GENETIC SUSCEPTIBILITY TO EARLY ONSET OF TRANSFORMING GROWTH FACTOR-BETA DRIVEN CARDIAC REMODELING IN MICE IS ASSOCIATED WITH EGR1 AND STAT3

Abstract

Objective: We have previously described that the severity of TGF-b induced cardiac remodeling was associated with genetic background differences in alb/TGF-b1 transgenic mice (with elevated plasma TGF-b1 levels) on B6 vs CBAxB6 strains. Early growth response factor-1 (EGR1) has been associated with kidney fibrosis, and we recently demonstrated non-canonical TGF-b induced STAT3 activation in vascular smooth muscle cells, but their role in cardiac fibrosis or hypertrophy was not yet elucidated. The present study investigated whether genetic susceptibility to TGF-b induced early cardiac remodeling is associated with transcription factors EGR1 and STAT3. Design and method: As the albumin promoter driven TGF-b1 transgene is expressed after birth only in males reaching early high plasma TGF-b1 levels, we investigated 14-day old male transgenic and wild type control mice. Blood pressure of TGF-b1 transgenic (B6-TGFb and CBAxB6-TGFb) mice, and wild type (B6 and CBAxB6) controls (n = 6–9/group) was assessed, then cardiac samples were harvested and analyzed for mRNA and protein expression. Data are presented as mean ± SD and evaluated using Kruskal-Wallis test with Dunn's post-hoc test. Results: Blood pressure was elevated in both transgenic strains as compared to controls (MAP mmHg, B6: 46 ± 3; CBAxB6: 48 ± 4; B6-TGFb:54 ± 9; CBAxB6-TGFb:68 ± 7, p < 0.01). Compared to B6-TGFb and wild type, CBAxB6-TGFb hearts showed 20-fold elevation in BNP mRNA relative expression (B6: 1.5 ± 0.9; CBAxB6: 2.3 ± 0.9; B6-TGFb:1.5 ± 1.0; CBAxB6-TGFb:23.5 ± 13,3 p < 0.001) associated with increased Collagen-I (B6: 1.3 ± 0.2; CBAxB6: 1.2 ± 0.1; B6-TGFb:1.2 ± 0.2; CBAxB6-TGFb:1.9 ± 0.6, p < 0.05) and EGR1 (B6: 0.9 ± 0.2; CBAxB6: 0.8 ± 0.3; B6-TGFb:0.9 ± 0.6; CBAxB6-TGFb:1.8 ± 0.5, p < 0.01) as well as STAT3 mRNA overexpression (B6: 0.8 ± 0.1; CBAxB6: 1.2 ± 0.2; B6-TGFb:1.1 ± 0.1; CBAxB6-TGFb:1.7 ± 0.6, p < 0.01) and STAT3 phosphorylation. Early cardiac remodeling was further associated with 12-fold and 2-fold overexpression of TIMP-1 (B6: 1.0 ± 0.4; CBAxB6: 0.8 ± 0.4; B6-TGFb:0.7 ± 0.3; CBAxB6-TGFb:12.2 ± 9.0, p < 0.01) and TIMP-2 (B6: 1.1 ± 0.1; CBAxB6: 1.2 ± 0.2; B6-TGFb:1.3 ± 0.4; CBAxB6-TGFb:2.1 ± 1.1, p < 0.05), respectively. Significant EGR1 immunoreactivity was detected only in cardiomyocytes of CBAxB6-TGFb hearts. Conclusions: We conclude that EGR1 and STAT3 might strongly contribute to the initiation and early progression of cardiac remodeling driven by high circulating TGF-b levels. We postulate that EGR1 and STAT3 could be potential targets to inhibit early cardiac remodeling.