Deletion of Kvβ2 Alters Murine Skeletal Muscle Morphology and Phenotype

Abstract

IntroductionMammalian skeletal muscle expresses various potassium channels that regulate myogenesis. Recent evidence points to the role of Kv1.5 in cell cycle progression in myoblasts as pharmacological inhibition of this channel in L6E9 cells inhibited G0/G1 transition. Additionally, skeletal muscle also expresses voltage‐gated potassium channel beta subunits 1–3 (Kvβ, 2, 3) of aldo‐keto reductases (AK6) family, although their role in skeletal myogenesis is not yet known. Given that Kvβ subunits binds to and regulate members of Kv1 family including Kv1.5, it is plausible that Kvβ subunits play a significant role in skeletal myogenesis.Hypothesiswe hypothesized that Kvβ2 modulates skeletal myogenesis.MethodsAge matched, 8–12 week old, wild type (Wt) and Kvβ2 knockout mice (KO) mice were used in this study. Transcript expression analysis of key transcription factors, muscle growth regulators and contractile genes was conducted utilizing real time quantitative PCR (qPCR). Myofiber size was estimated in biceps femoris muscle cross‐sections using Hematoxylin and eosin staining. Protein expression was assessed by Western blots in lysates isolated from Biceps femoris muscle.ResultsBody weight of KO mice recorded at 6, 11 or 16 weeks of age, was significantly (p < 0.05) less than that of age matched Wt mice. Body weight normalized to tibia length in 16 week old KO mice was nearly 30% less than that of age matched Wt mice. Biceps femoris muscle cross‐sections in KO mice revealed significantly smaller myofiber area when compared to that of Wt mice (p < 0.05). Myosin heavy chain mRNA expression profiles were also significantly different between the KO and Wt mice. when compared with that of Wt mice, gastrocnemius and biceps femoris of KO mice showed marginal (p < 0.1) to significantly (p < 0.05) higher expression of myosin heavy chain IIA and IIX isoforms, while myosin heavy chain I mRNA expression was not different between the groups. Soleus muscle of KO mice showed significantly higher myosin heavy chain I expression, while the expression of myosin heavy chain 2B was profoundly (p < 0.05) decreased. Interestingly, the expression of major myogenic regulatory factors was unchanged between the two genotypes, with the exception that MyoD expression showed a consistently decreasing trend in all three muscles of KO mice when compared with that of Wt. In C2C12 cells, Kvβ2 mRNA expression declined steadily during the course of differentiation reaching to approximately 10% of that observed before differentiation (p < 0.05).ConclusionOur data suggest that Kvβ2 subunit is essential for skeletal myogenesis. Kvβ2 appear to effect muscle fitness by altering myosin heavy chain composition, suggesting a significant role of Kvβ subunits in skeletal muscle size and phenotype determination.