The role of chemokine receptor CCR1-dependent macrophage recruitment for the progression of chronic kidney disease in murine Alport syndrome or type 2 diabetes

The global burden of chronic kidney diseases remains an ongoing
medical challenge. Therapies that can halt or reverse advanced
renal injury are not yet available. Increasing numbers of patients
progress to the end-stage renal failure and require renal
replacement therapy, the latter being associated with significant
mortality, a lower quality of life, and high costs for national
health systems. Thus, new treatment strategies that slow down, halt
or even revert progressive renal damage are requested. Chemokines
and their receptors are involved in the pathogenesis of renal
diseases. They mediate leukocytes and macrophages recruitment and
activation during initiation as well as progression of renal
inflammation. Infiltrating leukocytes are the major source for
proinflammatory and profibrotic cytokines and are therefore
critical for mediating fibroblast proliferation, differentiation
into myofibroblasts, matrix production, and tubular atrophy. Recent
advances in the understanding of the molecular mechanisms that
regulate renal leukocyte recruitment suggest chemokines and
chemokine receptors as novel targets for specific pharmacological
intervention. The aim of the present thesis was to investigate the
role of chemokine receptor CCR1 for the progression of chronic
kidney diseases, e.g. Alport disease and diabetic nephropathy. Two
different animal models were used: Col4A3-deficient mice and type 2
diabetic db/db mice with advanced diabetic nephropathy. We blocked
CCR1 in Col4A3-deficient mice with BX417, a small molecule CCR1
antagonist, and BL5923, a novel orally available antagonist with a
high specificity for human and murine CCR1 in uninephrectomized
type 2 diabetic db/db mice, respectively. Treatment with BX471
(25mg/kg) from weeks 6 to 10 of life improved survival of COL4A3-
deficient mice, characterized by glomerulosclerosis and subsequent
progressive tubulointerstitial injury, leading to fatal end-stage
renal disease (ESRD). Improvement was associated with less
interstitial macrophages, apoptotic tubular epithelial cells,
tubular atrophy, interstitial fibrosis, and less globally sclerotic
glomeruli. BX471 reduced total renal Ccl5 mRNA expression by
reducing the number of interstitial CCL5-positive cells in
inflammatory cell infiltrates. Intravital microscopy of the
cremaster muscle in male mice identified that BX471 or lack of CCR1
impaired leukocyte adhesion to activated vascular endothelium and
transendothelial leukocyte migration, whereas leukocyte rolling and
interstitial migration were not affected. Furthermore, in activated
murine macrophages, BX471 completely blocked CCL3-induced CCL5
production. When CCR1 was blocked with BL5923 (60mg/kg, b.i.d), the
interstitial recruitment of ex vivo labeled macrophages was
markedly decreased in uninephrectomized male db/db mice with type 2
diabetes. Similarly, BL5923 orally administered from month 5 to 6
of life reduced the numbers of interstitial macrophages in
uninephrectomized db/db mice. This was associated with reduced
numbers of Ki-67 proliferating tubular epithelial and interstitial
cells, tubular atrophy, and interstitial fibrosis in
uninephrectomized db/db mice. Glomerular pathology and proteinuria
were not affected by the CCR1 antagonist. BL5923 reduced renal mRNA
expression of Ccl2, Ccr1, Ccr2, Ccr5, Tgf-β1, and collagen I-α1
when compared to untreated uninephrectomized male db/db mice of the
same age. Thus, we identified a previously unrecognized role for
CCR1-dependent recruitment of interstitial macrophages for the
progression of chronic kidney disease in Alport disease and
diabetic nephropathy. These data identify CCR1 as a potential
therapeutic target for Alport disease and late stage diabetic
nephropathy or other progressive nephropathies associated with
interstitial macrophage infiltrates.