Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC24
Altered cardiac fibroblast proliferation during cardiac hypertrophy is modulated by calcium/calmodulin-dependent protein kinase IIδ
T. Martin1, A. Lawan1, R. Plevin1, A. Paul1, S. Currie1
1. SIPBS, Glasgow, United Kingdom.
Left ventricular hypertrophy (LVH) is an adaptive response to myocardial injury. Adaptations of the hypertrophic heart include (i) cardiac myocyte enlargement and calcium dysregulation, (ii) fibrosis due to collagen deposition by cardiac fibroblasts (CFs) and (iii) chronic inflammation. Calcium/calmodulin-dependent protein kinase IIδ (CaMKIIδ) has been highlighted as a key modulator of hypertrophic calcium handling however, little is known of its potential involvement in cardiac fibrosis or inflammation. Here, we examine the role of CaMKII in CF proliferation, an event that when uncontrolled, underlies development of fibrosis. We have developed and characterised a minimally invasive transverse aortic banding (MTAB) mouse model of LVH. Mice (C57, 25-30g) were anaesthetised with 3% Isoflurane in oxygen, maintained with 1.5% Isoflurane in oxygen and were given analgesic (60µg/kg Buprenorphine) intramuscularly. Heart weight:body weight ratios are significantly increased in MTAB compared to sham animals (6.4±0.5, n=12 cf. 5.1±0.18, n=11, p< 0.0001). LV contractility (% fractional shortening) is significantly depressed (33.8±1.6 cf. 41±2.8, p=0.03, in MTAB (n=12) versus sham (n=10)) and myocardial fibrosis, assessed by picosirius red staining of collagen, is significantly increased (5.9±1.6 cf. 0.55±0.2 (% area of staining in field measured), p=0.03, in MTAB (n=6) versus sham (n=4)). CaMKIIδ protein expression, assessed in parallel in cardiac homogenates (ratio to GAPDH), is significantly increased (0.77±0.14 cf. 0.35±0.03, p=0.03, in MTAB (n=9) versus sham (n=6)). Using CFs isolated from MTAB and sham animals, we have assessed whether (i) proliferation rates are altered following hypertrophy and (ii) whether CaMKIIδ may regulate CF proliferation. In response to Angiotensin II (1μM), CF proliferation (assessed by mean cell count from 10 random fields of view) increased over 72h with a significant difference in cell numbers between MTAB and sham cells evident after 48h (59.6±2.5 cf. 41.8±2.3, respectively, p=0.006, n=3). When cells were pre-treated for 1h with 5μM AIP (a specific inhibitor of CaMKII), proliferation was significantly decreased at 24h and this decrease was maintained at 48h and 72h in both sham (72h; 50.9±3.3 (untreated) cf. 29.8±0.6 (AIP-treated), respectively) and MTAB cells (72h; 71.0±7.2 (untreated) cf. 37.5±1.5 (AIP treated), respectively). This represented a 42% decrease in proliferation in sham cells and a 48% decrease in proliferation in MTAB cells following AIP treatment (n=3). Importantly, in cells isolated from both groups, AIP pre-treatment had no obvious effect on cell number at time zero (AIP-treated v’s untreated cells, sham p=0.270 and MTAB p=0.105). These results highlight a potential role for CaMKII in regulating CF proliferation during both normal and hypertrophic growth.
Where applicable, experiments conform with Society ethical requirements