Alport syndrome results from mutations of any of three type IV collagen genes COL4A3, COL4A4, or COL4A5, any of which result in the absence of all three proteins in the glomerular basement membrane. This is the underlying cause of the disease, which affects more than 1 in 5000 people worldwide. In humans and animal models, the disease presents as delayed onset and progressive, allowing a window for therapeutic intervention. We and others have published definitive works which point to a key role for dysregulation of matrix metalloproteinases (MMPs) as an underlying cause of Alport GBM pathology. How dysregulation of MMP gene regulation occurs, however, has remained unclear, as has the mechanism of glomerular disease initiation. We provide compelling evidence supporting the central hypothesis of this proposal that disease initiation results from altered signaling through 1321 integrin which activates expression of abnormal laminin in podocytes. These laminins (111 and 211) accumulate in the GBM and directly activate focal adhesion kinase, causing actin cytoskeletal rearrangement and maladaptive gene regulation, which promotes foot process effacement and proteolytic degradation of the GBM. We test this hypothesis in three specific aims. In the first aim we use cell culture and in vivo approaches to explore the role of altered 1321 integrin signaling through integrin linked kinase in the activation of abnormal laminin expression, and the role of abnormal laminins in FAK activation. A double transgenic mouse expressing 12 and 21 laminins under control of an inducible podocyte-specific promoter will determine whether abnormal GBM laminin deposition is sufficient to trigger Alport-like glomerular pathology and thus constitute the trigger for disease initiation. In the second aim we examine the relationship between FAK activation and cytoskeletal rearrangement and downstream maladaptive gene regulation including massive induction of matrix metalloproteinase 10 and 12 using a combination of small molecule inhibitor studies on cultured podocytes and in vivo combined with a conditional FAK knockout mouse. In the third aim we will examine the collaborative role of MMP-10 and MMP-12 in GBM destruction associated with Alport glomerular pathology. We will employ a genetic approach to produce mice that are null for COL4A3 and MMP-12, and conditional null for MMP-10 to determine whether blocking both of these MMPs provides a viable therapeutic intervention for possible application in the human Alport population. Successful completion of these aims will define the molecular mechanism of Alport glomerular disease initiation, which is a major step towards development of therapies aiming to arrest the disease in its pre-clinical state.
A targeted therapeutic approach for patients with Alport syndrome does not exist. Currently the 1 in 20,000 people with the disease are treated with ACE inhibitors, dialysis, and transplant. This work utilizes animal models to explore new therapeutic targets aimed at arresting the disease in its early stages.
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