Browsing by Author "Chung, Hyun Jae"

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    A Non-Canonical Function for NLRP3 and AIM2 in Kidney Diseases
    (2017) Chung, Hyun Jae; Muruve, Daniel; Hollenberg, Morley; Altier, Christophe
    NLRP3 and AIM2 are inflammasome-forming proteins that have been mostly studied in leukocytes. Canonical NLRP3 or AIM2 inflammasomes regulate cytokine maturation and pyroptosis via ASC and caspase-1 activation. Emerging studies demonstrate that NLRP3 or AIM2 is expressed in non-haematopoietic cells such as tubular epithelial cells (TEC) in the kidney. The central hypothesis of this thesis is that NLRP3 and AIM2 regulate host response to renal injury in the kidney. Primary mouse TEC lacking Nlrp3 displayed reduced caspase-8 activation downstream of the tumor necrosis factor (TNF) receptor and CD95. TNFα/cycloheximide treatment induced NLRP3/ASC/caspase-8 speck-like complex formation at the mitochondria during apoptosis. The assembly of NLRP3/ASC/caspase-8 specks was downstream of TNFR signaling and independent of caspase-1 or -11 activation. This data shows that NLRP3 and ASC form a conserved non-canonical platform for caspase-8 activation, independent of the inflammasome that regulates apoptosis within epithelial cells. Interestingly, AIM2 was detected primarily in podocytes in the glomerulus and distal tubules at a low level. In a mouse model of nephrotoxic serum (NTS)-mediated anti-GBM, Aim2-/- mice displayed increased glomerular cellular crescent (multilayered accumulation of activated parietal cells) formation, tubular injury and inflammation, and worse renal function compared to wild-type controls. In vitro outgrowth of podocyte lacking Aim2 was greater than wild-type and Aim2-/- podocytes did not express Nhps2 (podocin) mRNA, a podocyte maturation marker. Furthermore, AIM2 was found to augment transcriptional activity of Wilm’s tumour-1 that regulates Nphs1 expression. This data suggests that non-canonical AIM2 regulates podocyte maturation, proliferation and potentially podocyte-to-parietal cell trans-differentiation during cellular crescent formation in vivo. In a mouse model of kidney ischemia/reperfusion in vivo, a significant difference in tubular injury was not detected between wild type and Aim2-/- mice. In vitro, tubular Aim2 did not regulate caspase-8 activation during apoptosis, confirming a limited role for Aim2 in tubular cell death. However, Aim2 deficiency attenuated TGFβ-mediated Smad phosphorylation and αSMA induction. Overall, these data increase the understanding of NLRP3 and AIM2 biology in the kidney diseases and highlight overarching non-canonical roles for NLRP3 and AIM2 to regulate critical biological processes in the kidney independent of inflammasome activation
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    Pathogenesis of Renal Fibrosis: a Role for Proteinase-activated Receptor-2
    (2013-01-28) Chung, Hyun Jae; Hollenberg, Morley; Muruve, Daniel
    Renal fibrosis is the final manifestation of all progressive chronic kidney disease with a significant morbidity and mortality. However, the underlying mechanisms remain largely unknown. Proteinase-activated Receptor-2 (PAR2) is a G-protein-coupled receptor that is proteolytically activated by serine proteinases such as trypsin. In our in vitro studies, we found that stimulation of PAR2 in human proximal tubular cells with PAR2-activating peptide alone significantly upregulated expression of CCN2 and did so synergistically to augment Transforming growth factor-β (TGF-β)-induced CCN2 production. This synergy was reduced by MAPKinase inhibition. We also found that PAR2 deficiency in mice with unilateral ureteral obstruction (UUO) significantly reduced tubular injuries and fibrosis, and synthesis of renal collagen and α-smooth muscle actin at 7 days post UUO. Our findings demonstrate the potential contribution of PAR2 to renal injury and fibrosis at an early time point due to the ability of PAR2 to augment the production of a profibrotic cytokine.