Role of a novel PGC-1α isoform in gene transcription

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Peroxisome proliferator-activated receptor gamma co-activator 1α (PGC-1α) is a transcriptional coactivator that is critical for the metabolic adaptation of mammalian cells to diverse physiological stresses. In addition to this well-described function in the control of cell metabolism, the number of reports describing a protective role for PGC-1α against inflammation is on the rise. I report here a novel stress-dependent pro-inflammatory PGC-1α variant that I have identified in vitro in C2C12 mouse myoblasts and in vivo in mouse skeletal muscle. My unpublished results indicate that, compared to the canonical PGC-1α isoform (also known as PGC-1α(1)), the structure of this novel 72-kDa PGC-1α isoform, which I will call PGC-1α(72), is typified by its lack of the C-terminal 15 amino acids. The deleted C-terminal sequence encompasses a 9-amino-acid alpha helix that I previously reported to be essential for PGC-1α(1) to bind to the cap-binding protein (CBP)80 and to transactivate pro-myogenic PGC-1α-dependent genes. In contrast to PGC-1α(1), PGC-1α(72) lacks the CBP80-binding motif (CBM) and, as my data indicate, activates the transcription of pro-inflammatory genes. In the first aim of my research strategy, I propose to use C2C12 myoblasts to fully characterize the sequence of this novel PGC-1α(72) isoform, identify those transcription factors and RNA-binding proteins that regulate its expression in response to stress, and comprehensively determine the transcriptional network that it activates. In the second aim, I will take advantage of my finding that functional inhibition of the PGC-1α CBM phenocopies PGC-1α(72)-dependent expression of pro-inflammatory chemoattractants such as the chemokine CCL2. Elevated CCL2 plasma levels, which are observed with aging, have been recognized as important risk factors for numerous inflammatory diseases, including cardiac fibrosis, atherosclerosis and cancers. Mechanistically, CCL2 has been found to function in monocyte recruitment onto the endothelium of blood vessels and in monocyte infiltration into inflamed tissues. I will breed our newly characterized PGC-1αCBMmut mice with the Dystrophin-deficient Dmdmdx muscle inflammatory and premature aging mouse model and use derived primary myoblasts to infer the functional consequences of PGC-1α(72) expression, in particular those attributable to its lacking the CBM, to inflammation. In particular, I will determine how PGC-1αCBMmut triggers the CCL2-dependent recruitment of monocytes onto endothelial cells, their infiltration into cardiac tissues, and development of cardiac fibrosis in aging mice as a function of sex, i.e. in males vs. females. I view demonstrating the contribution of PGC-1αCBMmut to cardiac fibrosis as a proof of concept. It will provide fertile grounds to study the function of skeletal muscle PGC-1α(72) in the development of other aging- related inflammatory diseases. I hypothesize that understanding PGC-1α(72)-dependent gene regulation and its consequences to the development of inflammatory diseases will facilitate the development of new therapeutics, such as synthetic antisense oligonucleotides regulating splicing of PGC-1α pre-mRNA.