Activated protein C protects against diabetic nephropathy by inhibiting endothelial and podocyte apoptosis

Abstract

Data providing direct evidence for a causative link between endothelial dysfunction, microvascular disease and diabetic end-organ damage are scarce. Here we show that activated protein C (APC) formation, which is regulated by endothelial thrombomodulin, is reduced in diabetic mice and causally linked to nephropathy. Thrombomodulin-dependent APC formation mediates cytoprotection in diabetic nephropathy by inhibiting glomerular apoptosis. APC prevents glucose-induced apoptosis in endothelial cells and podocytes, the cellular components of the glomerular filtration barrier. APC modulates the mitochondrial apoptosis pathway via the protease-activated receptor PAR-1 and the endothelial protein C receptor EPCR in glucose-stressed cells. These experiments establish a new pathway, in which hyperglycemia impairs endothelial thrombomodulin-dependent APC formation. Loss of thrombomodulin-dependent APC formation interrupts cross-talk between the vascular compartment and podocytes, causing glomerular apoptosis and diabetic nephropathy. Conversely, maintaining high APC levels during long-term diabetes protects against diabetic nephropathy.

Caspase-1, but Not Caspase-3, Promotes Diabetic Nephropathy

“…Our in vitro analyses showing activation of caspase-3 and other apoptosis regulators (caspase-7, PARP1) in glucose-stressed podocytes are in agreement with earlier reports. 1,11,24 Notably, the detailed kinetic analyses revealed that the induction of apoptosis regulators is preceded by Nlrp3 induction and caspase-1 activation in vitro, supporting a prominent role of inflammasome activation for glucoseinduced cell damage. Of note, pyroptosis (cell death resulting from unfettered inflammasome activation) and apoptosis are not exclusive, and pathways leading to or triggered by these cell-death forms interact.…”

“…Previously, induction of caspase-3 or caspase-1 activation by high glucose concentrations has been reported in vitro. 3,11,12 However, direct comparative analyses providing insight into the kinetics are lacking. Hence, we analyzed the temporal pattern of inflammasome and apoptosis activation upon glucose stimulation (25 mM) in murine podocytes in vitro.…”

“…1,11 Of note, these studies frequently used a TUNEL assay to detect apoptosis. 1,11,20,21 However, the TUNEL assay is not specific for apoptosis and additionally detects other cell-death forms.…”

“…1,11 Of note, these studies frequently used a TUNEL assay to detect apoptosis. 1,11,20,21 However, the TUNEL assay is not specific for apoptosis and additionally detects other cell-death forms. 22,23 Importantly, both interventions, CIX and M-920, reduced glomerular cell death and in situ caspase-3/7 activity in this study, but the CIX inhibitor nevertheless failed to protect from dNP.…”

Multiple levels of regulation determine the role of the receptor for AGE (RAGE) as common soil in inflammation, immune responses and diabetes mellitus and its complications

“…Thus, binding of HMGB1 by TM might be a mechanism for terminating RAGE-mediated sustained inflammatory responses. In diabetes, TM production is reduced [65], which results in loss of this counter-regulatory pathway that is dependent on protein×protein interaction. Future studies need to show whether reconstitution of TM in experimental diabetes can reduce late diabetic complications by specifically interfering with the RAGE pathway.…”