Myoblasts from affected and non‐affected FSHD muscles exhibit morphological differentiation defects

Abstract

Facioscapulohumeral dystrophy (FSHD) is a muscular hereditary disease with a prevalence of 1 in 20,000 caused by a partial deletion of a subtelomeric repeat array on chromosome 4q. However, very little is known about the pathogenesis as well as the molecular and biochemical changes linked to the progressive muscle degeneration observed in these patients. Several studies have investigated possible pathophysiological pathways in FSHD myoblasts and mature muscle cells but some of these reports were apparently in contradiction. The discrepancy between these studies may be explained by differences between the sources of myoblasts. Therefore, we decided to thoroughly analyze affected and unaffected muscles from patients with FSHD in terms of vulnerability to oxidative stress, differentiation capacity and morphological abnormalities. We have established a panel of primary myoblast cell cultures from patients affected with FSHD and matched healthy individuals. Our results show that primary myoblasts are more susceptible to an induced oxidative stress than control myoblasts. Moreover, we demonstrate that both types of FSHD primary myoblasts differentiate into multi-nucleated myotubes, which present morphological abnormalities. Whereas control myoblasts fuse to form branched myotubes with aligned nuclei, FSHD myoblasts fuse to form either thin and branched myotubes with aligned nuclei or large myotubes with random nuclei distribution. In conclusion, we postulate that these abnormalities could be responsible for muscle weakness in patients with FSHD and provide an important marker for FSHD myoblasts.

A unique library of myogenic cells from facioscapulohumeral muscular dystrophy subjects and unaffected relatives: family, disease and cell function

“…12,26 The reasons behind these discrepancies remain to be determined, but the very low level of FRG2 expression and different qPCR assays might contribute. Also unlike previous studies, 14,16 we found no difference between FSHD and unaffected cells in responses to paraquat or hydrogen peroxide. Our results, however, are consistent with previous work 12 which found no significant differences between FSHD and unaffected myogenic cells in expression of FRG1 or other 4q genes such as PDLIM3.…”

“…6,[8][9][10][11][12][13][14][15] Some of these studies have suggested possible FSHD-specific phenotypes, including increased sensitivity to oxidative stress, 14,16 altered myotube morphology, 14 and altered expression of FRG1 18 or FRG2. 12 We found that proliferating and differentiating cultures of both FSHD and unaffected cells expressed similar patterns of FRG2 mRNA, and a recent study also found FRG2 mRNA in unaffected myoblasts and myotubes.…”

“…14,16 In particular, we examined the effects on cell viability of four types of stressors: (i) buthionine sulphoximine (BSO), which decreases intracellular glutathione by inhibition of gammaglutamylcysteine synthetase; 24 (ii) staurosporine, a kinase inhibitor that induces apoptotic cell death; 25 (iii) paraquat, a superoxide generator; and (iv) hydrogen peroxide. Each stressor was tested at a range of doses and times as used in previous studies 14,16,24,25 for the effect on cell viability (Supplementary Methods).…”

“…7 Many studies have, therefore, used primary myogenic cell cultures derived from FSHD subject biopsies to examine potential pathogenic mechanisms and therapeutic strategies. [8][9][10][11][12][13][14][15] Such studies have suggested several possible FSHD-specific phenotypes, including increased sensitivity to oxidative stress 14,16 and altered gene expression, [17][18][19][20] as well as expression of the long form of DUX4. 5,6 These findings have, however, sometimes not been consistent among laboratories.…”

β - catenin is central to DUX4 -driven network rewiring in facioscapulohumeral muscular dystrophy

“…Among these is the characteristic oxidative stress sensitivity of FSHD muscle/myoblasts [41,42]. Our work implicates HIF1-a signalling as critically perturbed in FSHD and shows that HIF1A displays strong positive correlation with b-catenin in FSHD samples, providing mechanism for previous observations of involvement of downstream components of the HIF1-a pathway in FSHD [20].…”