IHG-2, a Mesangial Cell Gene Induced by High Glucose, Is Human gremlin

Abstract

We used cloning in silico coupled with polymerase chain reaction to demonstrate that IHG-2 is part of the 3-untranslated region of gremlin, a member of the DAN family of secreted proteins that antagonize the bioactivities of members of the transforming growth factor (TGF)-␤ superfamily. Mesangial cell gremlin mRNA levels were induced by high glucose, cyclic mechanical strain, and TGF-␤1 in vitro, and gremlin mRNA levels were elevated in the renal cortex of rats with streptozotocin-induced diabetic nephropathy in vivo. gremlin expression was observed in parallel with induction of bone morphogenetic protein-2 (BMP-2), a target for gremlin in models of cell differentiation. Together these data indicate that (a) IHG-2 is gremlin, (b) gremlin is expressed in diabetic nephropathy in vivo, (c) both glycemic and mechanical strain stimulate mesangial cell gremlin expression in vitro, (d) high glucose induces gremlin, in part, through TGF␤-mediated pathways, and (e) Gremlin is a potential endogenous antagonist of BMPs within a diabetic glomerular milieu.

The Lipoxin A4 Receptor Is Coupled to SHP-2 Activation

“…We have previously demonstrated that the anti-proliferative effects of LXA 4 are mediated through activation of the ALXR and result in modulation of growth factor (PDGF and EGF) receptor phosphorylation leading to down-regulation of the PI 3-kinase signaling pathway (4,9,18). Here, we report that the ability of LXA 4 to reduce the tyrosine phosphorylation level of the PDGFR␤ is independent of inhibition of RTK activity but dependent on SHP-2 PTP activation.…”

“…These data suggest that the high affinity binding site for the recruitment of p85 (Tyr 751 ) is the site most likely to be modulated by LXA 4 , although both sites must be mutated before a complete block in the effect of LXA 4 is observed. These data are particularly noteworthy given that p85 is a component of the PI 3-kinase complex, and our previous data have demonstrated that LXA 4 inhibits MC PI 3-kinase activity in response to leukotriene D 4 and PDGF, respectively (4,18). Consistent with our observations in ALXR cells expressing the Y740F/Y751F mutant, PDGF-induced phosphorylation of Tyr 751 was significantly inhibited by preincubation with LXA 4 in primary MC as assessed by immunoblot analysis using an antibody specific against PDGFR␤-Y751 phosphorylation (supplemental data).…”

Evidence for a Role of Transforming Growth Factor (TGF)-β1 in the Induction of Postglomerular Albuminuria in Diabetic Nephropathy

“…Hence, there is a need for the development of other agents to be used in conjunction with insulin treatment to help prevent diabetes-related complications such as diabetic nephropathy. Figure 8 indicates how TGF-␤ production and its subsequent effect on albumin uptake by proximal tubule cells may be influenced by glucose (8), glycated albumin (43), AngII (44), and changes in TGF-␤-regulating proteins such as decreased BMP7 (14) and increased gremlin (45), a protein that decreases BMP7 production (46). High glucose may also influence albumin uptake by proximal tubule cells, which may or may not act via a TGF-␤-related mechanism (47).…”

High Glucose-altered Gene Expression in Mesangial Cells

“…This compares with blood glucose levels in age-matched control animals of between 50 and 80 mg/dl. RNA was extracted from the kidney cortex as described previously (9). With respect to the remnant kidney model, male Munich-Wistar rats (260 -290 g) underwent 5/6 nephrectomy as previously described (12).…”

“…The role of ROS on actin cytoskeleton regulatory protein mRNA levels in response to high glucose was investigated by culturing mesangial cells in either 30 mM glucose or 30 mM glucose with carbonyl cyanide m-chlorophenylhydrazone (CCCP) (Sigma) (0.5 M), an uncoupler of oxidative phosphorylation, for 7 days (7). To investigate the role of cyclical stretch, cells cultured on flexible plates were subjected to repeated cycles of computer-controlled, vacuum-driven mechanical stretch and relaxation using the Flexercell Strain Unit (Flex Cell International, Hillsborough, NH) as described previously (9).…”