The Mef2A Transcription Factor Coordinately Regulates a Costamere Gene Program in Cardiac Muscle

Abstract

The Mef2 family of transcription factors regulates muscle differentiation, but the specific gene programs controlled by each member remain unknown. Characterization of Mef2A knockout mice has revealed severe myofibrillar defects in cardiac muscle indicating a requirement for Mef2A in cytoarchitectural integrity. Through comprehensive expression analysis of Mef2A-deficient hearts, we identified a cohort of dysregulated genes whose products localize to the peripheral Z-disc/ costamere region. Many of these genes are essential for costamere integrity and function. Here we demonstrate that these genes are directly regulated by Mef2A, establishing a mechanism by which Mef2A controls the costamere. In an independent model system, acute knockdown of Mef2A in primary neonatal cardiomyocytes resulted in profound malformations of myofibrils and focal adhesions accompanied by adhesion-dependent programmed cell death. These findings indicate a role for Mef2A in cardiomyocyte survival through regulation of costamere integrity. Finally, bioinformatics analysis identified over-represented transcription factor-binding sites in this network of costamere promoters that may provide insight into the mechanism by which costamere genes are regulated by Mef2A. The global control of costamere gene expression adds another dimension by which this essential macromolecular complex may be regulated in health and disease.

MEF2 Transcription Factors Regulate Distinct Gene Programs in Mammalian Skeletal Muscle Differentiation

“…MEF2A was predicted to regulate genes involved in actin cytoskeletal rearrangement, consistent with its regulation of structural genes encoding proteins localized to the costamere in cardiac muscle (15,46). It is intriguing that regulation of the actin cytoskeleton was not identified among the top canonical pathways in the MEF2B, -C, or -D dysregulated gene sets, considering these MEF2 proteins have been shown to regulate muscle structural genes in vitro and in vivo (46).…”

“…shRNA Design and Knockdown-Adenoviruses carrying shRNAs were generated as described previously (15). Briefly, shRNA sequences targeting either Mef2b or Mef2d transcripts were generated using the BLOCK-iT RNAi TM designer system (Invitrogen).…”

“…These shRNAs were designed to target all mRNA transcripts generated from each Mef2 gene. Previously, we described the specific and robust knockdown of MEF2A and MEF2C using shRNA adenoviruses (11,15). We subsequently generated shRNAs to specifically target MEF2B (Fig.…”

MEF2A regulates the Gtl2-Dio3 microRNA mega-cluster to modulate WNT signaling in skeletal muscle regeneration

“…Adenoviruses carrying shRNAs specific for Mef2a or lacZ were generated as described previously (Ewen et al, 2011). Adenoviruses were used at a multiplicity of infection (MOI) of 25 for all assays.…”

Regulation of Hspb7 by MEF2 and AP-1: implications for Hspb7 in muscle atrophy

“…Therefore, identifying pathways that mediate actin cytoskeletal gene expression has implications for different types of muscle disease. MEF2 has a well-established role in sarcomere organization, because it regulates key target genes associated with the costamere and sarcomeric proteins (Ewen et al, 2011;Hinits and Hughes, 2007;Potthoff et al, 2007). There are fewer studies that have investigated the role of AP-1 in sarcomere integrity; however, in cardiomyocytes c-Jun has been shown to have an important role in promoting sarcomere gene expression and sarcomere integrity (Windak et al, 2013).…”