M. Amin Arnaout, MD

Institution: Massachusetts General Hospital
Research: Biology, structure and therapeutic targeting of integrins
Grants & Publications: Harvard Catalyst
Categories: MGH

A major research focus of the Arnaout Laboratory is to elucidate the structure and function of integrins, divalent cation-dependent cell adhesion receptors that play vital roles in normal cell physiology but also in common diseases. We use the information derived from our structural studies to design and test novel and safer anti- integrin drugs targeting inflammation, thrombosis, fibrosis, autoimmunity and cancer. The Laboratory uses cell, structure and molecular biology approaches and rodent and nonhuman primate (NHP) models for testing the generated compounds. Current projects are:

1. Integrins in proteinuric kidney disease. The stoichiometric cis association of the tetraspanin CD151 with podocyte integrin α3β1 is essential for stabilizing α3β1 in an active ligand binding conformation, thus maintaining the integrity of the glomerular filtration barrier (GFB). Other studies show that activation of αvβ3 in podocytes by inflammatory mediators, growth factors or mechanical/shear stress plays a critical role in disrupting the GFB. We are investigating the cellular, structural basis of the opposing roles α3β1 and αvβ3 play in regulating GFB homeostasis both in vitro and in rodent models of proteinuric kidney disease. inactivated genetically or pharmacologically in rodent models of proteinuric kidney disease.

2. Structural basis of platelet integrin αIIbβ3 activation and its therapeutic targeting. The paradigmatic platelet integrin αIIbβ3 plays a central non-redundant role in hemostasis but also in pathologic thrombosis. αIIbβ3 is normally kept in an inactive bent conformation on circulating platelets, but rapidly switches to an active (ligand-binding) conformation in response to inside-out signaling. The ligand-occupied receptor then transmits outside-in signals via the αβ transmembrane and cytoplasmic domains that initiate platelet adhesion, a response inadvertently produced by current drugs, leading to adverse outcomes, which has limited their clinical efficacy. The structural basis of bidirectional integrin signaling remains to be clarified. Ongoing studies are aimed at elucidating the structural basis of αIIbβ3 activation and developing compounds to avoid agonism while providing effective antagonism.

3. Role of integrin CD11b in delayed graft function (DGF). DGF is a manifestation of ischemia-reperfusion injury (IRI) in the transplanted kidney allograft. DGF is an important risk factor in T-cell or antibody- mediated biopsy-proven acute rejection, and the strongest risk factor for chronic allograft dysfunction exceeding even that of pre-transplant diabetes. We have shown that the archetypal innate immune receptor leukocyte integrin CD11b/CD18 mediates IRI in native NHP kidneys, and that a first-in-class anti- CD11b monoclonal antibody (mAb107) protected IRI native kidneys from otherwise irreversible kidney failure. We are evaluating the effect of limiting IRI with mAb107 on DGF in our well-studied NHP kidney transplant model. These studies have implications on preventing IRI of allogeneic pancreatic islets, a major cause of poor engraftment or progressive loss of allogeneic islet transplants in humans.

4. Abnormal metabolism in ADPKD. A hallmark of ADPKD cells is increased cell proliferation and aerobic glycolysis with upregulation of the glycolytic enzymes HK, PFK and PKM2 and down-regulation of LKB1/AMPK. Competitive inhibition of glycolysis with the non-metabolizable glucose analog 2-deoxy-D- glucose (DG) slowed disease progression in Pkd1 knockout mice. Yet the primary effector(s) that connects the underlying genetic defect in ADPKD to aberrant proliferation and Warburg metabolism remains to be identified. We now show that Warburg metabolism in the Pkd1 null mouse cells is β1 integrin-dependent and requires an extramitochondrial Plasma Membrane Electron Transport (PMET) redox system, which converts excess NADH back to NAD+ to fuel aerobic metabolism. We are evaluating the role of integrin β1 and PMET in energy utilization in tamoxifen-inducible mouse and human primary ADPKD cells, identify the β1 integrin signaling intermediates involved and the effect of PMET inhibition on rapid and slow kidney cyst growth in an inducible Pkd1 knockout mouse model.