Search

Due to rapidly increasing aging and obese population, chronic kidney disease (CKD) and CKD progression to dialysis, is a major health burden. A major factor in promoting CKD in aging is vascular stiffness comprising both large vessel and small vessel stiffness. Therefore, preventative strategies that target vascular stiffening and kidney injury in aging and obese population are an urgent need for improving vascular health and CKD outcomes. There is emerging evidence that the sodium glucose transporter 2 (SGLT2) promotes vascular stiffness and kidney injury under the setting of obesity and aging but mechanism and mediators are not known. In this regard we have reported d SGT2 inhibitor suppression of epithelial sodium channel in the endothelium (EnNaC) promotes endothelial stiffness which, in turn, promotes arterial stiffness, remodeling and inflammation. We have recently shown the key role of EnNaC activation contributing to vascular stiffness and kidney injury in the setting of obesity. Our more recent data suggest the role for EnNaC in mediating age-associated vascular stiffness and injury. We have further reported a role for reported upregulation of a novel serum and glucocorticoid inducible kinase 1 (SGK1)/EnNaC/ pathway that contributes to increased crosslinking of collagen and increased recruitment and activation of macrophages leading to increased aortic and kidney artery stiffness and inflammation. Therefore, our hypothesis is that SGLT2 activation of EnNaC promotes arterial stiffening and kidney injury in aging and obesity. The goal of this proposal is to fill the gap in our knowledge regarding novel mechanisms of age and obesity-associated aortic and renal artery stiffening and inflammation in the development of CKD. In Aim1, we will determine if enhanced activation of SGT2 /EnNaC pathway in aged and obese mice contributes to increased vascular stiffening and inflammation compared to younger control mice. In Aim 2, we will determine the mechanism by which SGLT2 upregulates EnNaC signaling under the setting of aging and obesity. We will use EnNaC KO mice to compare young (6 to 7months) and old (17 to 18 months) mice responses. We will explore distinct pathways and their synergistic effects on arterial stiffening with aging and obesity. To this point, the effects of SGLT2 on pathway specific signaling on EnNaC, through SGK1 signaling and oxidative stress and cytoskeleton/glycocalyx dynamics will be examined. The long-term goal of the proposed work is to determine the cellular and molecular mechanisms responsible for vascular stiffening and kidney injury and to develop strategies to reduce the burden of CKD, especially in aged and obese population.

In US, the number of people with hypertension varies between 80 to 116 million depending on the blood pressure cutoff criteria used and an overwhelming 84% of them are obese/overweight. With rising rates of obesity, the numbers of obese hypertensives are only going to increase. Salt sensitive hypertension constitutes about 50-60% of hypertension, and is more common in obese patients. Activation of the renin angiotensin aldosterone system (RAAS) and sympathetic nervous system contribute to the majority of salt sensitive hypertension. In fact, the mechanisms that lead to salt sensitivity may be interdependent on each other, which may be exacerbated by the high salt content of common US diets. Although the basic physiology of sodium homeostasis has well-established mechanisms, there exist many complex and redundant systems that regulate salt sensitivity beyond RAAS. This is important since inhibitors of RAAS have been used for decades to treat hypertension and salt sensitive hypertension but there are many patients who either cannot tolerate RAAS inhibition or are not sensitive to the inhibitors. In these subsets of patients and in obese hypertensives, it would be imperative to find novel modulators of salt-sensitive hypertension that can address both RAAS dependent and independent mechanisms. Several sodium transporters in the kidney are involved in salt retention/excretion and three medications currently used or approved for use in diabetes and chronic kidney disease (CKD), inhibit proximal (PT) and distal (DT) transporters. The sodium hydrogen exchanger 3 (NHE3), a major controller of sodium reabsorption in the PT, coimmunoprecipitates with dipeptidyl peptidase 4 (DPP4), an exopeptidase also abundantly expressed in the brush border. DPP4 inhibition suppressed sodium uptake into PTs in vitro. In addition, global DPP4KO mice on a high salt (HS) intake (1% NaCl) had increased urine output (UOP) and sodium excretion than DPP4WT littermates. Furthermore, DPP4KO mice fed a low salt (LS) diet (0.02% sodium) put out more sodium in the urine than DPP4WT mice, leading to a negative sodium balance. Similarly, higher sodium excretion and negative sodium balance was seen in obese DPP4KO compared to DPP4WT mice fed a Western Diet (high fat/high sugar). Importantly, obese DPP4KO mice had lower BP than DPP4WT on HS diet, suggesting salt sensitivity. A second transporter in the PT, sodium glucose transporter 2 (SGLT2) when inhibited in obese mice, also demonstrated higher sodium excretion under conditions of both HS and NS feeding, which was associated with reduction in BP. Lastly, epithelial sodium channel (ENaC) in the DT may play a role in salt sensitive hypertension. Taken together, DPP4, SGLT2 and ENaC inhibition may address the salt sensitive portion of hypertension in obesity. Therefore, it is hypothesized that “inhibition of SGLT2, DPP4 and ENaC in different segments of the nephron will regulate salt sensitivity in obesity hypertension”. The hypothesis will be addressed through the following Specific Aims: Aim 1 - investigate the mechanisms by which SGLTi and finerenone regulate salt sensitivity in obesity. Aim 2 - explore the dependence of salt sensitivity on PT and/or DT DPP4 in obese mice.

As the US and World population is aging, the incidence and prevalence of aging associated diseases such as diabetes and hypertension is increasing. Environmental factors such as diet, toxins (promoting) and exercise (mitigating) are thought to play a major role in the aging process. With the ongoing epidemic of overweight/obesity, the incidence of accelerated aging is on the rise. Moreover, it is beginning to be recognized that interorgan communication may play a role in mediating normal aging or accelerating the aging processes in conditions of overweight/obesity. In the cardiovascular system, the heart and the kidney are thought to communicate mostly via hemodynamic mechanisms but also through neural and peptide hormones. Recently, data is accumulating on the communication between organs via extracellular vesicles (EVs) and exosomes carrying proteins and/or microRNA and other modulators of organ injury. These EVs/exosomes “bud” or separate from the parent cell and travel via bloodstream to communicate with another organ. However, nothing is known on the communication between the heart and the kidney in obesity and aging. Normal aging in humans is characterized by diastolic dysfunction in the heart or an entity called heart failure with preserved ejection fraction, development of chronic kidney disease (CKD) with reduction of glomerular filtration rate (GFR) with or without proteinuria and progressive increase in arterial stiffness and hypertension. Similar findings were observed in aged mice which were fed a regular chow or control diet. However, the effect of overweight/obesity in accelerating the aging processes in humans is not well understood. The applicant’s laboratory has developed a Western Diet-fed mouse obesity model that mimics the pathophysiology of human obesity and aging including obesity related kidney disease akin to humans characterized by increasing proteinuria and early hyperfiltration followed by a decline in the GFR. In addition, the obese mice develop early diastolic dysfunction of the heart which increases in severity as the animals age and also develop systolic dysfunction which is not present in the lean aged mice. Moreover, the young obese mice exhibit many characteristics of aging including tissue inflammation, cellular senescence, defects in DNA repair, reactivation of developmental gene programs, stem cell exhaustion and metabolic dysfunction. In essence, the young obese mice exhibit hallmarks of aging evident in old regular chow-fed mice. Therefore, to understand how obesity alters the communication between heart and kidney to worsen aging related pathology and/or accelerates normal aging effects, the applicant will 1. Determine the proteins/signaling pathways that mediate interorgan communication between the heart and kidney in aging. Specifically, the role of EVs and exosomes will be assessed 2. To test whether blocking the communication of said proteins/signaling pathways will slow down the aging process. Specifically, the EVs/exosomes and proteins/pathways involved in aging will be targeted for slowing the processes.

Objective Obesity-related glomerulopathy is characterized initially by glomerular hyperfiltration with hypertrophy and then development of proteinuria. Putative mechanisms include endothelial dysfunction and filtration barrier injury due to oxidant stress and immune activation. There has been recent interest in targeting dipeptidyl peptidase 4 (DPP4) enzyme due to increasing role in non-enzymatic cellular processes. Methods We utilized the Zucker obese (ZO) rat, (aged 8 weeks) fed a normal chow or diet containing the DPP4 inhibitor linagliptin for 8 weeks (83mg/kg rat chow). Results Compared to lean controls, there were increases in plasma DPP4 activity along with proteinuria in ZO rats. ZO rats further displayed increases in glomerular size and podocyte foot process effacement. These findings occurred in parallel with decreased endothelial stromal-derived factor-1α (SDF-1α), increased oxidant markers, and tyrosine phosphorylation of nephrin and serine phosphorylation of the mammalian target of rapamycin (mTOR). DPP4 inhibition improved proteinuria along with filtration barrier remodeling, circulating and kidney tissue DPP4 activity, increased active glucagon like peptide–1 (GLP-1) as well as SDF-1α, and improved oxidant markers and the podocyte-specific protein nephrin. Conclusions These data support a role for DPP4 in glomerular filtration function and targeting DPP4 with inhibition improves oxidant stress-related glomerulopathy and associated proteinuria.