Podocyte Integrin-β 3 and Activated Protein C Coordinately Restrict RhoA Signaling and Ameliorate Diabetic Nephropathy
Authors: Madhusudhan Thati , Ghosh Sanchita , Wang Hongjie , Dong Wei , Gupta Dheerendra , Elwakiel Ahmed , Stoyanov Stoyan , Al-Dabet Moh’d Mohanad , Krishnan Shruthi , Biemann Ronald , Nazir Sumra , Zimmermann Silke , Mathew Akash , Gadi Ihsan , Rana Rajiv , Zeng-Brouwers Jinyang , Moeller Marcus J. , Schaefer Liliana , Esmon Charles T. , Kohli Shrey , Reiser Jochen , Rezaie Alireza R. , Ruf Wolfram , Isermann Berend 
Published: July 2020

Significance Statement
Signaling to integrins is complex and depends on ligands and their binding sites. Signaling-competent integrin ligands that protect podocyte function remain unknown. This study demonstrates that the coagulation protease-activated protein C (aPC) binds via its RGD sequence to podocyte integrin-β
3. Disruption of the aPC–integrin-β
3 interaction results in excess RhoA activation and podocyte dysfunction. These findings identify the RGD-mediated aPC–integrin-β
3 interaction as a rheostat of RhoA signaling, which is disrupted in diabetic nephropathy. Protease-activated receptor 1 (PAR1) antagonism could ameliorate excess RhoA signaling in the absence of aPC–integrin-β
3 interaction. These data identify a new function of podocyte integrin-β
3 and provide a mechanistic rationale for PAR antagonism as a therapeutic approach for diabetic nephropathy.

Background
Diabetic nephropathy (dNP), now the leading cause of ESKD, lacks efficient therapies. Coagulation protease–dependent signaling modulates dNP, in part via the G protein–coupled, protease-activated receptors (PARs). Specifically, the cytoprotective protease-activated protein C (aPC) protects from dNP, but the mechanisms are not clear.

Methods
A combination of in vitro approaches and mouse models evaluated the role of aPC-integrin interaction and related signaling in dNP.

Results
The zymogen protein C and aPC bind to podocyte integrin-β
3, a subunit of integrin-α
v
β
3. Deficiency of this integrin impairs thrombin-mediated generation of aPC on podocytes. The interaction of aPC with integrin-α
v
β
3 induces transient binding of integrin-β
3 with G
α13 and controls PAR-dependent RhoA signaling in podocytes. Binding of aPC to integrin-β
3
via its RGD sequence is required for the temporal restriction of RhoA signaling in podocytes. In podocytes lacking integrin-β
3, aPC induces sustained RhoA activation, mimicking the effect of thrombin. In vivo, overexpression of wild-type aPC suppresses pathologic renal RhoA activation and protects against dNP. Disrupting the aPC–integrin-β
3 interaction by specifically deleting podocyte integrin-β
3 or by abolishing aPC’s integrin-binding RGD sequence enhances RhoA signaling in mice with high aPC levels and abolishes aPC’s nephroprotective effect. Pharmacologic inhibition of PAR1, the pivotal thrombin receptor, restricts RhoA activation and nephroprotects RGE-aPChigh and wild-type mice.

Conclusions aPC–integrin-α
v
β
3 acts as a rheostat, controlling PAR1-dependent RhoA activation in podocytes in diabetic nephropathy. These results identify integrin-α
v
β
3 as an essential coreceptor for aPC that is required for nephroprotective aPC-PAR signaling in dNP.