TGFß instructs mTORC2 to activate PKCßII for increased TWIST1 expression in proximal tubular epithelial cell injury.

The plasticity of proximal tubular epithelial cells in response to TGFß contributes to the expression of TWIST1 to drive renal fibrosis. The mechanism of TWIST1 expression is not known. We show that both PI3 kinase and its target mTORC2 increase TGFß-induced TWIST1 expression. TGFß enhances phosphorylation on Ser-660 in the protein kinase C ßII (PKCßII) hydrophobic motif site. Remarkably, phosphorylation-deficient PKCßIIS660A, kinase-dead PKCßII, and PKCßII knockdown blocked TWIST1 expression by TGFß. Inhibition of TWIST1 arrested TGFß-induced tubular cell hypertrophy and the expression of fibronectin, collagen I (α2), and α-smooth muscle actin. By contrast, TWIST1 overexpression induced these pathologies. Interestingly, the inhibition of PKCßII reduced these phenomena, which were countered by the expression of TWIST1. These results provide the first evidence for the involvement of the mTORC2-PKCßII axis in TWIST1 expression to promote tubular cell pathology.

Oncoprotein DJ-1 interacts with mTOR complexes to effect transcription factor Hif1α-dependent expression of collagen I (α2) during renal fibrosis.

Proximal tubular epithelial cells respond to transforming growth factor ß (TGFß) to synthesize collagen I (α2) during renal fibrosis. The oncoprotein DJ-1 has previously been shown to promote tumorigenesis and prevent apoptosis of dopaminergic neurons; however, its role in fibrosis signaling is unclear. Here, we show TGFß-stimulation increased expression of DJ-1, which promoted noncanonical mTORC1 and mTORC2 activities. We show DJ-1 augmented the phosphorylation/activation of PKCßII, a direct substrate of mTORC2. In addition, coimmunoprecipitation experiments revealed association of DJ-1 with Raptor and Rictor, exclusive subunits of mTORC1 and mTORC2, respectively, as well as with mTOR kinase. Interestingly, siRNAs against DJ-1 blocked TGFß-stimulated expression of collagen I (α2), while expression of DJ-1 increased expression of this protein. In addition, expression of dominant negative PKCßII and siRNAs against PKCßII significantly inhibited TGFß-induced collagen I (α2) expression. In fact, constitutively active PKCßII abrogated the effect of siRNAs against DJ-1, suggesting a role of PKCßII downstream of this oncoprotein. Moreover, we demonstrate expression of collagen I (α2) stimulated by DJ-1 and its target PKCßII is dependent on the transcription factor hypoxia-inducible factor 1α (Hif1α). Finally, we show in the renal cortex of diabetic rats that increased TGFß was associated with enhanced expression of DJ-1 and activation of mTOR and PKCßII, concomitant with increased Hif1α and collagen I (α2). Overall, we identified that DJ-1 affects TGFß-induced expression of collagen I (α2) via an mTOR-, PKCßII-, and Hif1α-dependent mechanism to regulate renal fibrosis.

Homoarginine ameliorates diabetic nephropathy independent of nitric oxide synthase-3.

Recently we showed that homoarginine supplementation confers kidney protection in diabetic mouse models. In this study we tested whether the protective effect of homoarginine is nitric oxide synthase-3 (NOS3)-independent in diabetic nephropathy (DN). Experiments were conducted in NOS3 deficient (NOS3-/- ) mice and their wild type littermate using multiple low doses of vehicle or streptozotocin and treated with homoarginine via drinking water for 24 weeks. Homoarginine supplementation for 24 weeks in diabetic NOS3-/- mice significantly attenuated albuminuria, increased blood urea nitrogen, histopathological changes and kidney fibrosis, kidney fibrotic markers, and kidney macrophage recruitment compared with vehicle-treated diabetic NOS3-/- mice. Furthermore, homoarginine supplementation restored kidney mitochondrial function following diabetes. Importantly, there were no significant changes in kidney NOS1 or NOS2 mRNA expression between all groups. In addition, homoarginine supplementation improved cardiac function and reduced cardiac fibrosis following diabetes. These data demonstrate that the protective effect of homoarginine is independent of NOS3, which will ultimately change our understanding of the mechanism(s) by which homoarginine induce renal and cardiac protection in DN. Homoarginine protective effect in DN could be mediated via improving mitochondrial function.

Lactate Elicits ER-Mitochondrial Mg2+ Dynamics to Integrate Cellular Metabolism.

Mg2+ is the most abundant divalent cation in metazoans and an essential cofactor for ATP, nucleic acids, and countless metabolic enzymes. To understand how the spatio-temporal dynamics of intracellular Mg2+ (iMg2+) are integrated into cellular signaling, we implemented a comprehensive screen to discover regulators of iMg2+ dynamics. Lactate emerged as an activator of rapid release of Mg2+ from endoplasmic reticulum (ER) stores, which facilitates mitochondrial Mg2+ (mMg2+) uptake in multiple cell types. We demonstrate that this process is remarkably temperature sensitive and mediated through intracellular but not extracellular signals. The ER-mitochondrial Mg2+ dynamics is selectively stimulated by L-lactate. Further, we show that lactate-mediated mMg2+ entry is facilitated by Mrs2, and point mutations in the intermembrane space loop limits mMg2+ uptake. Intriguingly, suppression of mMg2+ surge alleviates inflammation-induced multi-organ failure. Together, these findings reveal that lactate mobilizes iMg2+ and links the mMg2+ transport machinery with major metabolic feedback circuits and mitochondrial bioenergetics.

TGFß acts through PDGFRß to activate mTORC1 via the Akt/PRAS40 axis and causes glomerular mesangial cell hypertrophy and matrix protein expression.

Interaction of transforming growth factor-ß (TGFß)-induced canonical signaling with the noncanonical kinase cascades regulates glomerular hypertrophy and matrix protein deposition, which are early features of glomerulosclerosis. However, the specific target downstream of the TGFß receptor involved in the noncanonical signaling is unknown. Here, we show that TGFß increased the catalytic loop phosphorylation of platelet-derived growth factor receptor ß (PDGFRß), a receptor tyrosine kinase expressed abundantly in glomerular mesangial cells. TGFß increased phosphorylation of the PI 3-kinase-interacting Tyr-751 residue of PDGFRß, thus activating Akt. Inhibition of PDGFRß using a pharmacological inhibitor and siRNAs blocked TGFß-stimulated phosphorylation of proline-rich Akt substrate of 40 kDa (PRAS40), an intrinsic inhibitory component of mTORC1, and prevented activation of mTORC1 in the absence of any effect on Smad 2/3 phosphorylation. Expression of constitutively active myristoylated Akt reversed the siPDGFRß-mediated inhibition of mTORC1 activity; however, co-expression of the phospho-deficient mutant of PRAS40 inhibited the effect of myristoylated Akt, suggesting a definitive role of PRAS40 phosphorylation in mTORC1 activation downstream of PDGFRß in mesangial cells. Additionally, we demonstrate that PDGFRß-initiated phosphorylation of PRAS40 is required for TGFß-induced mesangial cell hypertrophy and fibronectin and collagen I (α2) production. Increased activating phosphorylation of PDGFRß is also associated with enhanced TGFß expression and mTORC1 activation in the kidney cortex and glomeruli of diabetic mice and rats, respectively. Thus, pursuing TGFß noncanonical signaling, we identified how TGFß receptor I achieves mTORC1 activation through PDGFRß-mediated Akt/PRAS40 phosphorylation to spur mesangial cell hypertrophy and matrix protein accumulation. These findings provide support for targeting PDGFRß in TGFß-driven renal fibrosis.

Mitochondrial pyruvate and fatty acid flux modulate MICU1-dependent control of MCU activity.

The tricarboxylic acid (TCA) cycle converts the end products of glycolysis and fatty acid ß-oxidation into the reducing equivalents NADH and FADH2 Although mitochondrial matrix uptake of Ca2+ enhances ATP production, it remains unclear whether deprivation of mitochondrial TCA substrates alters mitochondrial Ca2+ flux. We investigated the effect of TCA cycle substrates on MCU-mediated mitochondrial matrix uptake of Ca2+, mitochondrial bioenergetics, and autophagic flux. Inhibition of glycolysis, mitochondrial pyruvate transport, or mitochondrial fatty acid transport triggered expression of the MCU gatekeeper MICU1 but not the MCU core subunit. Knockdown of mitochondrial pyruvate carrier (MPC) isoforms or expression of the dominant negative mutant MPC1R97W resulted in increased MICU1 protein abundance and inhibition of MCU-mediated mitochondrial matrix uptake of Ca2+ We also found that genetic ablation of MPC1 in hepatocytes and mouse embryonic fibroblasts resulted in reduced resting matrix Ca2+, likely because of increased MICU1 expression, but resulted in changes in mitochondrial morphology. TCA cycle substrate-dependent MICU1 expression was mediated by the transcription factor early growth response 1 (EGR1). Blocking mitochondrial pyruvate or fatty acid flux was linked to increased autophagy marker abundance. These studies reveal a mechanism that controls the MCU-mediated Ca2+ flux machinery and that depends on TCA cycle substrate availability. This mechanism generates a metabolic homeostatic circuit that protects cells from bioenergetic crisis and mitochondrial Ca2+ overload during periods of nutrient stress.

High glucose increases miR-214 to power a feedback loop involving PTEN and the Akt/mTORC1 signaling axis.

The mechanism of PTEN repression by high glucose in diabetic nephropathy is not known. Using proximal tubular cells, we show that inhibition of PI3 kinase/Akt and their inactive enzymes prevents high glucose-induced PTEN downregulation. Similarly, rapamycin (Rapa) and shRaptor block suppression of PTEN by high glucose. In contrast, the constitutive activation of Akt and mechanistic target of rapamycin (mTOR)C1 decrease the expression of PTEN, similarly to high glucose. Remarkably, PI3 kinase/Akt/mTORC1 inhibition significantly attenuates high glucose-stimulated increase in miR-214, which targets PTEN, while constitutively active Akt/mTORC1 increases miR-214. Furthermore, anti-miR-214 and mTORC1 inhibition block high glucose-induced hypertrophy and fibronectin expression. These results reveal the first evidence for the presence of a high glucose-forced positive feedback conduit between the three-layered kinase cascade and miR-214/ PTEN in tubular cell injury.

Evaluation of antioxidant activity and characterization of phenolic constituents of Phyllanthus amarus root.

The antioxidant property of the 70% aqueous ethanol extract of Phyllanthus amarus roots and its ether-soluble, ethyl acetate-soluble, and aqueous fractions were investigated by various in vitro assays. The root extracts showed higher DPPH, hydroxyl, superoxide, and nitric oxide radical scavenging and reducing power activity. Among all the samples, the ethyl acetate-soluble fraction demonstrated highest radical scavenging activity and total phenolics content. Twenty-eight different phenolic compounds were identified by LCMS/MS analysis of the ethyl acetate-soluble fraction. The majority of the compounds were found to exist as their glycosides, and many of these were gallic acid derivatives. Free epicatechin and gallic acid were also identified in the ethyl acetate-soluble fraction. The present investigation suggested that P. amarus root is a potent antioxidant and can be used for the prevention of diseases related to oxidative stress.

Bilirubin clearance and antioxidant activities of ethanol extract of Phyllanthus amarus root in phenylhydrazine-induced neonatal jaundice in mice.

The ability of ethanol extract of Phyllanthus amarus root (EEPA) to decrease bilirubin level and oxidative stress in phenylhydrazine-induced neonatal jaundice in mice was investigated. Administration of phenylhydrazine (75 mg/kg b.w.) significantly elevated total and unconjugated serum bilirubin level compared to control mice. EEPA (5, 10, and 20 mg/kg b.w., oral) dose-dependently reduced the bilirubin level. EEPA treatment also upregulated hepatic CAR and CYP3A1, accounting for its ability to facilitate bilirubin clearance. A single dose of EEPA (20 mg/kg b.w.) induced higher level of bilirubin clearance than phototherapy, widely used for treating neonatal jaundice. Furthermore, phenylhydrazine administration significantly increased MDA, protein carbonyl, and total thiol content and lowered the GSH level along with superoxide dismutase and catalase activity in erythrocyte compared to the control group. Single administration of EEPA (20 mg/kg b.w.) significantly reversed the trend. Presence of gallic acid, gentisic acid, and ortho-coumaric acid in EEPA was identified by HPLC analysis. Amongst these, the major phenolic constituent, gallic acid, exhibited significant bilirubin-lowering effect. These results suggested that P. amarus may be beneficial in reducing bilirubin level as well as oxidative stress in neonatal jaundice.