Comparative Analysis of Hypertensive Tubulopathy in Animal Models of Hypertension and Its Relevance to Human Pathology.

Assessment of hypertensive tubulopathy for more than fifty animal models of hypertension in experimental pathology employs criteria that do not correspond to lesional descriptors for tubular lesions in clinical pathology. We provide a critical appraisal of experimental hypertension with the same approach used to estimate hypertensive renal tubulopathy in humans. Four models with different pathogenesis of hypertension were analyzed-chronic angiotensin (Ang) II-infused and renin-overexpressing (TTRhRen) mice, spontaneously hypertensive (SHR), and Goldblatt two-kidney one-clip (2K1C) rats. Mouse models, SHR, and the nonclipped kidney in 2K1C rats had no regular signs of hypertensive tubulopathy. Histopathology in animals was mild and limited to variations in the volume density of tubular lumen and epithelium, interstitial space, and interstitial collagen. Affected kidneys in animals demonstrated lesion values that are significantly different compared with healthy controls but correspond to mild damage if compared with hypertensive humans. The most substantial human-like hypertensive tubulopathy was detected in the clipped kidney of 2K1C rats. For the first time, our study demonstrated the regular presence of chronic progressive nephropathy (CPN) in relatively young mice and rats with induced hypertension. Because CPN may confound the assessment of rodent models of hypertension, proliferative markers should be used to verify nonhypertensive tubulopathy.

The Proteome of Circulating Large Extracellular Vesicles in Diabetes and Hypertension.

Hypertension and diabetes induce vascular injury through processes that are not fully understood. Changes in extracellular vesicle (EV) composition could provide novel insights. Here, we examined the protein composition of circulating EVs from hypertensive, diabetic and healthy mice. EVs were isolated from transgenic mice overexpressing human renin in the liver (TtRhRen, hypertensive), OVE26 type 1 diabetic mice and wild-type (WT) mice. Protein content was analyzed using liquid chromatography-mass spectrometry. We identified 544 independent proteins, of which 408 were found in all groups, 34 were exclusive to WT, 16 were exclusive to OVE26 and 5 were exclusive to TTRhRen mice. Amongst the differentially expressed proteins, haptoglobin (HPT) was upregulated and ankyrin-1 (ANK1) was downregulated in OVE26 and TtRhRen mice compared with WT controls. Conversely, TSP4 and Co3A1 were upregulated and SAA4 was downregulated exclusively in diabetic mice; and PPN was upregulated and SPTB1 and SPTA1 were downregulated in hypertensive mice, compared to WT mice. Ingenuity pathway analysis identified enrichment in proteins associated with SNARE signaling, the complement system and NAD homeostasis in EVs from diabetic mice. Conversely, in EVs from hypertensive mice, there was enrichment in semaphroin and Rho signaling. Further analysis of these changes may improve understanding of vascular injury in hypertension and diabetes.

High fat diet is protective against kidney injury in hypertensive-diabetic mice, but leads to liver injury.

Chronic kidney disease (CKD) is a worldwide health burden with increases risk of end-stage renal function if left untreated. CKD induced in the context of metabolic syndrome (MS) increases risks of hypertension, hyperglycemia, excess body fat and dyslipidemia. To test if combining a high-fat diet (HFD) regimen onto the hypertensive/ diabetic phenotype would mimic features of MS induced-CKD in mice, hyperglycemia was induced in genetically hypertensive mice (Lin), followed by HFD regimen. For that, 8-week-old male were subjected to streptozotocin (STZ) intraperitoneal (i.p.) injections (50 mg/kg, 5 days consecutive). LinSTZ were fed a 60% kCal HFD for 8 weeks. Lin mice treated with STZ developed polydipsia, became hypertensive and hyperglycemic. HFD induced weight gain, protected against glomerular hypertrophy, scarring, and albuminuria at endpoint compared to regular diet fed LinSTZ. On the other hand, HFD induced steatosis, liver fibrosis, inflammation, and increase in AST/ALT ratio, characteristics of non-alcoholic liver disease. Taken together, our results show that LinSTZ mice fed a HFD did not lead to a more robust model of MS-induced CKD, protected against kidney injury, but inducing liver damage. More studies are necessary to understand the kidney protective mechanisms of HFD when superimposed with hypertension and type 1 diabetes.

Comparative analysis of hypertensive nephrosclerosis in animal models of hypertension and its relevance to human pathology. Glomerulopathy.

Current research on hypertension utilizes more than fifty animal models that rely mainly on stable increases in systolic blood pressure. In experimental hypertension, grading or scoring of glomerulopathy in the majority of studies is based on a wide range of opinion-based histological changes that do not necessarily comply with lesional descriptors for glomerular injury that are well-established in clinical pathology. Here, we provide a critical appraisal of experimental hypertensive glomerulopathy with the same approach used to assess hypertensive glomerulopathy in humans. Four hypertensive models with varying pathogenesis were analyzed-chronic angiotensin II infused mice, mice expressing active human renin in the liver (TTRhRen), spontaneously hypertensive rats (SHR), and Goldblatt two-kidney one-clip rats (2K1C). Analysis of glomerulopathy utilized the same criteria applied in humans-hyalinosis, focal segmental glomerulosclerosis (FSGS), ischemic, hypertrophic and solidified glomeruli, or global glomerulosclerosis (GGS). Data from animal models were compared to human reference values. Kidneys in TTRhRen mice, SHR and the nonclipped kidneys in 2K1C rats had no sign of hyalinosis, FSGS or GGS. Glomerulopathy in these groups was limited to variations in mesangial and capillary compartment volumes, with mild increases in collagen deposition. Histopathology in angiotensin II infused mice corresponded to mesangioproliferative glomerulonephritis, but not hypertensive glomerulosclerosis. The number of nephrons was significantly reduced in TTRhRen mice and SHR, but did not correlate with severity of glomerulopathy. The most substantial human-like glomerulosclerotic lesions, including FSGS, ischemic obsolescent glomeruli and GGS, were found in the clipped kidneys of 2K1C rats. The comparison of affected kidneys to healthy control in animals produces lesion values that are numerically impressive but correspond to mild damage if compared to humans. Animal studies should be standardized by employing the criteria and classifications established in human pathology to make experimental and human data fully comparable for comprehensive analysis and model improvements.

Fatty acid mimetic PBI-4547 restores metabolic homeostasis via GPR84 in mice with non-alcoholic fatty liver disease.

Non-alcoholic Fatty Liver Disease (NAFLD) is the most common form of liver disease and is associated with metabolic dysregulation. Although G protein-coupled receptor 84 (GPR84) has been associated with inflammation, its role in metabolic regulation remains elusive. The aim of our study was to evaluate the potential of PBI-4547 for the treatment of NAFLD and to validate the role of its main target receptor, GPR84. We report that PBI-4547 is a fatty acid mimetic, acting concomitantly as a GPR84 antagonist and GPR40/GPR120 agonist. In a mouse model of diet-induced obesity, PBI-4547 treatment improved metabolic dysregulation, reduced hepatic steatosis, ballooning and NAFLD score. PBI-4547 stimulated fatty acid oxidation and induced gene expression of mitochondrial uncoupling proteins in the liver. Liver metabolomics revealed that PBI-4547 improved metabolic dysregulation induced by a high-fat diet regimen. In Gpr84-/- mice, PBI-4547 treatment failed to improve various key NAFLD-associated parameters, as was observed in wildtype littermates. Taken together, these results highlight a detrimental role for the GPR84 receptor in the context of meta-inflammation and suggest that GPR84 antagonism via PBI-4547 may reflect a novel treatment approach for NAFLD and its related complications.

Vascular contributions to 16p11.2 deletion autism syndrome modeled in mice.

While the neuronal underpinnings of autism spectrum disorder (ASD) are being unraveled, vascular contributions to ASD remain elusive. Here, we investigated postnatal cerebrovascular development in the 16p11.2df/+ mouse model of 16p11.2 deletion ASD syndrome. We discover that 16p11.2 hemizygosity leads to male-specific, endothelium-dependent structural and functional neurovascular abnormalities. In 16p11.2df/+ mice, endothelial dysfunction results in impaired cerebral angiogenesis at postnatal day 14, and in altered neurovascular coupling and cerebrovascular reactivity at postnatal day 50. Moreover, we show that there is defective angiogenesis in primary 16p11.2df/+ mouse brain endothelial cells and in induced-pluripotent-stem-cell-derived endothelial cells from human carriers of the 16p11.2 deletion. Finally, we find that mice with an endothelium-specific 16p11.2 deletion (16p11.2ΔEC) partially recapitulate some of the behavioral changes seen in 16p11.2 syndrome, specifically hyperactivity and impaired motor learning. By showing that developmental 16p11.2 haploinsufficiency from endothelial cells results in neurovascular and behavioral changes in adults, our results point to a potential role for endothelial impairment in ASD.

Prostaglandin E2 receptor EP1 (PGE2/EP1) deletion promotes glomerular podocyte and endothelial cell injury in hypertensive TTRhRen mice.

Prostaglandin E2 receptor EP1 (PGE2/EP1) promotes diabetic renal injury, and EP1 receptor deletion improves hyperfiltration, albuminuria, and fibrosis. The role of EP1 receptors in hypertensive kidney disease (HKD) remains controversial. We examined the contribution of EP1 receptors to HKD. EP1 null (EP1-/-) mice were bred with hypertensive TTRhRen mice (Htn) to evaluate kidney function and injury at 24 weeks. EP1 deletion had no effect on elevation of systolic blood pressure in Htn mice (HtnEP1-/-) but resulted in pronounced albuminuria and reduced FITC-inulin clearance, compared with Htn or wild-type (WT) mice. Ultrastructural injury to podocytes and glomerular endothelium was prominent in HtnEP1-/- mice; including widened subendothelial space, subendothelial lucent zones and focal lifting of endothelium from basement membrane, with focal subendothelial cell debris. Cortex COX2 mRNA was increased by EP1 deletion. Glomerular EP3 mRNA was reduced by EP1 deletion, and EP4 by Htn and EP1 deletion. In WT mice, PGE2 increased chloride reabsorption via EP1 in isolated perfused thick ascending limb (TAL), but PGE2 or EP1 deletion did not affect vasopressin-mediated chloride reabsorption. In WT and Htn mouse inner medullary collecting duct (IMCD), PGE2 inhibited vasopressin-water transport, but not in EP1-/- or HtnEP1-/- mice. Overall, EP1 mediated TAL and IMCD transport in response to PGE2 is unaltered in Htn, and EP1 is protective in HKD.

PBI-4050 via GPR40 activation improves adenine-induced kidney injury in mice.

PBI-4050 (3-pentylbenzenacetic acid sodium salt), a novel first-in-class orally active compound that has completed clinical Phases Ib and II in subjects with chronic kidney disease (CKD) and metabolic syndrome respectively, exerts antifibrotic effects in several organs via a novel mechanism of action, partly through activation of the G protein receptor 40 (GPR40) receptor. Here we evaluate the effects of PBI-4050 in both WT and Gpr40-/- mice on adenine-induced tubulointerstitial injury, anemia and activation of the unfolded protein response (UPR) pathway. Adenine-induced CKD was achieved in 8-week-old C57BL/6 mice fed a diet supplemented with 0.25% adenine. After 1 week, PBI-4050 or vehicle was administered daily by oral-gavage for 3 weeks. Gpr40-/- mice were also subjected to adenine-feeding, with or without PBI-4050 treatment. PBI-4050 improved renal function and urine concentrating ability. Anemia was present in adenine-fed mice, while PBI-4050 blunted these effects and led to significantly higher plasma erythropoietin (EPO) levels. Adenine-induced renal fibrosis, endoplasmic reticulum (ER) stress and apoptosis were significantly decreased by PBI-4050. In parallel, Gpr40-/- mice were more susceptible to adenine-induced fibrosis, renal function impairment, anemia and ER stress compared with WT mice. Importantly, PBI-4050 treatment in Gpr40-/- mice failed to reduce renal injury in this model. Taken together, PBI-4050 prevented adenine-induced renal injury while these beneficial effects were lost upon Gpr40 deletion. These data reinforce PBI-4050's use as a renoprotective therapy and identify GPR40 as a crucial mediator of its beneficial effects.

Podocyte NADPH Oxidase 5 Promotes Renal Inflammation Regulated by the Toll-Like Receptor Pathway.

AIMS: Oxidative stress associated with a proinflammatory state occurs in endothelial dysfunction, hypertension, chronic kidney disease, and diabetes. The NADPH oxidase (Nox) family of reactive oxygen species (ROS) generating enzymes is implicated in these processes, yet little information regarding the role of Nox5 is available. Our aim was to investigate the role of Nox5 in promoting renal inflammation and identify mechanisms regulating its activity. RESULTS: Mice with podocyte-specific Nox5 (Nox5pod+) expression demonstrated greater glomerular inflammation and increased expression of Toll-like receptors (TLRs) and proinflammatory cytokines. In a lipopolysaccharide (LPS) model of acute kidney injury, Nox5pod+ and control littermates exhibited increased TLR and Nox1 expression. Compared with control littermates, Nox5pod+ animals developed greater glomerular inflammation and ROS production. Immortalized human podocytes (hPODs) incubated with LPS demonstrated TLR induction, increased Nox5 expression, and enhanced ROS production. Inhibition of interleukin-1 receptor-associated kinases (IRAK)-1 and -4 that lie downstream of TLR inhibited LPS-induced ROS production. Interaction between IRAK1 and Nox5 was confirmed by coimmunoprecipitation. Furthermore, LPS treatment of hPODs resulted in phosphorylation of threonine residue(s) in Nox5 that was attenuated by an IRAK1/4 inhibitor. Innovation and Conclusion: These results are the first to demonstrate that Nox5 is a downstream target of the TLR pathway and that Nox5-derived ROS may be modulated by IRAK1/4 activity. Nox5-derived ROS in podocytes can promote a proinflammatory state in the kidney via induction of cytokine expression and upregulation of TLRs leading to a feed-forward loop in which TLR activation enhances Nox5-mediated ROS production.

GRK2 knockdown in mice exacerbates kidney injury and alters renal mechanisms of blood pressure regulation.

The renin-angiotensin system regulates blood pressure and fluid balance in the body primarily via angiotensin receptor 1 (AT1R). Renal AT1R was found to be primarily responsible for Ang II-mediated hypertension. G protein-coupled receptor kinase 2 (GRK2) modulates AT1R desensitization and increased GRK2 protein expression is reported in hypertensive patients. However, the consequences of GRK2 inhibition on kidney functions remain unknown. We employed shGRK2 knockdown mice (shGRK2 mice) to test the role of GRK2 in kidney development and function that can be ultimately linked to the hypertensive phenotype detected in shGRK2 mice. GRK2 knockdown reduced kidney size, nephrogenesis and glomerular count, and impaired glomerular filtration. Glomerular damage in adult shGRK2 mice was associated with increased renin- and AT1R-mediated production of reactive oxygen species. The AT1R blocker, Losartan, normalized elevated blood pressure and markedly improved glomerular filtration in the shGRK2 knockdown mice. Our findings provide evidence for the crucial role of GRK2 in renal regulation of blood pressure. It also suggests that the detrimental outcomes of GRK2 inhibitors on the kidney should be carefully examined when used as antihypertensive.

Hyperfiltration in ubiquitin C-terminal hydrolase L1-deleted mice.

Neuronal ubiquitin C-terminal hydrolase L1 (UCHL1) is a deubiquitinating enzyme that maintains intracellular ubiquitin pools and promotes axonal transport. Uchl1 deletion in mice leads to progressive axonal degeneration, affecting the dorsal root ganglion that harbors axons emanating to the kidney. Innervation is a crucial regulator of renal hemodynamics, though the contribution of neuronal UCHL1 to this is unclear. Immunofluorescence revealed significant neuronal UCHL1 expression in mouse kidney, including periglomerular axons. Glomerular filtration rate trended higher in 6-week-old Uchl1-/- mice, and by 12 weeks of age, these displayed significant glomerular hyperfiltration, coincident with the onset of neurodegeneration. Angiotensin converting enzyme inhibition had no effect on glomerular filtration rate of Uchl1-/- mice indicating that the renin-angiotensin system does not contribute to the observed hyperfiltration. DCE-MRI revealed increased cortical renal blood flow in Uchl1-/- mice, suggesting that hyperfiltration results from afferent arteriole dilation. Nonetheless, hyperglycemia, cyclooxygenase-2, and nitric oxide synthases were ruled out as sources of hyperfiltration in Uchl1-/- mice as glomerular filtration rate remained unchanged following insulin treatment, and cyclooxygenase-2 and nitric oxide synthase inhibition. Finally, renal nerve dysfunction in Uchl1-/- mice is suggested given increased renal nerve arborization, decreased urinary norepinephrine, and impaired vascular reactivity. Uchl1-deleted mice demonstrate glomerular hyperfiltration associated with renal neuronal dysfunction, suggesting that neuronal UCHL1 plays a crucial role in regulating renal hemodynamics.

A Newly Discovered Antifibrotic Pathway Regulated by Two Fatty Acid Receptors: GPR40 and GPR84.

Numerous clinical conditions can lead to organ fibrosis and functional failure. There is a great need for therapies that could effectively target pathophysiological pathways involved in fibrosis. GPR40 and GPR84 are G protein-coupled receptors with free fatty acid ligands and are associated with metabolic and inflammatory disorders. Although GPR40 and GPR84 are involved in diverse physiological processes, no evidence has demonstrated the relevance of GPR40 and GPR84 in fibrosis pathways. Using PBI-4050 (3-pentylbenzeneacetic acid sodium salt), a synthetic analog of a medium-chain fatty acid that displays agonist and antagonist ligand affinity toward GPR40 and GPR84, respectively, we uncovered an antifibrotic pathway involving these receptors. In experiments using Gpr40- and Gpr84-knockout mice in models of kidney fibrosis (unilateral ureteral obstruction, long-term post-acute ischemic injury, and adenine-induced chronic kidney disease), we found that GPR40 is protective and GPR84 is deleterious in these diseases. Moreover, through binding to GPR40 and GPR84, PBI-4050 significantly attenuated fibrosis in many injury contexts, as evidenced by the antifibrotic activity observed in kidney, liver, heart, lung, pancreas, and skin fibrosis models. Therefore, GPR40 and GPR84 may represent promising molecular targets in fibrosis pathways. We conclude that PBI-4050 is a first-in-class compound that may be effective for managing inflammatory and fibrosis-related diseases.

PGE2 EP1 receptor inhibits vasopressin-dependent water reabsorption and sodium transport in mouse collecting duct.

PGE2 regulates glomerular hemodynamics, renin secretion, and tubular transport. This study examined the contribution of PGE2 EP1 receptors to sodium and water homeostasis. Male EP1-/- mice were bred with hypertensive TTRhRen mice (Htn) to evaluate blood pressure and kidney function at 8 weeks of age in four groups: wildtype (WT), EP1-/-, Htn, HtnEP1-/-. Blood pressure and water balance were unaffected by EP1 deletion. COX1 and mPGE2 synthase were increased and COX2 was decreased in mice lacking EP1, with increases in EP3 and reductions in EP2 and EP4 mRNA throughout the nephron. Microdissected proximal tubule sglt1, NHE3, and AQP1 were increased in HtnEP1-/-, but sglt2 was increased in EP1-/- mice. Thick ascending limb NKCC2 was reduced in the cortex but increased in the medulla. Inner medullary collecting duct (IMCD) AQP1 and ENaC were increased, but AVP V2 receptors and urea transporter-1 were reduced in all mice compared to WT. In WT and Htn mice, PGE2 inhibited AVP-water transport and increased calcium in the IMCD, and inhibited sodium transport in cortical collecting ducts, but not in EP1-/- or HtnEP1-/- mice. Amiloride (ENaC) and hydrochlorothiazide (pendrin inhibitor) equally attenuated the effect of PGE2 on sodium transport. Taken together, the data suggest that EP1 regulates renal aquaporins and sodium transporters, attenuates AVP-water transport and inhibits sodium transport in the mouse collecting duct, which is mediated by both ENaC and pendrin-dependent pathways.

Vascular Smooth Muscle-Specific EP4 Receptor Deletion in Mice Exacerbates Angiotensin II-Induced Renal Injury.

AIMS: Cyclooxygenase inhibition by non-steroidal anti-inflammatory drugs is contraindicated in hypertension, as it may reduce glomerular filtration rate (GFR) and renal blood flow. However, the identity of the specific eicosanoid and receptor underlying these effects is not known. We hypothesized that vascular smooth muscle prostaglandin E2 (PGE2) E-prostanoid 4 (EP4) receptor deletion predisposes to renal injury via unchecked vasoconstrictive actions of angiotensin II (AngII) in a hypertension model. Mice with inducible vascular smooth muscle cell (VSMC)-specific EP4 receptor deletion were generated and subjected to AngII-induced hypertension. RESULTS: EP4 deletion was verified by PCR of aorta and renal vessels, as well as functionally by loss of PGE2-mediated mesenteric artery relaxation. Both AngII-treated groups became similarly hypertensive, whereas albuminuria, foot process effacement, and renal hypertrophy were exacerbated in AngII-treated EP4VSMC-/- but not in EP4VSMC+/+ mice and were associated with glomerular scarring, tubulointerstitial injury, and reduced GFR. AngII-treated EP4VSMC-/- mice exhibited capillary damage and reduced renal perfusion as measured by fluorescent bead microangiography and magnetic resonance imaging, respectively. NADPH oxidase 2 (Nox2) expression was significantly elevated in AngII-treated EP4-/- mice. EP4-receptor silencing in primary VSMCs abolished PGE2 inhibition of AngII-induced Nox2 mRNA and superoxide production. INNOVATION: These data suggest that vascular EP4 receptors buffer the actions of AngII on renal hemodynamics and oxidative injury. CONCLUSION: EP4 agonists may, therefore, protect against hypertension-associated kidney damage. Antioxid. Redox Signal. 25, 642-656.

Prostaglandin E2 increases proximal tubule fluid reabsorption, and modulates cultured proximal tubule cell responses via EP1 and EP4 receptors.

Renal prostaglandin (PG) E2 regulates salt and water transport, and affects disease processes via EP1-4 receptors, but its role in the proximal tubule (PT) is unknown. Our study investigates the effects of PGE2 on mouse PT fluid reabsorption, and its role in growth, sodium transporter expression, fibrosis, and oxidative stress in a mouse PT cell line (MCT). To determine which PGE2 EP receptors are expressed in MCT, qPCR for EP1-4 was performed on cells stimulated for 24 h with PGE2 or transforming growth factor beta (TGFß), a known mediator of PT injury in kidney disease. EP1 and EP4 were detected in MCT, but EP2 and EP3 are not expressed. EP1 was increased by PGE2 and TGFß, but EP4 was unchanged. To confirm the involvement of EP1 and EP4, sulprostone (SLP, EP1/3 agonist), ONO8711 (EP1 antagonist), and EP1 and EP4 siRNA were used. We first show that PGE2, SLP, and TGFß reduced H(3)-thymidine and H(3)-leucine incorporation. The effects on cell-cycle regulators were examined by western blot. PGE2 increased p27 via EP1 and EP4, but TGFß increased p21; PGE2-induced p27 was attenuated by TGFß. PGE2 and SLP reduced cyclinE, while TGFß increased cyclinD1, an effect attenuated by PGE2 administration. Na-K-ATPase α1 (NaK) was increased by PGE2 via EP1 and EP4. TGFß had no effect on NaK. Additionally, PGE2 and TGFß increased fibronectin levels, reaching 12-fold upon co-stimulation. EP1 siRNA abrogated PGE2-fibronectin. PGE2 also increased ROS generation, and ONO-8711 blocked PGE2-ROS. Finally, PGE2 significantly increased fluid reabsorption by 31 and 46% in isolated perfused mouse PT from C57BL/6 and FVB mice, respectively, and this was attenuated in FVB-EP1 null mice. Altogether PGE2 acting on EP1 and EP4 receptors may prove to be important mediators of PT injury, and salt and water transport.

A novel mouse model of advanced diabetic kidney disease.

Currently available rodent models exhibit characteristics of early diabetic nephropathy (DN) such as hyperfiltration, mesangial expansion, and albuminuria yet features of late DN (hypertension, GFR decline, tubulointerstitial fibrosis) are absent or require a significant time investment for full phenotype development. Accordingly, the aim of the present study was to develop a mouse model of advanced DN with hypertension superimposed (HD mice). Mice transgenic for human renin cDNA under the control of the transthyretin promoter (TTRhRen) were employed as a model of angiotensin-dependent hypertension. Diabetes was induced in TTRhRen mice through low dose streptozotocin (HD-STZ mice) or by intercrossing with OVE26 diabetic mice (HD-OVE mice). Both HD-STZ and HD-OVE mice displayed more pronounced increases in urinary albumin levels as compared with their diabetic littermates. Additionally, HD mice displayed renal hypertrophy, advanced glomerular scarring and evidence of tubulointerstitial fibrosis. Both HD-OVE and HD-STZ mice showed evidence of GFR decline as FITC-inulin clearance was decreased compared to hyperfiltering STZ and OVE mice. Taken together our results suggest that HD mice represent a robust model of type I DN that recapitulates key features of human disease which may be significant in studying the pathogenesis of DN and in the assessment of putative therapeutics.

Urinary podocyte microparticles identify prealbuminuric diabetic glomerular injury.

Microparticles (MPs) are small (0.1-1.0 µm) vesicles shed from the surface of cells in response to stress. Whether podocytes produce MPs and whether this production reflects glomerular injury are unclear. We examined MP formation in cultured human podocytes (hPODs) and diabetic mice. hPODs were exposed to cyclical stretch, high glucose (HG; 25 mM), angiotensin II, or TGF-ß. Urinary podocyte MPs were assessed in three mouse models of diabetic nephropathy: streptozotocin (STZ)-treated, OVE26, and Akita mice. Cyclic stretch and HG increased MP release as assessed by flow cytometry (P<0.01 and P<0.05, respectively, versus controls). Inhibition of Rho-kinase (ROCK) with fasudil blocked HG-induced podocyte MP formation. STZ-treated (8 weeks) mice exhibited increased urinary podocyte MPs compared with age-matched nondiabetic mice. Similarly, 16-week-old OVE26 mice had elevated levels of urinary podocyte MPs compared with wild-type littermates (P<0.01). In 1 week post-STZ-treated and 6- and 12-week-old Akita mice, urinary podocyte MPs increased significantly compared with those MPs in nondiabetic mice, despite normal urinary albumin levels. Our results indicate that podocytes produce MPs that are released into urine. Podocyte-derived MPs are generated by exposure to mechanical stretch and high glucose in vitro and could represent early markers of glomerular injury in diabetic nephropathy.

Nephropathy and elevated BP in mice with podocyte-specific NADPH oxidase 5 expression.

NADPH oxidase (Nox) enzymes are a significant source of reactive oxygen species, which contribute to glomerular podocyte dysfunction. Although studies have implicated Nox1, -2, and -4 in several glomerulopathies, including diabetic nephropathy, little is known regarding the role of Nox5 in this context. We examined Nox5 expression and regulation in kidney biopsies from diabetic patients, cultured human podocytes, and a novel mouse model. Nox5 expression increased in human diabetic glomeruli compared with nondiabetic glomeruli. Stimulation with angiotensin II upregulated Nox5 expression in human podocyte cultures and increased reactive oxygen species generation. siRNA-mediated Nox5 knockdown inhibited angiotensin II-stimulated production of reactive oxygen species and altered podocyte cytoskeletal dynamics, resulting in an Rac-mediated motile phenotype. Because the Nox5 gene is absent in rodents, we generated transgenic mice expressing human Nox5 in a podocyte-specific manner (Nox5(pod+)). Nox5(pod+) mice exhibited early onset albuminuria, podocyte foot process effacement, and elevated systolic BP. Subjecting Nox5(pod+) mice to streptozotocin-induced diabetes further exacerbated these changes. Our data show that renal Nox5 is upregulated in human diabetic nephropathy and may alter filtration barrier function and systolic BP through the production of reactive oxygen species. These findings provide the first evidence that podocyte Nox5 has an important role in impaired renal function and hypertension.

PTGER1 deletion attenuates renal injury in diabetic mouse models.

We hypothesized that the EP1 receptor promotes renal damage in diabetic nephropathy. We rendered EP1 (PTGER1, official symbol) knockout mice (EP1(-/-)) diabetic using the streptozotocin and OVE26 models. Albuminuria, mesangial matrix expansion, and glomerular hypertrophy were each blunted in EP1(-/-) streptozotocin and OVE26 cohorts compared with wild-type counterparts. Although diabetes-associated podocyte depletion was unaffected by EP1 deletion, EP1 antagonism with ONO-8711 in cultured podocytes decreased angiotensin II-mediated superoxide generation, suggesting that EP1-associated injury of remaining podocytes in vivo could contribute to filtration barrier dysfunction. Accordingly, EP1 deletion in OVE26 mice prevented nephrin mRNA expression down-regulation and ameliorated glomerular basement membrane thickening and foot process effacement. Moreover, EP1 deletion reduced diabetes-induced expression of fibrotic markers fibronectin and α-actin, whereas EP1 antagonism decreased fibronectin in cultured proximal tubule cells. Similarly, proximal tubule megalin expression was reduced by diabetes but was preserved in EP1(-/-) mice. Finally, the diabetes-associated increase in angiotensin II-mediated constriction of isolated mesenteric arteries was blunted in OVE26EP1(-/-) mice, demonstrating a role for EP1 receptors in the diabetic vasculature. These data suggest that EP1 activation contributes to diabetic nephropathy progression at several locations, including podocytes, proximal tubule, and the vasculature. The EP1 receptor facilitates the actions of angiotensin II, thereby suggesting that targeting of both the renin-angiotensin system and the EP1 receptor could be beneficial in diabetic nephropathy.

Mechanical stretch and prostaglandin E2 modulate critical signaling pathways in mouse podocytes.

Elevated glomerular capillary pressure (Pgc) and hyperglycemia contribute to glomerular filtration barrier injury observed in diabetic nephropathy (DN). Previous studies showed that hypertensive conditions alone or in combination with a diabetic milieu impact podocyte cellular function which results in podocyte death, detachment or hypertrophy. The present study was aimed at uncovering the initial signaling profile activated by Pgc (mimicked by in vitro mechanical stretch), hyperglycemia (high glucose (HG), 25mM d-glucose) and prostaglandin E(2) (PGE(2)) in conditionally-immortalized mouse podocytes. PGE(2) significantly reduced the active form of AKT by selectively blunting its phosphorylation on S473, but not on T308. AKT inhibition by PGE(2) was reversed following either siRNA-mediated EP(4) knockdown, PKA inhibition (H89), or phosphatase inhibition (orthovanadate). Podocytes treated for 20min with H(2)O(2) (10(-4)M), which mimics reactive oxygen species generation by cells challenged by hyperglycemic or enhanced Pgc conditions, significantly increased the levels of active p38 MAPK, AKT, JNK and ERK1/2. Interestingly, stretch and PGE(2) each significantly reduced H(2)O(2)-mediated AKT phosphorylation and was reversed by pretreatment with orthovanadate while stretch alone reduced GSK-3beta inhibitory phosphorylation at ser-9. Finally, mechanical stretch alone or in combination with HG, induced ERK1/2 and JNK activation, via the EGF receptor since AG1478, a specific EGF receptor kinase inhibitor, blocked this activation. These results show that cellular signaling in podocytes is significantly altered under diabetic conditions (i.e., hyperglycemia and increased Pgc). These changes in MAPKs and AKT activities might impact cellular integrity required for a functional glomerular filtration barrier thereby contributing to the onset of proteinuria in DN.