The genetics of hypertension modifies the renal cell replication response induced by experimental diabetes

Diabetes and pregnancy in Wistar rats: renal effects for mothers in the postpartum period

In this study, diabetes mellitus (DM) was induced in Wistar rats during pregnancy and maintained in the postpartum period (PP) and we evaluated systolic blood pressure (SBP), glomerular filtration rate (GFR) and renal immunohistochemical and morphometric studies from different groups: G1 (non-pregnant control rats), G2 (non-pregnant diabetic rats), G3 (control mothers) and G4 (diabetic mothers). We found that there were no differences in relation to SBP, but there was a tendency for reduction in GFR from G4 compared with the other groups (G). There was increased total kidney weight/body weight ratio of G4 compared with other G. There were increase in glomerular tuft area in G3 and G4 compared with G1 and G2. G2 and G4 showed even higher percentage of cortical collagen. G3 showed increased glomerular proliferating cells compared with G1 and G2, while in G4 this number was smaller than G3. Cell proliferation was higher in the tubulointerstitial (TBI) compartment from G4. Glomerular and TBI α-smooth muscle actin expression was increased in G4 compared with other G. The glomerular p-p38 expression showed a pattern similar to proliferation cell nuclear antigen, with a reduction of p-p38 in G4 relative to other G. The immunoreactivity of p-JNK was higher in both the glomeruli and TBI compartment in G4 compared with G1, G2 and G3. The DM induced during pregnancy and maintained in the PP resulted in renal structural and functional changes to mothers. In addition, altered mitogen-activated protein kinase expression in association with these changes may play an important role in renal damage observed in the present investigation.

NMDA receptors participate in the progression of diabetic kidney disease by decreasing Cdc42-GTP activation in podocytes

Podocytes play important roles in the progression of diabetic kidney disease (DKD) and these roles are closely associated with cytoskeletal actin dynamics. N-Methyl-d-aspartate receptors (NMDARs), which consist of two functional NR1 subunits and two regulatory NR2 subunits, are widely expressed in the brain but are also found in podocytes. Here, we found increased NR1 expression in two diabetic mouse models and in podocytes incubated in high glucose (HG). In diabetic mice, knockdown of NR1 using lentivirus carrying NR1-shRNA ameliorated the pathological features associated with DKD, and reversed the decreased expression of synaptopodin and Wilms' tumour-1. In podocytes incubated with HG, NR1 was secreted from the endoplasmic reticulum and this was blocked by bisindolylmaleimide I. NR1 knockdown decreased the cell shape remodelling, cell collapse, bovine serum albumin permeability, and migration induced by HG. After HG incubation, levels of cell division control protein 42 (Cdc42) and its active form increased, and a significantly higher Cdc42-GTP level, increased Cdc42 translocation onto the leading edges, and lower migration ability were found in podocytes with NR1 knockdown. Increases in the number and length of filopodia were found in podocytes with NR1 knockdown but these were abolished by Cdc42-GTP blockade with ML141. In conclusion, the activation of NMDARs plays an important role in DKD by reducing Cdc42-GTP activation. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Tempol reduces podocyte apoptosis via PARP signaling pathway in experimental diabetes mellitus

BACKGROUND/AIMS

In diabetic hypertensive rats, tempol reduces albuminuria by restoring the redox imbalance. Increased formation of reactive oxygen species leading to activation of poly(ADP-ribose) polymerase (PARP)-1 and podocyte loss by apoptosis contribute to albuminuria in diabetes mellitus (DM). In the present study, we investigated the hypothesis that in DM tempol reduces albuminuria by inhibition of PARP-induced podocyte apoptosis.

METHODS

DM was induced in 4-week-old spontaneously hypertensive rats by streptozotocin. Mouse and human podocyte cell lines were cultured in normal or high-glucose conditions, with or without tempol and/or a PARP-1 inhibitor, PJ34.

RESULTS

In diabetic rats, tempol treatment did not affect plasma glucose levels or systolic blood pressure. Albuminuria was higher in diabetic rats, and it was reduced by tempol. DM leads to an elevation of glomerular apoptotic cells and to podocyte loss; both were prevented by tempol treatment. DM increases the expression of poly(ADP-ribose)-modified proteins in isolated glomeruli, and it was reduced by tempol. In vitro, high glucose increased caspase-3 activity and led to a higher number of apoptotic cells that were prevented by tempol and the PARP-1 inhibitor.

CONCLUSION

In DM, tempol reduces albuminuria associated with reduction of podocyte apoptosis and decreasing oxidative stress via PARP signaling.

The contribution of hypertension to diabetic nephropathy and retinopathy: the role of inflammation and oxidative stress

Diabetes and hypertension frequently coexist and constitute the most notorious combination for the pathogenesis of diabetic nephropathy and retinopathy. Large clinical trials have clearly demonstrated that tight control of glycemia and/or blood pressure significantly reduces the incidence and progression of diabetic retinopathy (DR) and nephropathy. However, the mechanism by which hypertension interacts with diabetes to induce and/or exacerbate nephropathy and retinopathy is very unclear. Substantial evidence implicates the involvement of chronic inflammation and oxidative stress in the pathogenesis of DR and nephropathy. In addition, hypertension causes oxidative stress and inflammation in the kidney and retina. In the present review, we summarized data obtained from our research along with those from other groups to better understand the role of hypertension in the pathogenesis of diabetic nephropathy and retinopathy. It is suggested that oxidative stress and inflammation may be common denominators of kidney and retinal damage in the concomitant presence of diabetes and hypertension.

Which comes first: Renal inflammation or oxidative stress in spontaneously hypertensive rats?

The present study was undertaken to identify whether inflammation or oxidative stress is the primary abnormality in the kidney in spontaneously hypertensive rats (SHR). Renal inflammation and oxidative stress were evaluated in 2- and 3-week-old prehypertensive SHR and age-matched genetically normotensive control Wistar-Kyoto (WKY) rats. Blood pressure was similar in WKY and SHR rats at 2 and 3 weeks, of age. Renal inflammation (macrophage and nuclear factor-kappaB) was elevated in SHR at 3 weeks, but not at 2 weeks, of age compared with age-matched WKY rats. Renal oxidative stress (nitrotyrosine, 8-hydroxy-2'-deoxyguanosine and p47phox) was also clearly elevated in 3-week-old SHR compared with age-matched WKY rats. Additionally, NADPH oxidase subunit p47phox was found elevated in 2-week-old SHR compared to age-matched WKY rats. Moreover, antioxidant (N-acetyl-L-cysteine and Tempol) treatment reduced renal inflammation in prehypertensive SHR. We therefore conclude that the oxidative stress appears before inflammation as a primary abnormality in the kidney in prehypertensive SHR.

Arterial hypertension exacerbates oxidative stress in early diabetic retinopathy

The present study was undertaken to investigate the redox status in the retina of an experimental model that combines hypertension and diabetes. Spontaneously hypertensive rats (SHR) and their control Wystar Kyoto (WKY) rats were rendered diabetic and, after 20 days, the rats were sacrificed and the retinas collected. The superoxide production was higher in diabetic than in control WKY (p < 0.03) and SHR rats showed elevated superoxide production compared with WKY groups (p < 0.009). The glutathione antioxidant system was diminished only in diabetic SHR (p < 0.04). Tirosyne nitration was higher in diabetic WKY and control SHR compared with control WKY (p < 0.03), and further increment was observed in diabetic SHR (p < 0.02). The DNA damage estimated by immunohystochemistry for 8-OHdG was higher in control SHR than in WKY, mainly in diabetic SHR (p < 0.0001). Hypertension aggravates oxidative-induced cytotoxicity in diabetic retina due to increasing of superoxide production and impairment of antioxidative system.

Prevention of hypertension abrogates early inflammatory events in the retina of diabetic hypertensive rats

Hypertension is an important risk factor associated with development and progression of diabetic retinopathy (DR). The mechanisms by which hypertension increases the risk for DR are poorly understood. As the inflammatory mechanisms play a pivotal role in the pathogenesis of DR, in the present study, we investigated the effects of diabetes, hypertension, and combination of diabetes and hypertension on early inflammatory phenomena in the retina, and the effects of blood pressure control on retinal inflammation. Four-week-old spontaneously hypertensive rats (SHR) and their normotensive counterpart Wistar Kyoto (WKY) rats were rendered diabetic by intravenous injection of streptozotocin. Diabetic SHR rats were randomized to receive no antihypertensive drug (Sd), an antihypertensive drug that acts on renin-angiotensin system (losartan, Sd+Los), or antihypertensive drug that do not affect renin-angiotensin system (triple therapy, Sd+Tri). After 20 days, rats were sacrificed and the retinas were collected. The number of immunohistochemically detected ED1/microglial positive cells and the expression of ICAM-1 in the retina were significantly higher in diabetic SHR than in control SHR (p=0.003). The NF-kappaB p65 levels were higher in SHR compared with WKY groups (p=0.001) and its increment in diabetic SHR was not significant. These abnormalities in diabetic SHR rats were completely prevented by both types of antihypertensive drugs. The concomitance of diabetes and hypertension leads to exuberant inflammatory response in the retina, and the prevention of hypertension abrogates these abnormalities. It is suggested that the inflammatory events may be involved in the mechanism by which hypertension exacerbates retinopathy in patients with diabetes.

Prevention of Hypertension with or without Renin-Angiotensin System Inhibition Precludes Nephrin Loss in the Early Stage of Experimental Diabetes Mellitus

BACKGROUND AND AIMS

Several lines of clinical evidence support the concept that the reduction of blood pressure may be useful in the prevention of diabetic kidney disease. In young diabetic spontaneously hypertensive rats (SHR), prevention of hypertension reduces several early renal abnormalities including albuminuria. However, the contribution of nephrin loss to albuminuria in this early stage of experimental diabetes is unknown. Therefore, we investigated whether elevation of albuminuria in young diabetic SHR is associated with nephrin loss, and if prevention of hypertension, with or without inhibition of the renin-angiotensin system, precludes these abnormalities.

METHODS

Diabetes was induced by streptozotocin injection in 4-week-old still normotensive SHR and their genetically normotensive control, Wistar-Kyoto rats. Diabetic SHR were randomized for no treatment, or treatment with captopril, losartan, or triple therapy (hydrochlorothiazide, reserpine and hydralazine) for 20 days.

RESULTS

The increase in systolic blood pressure was equally prevented by all treatments. Albuminuria was higher in diabetic SHR and similarly reduced (p < 0.05) by captopril, losartan, and triple therapy. Glomerular expression of nephrin was significantly reduced in diabetic SHR in comparison with non-diabetic controls. The antihypertensive treatment prevented the reduction in glomerular expression of nephrin.

CONCLUSIONS

These results demonstrate that the loss of nephrin is associated with albuminuria in a model of genetic hypertension and diabetes, and that the prevention of development of hypertension restores nephrin and prevents albuminuria. This finding suggests a crucial role of blood pressure in diabetes as determinant of nephrin expression and albuminuria.

Hypertension induces oxidative stress but not macrophage infiltration in the kidney in the early stage of experimental diabetes mellitus

BACKGROUND

The combination of diabetes and hypertension increases the incidence and severity of kidney disease in an additive manner. Inflammatory and oxidative stress mechanisms contribute to renal damage in both diabetes and hypertension. Therefore, we investigated whether renal macrophage infiltration and oxidative stress events are additive from the beginning in diabetic animals with coexisting hypertension.

METHODS

Diabetes was induced in spontaneously hypertensive rats (SHRs) and their genetically normotensive control Wistar Kyoto (WKY) rats by streptozotocin injection at 12 weeks of age for 10 days, and the effects of hyperglycemia on renal macrophage infiltration and oxidative stress were evaluated.

RESULTS

Blood pressure was higher in SHR than in WKY groups. Markers of oxidative stress-induced DNA and protein modification, 8-hydroxy- 2'-deoxyguanosine (8-OHdG) and nitrotyrosine, respectively, and the antioxidant glutathione levels were found to be similar in WKY-control and WKY-diabetic groups. However, 8-OHdG was significantly elevated (p = 0.014), the nitrotyrosine level tended to be elevated (p = 0.068) and the glutathione level was significantly reduced (p = 0.034) in the SHR-diabetic group compared to the SHR-control group. On the other hand, glomerular and tubulointerstitial macrophage infiltration was significantly higher in both WKY-diabetic and SHR-diabetic groups than the respective control groups.

CONCLUSIONS

A short duration of diabetes mellitus induces renal oxidative stress in the presence of hypertension; however, renal macrophage infiltration becomes evident in early diabetes regardless of the presence or absence of hypertension. We conclude that the combination of diabetes and hypertension adversely affects oxidative stress in the kidney, but the combination has no additive effect on renal macrophage infiltration, at least in early diabetes.

Effects of tight blood pressure control on glomerular hypertrophy in a model of genetic hypertension and experimental diabetes mellitus

The aim of this study was to evaluate the effect of prevention of hypertension on glomerular hypertrophy, renal cell replication and accumulation of glomerular fibronectin in a model of genetic hypertension and experimental diabetes. Four-week-old streptozotocin induced spontaneously hypertensive rats (SHR) were randomized for no treatment, or for treatment with captopril, losartan or triple therapy (hydrochlorothiazide, reserpine and hydralazine) for 20 days. Increase in systolic blood pressure was equally prevented by captopril (118+/-15 mmHg), losartan (111+/-9) and triple therapy (112+/-14, p<0.0001). Glomerular size was higher (p<0.005) in diabetic SHR (27,300+/-2130 microm(2)) compared with non-diabetic SHR (23,800+/-307). The antihypertensive therapy with captopril (23,900+/-175), losartan (23,800+/-120), and triple therapy (23,400+/-210) prevented the glomerular enlargement in diabetic SHR. Glomerular expression of fibronectin was increased in diabetic SHR (7.61+/-1.22 densitometric unit) as compared to the controls (2.27+/-2.15, p<0.0001), and was decreased (p<0.0001 vs diabetic SHR) with captopril (2.49+/-1.42), losartan (1.57+/-1.1) and triple therapy (2.04+/-1.42). The number of replicating glomerular cell significantly decreased in diabetic SHR and it was restored by all three antihypertensive regimes. The glomerular expression of p27(Kip1) was increased in diabetic SHR but it was not modified by antihypertensive treatment. Strict blood pressure control, in diabetic SHR independently of the class of antihypertensive agent, restores glomerular hypertrophy and renal cellular replication, and prevents the increment in glomerular fibronectin.

Functional and structural postglomerular alterations in the kidney of prehypertensive spontaneously hypertensive rats

The kidney plays a major role in the development of hypertension. Following the Borst-Guyton theory of an altered set-point for fluid and electrolyte homeostasis we aim to investigate functional and structural renal parameter during the development of hypertension. Therefore we focus on counter current exchange related factors. We compared 4 and 8 weeks old Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) concerning basic renal parameters as creatinine and phosphorus clearance and urinary osmolality. Mean arterial pressure (MAP) was measured intra-arterially. Vasa recta were investigated using immunohistochemistry for alpha-smooth-muscle actin (ASMA) and plastification for geometric analyses. Blood pressure was not yet significantly elevated in SHR at 4 weeks but at 8 weeks it was higher in SHR (116+/-7 vs. 102+/-4 mm Hg; p<0.01). Kidney weight/body weight ratio was lower in SHR at both ages. In 4 weeks old SHR, phosphorus clearance and urinary osmolality were decreased compared to WKY [0.02+/-0.01 vs. 0.05+/-0.02 (ml/min* 100 g BW) p < 0.03; 14.2+/-2.2 vs. 18.9+/-2.9 (osmol/kg*24 h urine) p < 0.051 indicating reduced tubular reabsorption. At 8 weeks phosphorus clearance and urinary osmolality were comparable to WKY. alpha-Actin was found in vasa recta in a 4-times higher degree in SHR with a predominant location in the outer medulla. Radii of vasa recta in the outer medulla decreased during development. In plastificated sections vasa recta of SHR revealed sphincter-like pattern. Functional and structural alterations related to the counter current exchanger are already evident in prehypertensive SHR. During development of hypertension both factors get adapted to higher blood pressure level. Sphincter-like structures in vasa recta suggest contractility of pericytes/vascular smooth muscle cells (vSMC). As these were just seen in SHR that might allude to a higher potential to contract. We conclude that differences in postglomerular structure and function may contribute to the development of hypertension in SHR.