Sex-Based Differences in Proximal Tubule Endocytic Capacity in Mice

Abstract

Women are more protected from acute kidney injury, and chronic kidney disease (CKD) in women progresses more slowly to end-stage renal disease compared to men. CKD involves changes in the integrity of the glomerular barrier function with consequent proteinuria. The kidney proximal tubule (PT) normally reclaims albumin and other filtered proteins via receptor-mediated endocytosis facilitated by the multiligand receptors megalin and cubilin. PT health, and ultimately kidney function, is impacted by the uptake of excess albumin and by nephrotoxic drugs that enter cells in a megalin/cubilin dependent manner. Recent transcriptomic studies in mice have shown differences in the expression of megalin and cubilin between males and females and across the S1, S2, and S3 sub-segments that comprise the PT. Additionally, reduced reabsorption of water and salt by the PT has been demonstrated in female rodents. These differences in PT receptor expression and functionality likely contribute to sex-based differences in PT endocytic capacity. To determine if there are sex-based differences in the recovery of filtered proteins by the PT, urine and kidney tissue were collected from five male and five female 13-week-old C57BL/6 mice. Urinary albumin was quantified by ELISA. Kidneys were processed for Western blotting and immunofluorescence staining. We used imaging-based approaches to quantify the expression and distribution of albumin, megalin, and cubilin in SGLT2-positive S1 and SGLT2-negative, OAT1-positive S2 segments. Under normal conditions, S1 had greater intensity of subapical albumin staining in both males and females. However, females had greater intensity of albumin staining in S2 normalized to S1 compared to males. Female mice had lower levels of urinary albumin excretion when normalized to creatinine than males. Female mice had greater expression of total megalin (1.5x) and cubilin (1.4x) and decreased expression of NHE3 (0.7x) in the kidney cortex. Male and female mice had similar levels of megalin expression and surface localization in S1, however female mice had greater expression and surface localization of megalin in S2. Males had greater colocalization of megalin with lysosomal marker, LAMP1. In both males and females, the colocalization of megalin with LAMP1 decreased from S1 to S2. Together, these data suggest that, at baseline in female mice, S2 has greater endocytic capacity and contributes more to the uptake of normally filtered albumin than in males. This increased capacity could explain the reduced urinary excretion of albumin observed in rodent injury models and in women with CKD. Current studies are focused on incorporating these sex-based differences into a multiscale mathematical model of protein uptake along the length of the PT. National Institutes of Health: T32 DK007052, F31 DK121394, R01 DK125049, R01 DK118726, R01 DK083785, S10 OD021627, S10 OD028596, U54 DK137329, ASN Foundation for Kidney Research Pre-Doctoral Fellowship Award. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.