Background: Although calcineurin inhibitors (CNIs) such as tacrolimus and cyclosporin have dramatically improved the quality of patient care, long-term therapy causes irreversible damage to the kidneys in the form of renal fibrosis. These morphologic changes ultimately lead to a decline in renal function and can progress to end-stage renal failure. These detrimental outcomes present a critical need to identify the driving mechanisms by which CNIs cause renal damage.
Objective: It is well established that TGFb is a major contributor to CNI-induced renal fibrosis. However, the underlying mechanisms remain unknown. The objectives of this study are to 1) investigate whether TGFb secretion is required to stimulate TGFb receptor signaling in a model of CNI-induced renal fibrosis and 2) investigate whether calcineurin plays a critical role in regulating TGFb receptor activity.
Experimental
Design: To examine the role of calcineurin inhibition in altered TGFb receptor signaling, wild type mice were treated with either vehicle (0.01% ethanol) or 10 mg/kg tacrolimus for 7 days. To confirm in vivo findings, wild-type mouse renal cortical fibroblasts were treated with either vehicle (0.01% ethanol) or 1nM tacrolimus for 24 hours in the presence and absence of anti-TGFb neutralizing antibodies. TGFb receptor expression and activation, TGFb receptor downstream signaling mediators, profibrotic markers and calcineurin activity were analyzed.
Results: Findings demonstrate that tacrolimus-induced loss of calcineurin activity is accompanied with enhanced TGFb receptor activation and signaling. Notably, increasing concentrations of anti-TGFb neutralizing antibodies failed to abolish aberrant TGFb signaling and increased expression of profibrotic markers.
Conclusions: Together, these results demonstrate that 1) CNIs promote ligand-independent TGFb signaling and 2) calcineurin plays a functional role in regulating TGFb receptor activity.
Significance: This study elucidates a direct pharmacological mechanism by which CNIs promote renal fibrosis and provides a physiological role of calcineurin in regulating TGFb receptor activity. Further insight into the role of calcineurin in regulating TGFb receptor activity could improve the long-term outcomes of patients on chronic CNI therapy.
lt;bgt;Funding Source:lt;/bgt;lt;bgt; lt;/bgt;AHA-16SDG27080009 and NIH-R21DK119879