The MEK/ERK Module Is Reprogrammed in Remodeling Adult Cardiomyocytes

Abstract

Fetal and hypertrophic remodeling are hallmarks of cardiac restructuring leading chronically to heart failure. Since the Ras/Raf/MEK/ERK cascade (MAPK) is involved in the development of heart failure, we hypothesized, first, that fetal remodeling is different from hypertrophy and, second, that remodeling of the MAPK occurs. To test our hypothesis, we analyzed models of cultured adult rat cardiomyocytes as well as investigated myocytes in the failing human myocardium by western blot and confocal microscopy. Fetal remodeling was induced through endothelial morphogens and monitored by the reexpression of Acta2, Actn1, and Actb. Serum-induced hypertrophy was determined by increased surface size and protein content of cardiomyocytes. Serum and morphogens caused reprogramming of Ras/Raf/MEK/ERK. In both models H-Ras, N-Ras, Rap2, B- and C-Raf, MEK1/2 as well as ERK1/2 increased while K-Ras was downregulated. Atrophy, MAPK-dependent ischemic resistance, loss of A-Raf, and reexpression of Rap1 and Erk3 highlighted fetal remodeling, while A-Raf accumulation marked hypertrophy. The knock-down of B-Raf by siRNA reduced MAPK activation and fetal reprogramming. In conclusion, we demonstrate that fetal and hypertrophic remodeling are independent processes and involve reprogramming of the MAPK.

The Role of Oncostatin M and Its Receptor Complexes in Cardiomyocyte Protection, Regeneration, and Failure

“…In ischemic cultures, fetal remodeling results in the protection of adult cardiomyocytes in a way that was little observed after hypertrophic remodeling [100,113,116]. These observations lead to three conclusions that are integrated into an overall scheme of cardiac adaptation, regeneration, and failure, as discussed later: First, the growth factor/cytokine compositions of morphogens and sera differ substantially.…”

“…The most commonly used growth stimulant and maintenance medium for cardiomyocytes is fetal calf serum (FCS), which is usually used at concentrations between 5% and 20%. FCS induces hypertrophic remodeling of cultured adult cardiomyocytes characterized by cell surface enlargement, protein accumulation, and restoration of cell-cell contacts by in situ spreading, resulting in a cross-striated confluent layer of contracting cardiomyocytes with time [46,100,113]. Importantly, serum from human patients with coronary artery disease and dilated cardiomyopathy elicits similar and even more rapid effects, indicating a comparable composition of cardioactive growth factors [100,113,116].…”

“…In addition to the potential for selective activation of OSM receptor complexes, adult rat cardiomyocyte cultures are well-suited to siRNA-based transcriptome and proteome studies that allow for detailed analysis of signal transduction cascades and the effects of a single knockdown on cardiomyocytes. For example, B-Raf, a signaling component of the Ras/Raf/MEK/Erk cascade, has been identified as a master regulator of ischemic resistance in adult cardiomyocytes [8,113]. Moreover, these cultures use mechanisms similar to cardiomyocytes in the damaged myocardium to re-establish cellcell contacts and eventually form a synchronously contracting tissue-like layer with wellestablished sarcomeres [3,10,15,24,46,100,114,115].…”

“…FCS induces hypertrophic remodeling of cultured adult cardiomyocytes characterized by cell surface enlargement, protein accumulation, and restoration of cell-cell contacts by in situ spreading, resulting in a cross-striated confluent layer of contracting cardiomyocytes with time [46,100,113]. Importantly, serum from human patients with coronary artery disease and dilated cardiomyopathy elicits similar and even more rapid effects, indicating a comparable composition of cardioactive growth factors [100,113,116]. In contrast, stimulation with secreted factors (morphogens) from cardiac microvascular endothelial cells of patients with dilated cardiomyopathy results in fetal remodeling characterized by severe cardiomyocyte elongation and rapid restoration of cardiomyocyte-cardiomyocyte contacts, atrophy, and the activation of the fetal gene program [116].…”

Myocardial Accumulations of Reg3A, Reg3γ and Oncostatin M Are Associated with the Formation of Granulomata in Patients with Cardiac Sarcoidosis

“…The activity of this interleukin-6 family member can be recognized by the relocalization of radixin, by the activation of Stat3, the elongated and partly sharp cardiomyocyte shape and the strong re-expression of Actn1. This non-muscle actinin is a reliable marker of cardiomyocyte remodeling and dedifferentiation [ 10 , 29 , 30 , 31 ]. Since the release of oncostatin M in the infiltrated myocardium is restricted to cells of a monocytic lineage and T-lymphocytes [ 30 , 32 ], invading phagocytes might fuel the OSM/OSMR/Stat3/Reg3 axis by increasing the number of OSM-secreting macrophages (see the hypothetical scheme in Figure 7 ).…”