The functional role of the JAK–STAT pathway in post-infarction remodeling

Objectives: Recently, the Janus kinase/signal transducer and activator of transcription (JAK–STAT) signaling pathway was found to be prominently associated with activation of the autocrine loop of the heart tissue-localized renin angiotensin system (RAS). We investigated if the JAK–STAT pathway is activated in the post-myocardial infarction (MI) non-ischemic myocardium (NIM), destined to undergo remodeling and whether blockade of the pathway in vivo can modify early post-MI remodeling. Methods: We investigated the time course of tyrosine phosphorylation of JAK–STAT and gp130 proteins in the NIM of post-MI rat heart as well as the binding activity of STAT proteins to the St-domain of the angiotensinogen gene promoter. We further compared the effects of in vivo blockade of RAS by the AT₁ receptor (AT₁R) blocker losartan with the in vivo blockade of JAK–STAT pathway by the specific JAK2 blocker tyrphostin AG490 on certain aspects of early post-MI remodeling. Results: We showed that JAK2, STATs 1, 3, 5a and 6 and gp130 proteins are tyrosine phosphorylated as early as 5–30 min post-MI and that STATs 1, 3, and 5a remain activated up to 7 days post-MI. Gel mobility shift assay showed a strong binding activity of STAT proteins to the St-domain of angiotensinogen gene promoter in 1-day post-MI NIM. The binding was significantly reduced in rat hearts previously treated with losartan or tyrphostin AG490. Supershift experiments identified STATs 3 and 5a as specifically interacting with the St-domain. Both AT₁R and JAK2 blockade resulted in significant amelioration of the increase of protein phosphatase 1 activity and decrease in basal level of p16-phospholamban that may underlie early diastolic dysfunction, as well as partial amelioration of early downregulation of Kv4.2 gene expression that may underlie increased arrhythmogenicity of 3-day post-MI heart. On the other hand, while blockade of AT₁R significantly ameliorated apoptotic changes in 1-day post-MI border zone, blockade of JAK2 increased apoptosis. Conclusions: The study provides compelling evidence in favor of the linkage of the JAK–STAT pathway with the angiotensin II autocrine loop and uncovers a mechanism by which selective activation of a set of STAT proteins underlies mobilization of the gene activation program intrinsic to post-MI remodeling. It also suggests that drugs that inhibit JAK–STAT phosphorylation may provide a new approach to modify post-MI remodeling. This needs to be confirmed in long term in vivo studies in the post-MI heart. [Copyright &y& Elsevier]