WNT/β-catenin signaling suppresses DUX4 expression and prevents apoptosis of FSHD muscle cells

Gregory Block PhD
Gregory Block PhD

New research out of Dr. Daniel Miller's lab addresses one of the most challenging aspects of studying FSHD: the ability to model the disease in cultured cells or animal models. Modeling the disease is a critical piece of the puzzle to understand disease processes in order to screen for compounds or genes that may lead to therapies. DUX4 is a transcription factor protein that is believed to be critical for the initiation of muscle death in FSHD. For example, a number of labs have shown that if DUX4 is introduced artificially into cells, those cells will die. In the past, researchers have relied on indirect means to understand DUX4 because the protein is expressed in low abundance and is very difficult to detect. The question that has been nagging the field is if DUX4 is expressed at such low levels in muscle, how does it cause problems?

In the work, first-authored by Friends of FSH Research Scholar Gregory Block, as well as Divya Narayanan, Amanda Amell and Lisa Petek, they were able to more efficiently coax cultured muscle from FSHD patients towards a differentiated state. This allowed them to finally observe natural DUX4 at levels high enough to induce cell death. This puts them in a position where they have two metrics that can be quantied: DUX4 levels and DUX4-induced death of differentiated muscle cells.

Being able to detect and measure naturally produced DUX4 has allowed the lab to ask whether disruption of other genes or cellular signaling pathways may change DUX4 expression. If so, these pathways could be hijacked for therapeutic intervention in the disease. Collaboration with another lab at the University of Washington, lead by Randall T. Moon and his postdoc Kathryn Davidson, provided the necessary tools and expertise to ask whether a class of important signaling proteins, called Wnts, were involved in DUX4 expression. Treatment of cells with certain molecules that either exacerbate or mitigate Wnt signaling resulted in profound changes in DUX4 expression. When DUX4 expression was reduced by Wnt activation, the muscle cells in their dish no longer died.

Muscle cells obtained from an FSHD patient were differentiated into myotubes. Each myotube is labeled in green and contains hundreds of nuclei (blue dots). DUX4 is detected using an antibody that results in red labeling inside the nuclei. Download High resolution image

The observation that treatment of cells with certain Wnts can shut off DUX4 and prevent muscle cell death, opens up more questions that the lab is now ready to answer. For example, what other cellular pathways govern DUX4 expression? Which of the pathways are amenable to drug intervention? As they dive deeper into the biology of Wnts in skeletal muscle they will discover a network of proteins and molecules that regulate DUX4 while developing the tools needed to expand from Wnt biology into other pathways. This strategy will expose novel therapeutic candidates that will hopefully prevent or slow disease progression in patients with FSHD.

Published in Human Molecular Genetics.

See 2013 Scholor grant on Mechanism of Wnt Signaling in Facioscapulohumeral Muscular Dystrophy.