PPARγ is a gatekeeper for extracellular matrix and vascular cell homeostasis: beneficial role in pulmonary hypertension and renal/cardiac/pulmonary fibrosis.

PURPOSE OF REVIEW: Pulmonary arterial hypertension (PAH) is characterized by pulmonary arterial endothelial cell (PAEC) dysfunction and apoptosis, pulmonary arterial smooth muscle cell (PASMC) proliferation, inflammation, vasoconstriction, and metabolic disturbances that include disrupted bone morphogenetic protein receptor (BMPR2)-peroxisome proliferator-activated receptor gamma (PPARγ) axis and DNA damage. Activation of PPARγ improves many of these mechanisms, although erroneous reports on potential adverse effects of thiazolidinedione (TZD)-class PPARγ agonists reduced their clinical use in the past decade. Here, we review recent findings in heart, lung, and kidney research related to the pathobiology of vascular remodeling and tissue fibrosis, and also potential therapeutic effects of the PPARγ agonist pioglitazone. RECENT FINDINGS: Independent of its metabolic effects (improved insulin sensitivity and fatty acid handling), PPARγ activation rescues BMPR2 dysfunction, inhibits TGFβ/Smad3/CTGF and TGFβ/pSTAT3/pFoxO1 pathways, and induces the PPARγ/apoE axis, inhibiting vascular remodeling. PPARγ activation dampens mtDNA damage via PPARγ/UBR5/ATM pathway, improves function of endothelial progenitor cells (EPCs), and decrease renal fibrosis by repressing TGFβ/pSTAT3 and TGFβ/EGR1. SUMMARY: Pharmacological PPARγ activation improves many hallmarks of PAH, including dysfunction of BMPR2-PPARγ axis, PAEC, PASMC, EPC, mitochondria/metabolism, and inflammation. Recent randomized controlled trials, including IRIS (Insulin Resistance Intervention After Stroke Trial), emphasize the beneficial effects of PPARγ agonists in PAH patients, leading to recent revival for clinical use

Sustained hyperosmolarity increses TGF-beta1 and Egr-1 expression in the rat renal medulla.

BACKGROUND: Although TGF-ss and the transcription factor Egr-1 play an important role in both kidney fibrosis and in response to acute changes of renal medullary osmolarity, their role under sustained hypo- or hyperosmolar conditions has not been elucidated. We investigated the effects of chronic hypertonicity and hypotonicity on the renal medullary TGF-ss and Egr-1 expression. METHODS: Male adult Sprague Dawley rats (n = 6/group) were treated with 15 mg/day furosemide, or the rats were water restricted to 15 ml/200 g body weight per day. Control rats had free access to water and rodent chow. Kidneys were harvested after 5 days of treament. In cultured inner medullary collecting duct (IMCD) cells, osmolarity was increased from 330 mOsm to 900 mOsm over 6 days. Analyses were performed at 330, 600 and 900 mOsm. RESULTS: Urine osmolarity has not changed due to furosemide treatment but increased 2-fold after water restriction (p < 0.05). Gene expression of TGF-ss and Egr-1 increased by 1.9-fold and 7-fold in the hypertonic medulla, respectively (p < 0.05), accompanied by 6-fold and 2-fold increased c-Fos and TIMP-1 expression, respectively (p < 0.05) and positive immunostaining for TGF-ss and Egr-1 (p < 0.05). Similarly, hyperosmolarity led to overexpression of TGF-ss and Egr-1 mRNA in IMCD cells (2.5-fold and 3.5-fold increase from 330 to 900 mOsm, respectively (p < 0.05)) accompanied by significant c-Fos and c-Jun overexpressions (p < 0.01), and increased Col3a1 and Col4a1 mRNA expression. CONCLUSION: We conclude that both TGF-ss and Egr-1 are upregulated by sustained hyperosmolarity in the rat renal medulla, and it favors the expression of extracellular matrix components

LPS-induced delayed preconditioning is mediated by hsp90 and involves the heat shock response in mouse kidney.

INTRODUCTION: We and others demonstrated previously that preconditioning with endotoxin (LPS) protected from a subsequent lethal LPS challenge or from renal ischemia-reperfusion injury (IRI). LPS is effective in evoking the heat shock response, an ancient and essential cellular defense mechanism, which plays a role in resistance to, and recovery from diseases. Here, by using the pharmacological Hsp90 inhibitor novobiocin (NB), we investigated the role of Hsp90 and the heat shock response in LPS-induced delayed renal preconditioning. METHODS: Male C57BL/6 mice were treated with preconditioning (P: 2 mg/kg, ip.) and subsequent lethal (L: 10 mg/kg, ip.) doses of LPS alone or in combination with NB (100 mg/kg, ip.). Controls received saline (C) or NB. RESULTS: Preconditioning LPS conferred protection from a subsequent lethal LPS treatment. Importantly, the protective effect of LPS preconditioning was completely abolished by a concomitant treatment with NB. LPS induced a marked heat shock protein increase as demonstrated by Western blots of Hsp70 and Hsp90. NB alone also stimulated Hsp70 and Hsp90 mRNA but not protein expression. However, Hsp70 and Hsp90 protein induction in LPS-treated mice was abolished by a concomitant NB treatment, demonstrating a NB-induced impairment of the heat shock response to LPS preconditioning. CONCLUSION: LPS-induced heat shock protein induction and tolerance to a subsequent lethal LPS treatment was prevented by the Hsp90 inhibitor, novobiocin. Our findings demonstrate a critical role of Hsp90 in LPS signaling, and a potential involvement of the heat shock response in LPS-induced preconditioning

The Effect of Combined Treatment with the (Pro)Renin Receptor Blocker HRP and Quinapril in Type 1 Diabetic Rats

Background/Aims: Diabetic nephropathy remains a major clinical problem. The effects of prorenin might be adverse, but the literature data are controversial. We compared the renal effects of the (pro)renin receptor ((P)RR) blockade and angiotensin converting enzyme (ACE) inhibition on the progression of diabetic nephropathy in rats. Methods: Diabetes (DM) was induced by ip. streptozotocin administration in adult male Sprague-Dawley rats, followed by eight weeks of treatment with the (P)RR blocker „handle region” decoy peptide (HRP, 0,1 mg/kg/day) or with the ACE inhibitor Quinapril (Q, 50 mg/kg/day) and grouped as follows: 1. Control (n=10); 2. DM (n=8); 3. DM+HRP (n=6); 4. DM+Q (n=10); 5. DM+Q+HRP (n=10). Renal functional parameters, histology and gene expressions were evaluated. Results: HRP reduced glomerulosclerosis and podocyte desmin expression, but did not affect proteinuria and tubular ERK(1/2) phosphorylation. Both Q and Q+HRP treatment reduced proteinuria, glomerular and tubular damage, tubular TGF-ß1 expression and ERK(1/2) phosphorylation to the same extent. Conclusion: The effects of HRP were partially beneficial on diabetic kidney lesions as HRP reduced damage but did not improve tubular damage and failed to reduce ERK(1/2) phosphorylation in rats. The combination of HRP with Quinapril had no additive effects over Quinapril monotherapy on the progression of diabetic nephropathy

Characterization and Role of SCAI during Renal Fibrosis and Epithelial-Mesenchymal Transition.

During progressive tubulointerstitial fibrosis, renal tubular epithelial cells transform into alpha-smooth muscle actin (SMA)- expressing myofibroblasts via epithelial-mesenchymal transition (EMT). SMA expression is regulated by transforming growth factor (TGF)-beta1 and cell contact disruption, through signaling events targeting the serum response factor-myocardin-related transcription factor (MRTF) complex. MRTFs are important regulators of fibrosis, tumor cell invasion, and metastasis. Consistent with the role of MRTFs in tumor progression, suppressor of cancer cell invasion (SCAI) was recently identified as a negative regulator of MRTF. Herein, we studied the role of SCAI in a fibrotic EMT model established on LLC-PK1 cells. SCAI overexpression prevented SMA promoter activation induced by TGF-beta1. When co-expressed, it inhibited the stimulatory effects of MRTF-A or MRTF-B or the constitutive active forms of RhoA, Rac1, or Cdc42 on the SMA promoter. SCAI interfered with TGF-beta1-induced SMA, connective tissue growth factor, and calponin protein expression; it rescued TGF-beta1- induced E-cadherin down-regulation. IHC studies on human kidneys showed that SCAI expression is reduced during fibrosis. Kidneys of diabetic rats and mice with unilateral ureteral obstruction depicted significant loss of SCAI expression. In parallel with the decrease of SCAI protein expression, diabetic rat and mouse kidneys with unilateral ureteral obstruction showed SMA expression, as evidenced by using Western blot analysis. Finally, TGF-beta1 treatment of LLC-PK1 cells attenuated SCAI protein expression. These data suggest that SCAI is a novel transcriptional cofactor that regulates EMT and renal fibrosis