Exploring Sex Differences in Renal Sodium Transporters with Four Core Genotype (FCG) Model

In the kidney, sex-specific differences in Na+ transporter profiles along the nephron are now evident ("transporters" = co-transporters, channels, claudins and pumps, their phosphorylation (p)): females (F) exhibit variable differences vs males (M) along the proximal tubule (PT) and higher distal (DT) and collecting duct (CD) Na+ transporter abundance and activity vs. M. Circulating levels of gonadal hormones determine sex differences in many physiologic traits, however, recent studies indicate that sex differences may also be due to the sex chromosome complement (SCC; XX vs.XY). The novel FCG C57BL/6 mouse model dissociates gonadal sex (ovaries (F) or testes (M)) from sex chromosomal complement (SCC; XX, XY). That is, traits influenced by gonadal hormones are similar between MXX and MXY (testes) vs FXX and FXY (ovaries); whereas traits influenced by SCC are similar between MXX and FXX vs. MXY and FXY (independent of gonads). METHOD: We implemented the 4CG model with transporter profiling (semi-quantitative immunoblotting; n = 4-5 mice/genotype) to reveal the contributions of gonadal hormones vs. SCC on the sexual dimorphisms in transporter protein abundance along the nephron. RESULTS: (all P<0.05): Along the PT: OAT1 was lower and AQP1 and SGLT2 higher in abundance in gonadal F (FXX) vs M (MXY); SCC also contributed to differences: NHE3 was lower by 15-30% in MXX vs. MXY and SGLT2 was 15% lower in FXY vs FXX. Inthe medullary thick ascending limb (TAL): alpha and beta NKATPase are 60% higher in FXX vs MXY and 25-30% lower in FXY vs FXX; alpha was 15% lower in MXX vs. MXY. Along the cortical TAL and DT: NKCC2, NKCC2p, NCC, NCCp, alpha and beta NKATPase, claudin 7, SPAK and SPAKp kinase abundance were 1.4 - 2.6 - fold higher in FXX vs MXY; SCC differences were limited to 15%, 30%, and 20% lower NCC, and NCCp, and claudin 7 in MXX vs MXY, respectively. Along the CD: ENaC subunits were 30-50% higher, claudin-8 2-fold higher, pendrin and UMOD 20% higher in FXX vs. MXY; SCC differences included 15-20% lower ROMK and Kir 4.1 and ENaC beta and gamma subunits in MXX vs MXY. Results provide evidence for impact of both gonadal hormones and SCC on kidney transporter abundance, in some cases, offsetting the effects of the other. Further progress will come from defining whether X vs Y genes contribute to the differences. These findings have potential impact on electrolyte and blood pressure (patho)physiology in F vs. M.