Characterization of the Regulation and Function of Family with Sequence Similarity 83D (Fam83d) in Skeletal Muscle

Abstract

Skeletal muscle atrophy is a serious condition that can arise due to aging, cancer, corticosteroid exposure, and denervation. To better characterize the molecular genetic events of neurogenic atrophy, a previous study isolated mouse gastrocnemius muscle from mice at 3 and 14 days following sciatic nerve denervation. The gene expression profile in the denervated muscle tissue was then analyzed by microarray and compared to control muscle tissue to identify novel neurogenic atrophy‐induced genes. The microarray data revealed for the first time that Fam83d is expressed in skeletal muscle and is significantly induced in response to denervation. Quantitative PCR (qPCR) analysis revealed that Fam83d is more highly expressed in proliferating myoblasts compared to differentiated myotubes. Characterization of the transcriptional regulation of Fam83d was analyzed by cloning fragments of the proximal promoter region located immediately upstream from the start of transcription and fusing them with a reporter gene. The reporter plasmids were then transfected into C2C12 mouse muscle cells alone or in combination with myogenic regulatory factor expression plasmids, resulting in a differential effect on reporter activity. Analysis of the promoter of Fam83d revealed conserved E‐box elements in the proximal regulatory region, which are known myogenic regulatory factor (MRF) binding sites. To assess where Fam83d is localized in the cell, we fused Fam83d with green fluorescent protein (GFP), transfected the Fam83d‐GFP expression plasmid into C2C12 mouse myoblasts cells, visualized by confocal microscopy, and observed that Fam83d is localized exclusively to the cytoplasm. It has recently been determined that Fam83d contains a putative phospholipase domain, is mis‐regulated in several different cancer types, and may modulate MAP Kinase signaling. Therefore, Fam83d was ectopically expressed in cultured muscle cells and markers of muscle cell differentiation and MAP Kinase signaling were analyzed. Fam83d overexpression resulted in significantly repressed levels of myosin heavy chain and myogenin expression, while levels of phosphorylated ERK were dramatically repressed. The discovery that Fam83d is expressed in skeletal muscle combined with the observation that Fam83d, a potential modulator of MAP Kinase signaling, is induced in response to neurogenic atrophy helps further our understanding of the molecular and cellular events of skeletal muscle wasting.Support or Funding InformationThe work was support by University of North Florida Transformational Learning Opportunity grants and a University of North Florida Foundation Board Grant to D.W.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.