Effect of PGC1-beta ablation on myonuclear organisation

Ryan Beedour,Julien Ochala,Jacob A Ross,Yotam Levy

doi:10.1007/s10974-019-09549-3

Ryan Beedour, Julien Ochala + Show 2 more

Open Access

https://doi.org/10.1007/s10974-019-09549-3

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Abstract

Skeletal muscle fibres are large, elongated multinucleated cells. Each nucleus within a myofibre is responsible for generating gene products for a finite volume of cytoplasm—the myonuclear domain (MND). Variation in MND sizes during atrophy, hypertrophy and disease states, are common. The factors that contribute to definitive MND sizes are not yet fully understood. Previous work has shown that peroxisome proliferator-activated receptor gamma coactivator 1α (PGC1-α) modulates MND volume, presumably to support increased biogenesis of mitochondria. The transcriptional co-regulator peroxisome proliferator-activated receptor gamma coactivator 1β (PGC1-β) is a homologue of PGC1-α with overlapping functions. To investigate the role of this protein in MND size regulation, we studied a mouse skeletal muscle specific knockout (cKO). Myofibres were isolated from the fast twitch extensor digitorum longus (EDL) muscle, membrane-permeabilised and analysed in 3 dimensions using confocal microscopy. PGC1-β ablation resulted in no significant difference in MND size between cKO and wild type (WT) mice, however, subtle differences in nuclear morphology were observed. To determine whether these nuclear shape changes were associated with alterations in global transcriptional activity, acetyl histone H3 immunostaining was carried out. We found there was no significant difference in nuclear fluorescence intensity between the two genotypes. Overall, the results suggest that PGC-1α and PGC-1β play different roles in regulating nuclear organisation in skeletal muscle; however, further work is required to pinpoint their exact functions.

Highlights

A skeletal muscle fibre is typically 10 to 80 μm in diameter and can be up to 25 cm in length
We have recently demonstrated that the transcriptional coactivator, peroxisome proliferator-activated receptor-γ coactivator 1-α (PGC-1α), plays an essential role in muscle metabolism in general, and the determination of myonuclear domain (MND) sizes in particular (Ross et al 2017)
Data are presented as mean ± standard error of the mean (SEM)

Summary

Introduction

A skeletal muscle fibre ( known as a myofibre) is typically 10 to 80 μm in diameter and can be up to 25 cm in length Myofibres of this size cannot be supported by a single myonucleus (Hall and Ralston 1989; Edgerton and Roy 1991; Ralston and Hall 1992). Hundreds of nuclei are needed to support and coordinate the large and lengthy myofibres (Hall and Ralston 1989; Edgerton and Roy 1991; Ralston and Hall 1992; Levy et al 2018). If MNDs are too large, portions of the fibre may not receive enough mRNA or proteins necessary for function, leading to dysfunction (Qaisar et al 2012; Levy et al 2018). Despite its crucial importance, the signalling pathways fine tuning MND volumes remain unclear

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