An inducible knockout of Dicer in adult mice does not affect endurance exercise-induced muscle adaptation

Abstract

The contractile and metabolic properties of adult skeletal muscle change in response to endurance exercise. The mechanisms of transcriptional regulation in exercise-induced skeletal muscle adaptation, including fiber-type switching and mitochondrial biogenesis, have been investigated intensively, whereas the role of microRNA (miRNA)-mediated posttranscriptional gene regulation is less well understood. We used tamoxifen-inducible Dicer1 knockout (iDicer KO) mice to reduce the global expression of miRNAs in adult skeletal muscle and subjected these mice to 2 wk of voluntary wheel running. Dicer mRNA expression was completely depleted in fast-twitch plantaris muscle after tamoxifen injection. However, several muscle-enriched miRNAs, including miR-1 and miR-133a, were reduced by only 30–50% in both the slow and fast muscles. The endurance exercise-induced changes that occurred for many parameters (i.e., fast-to-slow fiber-type switch and increases in succinate dehydrogenase, respiratory chain complex II, and citrate synthase activity) in wild type (WT) also occurred in the iDicer KO mice. Protein expression of myosin heavy chain IIa, peroxisome proliferator-activated receptor-γ coactivator-1α, and cytochrome c complex IV was also increased in the iDicer KO mice by the voluntary running. Furthermore, there was no significant difference in oxygen consumption rate in the isolated mitochondria between the WT and iDicer KO mice. These data indicate that muscle-enriched miRNAs were detectable even after 4 wk of tamoxifen treatment and there was no apparent specific endurance-exercise-induced muscle phenotype in the iDicer KO mice.

Conditional Deletion of Dicer in Adult Mice Impairs Skeletal Muscle Regeneration

“…To investigate the role of miRNAs in muscle regeneration, we first generated a mutant mouse with the tamoxifen-inducible disruption of the Dicer gene (iDicer KO). Consistent with our previous data [19], a real-time PCR analysis confirmed the significant reduction in Dicer mRNA expression in the tibialis anterior (TA) muscles of the iDicer KO mice (Figure 1A), whereas the expression levels of the muscle-enriched miRNAs miR-1, miR-133a and miR-26a, and other miRNAs (miR-15b, miR-20a, miR-199a-3p, miR-214, miR-146a, miR-21 and miR-24) were modestly reduced in the iDicer KO mice (Figure 1B).…”

“…Our data showed that the muscle-enriched miRNAs were highly stable in the TA muscle of the iDicer KO mice (Figure 1B), which is consistent with our previous report [19]. Similarly, recent data on tamoxifen-inducible, skeletal muscle-specific Dicer knockout (HSA-MCM; Dicer fl/fl ) mice showed that the expression levels of miRNAs including miR-1, miR-133a and miR-206 were slightly affected by the Dicer depletion [32].…”

“…All mice were maintained in temperature-controlled quarters (21 °C) under a 12 h light–dark cycle and provided with a standard chow diet. The generation of tamoxifen-inducible Dicer knockout (CAG-Cre ERT2 , Dicer fl/fl ) mice has been described previously [19]. The mice were maintained in a B6 background and intraperitoneally injected with 1 mg of tamoxifen at 8 weeks old for 5 consecutive days.…”

Inducible and reversible inhibition of miRNA-mediated gene repression in vivo

“…In previous studies where Dicer1 was conditionally ablated in the skeletal muscle of adult mice, muscle regeneration was impaired after acute injury, but no effect on muscle morphology or function was observed during homeostasis ( Oikawa et al, 2019a ; Oikawa et al, 2019b ; Vechetti et al, 2019 ). An explanation for this difference is that in the Dicer1 conditional knockout experiments miRNA levels were only partially reduced even weeks after Dicer1 ablation, likely reflecting the high stability of these short non-coding RNAs.…”

Inducible and reversible inhibition of miRNA-mediated gene repression in vivo

“…In previous studies where Dicer1 was conditionally ablated in the skeletal muscle of adult mice, muscle regeneration was impaired after acute injury, but no effect on muscle morphology or function was observed during homeostasis 24,81,82 . An explanation for this difference is that in the Dicer1 conditional knockout experiments miRNA levels were only partially reduced even weeks after Dicer1 ablation, likely reflecting the high stability of these short non-coding RNAs.…”