Sodium-independent mechanisms of edema in nephrotic syndrome

The National Institute of Diabetes and Digestive and Kidney Diseases awarded Rush University Medical Center $749,087 on September 1, 2026, under the Diabetes, Digestive, and Kidney Diseases Extramural Research program (CFDA 93.847) to investigate sodium-independent mechanisms of edema in nephrotic syndrome.

The project studies the role of circulating angiopoietin-like 4 (ANGPTL4), specifically its C-fragment, as a mediator of skin capillary endothelial permeability in nephrotic syndrome-related edema. Work includes inducing nephrotic syndrome in rodent models to quantify edema formation and developing surrogate in vitro assays using dermal endothelial cells; developing a novel ex vivo three-dimensional reconstruction method for rodent skin biopsies using microcomputed tomography; conducting x-ray crystallography to identify exposed portions of rat and human ANGPTL4-C region; developing monoclonal antibodies to selectively deplete rat ANGPTL4 C-fragment; and studying mechanisms by which C-ANGPTL4 fragments induce increased endothelial permeability in animal models and cultured dermal endothelial cells.

Performance occurs at Chicago, Illinois. The period of performance runs from September 1, 2026, through May 31, 2031. This is a Project Grant, a standard assistance type under the program that supports extramural basic and clinical biomedical research improving understanding of disease mechanisms and leading to improved prevention, diagnosis, and treatment of diabetes, digestive, and kidney diseases.

Abstract

The pathogenesis of edema in nephrotic syndrome involves sodium retention by the kidney and putative factors/proteins in the nephrotic circulatory milieu that increase skin capillary endothelial permeability. Preliminary work in our lab suggests that the circulating glycoprotein angiopoietin-like 4 (ANGPTL4) may be a major mediator of dermal capillary endothelial permeability. ANGPTL4 in the circulation is present in 3 naturally occurring forms: the intact oligomer, the oligomeric n-fragment and the monomeric c-fragment. Proof of concept studies involving overexpression of RAT ANGPTL4 from adipose tissue in rats suggest that high ANGPTL4 levels promote edema, but do not distinguish between the different forms. Depletion studies using specific antibodies targeting the n- and c-fragments, and ancillary studies using purified full length oligomer, suggest that the ANGPTL4 c-fragment may be the key mediator of skin capillary endothelial permeability in nephrotic syndrome related edema. In this proposal, we will study the following: in specific aim 1, nephrotic syndrome will be induced in rodent models to quantify edema formation and develop surrogate in vitro assays using dermal endothelial cells. Aside from using evans blue and skin fold thickness measurements to quantify edema, a novel EX vivo method for 3D reconstruction of rodent skin biopsies using microct will be developed. X-RAY crystallography studies will be conducted to identify parts of RAT and human ANGPTL4-c region that are exposed in the c-fragment but sequestered in the oligomer. Monoclonal antibodies will be developed to selectively deplete RAT ANGPTL4 c-fragment without depletion of the full length oligomer. In specific aim 2, mechanisms by which c-ANGPTL4 fragments induce increased endothelial permeability in nephrotic syndrome will be studied in animal models and in cultured dermal endothelial cells . Effects on the expression and distribution of integrin Β1, VE-cadherin and claudin-5, and effect of knockdown of these proteins in cultured cells incubated with c- ANGPTL4 fragments will be assessed. In specific aim 3, monoclonal antibodies developed in aim 1 will be tested in RAT models to assess for diuresis and reduction of edema, alone or in synergy with diuretics. For antibodies that can reduce edema, monoclonal antibodies will be developed to corresponding regions in human c-ANGPTL4 fragments, which will then be tested in vitro. A potential for future studies for these monoclonal antibodies with an ANGPLT4 knockout with human ANGPTL4 knock-in RAT model is discussed.