A nuclear complex of rictor and insulin receptor substrate-2 is associated with albuminuria in diabetic mice

Targeted deletion of von-Hippel-Lindau in the proximal tubule conditions the kidney against early diabetic kidney disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease. Glomerular hyperfiltration and albuminuria subject the proximal tubule (PT) to a subsequent elevation of workload, growth, and hypoxia. Hypoxia plays an ambiguous role in the development and progression of DKD and shall be clarified in our study. PT-von-Hippel-Lindau (Vhl)-deleted mouse model in combination with streptozotocin (STZ)-induced type I diabetes mellitus (DM) was phenotyped. In contrary to PT-Vhl-deleted STZ-induced type 1 DM mice, proteinuria and glomerular hyperfiltration occurred in diabetic control mice the latter due to higher nitric oxide synthase 1 and sodium and glucose transporter expression. PT Vhl deletion and DKD share common alterations in gene expression profiles, including glomerular and tubular morphology, and tubular transport and metabolism. Compared to diabetic control mice, the most significantly altered in PT Vhl-deleted STZ-induced type 1 DM mice were Ldc-1, regulating cellular oxygen consumption rate, and Zbtb16, inhibiting autophagy. Alignment of altered genes in heat maps uncovered that Vhl deletion prior to STZ-induced DM preconditioned the kidney against DKD. HIF-1α stabilization leading to histone modification and chromatin remodeling resets most genes altered upon DKD towards the control level. These data demonstrate that PT HIF-1α stabilization is a hallmark of early DKD and that targeting hypoxia prior to the onset of type 1 DM normalizes renal cell homeostasis and prevents DKD development.

Covalent modification of nephrilin peptide with valproic acid increases its efficacy as a therapeutic in burn trauma

Introduction:

Nephrilin peptide, a designed inhibitor of Rictor complex, modulates systemic responses to trauma, alleviating clinically relevant variables in a rat scald model and sepsis mortality in a mouse model. This study explores the possibility that chemical conjugation of small molecules to the aminoterminus of nephrilin can modify its biological activity in the rat scald model.

Methods:

One of four molecules (valproic acid, decanoic acid, fenofibric acid and ibuprofen) was chemically attached to the amino terminus of nephrilin during synthesis. Animals were treated with each modified nephrilin by subcutaneous bolus injection on days 1–7 post-burn.

Results:

Compared to nephrilin, valproic acid-modified nephrilin showed significantly (all p < 0.05) improved systemic effects on kidney function (creatinine 0.17 ± 0.03 vs 0.31 ± 0.09 mg/dL), glycemic control (AUC 57.5 ± 40 vs 136.4 ± 69.2 mg.dL.hr), inflammation (IL-6 24 ± 9 vs 39 ± 8 pg/ml), pathological angiogenesis (1.46 ± 0.87 vs 6.53 ± 3.16 pct pixels) and weight gain (3.74 ± 0.31 vs 2.99 ± 0.53 slope), all variables previously shown to bear upon clinically relevant burn injury outcomes.

Conclusion:

Modification of nephrilin with valproic acid increases the efficacy of nephrilin peptide in burns.

Transcriptional re-programming in rat central nervous system two weeks after burn trauma: the impact of nephrilin treatment on the expression of oxidative stress-related genes

INTRODUCTION

Survivors of severe burns suffer lifetime neuroinflammatory consequences manifested by higher incidence of major depression and neurodegenerative disease. In a scald model, nephrilin peptide has previously been shown to protect rats from loss of lean body mass, kidney function and glycaemic control, complications that have also been shown to endure in burn patient populations. Nephrilin's mechanism of action has been suggested to involve protection from excessive oxidative stress.

METHODS

Using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) amplification of transcripts in total RNA extracted from dorsal root ganglia of male rats 14 days after exposure to thermal insult, we query the relative levels of expression of 34 genes believed to be associated with oxidative stress biology in the central nervous system (CNS). We use these data to explore the central role of oxidative stress in astrogliosis, immunosuppression and mitochondrial homeostasis.

RESULTS AND DISCUSSION

Rats that received nephrilin treatment (4 mg/kg by subcutaneous bolus injection once daily for seven days after scald injury) showed significantly reduced elevations in gene expression of some key genes such as NOX2, GFAP, AQP4 and RAC1, but not of others such as NOX4, STEAP4, ARG1 and CCL2.

CONCLUSION

The implications of these data with reference to nephrilin's potential clinical utility for mitigating the enduring effects of burn trauma on the CNS are discussed. Nephrilin reduces the expression of some genes implicated in neurodegeneration after burn insult.

LAY SUMMARY

Nephrilin peptide is a novel treatment for short- and long-term systemic effects of burn trauma. This study measures the capability of nephrilin to address post-traumatic neurodegenerative disease by looking at the expression of genes in the central nervous system, in a rat scald model. Nephrilin appears to have beneficial effects by reducing the expression of some key genes known to be relevant in neurodegenerative processes, but not others.

Positive effects of ferric iron on the systemic efficacy of nephrilin peptide in burn trauma

INTRODUCTION

Nephrilin peptide is a designed inhibitor of Rictor complex (also known as mTORC2), an evolutionarily conserved assembly believed to modulate responses to cellular stress. We previously demonstrated the ability of nephrilin peptide to suppress neuroinflammation, loss of body mass, glycaemic control and kidney function in a rat scald model, as well as sepsis mortality in a mouse model. The present study explores the effect of nephrilin plus iron formulations on clinically relevant outcomes in the rat scald model.

METHODS

Animals were treated with nephrilin by subcutaneous bolus injection on post-burn days 1-7. Equimolar ferric iron in the formulation improved the positive systemic effects of nephrilin on kidney function, glycaemic control, oxidative stress, early hyperinflammation, late inflammasome activation, hyperangiogenesis and body mass, all variables previously shown to bear upon clinically relevant burn injury outcomes. The sparing effects of nephrilin-iron were demonstrated in both sexes.

DISCUSSION

Surprisingly, optimum daily treatment doses were in the range of 2-4 mg/kg, while 8 mg/kg was less effective, suggesting the possibility of marginal pro-oxidant effects from the 'free' iron fraction. Thus, although ferric iron in the nephrilin formulation is clearly helpful, care must be exercised to select an optimum treatment dose.

CONCLUSION

Iron increases the efficacy of nephrilin peptide in burns.

Epigenetic memory of oxidative stress: does nephrilin exert its protective effects via Rac1?

Aim

Nephrilin peptide, a designed inhibitor of Rictor complex (mTORC2), exerts pleiotropic protective effects in metabolic, xenobiotic and traumatic stress models. Stress can generate enduring epigenetic changes in gene function. In this work we examine the possibility that nephrilin treatment protects against acute and enduring global changes in oxidative metabolism, with a focus on the Rictor-complex-mediated activation of Rac1, a subunit of NADPH oxidase (Nox) via PKCs, Prex1 and p66shc.

Methods

Given the wide range of animal models in which nephrilin peptide has previously demonstrated effectiveness in vivo, we chose three different experimental systems for this investigation: dermal fibroblasts, renal proximal tubule epithelial cells (PTECs), and kidney tissue and urine from an animal model of burn trauma in which nephrilin was previously shown to prevent loss of kidney function.

Results

(1) Nephrilin protects dermal fibroblasts from loss of viability and collagen synthesis after ultraviolet A (UV-A) or H₂O₂ insult. (2) Nephrilin reduces reactive oxygen species (ROS) formation by H₂O₂–treated (PTECs) with or without nicotine pretreatment. Using RNA arrays and pathway analysis we demonstrate that nicotine and H₂O₂-treated PTECs specifically induced Rac1 gene networks in these cells. (3) Using kidney tissue and urine from the burn trauma model we demonstrate significant elevations of [a] 8-aminoprostane in urine; [b] kidney tissue histone modification and DNA methylation; and [c] post-transcriptional phosphorylation events consistent with Rac1 activation in kidney tissue.

Conclusion

Nephrilin protects against oxidative stress, possibly by modulating the activation of Rac1.

IRS proteins and diabetic complications

IRS proteins are cellular adaptor molecules that mediate many of the key metabolic actions of insulin. When tyrosine is phosphorylated by the activated insulin receptor, IRS proteins recruit downstream effectors, such as phosphoinositide 3-kinase and mitogen-activated protein kinase, in order to elicit cellular responses such as glucose uptake, lipid metabolism and cell proliferation. There are two main IRS proteins in humans (IRS1 and IRS2), both of which are widely expressed. Given their central role in the insulin signalling pathway, it is not surprising that male mice lacking Irs1 or Irs2 present with elevated blood glucose or type 2 diabetes, respectively. For reasons yet to be identified, female Irs2 (-/-) mice do not develop type 2 diabetes. A number of organs are affected by complications of diabetes; macrovascular complications include stroke and coronary artery disease, while nephropathy, neuropathy and retinopathy fall into the category of microvascular complications. Given the serious consequences of these complications on patient morbidity and mortality, it is essential to identify the molecular pathogenesis underlying diabetic complications, with a view to improving therapeutic intervention and patient outcomes. A number of recently published papers have converged on the hypothesis that the loss of insulin signalling and IRS proteins is instrumental to the development and/or progression of diabetic complications. This review will summarise some highlights from the published work in which this hypothesis is discussed.

Evaluation of Akt and RICTOR Expression Levels in Astrocytomas of All Grades

The mammalian target of rapamycin (mTOR) binds to several protein partners and forms two complexes, termed mTOR complexes 1 and 2 (mTORC1/2), that differ in components, substrates, and regulation. mTORC2 contains the protein Rapamycin-insensitive companion of mTOR (RICTOR); phosphorylates kinases of the AGC family, such as Akt; and controls the cytoskeleton. Even though the regulation of mTORC2 activity remains poorly understood, the hyperactivation of this signaling pathway has been shown to contribute to the oncogenic properties of gliomas in experimental models. In this work, we evaluated expression and phosphorylation of Akt, and expression of RICTOR and Ki-67 in 195 human astrocytomas of different grades (38 cases of grade I, 49 grade II, 15 grade III, and 93 grade IV) and 30 normal brains. Expression and phosphorylation of Akt increased with histological grade and correlated with a worse overall survival in glioblastomas (GBMs). RICTOR was overexpressed in grade I and II astrocytomas and demonstrated a shift to nuclear localization in GBMs. Nuclear RICTOR was associated to increased proliferation in GBMs. Our results point to an increase in total and phosphorylated Akt in high-grade gliomas and to a possible role of RICTOR in proliferations of high-grade GBM cells.

Therapeutic potential of serum and glucocorticoid inducible kinase inhibition

INTRODUCTION

Expression of serum-and-glucocorticoid-inducible kinase-1 (SGK1) is low in most cells, but dramatically increases under certain pathophysiological conditions, such as glucocorticoid or mineralocorticoid excess, inflammation with TGFβ release, hyperglycemia, cell shrinkage and ischemia. SGK1 is activated by insulin and growth factors via phosphatidylinositide-3-kinase, 3-phosphoinositide-dependent kinase and mammalian target of rapamycin. SGK1 sensitive functions include activation of ion channels (including epithelial Na(+) channel ENaC, voltage gated Na(+) channel SCN5A transient receptor potential channels TRPV4 - 6, Ca(2+) release activated Ca(2+) channel Orai1/STIM1, renal outer medullary K(+) channel ROMK, voltage gated K(+) channels KCNE1/KCNQ1, kainate receptor GluR6, cystic fibrosis transmembrane regulator CFTR), carriers (including Na(+),Cl(-) symport NCC, Na(+),K(+),2Cl(-) symport NKCC, Na(+)/H(+) exchangers NHE1 and NHE3, Na(+), glucose symport SGLT1, several amino acid transporters), and Na(+)/K(+)-ATPase. SGK1 regulates several enzymes (e.g., glycogen synthase kinase-3, ubiquitin-ligase Nedd4-2) and transcription factors (e.g., forkhead transcription factor 3a, β-catenin, nuclear factor kappa B).

AREAS COVERED

The phenotype of SGK1 knockout mice is mild and SGK1 is apparently dispensible for basic functions. Excessive SGK1 expression and activity, however, contributes to the pathophysiology of several disorders, including hypertension, obesity, diabetes, thrombosis, stroke, fibrosing disease, infertility and tumor growth. A SGK1 gene variant (prevalence ∼ 3 - 5% in Caucasians and ∼ 10% in Africans) is associated with hypertension, stroke, obesity and type 2 diabetes. SGK1 inhibitors have been developed and shown to reduce blood pressure of hyperinsulinemic mice and to counteract tumor cell survival.

EXPERT OPINION

Targeting SGK1 may be a therapeutic option in several clinical conditions, including metabolic syndrome and tumor growth.

Mammalian target of rapamycin complex 2 regulates inflammatory response to stress

OBJECTIVE AND DESIGN

To explore the role of mammalian target of rapamycin 2 (mTORC2) in the activation of inflammatory and oxidative responses in rodent models of acute injury and metabolic stress.

MATERIAL

The impact of nephrilin, an inhibitor of mTORC2 complex, was assessed in three CD-1 mouse models of acute xenobiotic stress and in a hypertensive Dahl rat model of metabolic stress.

METHODS

Animals received daily subcutaneous bolus injections of saline or 4 mg/kg nephrilin. Tissues were assayed by ELISA, gene arrays and immunohistochemical staining.

RESULTS

Nephrilin significantly inhibited elevations in plasma tumor necrosis factor-alpha, kidney substance P, and CX3CR1, and urinary lipocalin-2 [urinary neutrophil gelatinase-associated lipocalin (uNGAL)] in models of acute xenobiotic stress. UCHL1 gene expression levels dropped and plasma HMGB1 levels rose in the rhabdomyolysis model. Both effects were reversed by nephrilin. The inhibitor also blocked diet-induced elevations of uNGAL and albumin-creatinine ratio (UACR) as well as kidney tissue phosphorylation of PKC-beta-2-T641 and p66shc-S36, and reduced dark ring-like staining of nuclei by anti-phos-p66shc-S36 antibody in frozen sections of diseased kidneys from hypertensive Dahl rats fed an 8 % NaCl diet for 4 weeks.

CONCLUSIONS

Taken together, our results suggest a role for mTORC2 in the inflammatory-oxidative responses to stress.