Brown adipose tissue derived nidogen-2 as a diabetes therapeutic

About This Grant

Diabetes is characterized by insufficient insulin, and both type 1 (T1D) and advanced type 2 diabetes (T2D) are treated with insulin. One drawback of insulin-only therapy is the risk of hypoglycemia, and alternatives could improve the quality of life for people with diabetes. Destruction of β-cells in T1D also causes glucagon hypersecretion from the of α-cells. Thus, researchers have targeted hyperglucagonemia as a potential therapy in conjunction with insulin. Using glucagon receptor antagonists (GRA) to reduce the action of excess glucagon restores euglycemia in patients with diabetes and allows them to avoid hypoglycemic episodes. Surprising data from our lab show that diabetic phenotypes can be corrected by subcutaneous transplants of embryonic brown adipose tissue (BAT) without measurable insulin. In T1D animal models with BAT transplants, we measure a rapid and robust reduction of plasma glucagon, followed by progressive reversal of clinical signs of diabetes. While blocking glucagon action with GRAs leads to show-stopping side effects, returning glucagon levels to normal by reducing hypersecretion is not expected to cause similar complications. Our preliminary data show that a large molecular weight fraction (CB-100) of BAT secretions inhibits glucagon release from both mouse and human islets, activates the insulin receptor in vitro, and reverses diabetes phenotypes when injected daily in vivo. This reversal happens within days and lasts many weeks after cessation of the injections. The CB-100 fraction also promotes white adipocyte differentiation and browning, supports healthy BAT, and enhances glucose uptake in adipose tissue, skeletal muscle, and liver. From this fraction, we identified nidogen-2 as a critical secreted protein that reverses hyperglycemia in NOD mice, inhibits glucagon secretion from pancreatic α-cells, and mimics other actions of the entire secreted fraction. Nidogen-2 is a ~150 kDa basement membrane assembly protein that is highly expressed in embryonic tissue and known to be cleaved in vivo. Nidogen-2 secreted from BAT does not exhibit full-length protein, but rather a ladder of nidogen-2 fragments. Based on these data, we hypothesize that a fragment of nidogen-2 targets the α-cell directly and that the same or another fragment activates insulin receptors leading to the reversal of diabetes phenotypes when injected in vivo. To test this hypothesis, we propose two Specific Aims, 1) to determine the fragments of nidogen-2 that inhibit glucagon secretion and activate insulin receptors, and 2) to determine the α-cell target of nidogen-2 and its fragments. This research will establish a novel signaling role for nidogen-2, beyond its traditional classification as an extracellular matrix protein. Our results will also establish a nidogen-2 derived peptide as a novel diabetes treatment that could be used in conjunction with insulin treatment. We expect that a complementary therapy would allow patients to maintain euglycemia at near-normal levels with less insulin dose and less worry about hypoglycemia. The work proposed here will focus on T1D models, but we expect that the results will also be broadly applicable to advanced T2D.