Hyperglycemia alters renal cell responsiveness to pressure in a model of malignant hypertension

The molecular mechanisms of peptidyl-prolyl cis/trans isomerase Pin1 and its relevance to kidney disease

Pin1 is a member of the peptidyl-prolyl cis/trans isomerase subfamily and is widely expressed in various cell types and tissues. Alterations in Pin1 expression levels play pivotal roles in both physiological processes and multiple pathological conditions, especially in the onset and progression of kidney diseases. Herein, we present an overview of the role of Pin1 in the regulation of fibrosis, oxidative stress, and autophagy. It plays a significant role in various kidney diseases including Renal I/R injury, chronic kidney disease with secondary hyperparathyroidism, diabetic nephropathy, renal fibrosis, and renal cell carcinoma. The representative therapeutic agent Juglone has emerged as a potential treatment for inhibiting Pin1 activity and mitigating kidney disease. Understanding the role of Pin1 in kidney diseases is expected to provide new insights into innovative therapeutic interventions and strategies. Consequently, this review delves into the molecular mechanisms of Pin1 and its relevance in kidney disease, paving the way for novel therapeutic approaches.

Response of Renal Podocytes to Excessive Hydrostatic Pressure: a Pathophysiologic Cascade in a Malignant Hypertension Model

BACKGROUND/AIMS

Renal injuries induced by increased intra-glomerular pressure coincide with podocyte detachment from the glomerular basement membrane (GBM). In previous studies, it was demonstrated that mesangial cells have a crucial role in the pathogenesis of malignant hypertension. However, the exact pathophysiological cascade responsible for podocyte detachment and its relationship with mesangial cells has not been fully elucidated yet and this was the aim of the current study.

METHODS

Rat renal mesangial or podocytes were exposed to high hydrostatic pressure in an in-vitro model of malignant hypertension. The resulted effects on podocyte detachment, apoptosis and expression of podocin and integrinβ1 in addition to Angiotensin-II and TGF-β1 generation were evaluated. To simulate the paracrine effect podocytes were placed in mesangial cell media pre-exposed to pressure, or in media enriched with Angiotensin-II, TGF-β1 or receptor blockers.

RESULTS

High pressure resulted in increased Angiotensin-II levels in mesangial and podocyte cells. Angiotensin-II via the AT1 receptors reduced podocin expression and integrinβ1, culminating in detachment of both viable and apoptotic podocytes. Mesangial cells exposed to pressure had a greater increase in Angiotensin-II than pressure-exposed podocytes. The massively increased concentration of Angiotensin-II by mesangial cells, together with increased TGF-β1 production, resulted in increased apoptosis and detachment of non-viable apoptotic podocytes. Unlike the direct effect of pressure on podocytes, the mesangial mediated effects were not related to changes in adhesion proteins expression.

CONCLUSIONS

Hypertension induces podocyte detachment by autocrine and paracrine effects. In a direct response to pressure, podocytes increase Angiotensin-II levels. This leads, via AT1 receptors, to structural changes in adhesion proteins, culminating in viable podocyte detachment. Paracrine effects of hypertension, mediated by mesangial cells, lead to higher levels of both Angiotensin-II and TGF-β1, culminating in apoptosis and detachment of non-viable podocytes.

p66Shc: A novel biomarker of tubular oxidative injury in patients with diabetic nephropathy

Increased p66Shc expression has been associated with diabetic nephropathy (DN). However, whether p66Shc can serve as a potential biomarker for tubular oxidative injury in DN is unknown. We measured the expression of p66Shc in peripheral blood monocytes (PBMs) and renal biopsy tissues from DN patients and then analysed the relationship between p66Shc expression and the clinical characteristics of patients with DN. Patients were divided into 4 groups (class IIa, class IIb, class III and the control group). qPCR, Western blotting and immunohistochemistry were performed. The results showed that both p66Shc and p-p66Shc expression significantly increased in PBMs and kidney tissues of DN patients. Moreover, Spearman’s correlation and multiple regression analyses were carried out. A positive relationship between the p66Shc expression and oxidative stress was found. p66Shc and oxidative stress were significant predictors of the degree of tubular damage. In addition, p66Shc expression was positively correlated with the concentrations of β-NAG, UACR and 8-OHdG, low-density lipoprotein and blood glucose levels, and duration of diabetes in patients with DN from class IIa to class III. These data indicated that increased expression of p66Shc may serve as a therapeutic target and a novel biomarker of DN.

Human kidney proximal tubule cells are vulnerable to the effects of Rauwolfia serpentina

Rauwolfia serpentina (or Snake root plant) is a botanical dietary supplement marketed in the USA for maintaining blood pressure. Very few studies have addressed the safety of this herb, despite its wide availability to consumers. Its reported pleiotropic effects underscore the necessity for evaluating its safety. We used a human kidney cell line to investigate the possible negative effects of R. serpentina on the renal system in vitro, with a specific focus on the renal proximal tubules. We evaluated cellular and mitochondrial toxicity, along with a variety of other kidney-specific toxicology biomarkers. We found that R. serpentina was capable of producing highly detrimental effects in our in vitro renal cell system. These results suggest more studies are needed to investigate the safety of this dietary supplement in both kidney and other target organ systems.

New insight into the molecular drug target of diabetic nephropathy

Diabetic nephropathy (DN) lowered quality of life and shortened life expectancy amongst those affected. Evidence indicates interaction between advanced glycation end products (AGEs), activated protein kinase C (PKC) and angiotensin II exacerbate the progression of DN. Inhibitors of angiotensin-converting enzyme (ACEIs), renin angiotensin aldosterone system (RAAS), AGEs, and PKC have been tested for slowing down the progression of DN. The exact molecular drug targets that lead to the amelioration of renal injury in DN are not well understood. This review summarizes the potential therapeutic targets, based on putative mechanism in the progression of the disease.

Mesangial cells are responsible for orchestrating the renal podocytes injury in the context of malignant hypertension

AIM

Two populations of renal cells fully possess functional contractile cell apparatus: mesangial cells and podocytes. Previous studies demonstrated that in the context of malignant hypertension overproduction of Angiotensin-II by the contracting mesangial cells aggravated hypercellularity and apoptosis of adjacent cell populations. The role of podocytes in pathogenesis of malignant hypertension is unclear. We investigated responsiveness of normal vs. hyperglycaemic podocytes to pressure in a model of malignant hypertension.

METHODS

Rat renal podocytes and mesangial cells were subjected to high hydrostatic pressure, using an in vitro model of malignant hypertension. Part of them was pre-exposed to hyperglycaemic medium. Alternatively, the cells were cultured in conditioned medium collected from mesangial cells pre-exposed to pressure.

RESULTS

Angiotensin-II was significantly increased in normoglycaemic mesangial cells subjected to pressure, triggering enhanced proliferation and apoptosis. No augmented Angiotensin-II, proliferation or apoptosis were evident in pressure-exposed normoglycaemic podocytes. In hyperglycaemic mesangial cells, but not podocytes, basal Angiotensin-II and apoptosis were augmented, along with abrogated proliferation. Challenge with exogenous Angiotensin-II or Angiotensin-II-containing conditioned medium, induced apoptosis both in podocytes and mesangial cells.

CONCLUSIONS

1. Unlike mesangial cells, podocytes do not respond to high pressure or hyperglycaemia per se. Resultantly, neither high pressure nor hyperglycaemia, trigger apoptosis of podocytes in vitro. However, surplus of Angiotensin-II, amply produced in vivo by the adjacent mesangial cells, would seem to be sufficient for initiating apoptosis of both mesangial cells and podocytes. 2. Hyperglycaemia abrogates cell replication. Resultantly, in diabetic patients regeneration of renal tissue damaged by the incidence of malignant hypertension may become compromised or completely lost.

Hyperglycaemia emerging during general anaesthesia induces rat acute kidney injury via impaired microcirculation, augmented apoptosis and inhibited cell proliferation

AIM

Major surgery under general anaesthesia frequently triggers acute kidney injury by yet unknown mechanisms. We investigated the role of anaesthesia-triggered systemic hyperglycaemia in impairment of renal functioning, renal tissue injury, intra-renal Angiotensin-II synthesis and endogenous insulin production in anaesthetized rats.

METHODS

Eighty-eight Sprague-Dawley rats underwent general anaesthesia for 1 h by different anaesthetic compounds. Some of the animals were either injected with high glucose, or received insulin prior to anaesthesia. Blood pressure, renal functioning estimated by cystatin-C and urea, renal perfusion evaluated by laser Doppler technique, blood glucose and insulin were surveyed. Subsequently, rat kidneys were excised, to be used for immunohistochemical examinations or preparation of renal extracts for intra-renal Angiotensin-II measurements.

RESULTS

Elevated blood sugar was observed 5 min following induction of anaesthesia, concurrently with deterioration of renal functioning, drop of systemic blood pressure and decreased renal blood flow. Blood insulin concentrations positively correlated with glucose levels. Intra-renal Angiotensin-II was significantly augmented. Immunohistochemical examinations demonstrated enhanced staining for pro-apoptotic proteins and negligible cell proliferation in tubular tissues. Renal damage resultant from anaesthesia-induced hyperglycaemia could be attenuated by insulin injections. Rats challenged with glucose prior to anaesthesia demonstrated cumulative hyperglycaemia, further increase in insulin secretion, drop of renal blood flow and increased apoptosis. The effects were specific, since they could not be mimicked by replacing glucose with mannose.

CONCLUSION

Anaesthesia-induced hyperglycaemia affects intra-renal auto-regulation via decreased renal perfusion, thus triggering renal function deterioration and tubular injury. Increased intra-renal Angiotensin-II aggravates the damage. Tight hypoglycaemic control might prevent or, at least, attenuate anaesthesia-induced renal injury.

p66Shc mediates high-glucose and angiotensin II-induced oxidative stress renal tubular injury via mitochondrial-dependent apoptotic pathway

p66Shc, a promoter of apoptosis, modulates oxidative stress response and cellular survival, but its role in the progression of diabetic nephropathy is relatively unknown. In this study, mechanisms by which p66Shc modulates high-glucose (HG)- or angiotensin (ANG) II-induced mitochondrial dysfunction were investigated in renal proximal tubular cells (HK-2 cells). Expression of p66Shc and its phosphorylated form (p-p66Shc, serine residue 36) and apoptosis were notably increased in renal tubules of diabetic mice, suggesting an increased reactive oxygen species production. In vitro, HG and ANG II led to an increased expression of total and p-p66Shc in HK-2 cells. These changes were accompanied with increased production of mitochondrial H(2)O(2), reduced mitochondrial membrane potential, increased translocation of mitochondrial cytochrome c from mitochondria into cytosol, upregulation of the expression of caspase-9, and ultimately reduced cell survival. Overexpression of a dominant-negative Ser36 mutant p66Shc (p66ShcS36A) or treatment of p66Shc- or PKC-β-short interfering RNAs partially reversed these changes. Treatment of HK-2 cells with HG and ANG II also increased the protein-protein association between p-p66Shc and Pin1, an isomerase, in the cytosol, and with cytochrome c in the mitochondria. These interactions were partially disrupted with the treatment of PKC-β inhibitor or Pin1-short interfering RNA. These data suggest that p66Shc mediates HG- and ANG II-induced mitochondrial dysfunctions via PKC-β and Pin1-dependent pathways in renal tubular cells.