Functional implications of sexual dimorphism of transporter patterns along the rat proximal tubule: modeling and analysis

Sex differences in diabetes and kidney disease: mechanisms and consequences

Type 1 and type 2 diabetes, along with their accompanying hyperglycemia, are associated with a multitude of comorbidities including the development of diabetic kidney disease. Although the hallmarks of these metabolic disorders have been well characterized in population and animal studies, it is becoming increasingly apparent that diabetes manifests itself differently in men and women. This review summarizes the recent diabetic literature with a focus on known sex differences in clinical and preclinical studies. It explores the physiological differences of glucose handling and the development of diabetes between men and women. This review also uncovers potential mechanisms for these differences, honing in on the vital role that sex hormone signaling plays in the progression of diabetes and renal complications.

A model of uric acid transport in the rat proximal tubule

The objective of the present study was to theoretically investigate the mechanisms underlying uric acid transport in the proximal tubule (PT) of rat kidneys, and their modulation by factors, including Na+, parathyroid hormone, ANG II, and Na+-glucose cotransporter-2 inhibitors. To that end, we incorporated the transport of uric acid and its conjugate anion urate in our mathematical model of water and solute transport in the rat PT. The model accounts for parallel urate reabsorption and secretion pathways on apical and basolateral membranes and their coupling to lactate and α-ketoglutarate transport. Model results agree with experimental findings at the segment level. Net reabsorption of urate by the rat PT is predicted to be ~70% of the filtered load, with a rate of urate removal from the lumen that is 50% higher than the rate of urate secretion. The model suggests that apical URAT1 deletion significantly reduces net urate reabsorption across the PT, whereas ATP-binding cassette subfamily G member 2 dysfunction affects it only slightly. Inactivation of basolateral glucose transporter-9 raises fractional urate excretion above 100%, as observed in patients with renal familial hypouricemia. Furthermore, our results suggest that reducing Na+ reabsorption across Na+/H+ exchangers or Na+-glucose cotransporters augments net urate reabsorption. The model predicts that parathyroid hormone reduces urate excretion, whereas ANG II increases it. In conclusion, we have developed the first model of uric acid transport in the rat PT; this model provides a framework to gain greater insight into the numerous solutes and coupling mechanisms that affect the renal handing of uric acid.

Understanding sex differences in long-term blood pressure regulation: insights from experimental studies and computational modeling

Sex differences in blood pressure and the prevalence of hypertension are found in humans and animal models. Moreover, there has been a recent explosion of data concerning sex differences in nitric oxide, the renin-angiotensin-aldosterone system, inflammation, and kidney function. These data have the potential to reveal the mechanisms underlying male-female differences in blood pressure control. To elucidate the interactions among the multitude of physiological processes involved, one may apply computational models. In this review, we describe published computational models that represent key players in blood pressure regulation, and highlight sex-specific models and their findings.

Renal olfactory receptor 1393 contributes to the progression of type 2 diabetes in a diet-induced obesity model

Olfactory receptors are G protein-coupled receptors that serve to detect odorants in the nose. Additionally, these receptors are expressed in other tissues, where they have functions outside the canonical smell response. Olfactory receptor 1393 (Olfr1393) was recently identified as a novel regulator of Na⁺-glucose cotransporter 1 (Sglt1) localization in the renal proximal tubule. Glucose reabsorption in the proximal tubule (via Sglt1 and Sglt2) has emerged as an important contributor to the development of diabetes. Inhibition of Sglt2 is accepted as a viable therapeutic treatment option for patients with type 2 diabetes and has been shown to delay development of diabetic kidney disease. We hypothesized that Olfr1393 may contribute to the progression of type 2 diabetes, particularly the development of hyperfiltration, which has been linked to increased Na⁺ reabsorption in the proximal tubule via the Sglts. To test this hypothesis, Olfr1393 wild-type (WT) and knockout (KO) mice were challenged with a high-fat diet to induce early-stage type 2 diabetes. After 16 wk on the high-fat diet, fasting blood glucose values were increased and glucose tolerance was impaired in the male WT mice. Both of these effects were significantly blunted in the male KO mice. In addition, male and female WT mice developed diabetes-induced hyperfiltration, which was attenuated in the Olfr1393 KO mice and corresponded with a reduction in luminal expression of Sglt2. Collectively, these data indicate that renal Olfr1393 can contribute to the progression of type 2 diabetes, likely as a regulator of Na⁺-glucose cotransport in the proximal tubule.

Sex-specific long-term blood pressure regulation: Modeling and analysis

Hypertension is a global health challenge: it affects one billion people worldwide and is estimated to account for >60% of all cases or types of cardiovascular disease. In part because sex differences in blood pressure regulation mechanisms are not sufficiently well understood, fewer hypertensive women achieve blood pressure control compared to men, even though compliance and treatment rates are generally higher in women. Thus, the objective of this study is to identify which factors contribute to the sexual dimorphism in response to anti-hypertensive therapies targeting the renin angiotensin system (RAS). To accomplish that goal, we develop sex-specific blood pressure regulation models. Sex differences in the RAS, baseline adosterone level, and the reactivity of renal sympathetic nervous activity (RSNA) are represented. A novel aspect of the model is the representation of sex-specific vasodilatory effect of the bound angiotensin II type two receptor (AT2R-bound Ang II) on renal vascular resistance. Model simulations suggest that sex differences in RSNA are the largest cause of female resistance to developing hypertension due to the direct influence of RSNA on afferent arteriole resistance. Furthermore, the model predicts that the sex-specific vasodilatory effects of AT2R-bound Ang II on renal vascular resistance may explain the higher effectiveness of angiotensin receptor blockers in treating hypertensive women (but not men), compared to angiotensin converting enzyme inhibitors.