiveness and direct targets in NASH treatment are still unclear. Here, we show that long-term preventive and short-term therapeutic effects of MOTS-c treatments alleviate NASH-diet-induced liver steatosis, cellular apoptosis, inflammation, and fibrosis. Mitochondrial oxidative capacity and metabolites profiling analysis show that MOTS-c significantly reverses NASH-induced mitochondrial metabolic deficiency. Moreover, we identify that MOTS-c directly interacts with the BH3 domain of antiapoptotic B cell lymphoma-2 (Bcl-2), increases Bcl-2 protein stability, and suppresses Bcl-2 ubiquitination. By using a Bcl-2 inhibitor or adeno-associated virus (AAV)-mediated Bcl-2 knockdown, we further confirm that MOTS-c improves NASH-induced mitochondrial dysfunction, inflammation, and fibrosis, which are dependent on Bcl-2 function. Therefore, our findings show that MOTS-c is a potential therapeutic agent to inhibit the progression of NASH.

Regulation of nuclear transcription by mitochondrial RNA in endothelial cells

Chromatin-associated RNAs (caRNAs) form a relatively poorly recognized layer of the epigenome. The caRNAs reported to date are transcribed from the nuclear genome. Here, leveraging a recently developed assay for detection of caRNAs and their genomic association, we report that mitochondrial RNAs (mtRNAs) are attached to the nuclear genome and constitute a subset of caRNA, thus termed mt-caRNA. In four human cell types analyzed, mt-caRNAs preferentially attach to promoter regions. In human endothelial cells (ECs), the level of mt-caRNA-promoter attachment changes in response to environmental stress that mimics diabetes. Suppression of a non-coding mt-caRNA in ECs attenuates stress-induced nascent RNA transcription from the nuclear genome, including that of critical genes regulating cell adhesion, and abolishes stress-induced monocyte adhesion, a hallmark of dysfunctional ECs. Finally, we report increased nuclear localization of multiple mtRNAs in the ECs of human diabetic donors, suggesting many mtRNA translocate to the nucleus in a cell stress and disease-dependent manner. These data nominate mt-caRNAs as messenger molecules responsible for mitochondrial-nuclear communication and connect the immediate product of mitochondrial transcription with the transcriptional regulation of the nuclear genome.

Novel function of MOTS-c in mitochondrial remodelling contributes to its antiviral role during HBV infection

OBJECTIVE

Hepatitis B virus (HBV) infection causes substantial harm to mitochondrial activity, which hinders the development of effective treatments for chronic hepatitis B (CHB). The discovery of the mitochondrial-derived short peptide MOTS-c, which possesses multiple bioactivities, offers a promising new approach in treating HBV infection. This study aims to explore the diagnostic and therapeutic potential of MOTS-c in HBV-related diseases and its molecular mechanism.

DESIGN

In total, 85 healthy subjects and 404 patients with HBV infection, including 20 clinical treatment cohorts, were recruited for this study. MOTS-c levels were measured by ELISA and its diagnostic value was evaluated by receiving operating characteristic curve analysis. The therapeutic effect of MOTS-c was observed in multiple HBV-infected mice and cells through various techniques, including transcriptomic sequencing, flow cytometry, immunofluorescence and electron microscopy. Additionally, MOTS-c's potential interaction with myosin-9 (MYH9) and actin was predicted using immunoprecipitation, proteomics and target prediction software.

RESULTS

MOTS-c negatively correlates with HBV DNA expression (R=-0.71), and its AUC (the area under the curve) for distinguishing CHB from healthy controls is 0.9530, and IA (immune reactive) from IC (inactive HBV carrier) is 0.8689. Inhibition of HBV replication (with a 50-70% inhibition rate) was observed alongside improved liver function without notable toxicity in vitro or in vivo. MOTS-c was found to promote mitochondrial biogenesis and enhance the MAVS (mitochondrial antiviral signalling protein) signalling pathway. The impact is dependent on MOTS-c's ability to regulate MYH9-actin-mediated mitochondrial homeostasis.

CONCLUSION

MOTS-c has the potential to serve as a biomarker for the progression of HBV infection while also enhancing antiviral efficacy. These findings present a promising innovative approach for effectively treating patients with CHB. Furthermore, our research uncovers a novel role for MOTS-c in regulating MYH9-actin-mediated mitochondrial dynamics and contributing to mitochondrial biogenesis.

Mitochondria as a sensor, a central hub and a biological clock in psychological stress-accelerated aging

The theory that oxidative damage caused by mitochondrial free radicals leads to aging has brought mitochondria into the forefront of aging research. Psychological stress that encompasses many different experiences and exposures across the lifespan has been identified as a catalyst for accelerated aging. Mitochondria, known for their dynamic nature and adaptability, function as a highly sensitive stress sensor and central hub in the process of accelerated aging. In this review, we explore how mitochondria as sensors respond to psychological stress and contribute to the molecular processes in accelerated aging by viewing mitochondria as hormonal, mechanosensitive and immune suborganelles. This understanding of the key role played by mitochondria and their close association with accelerated aging helps us to distinguish normal aging from accelerated aging, correct misconceptions in aging studies, and develop strategies such as exercise and mitochondria-targeted nutrients and drugs for slowing down accelerated aging, and also hold promise for prevention and treatment of age-related diseases.

Six-day dry immersion leads to downregulation of slow-fiber type and mitochondria-related genes expression

The soleus muscle in humans is responsible for maintaining an upright posture and participating in walking and running. Under muscle disuse, it undergoes molecular signaling changes that result in altered force and work capacity. The triggering mechanisms and pathways of these changes are not yet fully understood. In this article, we aimed to detect the molecular pathways that are involved in the unloading-induced alterations in the human soleus muscle under 6-days of dry immersion. A 6-day dry immersion led to the downregulation of mitochondrial biogenesis and dynamics markers, upregulation of calcium-dependent CaMK II phosphorylation, enhanced PGC1α promoter region methylation, and altered muscle micro-RNA expression, without affecting p-AMPK content or fiber-type transformation.NEW & NOTEWORTHY Dry immersion dysregulates mitochondrial genes expression, affects mi-RNA expression and PGC1 promoter methylation.

The role of MOTS-c-mediated antioxidant defense in aerobic exercise alleviating diabetic myocardial injury

Myocardial remodeling and dysfunction are commonly observed in type 2 diabetes mellitus (T2DM). Aerobic exercise can partly alleviate diabetes-induced myocardial dysfunction through its antioxidant actions. MOTS-c is a potential exercise mimic. This study aimed to investigate the effects of MOTS-c on improving diabetic heart function and its mechanism and to identify whether MOTS-c improved antioxidant defenses due to aerobic exercise. Herein, we established a rat model of T2DM induced by high-fat diet combined with a low-dose streptozotocin injection. Interventions were performed using intraperitoneal injections of MOTS-c (i.p. 0.5 mg/kg/day, 7 days/week) or aerobic exercise training (treadmill, 20 m/min, 60 min/day, 5 days/week) for 8 weeks. Myocardial ultrastructure was assessed using transmission electron microscopy (TEM), myocardial lipid peroxidation levels (MDA), superoxide dismutase (SOD), glutathione (GSH), and catalase (CAT) levels were assessed using colorimetric methods, and molecular analyses including MOTS-c, Kelch-like ECH-associated protein 1 (Keap1), Nuclear factor E2-related factor 2 (Nrf2), adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK)and phospho-AMPK (p-AMPK) were examined using Western blot. The results showed that MOTS-c, with or without exercise, reduced myocardial ultrastructural damage and improved glucolipid metabolism and cardiac function in T2DM. Furthermore, MOTS-c increased antioxidant markers such as SOD, CAT, and the protein expression of myocardial MOTS-c, Keap1, Nrf2, and p-AMPK. MOTS-c with exercise treatment reduced myocardial MDA and increased p-AMPK significantly comparing to only exercise or MOTS-c alone. Our findings suggest that MOTS-c may be a helpful supplement for overcoming exercise insufficiency and improving myocardial structure and function in diabetes.

Mitohormesis

Perturbation of mitochondrial function can trigger a host of cellular responses that seek to restore cellular metabolism, cytosolic proteostasis, and redox homeostasis. In some cases, these responses persist even after the stress is relieved, leaving the cell or tissue in a less vulnerable state. This process-termed mitohormesis-is increasingly viewed as an important aspect of normal physiology and a critical modulator of various disease processes. Here, we review aspects of mitochondrial stress signaling that, among other things, can rewire the cell's metabolism, activate the integrated stress response, and alter cytosolic quality-control pathways. We also discuss how these pathways are implicated in various disease states from pathogen challenge to chemotherapeutic resistance and how their therapeutic manipulation can lead to new strategies for a host of chronic conditions including aging itself.

Exercise mitigates age-related metabolic diseases by improving mitochondrial dysfunction

The benefits of regular physical activity are related to delaying and reversing the onset of ageing and age-related disorders, including cardiomyopathy, neurodegenerative diseases, cancer, obesity, diabetes, and fatty liver diseases. However, the molecular mechanisms of the benefits of exercise or physical activity on ageing and age-related disorders remain poorly understood. Mitochondrial dysfunction is implicated in the pathogenesis of ageing and age-related metabolic diseases. Mitochondrial health is an important mediator of cellular function. Therefore, exercise alleviates metabolic diseases in individuals with advancing ageing and age-related diseases by the remarkable promotion of mitochondrial biogenesis and function. Exerkines are identified as signaling moieties released in response to exercise. Exerkines released by exercise have potential roles in improving mitochondrial dysfunction in response to age-related disorders. This review comprehensive summarizes the benefits of exercise in metabolic diseases, linking mitochondrial dysfunction to the onset of age-related diseases. Using relevant examples utilizing this approach, the possibility of designing therapeutic interventions based on these molecular mechanisms is addressed.

An efficient protocol for studying human pluripotent stem cell-derived myotube senescence

Sarcopenia, an age-related skeletal muscle condition characterized by a progressive decline in muscle mass and function, is linked to increased vulnerability, a higher likelihood of falls, and higher mortality rates in older individuals. A comprehensive understanding of the intricate mechanisms driving skeletal muscle aging is of great significance in both scientific and clinical fields. Consequently, myotube models that facilitate studying regulatory mechanisms underlying skeletal muscle aging are important tools required to advance intervention strategies against skeletal muscle aging and associated disorders. Here, we provide a detailed protocol to generate human pluripotent stem cells-derived myotubes and describe their applications in aging studies, as well as a troubleshooting for potential problems. Overall, this protocol serves as a valuable methodological reference for exploring the role and mechanism of genes involved in skeletal muscle aging.

Echocardiographic evaluation of cardiac reserve to detect subtle cardiac dysfunction in mice

AIMS

Cardiac reserve is a sensitive tool for early detection of cardiac dysfunction. However, cardiac reserve assessment by catecholamine stress echocardiography in mice varied in the doses of β-adrenergic agonists and the time point for measurements, which may lead to inaccurate readouts. This study aims to establish a standardized protocol for assessing cardiac reserve in mice.

MAIN METHODS

C57BL/6J mice under isoflurane anesthesia were intraperitoneally injected with varying doses of isoproterenol (Iso), and subjected to echocardiographic measurements.

KEY FINDINGS

Heart rate (HR), ejection fraction (EF), fractional shortening (FS), global longitudinal strain (GLS) and strain rate all reached peak values within 1-3 min after Iso injection at doses higher than 0.2 mg/kg. Compared with 0.1 mg/kg Iso, 0.2 mg/kg Iso resulted in higher HR, EF, FS and GLS, whereas doses higher than 0.2 mg/kg did not yield further increase. Cardiac response of female mice recapitulated main characteristics of those of male mice except that female mice displayed higher maximum HR and were more sensitive to higher doses of Iso. Furthermore, the advantages of present stress protocol over conventional baseline echocardiographic measurements were verified in comparisons of exercised vs. sedentary and aged vs. young mice for cardiac function evaluation.

SIGNIFICANCE

We developed a reproducible and sensitive approach to evaluate cardiac reserve by continuously monitoring cardiac function every minute for 3 min after 0.2 mg/kg Iso injection. This approach will enable detection of subtle cardiac dysfunction and accelerate innovative research in cardiac pathophysiology.

WDR23 mediates NRF2 proteostasis and cytoprotective capacity in the hippocampus

Pathogenic brain aging and neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease are characterized by chronic neuroinflammation and the accumulation of dysfunctional or misfolded proteins that lead to progressive neuronal cell death. Here we demonstrate that a murine model with global loss of the CUL4-DDB1 substrate receptor WDR23 ( Wdr23KO ) results in changes in multiple age-related hippocampal-dependent behaviors. The behavioral differences observed in Wdr23KO animals accompany the stabilization of the NRF2/NFE2L2 protein, an increase in RNA transcripts regulated by this cytoprotective transcription factor, and an increase in the steady state level of antioxidant defense proteins. Taken together, these findings reveal a role for WDR23-proteostasis in mediating cytoprotective capacity in the hippocampus and reveal the potential for targeting WDR23-NRF2 signaling interactions for development of therapies for neurodegenerative disorders.

HIGHLIGHTS

WDR23 regulates NRF2/NFE2L2 stability in the mouse hippocampus Loss of Wdr23 significantly increases the expression of NFE2L2/NRF2 target genes Global loss of WDR23 influences age-related behaviors differentially in males and females.

MOTS-c Serum Concentration Positively Correlates with Lower-Body Muscle Strength and Is Not Related to Maximal Oxygen Uptake-A Preliminary Study

The mitochondrial open reading frame of 12S rRNA-c (MOTS-c) is a mitochondrial-derived peptide that regulates the nuclear genome during stressful conditions such as hypoxia, which is typical of exercise and training. We aim to mainly investigate the relationship between serum MOTS-c concentration and muscle strength parameters measured during the countermovement jump test with oxygen consumption (VO2) measured during the cardiopulmonary exercise test to exhaustion. Physically active healthy volunteers (17 male, three female, median age 30 years), not involved in any regular exercise program or participating in any sports competitions, performed five consecutive countermovement jump tests and cardiopulmonary exercise tests until maximal exhaustion and underwent a body composition assessment by means of bioelectrical impedance analysis, and had serum MOTS-c concentration measured at rest. Serum MOTS-c concentration was positively correlated with the average power and average and maximal force of the jumps, both overall muscle mass and leg muscle mass, but not with body fat percentage. There was no correlation with peak VO2. A higher serum MOTS-c concentration is associated with greater muscle mass, force, and power generated during jumping in healthy individuals but not exercise capacity reflected by peak VO2. More studies are needed to better understand the physiological and clinical values of these findings and why MOTS-c is better associated with measures of muscle strength and not endurance in physically active people.

Mitochondrial microproteins: critical regulators of protein import, energy production, stress response pathways, and programmed cell death

Mitochondria rely upon the coordination of protein import, protein translation, and proper functioning of oxidative phosphorylation (OXPHOS) complexes I-V to sustain the activities of life for an organism. Each process is dependent upon the function of profoundly large protein complexes found in the mitochondria [translocase of the outer mitochondrial membrane (TOMM) complex, translocase of the inner mitochondrial membrane (TIMM) complex, OXPHOS complexes, mitoribosomes]. These massive protein complexes, in some instances more than one megadalton, are built up from numerous protein subunits of varying sizes, including many proteins that are ≤100-150 amino acids. However, these small proteins, termed microproteins, not only act as cogs in large molecular machines but also have important steps in inhibiting or promoting the intrinsic pathway of apoptosis, coordinate responses to cellular stress, and even act as hormones. This review focuses on microproteins that occupy the mitochondria and are critical for its function. Although the microprotein field is relatively new, researchers have long recognized the existence of these mitochondrial proteins as critical components of virtually all aspects of mitochondrial biology. Thus, recent studies estimating that hundreds of new microproteins of unknown function exist and are missing from current genome annotations suggests that the mitochondrial "microproteome" is a rich area for future biological investigation.

Evidence of natural selection in the mitochondrial-derived peptides humanin and SHLP6

Mitochondrial-derived peptides are encoded by mitochondrial DNA but have biological activity outside mitochondria. Eight of these are encoded by sequences within the mitochondrial 12S and 16S ribosomal genes: humanin, MOTS-c, and the six SHLP peptides, SHLP1-SHLP6. These peptides have various effects in cell culture and animal models, affecting neuroprotection, insulin sensitivity, and apoptosis, and some are secreted, potentially having extracellular signaling roles. However, except for humanin, their importance in normal cell function is unknown. To gauge their importance, their coding sequences in vertebrates have been analyzed for synonymous codon bias. Because they lie in RNA genes, such bias should only occur if their amino acids have been conserved to maintain biological function. Humanin and SHLP6 show strong synonymous codon bias and sequence conservation. In contrast, SHLP1, SHLP2, SHLP3, and SHLP5 show no significant bias and are poorly conserved. MOTS-c and SHLP4 also lack significant bias, but contain highly conserved N-terminal regions, and their biological importance cannot be ruled out. An additional potential mitochondrial-derived peptide sequence was discovered preceding SHLP2, named SHLP2b, which also contains a highly conserved N-terminal region with synonymous codon bias.

Mitochondrial polymorphism m.3017C>T of SHLP6 relates to heterothermy

Heterothermic thermoregulation requires intricate regulation of metabolic rate and activation of pro-survival factors. Eliciting these responses and coordinating the necessary energy shifts likely involves retrograde signalling by mitochondrial-derived peptides (MDPs). Members of the group were suggested before to play a role in heterothermic physiology, a key component of hibernation and daily torpor. Here we studied the mitochondrial single-nucleotide polymorphism (SNP) m.3017C>T that resides in the evolutionarily conserved gene MT-SHLP6. The substitution occurring in several mammalian orders causes truncation of SHLP6 peptide size from twenty to nine amino acids. Public mass spectrometric (MS) data of human SHLP6 indicated a canonical size of 20 amino acids, but not the use of alternative translation initiation codons that would expand the peptide. The shorter isoform of SHLP6 was found in heterothermic rodents at higher frequency compared to homeothermic rodents (p < 0.001). In heterothermic mammals it was associated with lower minimal body temperature (T b, p < 0.001). In the thirteen-lined ground squirrel, brown adipose tissue-a key organ required for hibernation, showed dynamic changes of the steady-state transcript level of mt-Shlp6. The level was significantly higher before hibernation and during interbout arousal and lower during torpor and after hibernation. Our finding argues to further explore the mode of action of SHLP6 size isoforms with respect to mammalian thermoregulation and possibly mitochondrial retrograde signalling.

Mitochondria-derived peptide SHLP2 regulates energy homeostasis through the activation of hypothalamic neurons

Small humanin-like peptide 2 (SHLP2) is a mitochondrial-derived peptide implicated in several biological processes such as aging and oxidative stress. However, its functional role in the regulation of energy homeostasis remains unclear, and its corresponding receptor is not identified. Hereby, we demonstrate that both systemic and intracerebroventricular (ICV) administrations of SHLP2 protected the male mice from high-fat diet (HFD)-induced obesity and improved insulin sensitivity. In addition, the activation of pro-opiomelanocortin (POMC) neurons by SHLP2 in the arcuate nucleus of the hypothalamus (ARC) is involved in the suppression of food intake and the promotion of thermogenesis. Through high-throughput structural complementation screening, we discovered that SHLP2 binds to and activates chemokine receptor 7 (CXCR7). Taken together, our study not only reveals the therapeutic potential of SHLP2 in metabolic disorders but also provides important mechanistic insights into how it exerts its effects on energy homeostasis.

Mitochondrial-derived vesicles in skeletal muscle remodeling and adaptation

Mitochondrial remodeling is crucial to meet the bioenergetic demand to support muscle contractile activity during daily tasks and muscle regeneration following injury. A set of mitochondrial quality control (MQC) processes, including mitochondrial biogenesis, dynamics, and mitophagy, are in place to maintain a well-functioning mitochondrial network and support muscle regeneration. Alterations in any of these pathways compromises mitochondrial quality and may potentially lead to impaired myogenesis, defective muscle regeneration, and ultimately loss of muscle function. Among MQC processes, mitophagy has gained special attention for its implication in the clearance of dysfunctional mitochondria via crosstalk with the endo-lysosomal system, a major cell degradative route. Along this pathway, additional opportunities for mitochondrial disposal have been identified that may also signal at the systemic level. This communication occurs via inclusion of mitochondrial components within membranous shuttles named mitochondrial-derived vesicles (MDVs). Here, we discuss MDV generation and release as a mitophagy-complementing route for the maintenance of mitochondrial homeostasis in skeletal myocytes. We also illustrate the possible role of muscle-derived MDVs in immune signaling during muscle remodeling and adaptation.

MOTS-c: A potential anti-pulmonary fibrosis factor derived by mitochondria

Pulmonary fibrosis (PF) is a serious lung disease characterized by diffuse alveolitis and disruption of alveolar structure, with a poor prognosis and unclear etiopathogenesis. While ageing, oxidative stress, metabolic disorders, and mitochondrial dysfunction have been proposed as potential contributors to the development of PF, effective treatments for this condition remain elusive. However, Mitochondrial open reading frame of the 12S rRNA-c (MOTS-c), a peptide encoded by the mitochondrial genome, has shown promising effects on glucose and lipid metabolism, cellular and mitochondrial homeostasis, as well as the reduction of systemic inflammatory responses, and is being investigated as a potential exercise mimetic. Additionally, dynamic expression changes of MOTS-c have been closely linked to ageing and ageing-related diseases, indicating its potential as an exercise mimetic. Therefore, the review aims to comprehensively analyze the available literature on the potential role of MOTS-c in improving PF development and to identify specific therapeutic targets for future treatment strategies.

The mitochondrial-derived peptide MOTS-c suppresses ferroptosis and alleviates acute lung injury induced by myocardial ischemia reperfusion via PPARγ signaling pathway

Acute lung injury (ALI) is a life-threatening complication of cardiac surgery that has a high rate of morbidity and mortality. Epithelial ferroptosis is believed to be involved in the pathogenesis of ALI. MOTS-c has been reported to play a role in regulating inflammation and sepsis-associated ALI. The purpose of this study is to observe the effect of MOTS-c on myocardial ischemia reperfusion (MIR)-induced ALI and ferroptosis. In humans, we used ELISA kits to investigate MOTS-c and malondialdehyde (MDA) levels in patients undergoing off-pump coronary artery bypass grafting (CABG). In vivo, we pretreated Sprague-Dawley rats with MOTS-c, Ferrostatin-1 and Fe-citrate(Ⅲ). We conducted Hematoxylin and Eosin (H&E) staining and detection of ferroptosis-related genes in MIR-induced ALI rats. In vitro, we evaluated the effect of MOTS-c on hypoxia regeneration (HR)-induced mouse lung epithelial-12 (MLE-12) ferroptosis and analyzed the expression of PPARγ through western blotting. We found that circulating MOTS-c levels were decreased in postoperative ALI patients after off-pump CABG, and that ferroptosis contributed to ALI induced by MIR in rats. MOTS-c suppressed ferroptosis and alleviated ALI induced by MIR, and the protective effect of MOTS-c- was dependent on PPARγ signaling pathway. Additionally, HR promoted ferroptosis in MLE-12 cells, and MOTS-c inhibited ferroptosis against HR through the PPARγ signaling pathway. These findings highlight the therapeutic potential of MOTS-c for improving postoperative ALI induced by cardiac surgery.

Β-GPA administration activates slow oxidative muscle signaling pathways and protects soleus muscle against the increased fatigue under 7-days of rat hindlimb suspension

Unloading of slow-twitch muscles results in increased muscle fatigue and the mechanisms of this effect are poorly studied. We aimed to analyze the role of high-energy phosphates accumulation during the first week of rat hindlimb suspension plays in a fiber-type phenotype shift towards fast-type fatigable muscle fibers. Male Wistar rats were divided into 3 groups (n = 8): C - vivarium control; 7HS - 7-day hindlimb suspension; 7HB - 7-day hindlimb suspension with intraperitoneal injection of beta-guanidine propionic acid (β-GPA, 400 mg/kg b w). β-GPA is a competitive inhibitor of creatine kinase and it reduces concentrations of ATP and phosphocreatine. In the 7HB group, β-GPA treatment protected a slow-type signaling network in an unloaded soleus muscle, including MOTS-C, AMPK, PGC1 α and micro-RNA-499. These signaling effects resulted in a preserved soleus muscle fatigue resistance, slow-type muscle fibers percentage and mitochondrial DNA copy number under muscle unloading.

Mitochondria-derived peptides in healthy ageing and therapy of age-related diseases

Mitochondrial-derived peptides (MDPs) are small bioactive peptides encoded by mitochondrial DNA and involved in various stress-protecting mechanisms. To date, eight mitochondrial-derived peptides have been identified: MOTS-c sequence is hidden in the 12 S rRNA gene (MT-RNR1), and the other 7 (humanin and small humanin-like peptides 1-6) are encoded by the 16 S rRNA (MT-RNR2) gene. While the anti-apoptotic, anti-inflammatory and cardioprotective activities of MDPs are well described, recent research suggests that MDPs are sensitive metabolic sensors, closely connected with mtDNA mutation-associated diseases and age-associated metabolic disorders. In this chapter, we focus on the recent progress in understanding the metabolo-protective properties of MDPs, their role in maintenance of the cellular and mitochondrial homeostasis associated with age-related diseases: Alzheimer's disease, cognitive decline, macular degeneration and cataracts. Also, we will discuss MDPs-based and MDPs-targeted interventions to treat age-related diseases and extend a healthy lifespan.

Exercise Improves the Coordination of the Mitochondrial Unfolded Protein Response and Mitophagy in Aging Skeletal Muscle

The mitochondrial unfolded protein response (UPRmt) and mitophagy are two mitochondrial quality control (MQC) systems that work at the molecular and organelle levels, respectively, to maintain mitochondrial homeostasis. Under stress conditions, these two processes are simultaneously activated and compensate for each other when one process is insufficient, indicating mechanistic coordination between the UPRmt and mitophagy that is likely controlled by common upstream signals. This review focuses on the molecular signals regulating this coordination and presents evidence showing that this coordination mechanism is impaired during aging and promoted by exercise. Furthermore, the bidirectional regulation of reactive oxygen species (ROS) and AMPK in modulating this mechanism is discussed. The hierarchical surveillance network of MQC can be targeted by exercise-derived ROS to attenuate aging, which offers a molecular basis for potential therapeutic interventions for sarcopenia.