Skeletal muscle nuclei in mice are not post-mitotic

Abstract

The skeletal muscle research field generally accepts that nuclei in skeletal muscle fibers (i.e., myonuclei) are post-mitotic and unable to proliferate. Because of previous data indicating DNA synthesis in skeletal muscle tissue, we hypothesized that skeletal muscle resident myonuclei can replicate in vivo. To test this hypothesis, we used a mouse model that facilitated temporal labeling with GFP following by deuterium oxide (D2O) labeling during normal cage activity, overload, and with satellite cell ablation. During normal cage activity, we observed deuterium enrichment into myonuclear DNA in 7 out of 7 plantaris (PLA), 6 out of 6 tibialis anterior (TA), 5 out of 7 gastrocnemius (GAST), and 7 out of 7 quadriceps (QUAD). The average fraction synthesis rates (FSR) of replicating myonuclei were: 0.0202 plus-or-minus sign 0.0093 in PLA, 0.0239 plus-or-minus sign 0.0040 in TA, 0.0076 plus-or-minus sign 0. 0058 in GAST, and 0.0138 plus-or-minus sign 0.0039 in QUAD, while EDL appeared not to have replicative myonuclei. These values were largely reproduced in our other conditions with increased rates in an overloaded plantaris muscle. We further showed that these replication events potentially resulted in polyploidy. With our new approach, we unambiguously demonstrated that mammalian myonuclei can replicate in vivo. The amounts of DNA synthesis differed by muscle and increased with mechanical overload. It also appears that there is endoreplication of resident myonuclei that results in polyploidy. These findings contradict the dogma that skeletal muscle myocytes are post-mitotic and open potential avenues to harness the intrinsic replicative ability of the cell for muscle maintenance and growth.

High‐fat diet increases electron transfer flavoprotein synthesis and lipid respiration in skeletal muscle during exercise training in female mice

“…For body water enrichment, 100 μL of plasma was placed in the inner well of an o-ring cap of inverted screw-capped tubes and placed in a heat block for overnight distillation at 80°C. Distilled samples were diluted 1:300 in ddH2O and analyzed on a liquid water isotope analyzer (Los Gatos Research, Los Gatos, CA, USA) against a standard curve prepared with samples containing different concentrations of D 2 O (Abbott et al, 2021;Borowik et al, 2023;Brown et al, 2021;Kobak et al, 2021).…”

The role of satellite cell-derived TRIM28 in mechanical load- and injury-induced myogenesis

“…Therefore, to address this, WT and KO mice were subjected to SA and treated with daily injections of 5-bromo-2'deoxyuridine (BrdU) for 14 days. BrdU labels DNA that has undergone replication, and since myonuclei have been shown to replicate DNA at an extremely low rate (33), the vast majority of BrdU-labeled myonuclei should be representative of satellite cells that have undergone proliferation, differentiation, and subsequent heterotypic fusion (31,34). As illustrated in Fig.…”