Targeting fibrosis in the Duchenne Muscular Dystrophy mice model: an uphill battle

Abstract

AimFibrosis is the most common complication from chronic diseases, and yet no therapy capable of mitigating its effects is available. Our goal is to unveil specific signallings regulating the fibrogenic process and to identify potential small molecule candidates that block fibrogenic differentiation of fibro/adipogenic progenitors.MethodWe performed a large-scale drug screen using muscle-resident fibro/adipogenic progenitors from a mouse model expressing EGFP under the Collagen1a1 promotor. We first confirmed that the EGFP was expressed in response to TGFβ1 stimulation in vitro. Then we treated cells with TGFβ1 alone or with drugs from two libraries of known compounds. The drugs ability to block the fibrogenic differentiation was quantified by imaging and flow cytometry. From a two-rounds screening, positive hits were tested in vivo in the mice model for the Duchenne muscular dystrophy (mdx mice). The histopathology of the muscles was assessed with picrosirius red (fibrosis) and laminin staining (myofiber size).Key findingsFrom the in vitro drug screening, we identified 21 drugs and tested 3 in vivo on the mdx mice. None of the three drugs significantly improved muscle histopathology.SignificanceThe in vitro drug screen identified various efficient compounds, none of them strongly inhibited fibrosis in skeletal muscle of mdx mice. To explain these observations, we hypothesize that in Duchenne Muscular Dystrophy, in which fibrosis is a secondary event due to chronic degeneration and inflammation, the drugs tested could have adverse effect on regeneration or inflammation, balancing off any positive effects and leading to the absence of significant results.

Targeted regulation of TAK1 counteracts dystrophinopathy in a DMD mouse model

“…We speculate that, in addition to myofibers, a pharmacological or shRNA-mediated knockdown approach can delete TAK1 in multiple cell types, leading to the discrepant phenotype. Indeed, a recent report shows that TAK1 controls the fibrogenic differentiation of fibro/adipogenic progenitor (FAP) cells in skeletal muscle and that pharmacological inhibition of TAK1 by 5-Z-7 Oxozeaenol considerably reduces gene expression of fibrotic molecules, such as Collagen 1a1 (Col1a1), connective tissue growth factor (CTGF), periostin (Postn), smooth muscle actin (Acta2), and fibronectin 1 (Fn1) in FAPs ( 54 ). While we have used genetic mouse models, both groups of mice were fed tamoxifen-containing chow starting from the last day of tamoxifen injection, for the entire duration of the experiment.…”

Temporal regulation of TAK1 to counteract muscular dystrophy

“…We speculate that pharmacological or shRNA mediated approach can delete TAK1 in multiple off-target cell types which can lead to the discrepant phenotype. Indeed, a recent report shows that TAK1 controls the fibrogenic differentiation of fibro/adipogenic progenitor (FAP) cells in skeletal muscle and pharmacological inhibition of TAK1 by 5-Z-7 Oxozeaenol drastically reduced expression of fibrotic genes such as Collagen 1a1 (Col1a1), connective tissue growth factor (CTGF), periostin (Postn), Smooth muscle actin (Acta2), and fibronectin (Fn1) in FAPs (62) .…”