Gender Differences In Renal Blood Flow In Response To Endothelin-1 In a Mouse Model Of Sickle Cell Disease

There is increasing evidence that Endothelin-1 (ET-1) plays a significant role in the pathogenesis of complications of sickle cell disease (SCD. SCD patients have elevated levels of endothelin-1 both in plasma and urine and ET-1 has been implicated in SCN, pain modulation, vaso-occlusive episodes, and acute chest syndrome. In the kidney, ET-1 is a potent vasoconstrictor, anti-natriuretic, and hypertrophic factor when signaling through the ETA receptor. ET-1 is released in response to shear stress, hypoxia, thrombin activation, and inflammatory cytokines, all of which are prevalent in SCD. Gender differences exist in other disease models, in which ET-1 plays a contributory pathophysiological role, with males typically exhibiting increased ET-1 mRNA expression, exaggerated ETA-mediated effects, and higher levels of renal injury. Little research exists highlighting the differences between males and females in SCD. It has been observed that the level of Hb F, a major modifier of disease severity in SCD, is higher in females compared to males. In addition, one study examined responses to chronic transfusion therapy, finding males to have increased vascular resistance and resulting decrease in oxygen delivery in response to transfusion when compared to females. We hypothesized that male SCD mice have enhanced ETA mediated responses to ET-1, ultimately leading to renal injury. To test this, we used male and female ‘HbS only’ knock in SCD mice to measure renal artery blood flow velocity (BFV) via laser Doppler flowmetry in response to an ET-1 bolus (1nm/kg in 100uL saline). Male mice had an exaggerated decrease in BFV relative to females at 1, 5, and 10 minutes post ET-1 infusion while renal artery diameter remained unchanged throughout the experiment (84.4±5.8 vs. 56±5.7% of BFV baseline at 10 minutes, p<0.05, n=6). A follow up experiment was performed to determine ET-1, ETA receptor, and ETB receptor mRNA expression in the cortex of male and female SCD mice via qPCR. Males and females surprisingly exhibited no significant difference in these parameters although there was a strong trend suggesting females have increased levels of ET-1 mRNA expression compared to males (1.62±0.51 fold increase vs. males, p=0.056, n=5-6). While the exaggerated sensitivity to an ET-1 bolus is partially explained by the relative decrease in ET-1 mRNA expression in males, we nevertheless expected to see differences in ETA/ETB receptor expression. However, receptor-ligand binding could perhaps offer an alternate explanation for this phenomenon. Sex hormones are heavily implicated in other sex differences studies and the potential protective role of estrogen and/or detrimental role for testosterone are both viable explanations for the dichotomy seen in SCD. These data demonstrate a novel sexual dimorphism for SCD, revealing new insights into sex-specific pathophysiology that could have broad effects on treatment strategies in sickle cell nephropathy.