Novel anti-inflammatory strategies for treating diabetic nephropathy.
2017-01-16T23:30:49Z (GMT) by
Diabetic nephropathy is the leading cause of end-stage kidney disease worldwide but current treatments remain suboptimal. Recent evidence has indicated that diabetic nephropathy is an inflammatory disease involving inflammatory cell accumulation, secretion of pro-inflammatory mediators and activation of pro-inflammatory cell signalling pathways. Thus, investigations into novel anti-inflammatory approaches may create opportunities for us to complement existing treatments or design even more potent therapies. Recent evidence indicates a prominent role for macrophages in the development and progression of diabetic nephropathy, and strategies which impair leukocyte migration into the kidney appears protective. In order to conclusively prove that macrophages are crucial targets, we need to study the effects of macrophage inhibition in the early stages of diabetic nephropathy (secondary prevention). Furthermore, previous approaches which impair leukocyte recruitment do not take into account the role of lymphocytes. To address these issues, we examined the effects of selectively inhibiting macrophages after the onset of albuminuria in a mouse model of Type 2 diabetes (Chapter 2). Diabetic mice were treated with a monoclonal antibody against the colony stimulating factor-1 receptor (c-fms). This treatment reduced macrophage accumulation and activation in the diabetic kidney, leading to a reduction in inflammation, hyperfiltration and fibrosis. We next examined the effects of lymphocyte deficiency on the development of diabetic nephropathy (Chapter 3). A genetic deficiency of RAG1 prevented lymphocytes infiltrating the kidneys in mice made diabetic with streptozotocin. RAG1-/- diabetic mice were protected from albuminuria but not from the development of renal fibrosis and loss of renal function. Thus, the role of lymphocytes in this disease is limited. The second half of the thesis examines the functional role of stress-activated protein kinases (SAPKs) in the development of diabetic nephropathy. SAPKs include the p38 mitogen-activated protein kinase (p38 MAPK) and c-Jun NH2-terminal kinase (JNK) intracellular signalling pathways. The activation of SAPKs is increased in kidneys early after the onset of diabetes, and have been implicated in mediating apoptosis, inflammation and fibrosis. In Chapter 4, we pursued p38 MAPK inhibition by genetic deletion of Mkk3, which codes for one of two upstream kinases that selectively activate p38 MAPK. Mkk3-/- mice were cross-bred with db/db mice prone to developing Type 2 diabetes. MKK3 deficiency attenuated p38 MAPK activation in diabetic kidneys despite compensatory upregulation of MKK6, which can also induce activation of p38 MAPK. Mkk3-/- diabetic mice also demonstrated reduced kidney MCP-1 expression, macrophage accumulation, albuminuria, tubulointerstitial injury and preserved renal function. Thus, we found that MKK3-p38 MAPK signalling is non-redundant in several pathogenic processes in diabetic nephropathy, and may be a viable target of intervention. Lastly, we examined the effects of inhibiting JNK in a model of Type 1 (streptozotocin-induced) diabetes associated with hypertension (Chapter 5). Diabetic spontaneously hypertensive rats with established albuminuria were treated with a selective JNK inhibitor (JK-II) for 10 weeks. JK-II attenuated macrophage accumulation in diabetic kidneys by 30%, in part due to suppression of macrophage proliferation. However, JNK inhibition resulted in an unexpected increase in albuminuria and did not protect diabetic kidneys from progressive injury. Macrophages, lymphocytes and SAPKs are some of the major components of inflammation which are thought to be pathologically important in diabetic nephropathy. My examination of the functional role of each of these components in this thesis has provided an increased understanding of diabetic renal inflammation and may help to determine which anti-inflammatory strategies are likely to be therapeutically effective in treating diabetic nephropathy.