Transcriptome analysis of collagen VI-related muscular dystrophy muscle biopsies [Microarray].

Collagen VI-related muscular dystrophies (COL6RD) are a rare, inherited group of congenital muscular dystrophies. The phenotype spans from an early-onset, severe, and rapidly progressive clinical course in Ullrich congenital muscular dystrophy (UCMD), to a late-onset, mild and slowly progressive form in Bethlem muscular dystrophy (BM). COL6RD are caused by pathogenic variants in any of the three collagen type VI genes (COL6A1, COL6A2, COL6A3), which cause absence, reduction, mislocalization, or dysfunction of the collagen VI microfibrils in the skeletal muscle extracellular matrix (myomatrix), leading to yet incompletely understood downstream effects. Pathologic alterations in muscle biopsies of COL6RD varies, ranging from severely dystrophic changes, to mildly myopathic, represented by isolated myofiber atrophy. In this study, we aim to define the pathophysiologic events responsible for the histologic alterations of muscle and their progression in COL6RD. Aided by automated image analysis, we reviewed COL6RD patient muscle biopsies (n=22) and stratified them to three groups based on the degree of fibrosis and muscle fiber atrophy. Using microarray and RNA-Seq, we then performed global gene expression profiling on the same muscle biopsies and compared it with controls (n=14). Different histologic groups were characterized by similar transcriptional signatures predominantly featuring the upregulation of myomatrix component genes and downregulation of skeletal muscle and mitochondrion-specific genes. Our results also identified the TGFβ1 pathway in strong correlation with the development of COL6RD pathology at the histologic level, beginning early in the disease process, preceding fibrosis, and increasing in direct correlation with increased histologic severity. Overall, our study identifies COL6RD as a primary disorder of the myomatrix and posits dysregulation of TGFβ1-dependent pathways as a potential factor in pathogenesis of the disease. RNA profiles for 36 human muscle biopsies were generated using the Illumina microarray. Included among the 36 biopsies sequenced were 14 from persons with no COL6RD mutation and 22 with a COL6RD mutaiton. For those biopsies sequenced having a COLD6RD mutation, three hisology-grades are represented; COL6RD-1, COL6RD-2, and COL6RD-3.