B7-1/CD80 is known as a bidirectional regulator of T cell activation and tolerance. We previously reported an unanticipated novel role for B7-1 in podocytes as inducible mediator of podocyte injury and proteinuria in humans and animals. B7-1 can be targeted by blocking antibodies such as Abatacept (CTLA4-Ig), which is currently used for the treatment of patients with rheumatoid arthritis. Our novel data obtained with this grant suggest that the anti-proteinuric action of CTLA4-Ig is independent of its inhibitory action on T cell costimulation but stems from a direct effect on podocytes. Our novel data further suggest that the upregulation of B7-1 in podocytes actively contributes to the pathogenesis of proteinuria by altering podocyte structure and function. Most importantly, they offer a rationale for the use o Abatacept as anti-proteinuric treatment. Here we propose to test our central hypothesis that induction of B7-1 expression in podocytes contributes to the pathogenesis of proteinuria by blocking talin mediated ?1 integrin activation in podocytes. We further hypothesize that Abatacept/CTLA4-Ig and possible Belatacept prevent proteinuria by blocking B7-1 signaling in podocytes. To test this hypothesis we propose two Specific Aims.
The first Aim will define the mechanistic role of B7-1 and the effects of its blockade on podocyte- matrix adhesion.
Specific Aim 2 will assess the anti-proteinuric therapeutic potential of B7-1 blockade in mice. If our hypothesis is correct, the work proposed here will have broad significance in the long-term, because it will firmly establish the rationale for a prospective clinical study of B7-1 blockade in patients with proteinuria, including cases of recurrent and non-recurrent FSGS. This should in the long-term enable us to develop novel therapies that tackle proteinuria and glomerulosclerosis by blocking B7-1 signaling in podocytes.

Public Health Relevance

Our work funded by this grant has provided novel insights into the pathogenesis and treatment of proteinuria. It led to the novel concept that B7-1 signaling in podocytes contributes to the pathogenesis of proteinuria by altering podocyte integrin signaling. The work proposed here should provide insight into the molecular mechanism whereby B7-1 expression in podocytes causes proteinuria. It should also establish the molecular rationale for the use of B7-1 blockade as anti-proteinuric therapy in patients with Rituximab-resistant recurrent FSGS and other proteinuric kidney diseases.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Mullins, Christopher V
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Massachusetts General Hospital
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Buvall, Lisa; Wallentin, Hanna; Sieber, Jonas et al. (2017) Synaptopodin Is a Coincidence Detector of Tyrosine versus Serine/Threonine Phosphorylation for the Modulation of Rho Protein Crosstalk in Podocytes. J Am Soc Nephrol 28:837-851
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