Alternative renin transcripts lacking exon 1 encode for a protein [exon(2–9)renin], which is synthetized in the cytosol and taken up by mitochondria. The expression of this alternative transcript is upregulated after myocardial infarction in rats. We therefore hypothesized that exon(2–9)renin protects cardiomyocytes from ischemia-related stress.

To investigate this hypothesis, we overexpressed exon(2–9)renin in cardiac H9c2 cells using the pIRES/neo vector. The control lines (H9c2 and pIRES) as well as the exon(2–9)renin transfected cells were exposed to oxidative stress by incubation with 100 mM and 400 mM hydrogen peroxide for 30 min. Thereafter, we determined the rates of necrosis (percentage of LDH release vs. LDH content) and apoptosis (Caspase^+, Annexin V⁺ cells), the mitochondrial membrane permeability (MMP) (MitoTracker) and the ATP content (CellTiter-Glo assay).

Exon(2–9)renin transfected cells were characterized by a significantly increased rate of apoptotis compared to control cells (Caspase⁺ cells: 19.5 2.7% vs. 7.8 1.0%, p<0.01). Following low oxidative stress the number of Caspase⁺ cells increased significantly to 26.7 4.2% and 34.4 5.6% in control and exon(2–9)renin transfected cells. Following high oxidative stress exon(2–9)renin transfected cells showed a significantly reduced necrotic damage (60.7 7.9 vs. 82.0 7.8, p<0.05). Also the mitochondrial derived apoptosis rate measured by the percentage of Annexin V⁺ cells was significantly reduced (50.3 8.4% vs. 73.2 7.8%, p<0.05). Furthermore, exon(2–9)renin transfected cells showed a significantly enhanced ATP content (36.4 4.9% vs. 14.3 4.9%, p<0.01) and an increased number of cells with an intact MMP (65.7 4.6% vs. 40.7 5.3%, p<0.01).

Our data suggest that exon(2–9)renin may protect cardiac cells against ischemia-related stress responses possibly by its beneficial effects on mitochondrial functions. Thus, in contrast to secretory renin, the cytosolic renin may be a target against an ischemia/reperfusion injury in the heart.