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Inositol Trisphosphate Receptor Contribution to Ventricular Cardiac Fibroblast Function in Healthy and Hypertrophied Mouse Hearts
Author(s) -
Currie Susan,
Martin Tamara Patricia,
Salleh Hanif,
McCluskey Claire,
Bushell Trevor John
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1178.2
Subject(s) - contractility , medicine , endocrinology , in vivo , receptor , inositol , cardiac function curve , ex vivo , chemistry , biology , heart failure , microbiology and biotechnology
Cardiac Fibroblasts play a critical role in pathological cardiac remodelling. Using a minimally invasive transverse aortic banding (MTAB) mouse model of cardiac hypertrophy, we investigated whether Inositol trisphosphate receptor type 2 (IP 3 R 2 ) expression and activity contributes not only to cardiac contractile dysfunction, but also to changes in cardiac fibroblast function. Cardiac contractility was assessed in vivo using echocardiography and in vitro using stimulation of isolated tissue preparations in organ baths. Cardiac fibroblasts were isolated from sham‐operated and MTAB hearts under sterile conditions using chunk digestion and maintained in short‐term culture. Quantitative immunoblot assessment of whole ventricular homogenates showed that IP 3 R 2 expression was significantly increased in MTAB hearts (IP 3 R 2 :GAPDH ratio: 0.378±0.06 vs 0.130±0.03, MTAB vs sham respectively, n=7, p<0.001). Further individual analysis of samples comparing in vivo contractile function with corresponding IP 3 R protein expression showed a clear distinction between the sham and MTAB groups. MTAB animals with <40% Fractional Shortening showed a clear correlation with higher expression of IP 3 R 2 (Spearman r=−0.79, p<0.05, n=15). The contribution of IP 3 R activity to contractile function was further assessed in vitro using isolated ventricular preparations stimulated with 1uM isoprenaline in the presence and absence of the Ca 2+ release modulator 2‐aminoethyl diphenylborinate (2‐APB) (10uM). Preparations from both MTAB and sham‐operated hearts showed reduced contractile activity in the presence of 2‐APB (~35% and 25% reduction respectively, n=2). Analysis of intracellular Ca 2+ release channel expression in isolated cardiac fibroblasts revealed a lack of any ryanodine receptor (RyR) expression but significant expression of IP 3 R 2 . In fibroblasts isolated from MTAB hearts, significantly higher expression of IP 3 R 2 was evident (IP 3 R 2 :GAPDH ratio: 0.252±0.02 vs 0.101±0.008, MTAB vs sham respectively, n=3, p<0.001) along with higher phosphorylation of IP 3 R at Ser1756. Fibroblasts from MTAB hearts also exhibited hyperproliferative growth characteristics as assessed following 1uM Angiotensin II stimulation of cells over a period of 48h (average cell number per area, 59.6±2.5 vs 41.8±2.3, MTAB vs sham, n=3, p=0.006). Treatment with 2‐APB significantly reduced both proliferation and Angiotensin II‐mediated Ca 2+ release in these cells. In conclusion and for the first time, we have shown increased IP 3 R 2 expression and IP 3 R phosphorylation specifically in ventricular cardiac fibroblasts isolated from hypertrophied hearts. Expression of IP 3 R 2 shows a strong correlation with cardiac contractility, where increased IP 3 R 2 expression not only parallels decreased contractile performance but may also influence fibroblast hyperproliferation. This highlights the possibility that altered Ca 2+ handling at the level of the cardiac fibroblast could be mechanistically important in pathological remodelling of the heart. Support or Funding Information British Heart FoundationBBSRC