We investigate the age-related metabolic changes that occur in aged and rejuvenated myoblasts using in vitro and in vivo models of aging. Metabolic and signaling experiments reveal that human senescent myoblasts and myoblasts from a mouse model of premature aging suffer from impaired glycolysis, insulin resistance, and generate Adenosine triphosphate by catabolizing methionine via a methionine adenosyl-transferase 2A-dependant mechanism, producing significant levels of ammonium that may further contribute to cellular senescence. Expression of the pluripotency factor NANOG downregulates methionine adenosyltransferase 2 A, decreases ammonium, restores insulin sensitivity, increases glucose uptake, and enhances muscle regeneration post-injury. Similarly, selective inhibition of methionine adenosyltransferase 2 A activates Akt2 signaling, repairs pyruvate kinase, restores glycolysis, and enhances regeneration, which leads to significant enhancement of muscle strength in a mouse model of premature aging. Collectively, our investigation indicates that inhibiting methionine metabolism may restore age-associated impairments with significant gain in muscle function.

Tristetraprolin (TTP; also known as NUP475, GOS24, or TIS11), encoded by Zfp36 , is an RNA‐binding protein that regulates target gene expression by promoting mRNA decay and preventing translation. Although previous studies have indicated that TTP deficiency is associated with systemic inflammation and a catabolic‐like skeletal phenotype, the mechanistic underpinnings remain unclear. Here, using both TTP‐deficient (TTPKO) and myeloid‐specific TTPKO (cTTPKO) mice, we reveal that global absence or loss of TTP in the myeloid compartment results in a reduced bone microarchitecture, whereas gain‐of‐function TTP knock‐in (TTPKI) mice exhibit no significant loss of bone microarchitecture. Flow cytometry analysis revealed a significant immunosuppressive immune cell phenotype with increased monocytic myeloid‐derived suppressor cells (M‐MDSCs) in TTPKO and cTTPKO mice, whereas no significant changes were observed in TTPKI mice. Single‐cell transcriptomic analyses of bone marrow myeloid progenitor cell populations indicated a dramatic increase in early MDSC marker genes for both cTTPKO and TTPKO bone marrow populations. Consistent with these phenotypic and transcriptomic data, in vitro osteoclastogenesis analysis of bone marrow M‐MDSCs from cTTPKO and TTPKO displayed enhanced osteoclast differentiation and functional capacity. Focused transcriptomic analyses of differentiated M‐MDSCs showed increased osteoclast‐specific transcription factors and cell fusion gene expression. Finally, functional data showed that M‐MDSCs from TTP loss‐of‐function mice were capable of osteoclastogenesis and bone resorption in a context‐dependent manner. Collectively, these findings indicate that TTP plays a central role in regulating osteoclastogenesis through multiple mechanisms, including induction of M‐MDSCs that appear to regulate skeletal phenotype.

Aging in females affects the ovaries before any other organ. This has a significant impact on women’s health. Aging results in the gradual depletion of ovarian follicles and a decline in oocyte quality. Studies have shown that cellular changes within ovaries manifest before the depletion of ovarian follicles. To understand the molecular mechanisms underlying these changes, we conducted a comprehensive analysis of gene expression changes in aging mouse ovaries. When RNA sequencing data from 6-month-old mice were compared to those from 12-month-old mice, we identified numerous differentially expressed genes, as well as transcript variants. Transcript variants arise from alternative transcription start sites (TSSs) and alternative pre-mRNA processing. Therefore, we further analyzed a specific set of regulators for these cellular processes. Our findings indicate that ovarian aging alters the expression of epigenetic regulators (ERs) and transcription factors (TFs) that are involved in alternative TSS usage. Ovarian aging also affects the expression of RNA-binding proteins (RBPs) and spliceosome components (SPs), which are essential for pre-mRNA processing. We noticed that variations in transcript variants were more pronounced than those found through gene expression analysis. While 8% of the known TFs and ERs were differentially expressed at the gene level, this increased to 30% at the transcript variant level. Similarly, 3% of the known RBPs but no known SPs were differentially expressed at the gene level, while this increased to 30% at the transcript variant level. These observations highlight the importance of focusing on transcript variants and their functions in aging research, as they may provide insight into the underlying biological processes involved.

Cellular gene expression varies in different physiological or pathological conditions. Conventional gene expression analysis assumes that each gene produces a single mRNA, which is not accurate. On average, genes express more than three mRNA isoforms. A particular cell type expresses different mRNA isoforms from a specific gene depending on its developmental or differentiation state. Different isoforms encode distinct proteins or noncoding regulatory RNAs, each with its own unique functions. Pathological states also alter the expression of transcript variants, which can either cause a disease or facilitate recovery. Still, the detection of mRNA isoforms or variants is not preferred to avoid complex analyses. As a result, gene expression studies often fail to identify the actual mRNA isoforms or variants associated with pathophysiology. In this article, we summarize the data on mRNA isoforms and disease-associated variants identified in various physiological and pathological conditions. These findings emphasize the importance of detecting mRNA isoforms for a better understanding of physiological or pathological conditions.

Background: High-intensity interval exercise (HIIE) is gaining interest as an alternative to traditional moderate-intensity exercise due to its shorter exercise regimens. Yet, it still induces significant muscular adaptations, including metabolic remodeling, enhanced mitochondrial biogenesis, and improved endurance capacity. Exercise has been shown to increase vitamin D receptor (VDR) expression acutely; however, the role of this effect and whether it occurs during HIIE remain to be elucidated. Objectives/Methods: Here, we investigated the time-dependent effects of a single bout of high-intensity interval exercise (HIIE) on systemic inflammatory cytokine profiles and gene expression, including VDR, in aged skeletal muscle. Sedentary aged mice (male C57Bl/6J at 24 months of age) were provided a 10-min HIIE session, and blood and tissues were harvested at 1-, 4-, and 24-h post-exercise, and compared with sedentary mice. Results: Our findings indicate that HIIE elicits a transient systemic inflammatory response peaking at 4 h post-exercise and returning to pre-exercise levels by 24 h. Using principal component analysis, we identified a similar pattern in the mRNA profiles, with clear clusters separating sedentary groups at 1 and 4 h after acute HIIE, but not after 24 h. Although VDR mRNA follows this pattern, protein expression, as determined by Western blot and immunohistochemical analysis, reveals persistence at 24 h. As VDR was localized to the periphery of muscle fibers, we investigated and found that VDR co-localizes with PAX7 (a marker for satellite cells) and F4/80-expressing macrophages. This suggests that the observed increase in VDR expression following exercise may be attributed to ancillary cell response during muscle remodeling. Conclusions: Together, these results provide novel insights into the transient molecular changes occurring 1 and 4 h after HIIE, which subsequently return to baseline after 24 h. This highlights the potential of HIIE in muscle adaptation and recovery, particularly in older individuals.

Frailty and cognitive decline are common during aging, increasing risks of disability and institutionalization. We have previously demonstrated in mice that short-session (≤10-min) high-intensity interval training (HIIT) is an effective intervention for frailty, but benefits for cognitive function and reducing hallmarks of aging have not been examined. Thus, we studied 24-month-old female C57BL/6J mice from our previous study that remained sedentary or performed a 10-min HIIT regimen 3 days a week for 8 weeks. We found HIIT improved cognition including T-maze alternation % and novel object recognition, but no differences were observed in the Barnes maze or light-dark preference. Further, we set out to examine impacts on the hallmarks of aging in liver, gastrocnemius muscle, and cortex brain tissues, including mitochondria, autophagy, cellular senescence, and telomere length. HIIT increased expression of mitochondrial complexes I and V, as well as PGC1α and SIRT3 in all tissues. Further, the autophagy marker beclin was elevated across all tissues, while p62 was increased in liver and muscle but not in the cortex, and LC3-II was lower in muscle and liver. The senescence marker p16 was lower in HIIT muscle and liver, whereas p21 decreased in liver, but there were increases in muscle. Finally, telomere lengths were greater in the liver, but no changes in muscle or cortex. Additionally, we identified differences in hallmarks of aging that underlie frailty measured using different mouse frailty tools. These results highlight the potential for multi-tissue geroprotective benefits of short-session HIIT to reduce frailty and improve cognition for healthy aging.