Left ventricular mass and cardiac function in SHRSP

Kirsten Douglas, Delyth Graham, Sarah Kettlewell, Anna F Dominiczak. BHF GCRC, Glasgow, United Kingdom.

Purpose: We previously identified a quantitative trait loci (QTL) for left ventricular mass index (LVMI) on rat chromosome 14 in an F2 cross between SHRSP and WKY, which was confirmed by generation of congenic strains SP.WKYGla14a (SHRSP background) and WKY.SPGla14a (WKY background). This study aimed to evaluate LVMI and left ventricular (LV) function in these congenic strains and identify candidate genes within the QTL region on rat chromosome 14.

Methods: 16-week old male SHRSP (n=15), SP.WKYGla14a (n=11), WKY (n=12) and WKY.SPGla14a (n=13) animals were imaged by echocardiography; LVMI (mg/mm), relative wall thickness (RWT), ejection fraction (EF %), stroke volume (SV) and cardiac output (CO) were calculated from m-mode images. LV diastolic function was assessed using pulse wave Doppler. Systolic blood pressure (SBP) was measured by radiotelemetry. Histochemistry was carried out using Masson’s Trichrome and picro-sirius red staining. Cardiomyocytes were isolated for cell sizing. Positional genes were identified by comparative mapping and analysed by qRT-PCR in whole heart tissue.

Results: SBP was significantly higher in WKY.SPGla14a versus WKY (P=0.008), with no significant difference observed between SHRSP and SP.WKYGla14a. LVMI, RWT and cardiomyocyte cell length were reduced in SP.WKYGla14a versus SHRSP (P=0.004, P=0.004, P=0.01 respectively) and increased in WKY.SPGla14 versus WKY (P<0.0001, P=0.001, P=0.01 respectively). Cell width was higher in WKY.SPGla14a versus WKY (P<0.0001). E/A ratio was significantly reduced in SHRSP versus SP.WKYGla14a (P<0.001) and in WKY.SPGla14a (P=0.01) versus WKY. Histochemistry of LV apex showed increased collagen deposits in SHRSP and WKY.SPGla14. Expression of candidate gene vitamin D binding protein (DBP) was higher in SP.WKYGla14a versus SHRSP (P=0.01) and reduced in WKY.SPGla14 versus WKY (P=0.01). In addition, Vitamin D receptor (VDR) and collagen type I expression was significantly higher in WKY.SPGla14a versus WKY (P=0.002).

Conclusions: We have confirmed a QTL for LVMI on rat chromosome 14 by the production of congenic strains demonstrating differences in LVMI in comparison to respective parental strains. In addition, SP.WKYGla14 has improved cardiac parameters to SHRSP despite equivalent SBP, with WKY.SPGla14 showing increased fibrosis and reduced LV diastolic function. Positional candidate gene DBP may contribute to hypertrophic and functional cardiac phenotypes in the SHRSP.