Abstract 11: Characterizing Gender-Specific Differences in Angiogenesis and Protection from Hypertension: Congenic Lines Lead to Identification of Btg2 as a Candidate Gene

Abstract

Whole and partial chromosome introgression from the Brown Norway (BN) rat into the Dahl Salt Sensitive (SS) rat is a valuable tool for identifying genes and pathways associated with disease phenotypes in the SS rat. We have created two congenic lines with BN substitutions differing by 22.9 Kbp. The congenic regions differ by one gene, Btg2 , and have 35 sequence variants, three of which occur in Btg2 . We have characterized angiogenesis and development of hypertension in these new strains, and since Btg2 is known to be modulated by estradiol, we measured both phenotypes in males and females. Mean arterial pressure (MAP) was measured by telemetry after three weeks of 8% NaCl diet. Angiogenesis was measured by electrical stimulation of one hindlimb (Tibialis anterior, TA, and Extensor digitorum longus, EDL) with the contralateral leg acting as control. Renal damage was assessed by 24-h protein/albumin excretion after two weeks on 8% NaCl diet. Btg2 expression was determined by QRT-PCR on renal cortex and medulla as well as stimulated and unstimulated TA muscle. Males from both lines had the same MAP following three weeks of 8% NaCl diet (Btg2 BN : 187±5 mmHg, Btg2 SS : 185±3). Females with Btg2 BN had significantly higher MAP (180±6 mmHg) than Btg2 SS females (153±7 mmHg). Angiogenesis in response to electrical stimulation was observed in Btg2 BN males (TA=20.0±4.5% increase in vessel density, EDL=15.8±5.8%), but not in Btg2 SS males (TA= 5.1±2.2%, EDL=4.4±2.7%). Females of both strains had angiogenesis (Btg2 BN : TA=9.8±6%, EDL=8.5±1.2%; Btg2 SS : TA=12.7±2.4%, EDL=12.1±4.1%). Btg2 BN females had significantly higher protein excretion than SS and Btg2 SS was significantly lower; males had no significant differences. Btg2 mRNA expression in male skeletal muscle displayed a 2-fold increase (stimulated to unstimulated) in Btg2 BN and a 3.5-fold increase in Btg2 SS . Males had no differences in expression in renal cortex or medulla, but females had significant differences in cortex (Btg2 BN : 1.8±0.2 fold change, Btg2 SS : 0.4±.01). These data suggest Btg2 expression may contribute to the development of hypertension and inhibited angiogenic response in SS rats, with gender-specific differences in the expression of this gene.