Changes in gene expression caused by genetic elimination of high molecular weight FGF2 are associated with prevention of stress‐induced cardiac systolic dysfunction

Abstract

Fibroblast growth factor 2 (FGF2) is produced as high (>20 kDa, Hi‐) and low molecular weight (18 kDa, Lo) isoforms in the heart. While administered Lo‐FGF2 has been established as a cardioprotective agent in multiple models of cardiac injury, there is limited information about the role of Hi‐FGF2 in the heart. To investigate the effect of endogenous Hi‐FGF2 we compared cardiac transcriptome (35240 targets, GeneChip™ Mouse Gene 2.0 ST Array (Affymetrix, 902119)) and systolic function between Hi‐FGF2 knock‐out mice, FGF2(Lo), expressing only Lo‐FGF2, and wild type mice, FGF2(WT), expressing both Hi‐FGF2 and Lo‐FGF2, under ‘normal’ (sham‐operated) and “stress” (pressure overload) conditions. Transaortic constriction surgery (TAC) was used to induce pressure overload. Echocardiography was done at baseline and at 4–8 weeks post‐surgery. Microarray analysis showed that under normal conditions, the absence of Hi‐FGF2 promoted changes in relative levels of 118 transcripts, including those associated with circadian rhythm regulation and heat shock protein (HSP70)‐associated apoptosis regulation. Comparative analysis of TAC surgery‐induced gene expression changes showed that 275 transcripts were differentially affected by the presence or absence of Hi‐FGF2 expression, most prominently the orphan nuclear receptor NR1D1 which is linked to regulation of circadian rhythm and metabolism. Under non‐stress conditions, systolic function was unaffected by endogenous Hi‐FGF2 expression. Pressure overload stress caused a decline in systolic function in the presence of endogenous Hi‐FGF2, at 4–8 weeks post‐TAC surgery, accompanied by increases in markers of myocardial stress/damage including B‐type natriuretic peptide (BNP) and the pro‐cell death protein BCL2/adenovirus E1B 19 kDa protein‐interacting protein‐3, Bnip3. In the absence of endogenous Hi‐FGF2, mice were protected from stress‐induced loss of systolic function and increases in BNP and Bnip3. TAC surgery induced Hi‐FGF2‐independent increases in: cardiac mass (heart weight/tibia length); cardiac fibrosis; transcripts linked to exracellular matrix remodeling. Increased cardiomyocyte size, however, was only observed in FGF2(WT) but not FGF2(Lo) hearts post‐TAC. It is suggested that elimination of endogenous Hi‐FGF2 elicits cardioprotection by increasing cardiac HSP70 (pre‐TAC surgery); and NR1D1, after TAC surgery.Support or Funding InformationFunding (EK, PAC, DJ) was provided by the Canadian Institutes for Health Research (FRN‐74733) and the Molson Women’s Heart Health Foundation (EK). MPC was supported by a CIHR Open Operating Grant (MOP136862). NK and RSN were the recipients of a Bank of Montreal studentship award via the St. Boniface Hospital Albrechtsen Research Centre and University of Manitoba funding to PAC.