Circadian Genes as Exploratory Biomarkers in DMD: Results From Both the mdx Mouse Model and Patients

Abstract

Duchenne muscular dystrophy (DMD) is a rare genetic disease due to dystrophin gene mutations which cause progressive weakness and muscle wasting. Circadian rhythm coordinates biological processes with the 24-h cycle and it plays a key role in maintaining muscle functions, both in animal models and in humans. We explored expression profiles of circadian circuit master genes both in Duchenne muscular dystrophy skeletal muscle and in its animal model, the mdx mouse. We designed a customized, mouse-specific Fluidic-Card-TaqMan-based assay (Fluid-CIRC) containing thirty-two genes related to circadian rhythm and muscle regeneration and analyzed gastrocnemius and tibialis anterior muscles from both unexercised and exercised mdx mice. Based on this first analysis, we prioritized the 7 most deregulated genes in mdx mice and tested their expression in skeletal muscle biopsies from 10 Duchenne patients. We found that CSNK1E, SIRT1, and MYOG are upregulated in DMD patient biopsies, consistent with the mdx data. We also demonstrated that their proteins are detectable and measurable in the DMD patients’ plasma. We suggest that CSNK1E, SIRT1, and MYOG might represent exploratory circadian biomarkers in DMD.

Circadian Clock in Muscle Disease Etiology and Therapeutic Potential for Duchenne Muscular Dystrophy

“…The loss of dystrophin in DMD, with the absence of its tethering to an intracellular actin skeleton network, could thus interrupt sarcolemma-cytoskeleton linkage to prevent SRF-mediated signal activation in myofiber which attenuates circadian clock function [99]. In mdx mice and DMD patients, gene expression analysis revealed that Bmal1, Cry1, and Cry2 were downregulated in the dystrophic muscles, together with altered myogenic pathway involving MyoD and myogenin [101]. Furthermore, the loss of dystrophin-mediated ECM-cytoskeleton linkage in the mdx mice was found to disrupt clock entrainment [102].…”

“…New cistromic analysis revealed that components of the Igf-1 and integrin-associated signaling pathways are direct transcriptional targets of the molecular clock network [28,154]. Given that distinct clock transcriptional outputs are known DMD therapeutic targets [101,154], testing potential synergistic actions of clock-targeting interventions to promote muscle mass, function, regenerative repair, and sarcolemma stability may present unique opportunities for DMD drug development. Mechanistic insights garnered from genetic loss-of-function models suggest that reinforcement or activation of clock function may mitigate dystrophic pathophysiology [24,25].…”