Absence of estrogen receptors delays myoregeneration and leads to intermuscular adipogenesis in a low estrogen status: Morphological comparisons in estrogen receptor alpha and beta knock out mice

Reduced myogenic differentiation capacity of satellite cell-derived myoblasts in male ICR mice compared with male C57BL/6 and BALB/c mice

Many strains of wild-type laboratory mice have been developed for studies in the life sciences, including skeletal muscle cell biology. Muscle regeneration capacity differs among wild-type mouse strains. However, few studies have focused on whether myogenic stem cells (satellite cells) are directly related to mouse strain-dependent myoregeneration gaps using in vitro culture models. In this study, we selected three major wild-type mouse strains, CD1 (outbred; Jcl:ICR [ICR]), C57BL/6NJcl (inbred; B6), and BALB/cAJcl (inbred; C), which are widely used in laboratory experiments. Initially, we compared myotube fusion capabilities using satellite cell-derived myoblasts. The results showed that cell cultures isolated from male ICR mice could not efficiently form myotubes owing to low expression levels of myogenic regulatory factors (e.g., MyoD, myogenin, myocyte enhancer factor [MEF] 2A, and MEF2C) compared with B6 and C mouse strains. Next, we compared the myofiber-type compositions of muscle tissues and cultured myotubes among male mice from each of the three strains. Although each muscle tissue used for satellite cell isolation similarly expressed fast-twitch myofiber markers in all mouse strains, male ICR-derived myoblasts formed abundant amounts of slow-type myotubes. By contrast, myotubes from male B6 and C mice expressed substantial levels of fast-twitch myofiber markers. We also performed a comparative experiment in female ICR, B6, and C mouse strains, similar to the male mouse experiments. The myogenic differentiation potencies of myoblasts and myofiber-type compositions of myotubes in female mouse strains were similar. Thus, male ICR-derived satellite cells (myoblasts) had low myogenic differentiation potential, which may be associated with the tendency slow-twitch myotube formation.

Depot-specific adiposity changes in ovariectomized mice on high-fat diet

Ovariectomized (OVX) mice serve as a key model for studying postmenopausal metabolic changes, particularly obesity, as they mimic the hormonal state of postmenopausal women. However, our understanding remains limited regarding how hormonal and dietary factors affect different adipose tissues. Furthermore, precise documentation of experimental procedures and their effects on specific adipose tissue depots is essential for reproducible translational research. This study investigated depot-specific adiposity development in OVX mice fed a high-fat diet (HFD), focusing on how reduced estrogen levels and dietary intervention affect distinct fat depots. We composed subcutaneous and visceral white adipose tissue (WAT) depots from sham-operated (Sham) and OVX female C57BL/6JJcl mice on a regular diet (RD) and high-fat diet (HFD) for 20 weeks. OVX mice on HFD gained significantly more weight than Sham controls. Adiposity increased in abdominal subcutaneous WAT (sWAT) and perirenal WAT (prWAT) of OVX mice, but not in mesenteric WAT (mWAT). Analysis of adipose tissue morphology revealed that OVX mice exhibited enlarged adipocyte cross-sectional areas under low estrogen (E2) conditions, suggesting enhanced adipogenesis in an estrogen-deficient state. These findings suggest that low estrogen condition accelerated adiposity, in a tissue site-dependent manner.

Diarylpropionitrile-stimulated ERβ nuclear accumulation promotes MyoD-induced muscle regeneration in mdx mice by interacting with FOXO3A

Duchenne muscular dystrophy (DMD) is an X-linked recessive progressive degenerative disease of skeletal muscle, characterized by intramuscular inflammation, muscle regeneration disorder and replacement of muscle with fibroadipose tissue. DMD is caused by the absence of normal dystrophy. Impaired self-renew ability and limited differentiation capacity of satellite cells are proved as main reasons for muscle regeneration failure. The deficiency of estrogen impedes the process of muscle regeneration. However, the role of estrogen receptor β (ERβ) in muscle regeneration is still unclear. This study aims to investigate the role and the pharmacological effect of ERβ activation on muscle regeneration in mdx mice. This study showed that mRNA levels of ERβ and myogenic-related genes both witnessed increasing trends in dystrophic context. Our results revealed that treatment with selective ERβ agonist (DPN, diarylpropionitrile) significantly increased myogenic differentiation 1 (MyoD-1) level and promoted muscle regeneration in mdx mice. Similarly, in mdx mice with muscle-specific estrogen receptor α (ERα) ablation, DPN treatment still promoted muscle regeneration. Moreover, we demonstrated that myoblasts differentiation was accompanied by raised nuclear accumulation of ERβ. DPN treatment augmented the nuclear accumulation of ERβ and, thus, contributed to myotubes formation. One important finding was that forkhead box O3A (FOXO3A), as a pivotal transcription factor in Myod-1 transcription, participated in the ERβ-promoted muscle regeneration. Overall, we offered an interesting explanation about the crucial role of ERβ during myogenesis.

Roles of Estrogen, Estrogen Receptors, and Estrogen-Related Receptors in Skeletal Muscle: Regulation of Mitochondrial Function

Estrogen is an essential sex steroid hormone that functions primarily in female reproductive system, as well as in a variety of tissues and organs with pleiotropic effects, such as in cardiovascular, nervous, immune, and musculoskeletal systems. Women with low estrogen, as exemplified by those in postmenopause, are therefore prone to suffer from various disorders, i.e., cardiovascular disease, dementia, metabolic syndrome, osteoporosis, sarcopenia, frailty, and so on. Estrogen regulates the expression of its target genes by binding to its cognate receptors, estrogen receptors (ERs) α and β. Notably, the estrogen-related receptors (ERRs) α, β, and γ are originally identified as orphan receptors that share substantial structural homology and common transcriptional targets with ERs. Accumulating evidence suggests that ERs and ERRs play crucial roles in skeletal muscles, such as muscle mass maintenance, muscle exercise physiology, and muscle regeneration. In this article, we review potential regulatory roles of ERs and ERRs in muscle physiology, particularly with regard to mitochondrial function and metabolism.

Estrogen modulates the skeletal muscle regeneration process and myotube morphogenesis: morphological analysis in mice with a low estrogen status

The purpose of this study was to elucidate the functions of estrogen and two estrogen receptors (ERs; ERα and ERβ) in the myoregeneration process and morphogenesis. Cardiotoxin (CTX) was injected into the tibialis anterior (TA) muscles of ovariectomized (OVX) mice to induce muscle injury, and subsequent myoregeneration was morphologically assessed. The diameter of regenerated myotubes in OVX mice was significantly smaller than that in intact mice at all time points of measurement. OVX mice also showed lower muscle recovery rates and slower speeds than did intact mice. ER protein levels showed a predominance of ERβ over ERα in both intact and OVX states. The ERβ level was increased significantly at 7 days after CTX injection in OVX mice and remained at a high level until 14 days. In addition, continuous administration of E2 to OVX mice in which muscle injury was induced resulted in a significantly larger diameter of regenerated myotubes than that in mice that did not receive estrogen. The results indicate that estrogen is an essential factor in the myoregeneration process since estrogen depletion delayed myoregeneration in injured muscles and administration of estrogen under the condition of a low estrogen status rescued delayed myoregeneration. The results strongly suggested that ERβ may be a factor that promotes myoregeneration more than does ERα.