A-Kinase Anchoring Proteins (AKAPs) act as molecular scaffolds to direct context-dependent signaling events associated with cell growth, migration, and differentiation. One of the major downstream substrates for AKAP signaling is the CREB transcription factor, whose functionality in vascular smooth muscle cells (VSMC) is not well understood, particularly with respect to downstream target genes. We identified Akap12 in a screen for retinoid-induced genes in VSMC and have shown a specific isoform, AKAP12A, to be a marker for VSMC differentiation based on its mRNA expression control through serum response factor (SRF) and the potent SRF coactivator, Myocardin (MYOCD) and its down-regulation in experimental and clinical vascular diseases;another isoform (Akap12b) is low in VSMC in vivo, but increases upon cell culture. Genetic inactivation of the entire Akap12 locus results in elevated VSMC migration, proliferation, and IL6 expression. In vitro knockdown studies demonstrate an important role for AKAP12A in the control of lipid uptake and inflammatory gene expression. Importantly, AKAP12A coordinates CREB-dependent gene transcription in VSMC, including novel activation of VSMC-specific CNN1, which confers profound resistance to lipid accumulation and inflammatory gene expression in vitro and neointimal disease when overexpressed in transgenic mice. Further, AKAP12A augments MYOCD-dependent transactivation, a key molecular process in the differentiation of VSMC. Based on these strong preliminary and published data from the applicant's lab and those of other labs, we seek to test the novel hypothesis that SRF-dependent AKAP12A maintains normal VSMC homeostasis. We propose a series of inter-related specific aims that will directly test this hypothesis by (1) elucidating the transcriptional and post-transcriptional regulatory control of Akap12a using transgenic mouse models and microRNA analyses (Specific Aim 1);(2) elucidating the role of AKAP12A in vascular disease using innovative genetic mouse models crossed with SMC-specific Cre recombinase mice our lab has developed or recently acquired (Specific Aim 2);and (3) defining the AKAP12A-regulated "CREBome" in VSMC through state-of-the-art next generation sequencing of RNA or chromatin immunoprecipitated CREB binding sequences derived from wildtype or Akap12a knockout mouse aortic SMC. It is expected that the information obtained through these focused studies will establish a new and important role for AKAP12A in antagonizing perturbations to normal vessel wall homeostasis. This information will, in turn, spark efforts to develop pharmacological or genetic interventions that would either thwart the dramatic loss in AKAP12A in such diseases as atherosclerosis or iatrogenic-induced vascular occlusion or induce specific downstream AKAP12A substrates such as critical CREB-dependent target genes (CNN1) necessary to prevent or reverse disease progression. We also imagine that information obtained here will have direct applications in other disease contexts where AKAP12A expression and downstream activities are compromised (e.g., cancer).
Human diseases often result when cells cannot maintain normal function in the face of external and internal stressors. Through focused studies on the regulation and function of one gene called AKAP12A, we will gain new molecular insight into how disease-evoking stimuli change the normal programming of vascular smooth muscle cells, thus contributing to such blood vessel diseases as atherosclerosis and transplant arteriopathy.
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