Origin of renal myofibroblasts in the model of unilateral ureter obstruction in the rat

Abstract

Tubulo-interstitial Wbrosis is a constant feature of chronic renal failure and it is suspected to contribute importantly to the deterioration of renal function. In the Wbrotic kidney there exists, besides normal Wbroblasts, a large population of myoWbroblasts, which are supposedly responsible for the increased production of intercellular matrix. It has been proposed that myoWbroblasts in chronic renal failure originate from the transformation of tubular cells via epithelial-mesenchymal transition (EMT) or from inWltration by bone marrow-derived precursors. Little attention has been paid to the possibility of a transformation of resident Wbroblasts into myoWbroblasts in renal Wbrosis. Therefore we examined the fate of resident Wbroblasts in the initial phase of renal Wbrosis in the classical model of unilateral ureter obstruction (UUO) in the rat. Rats were perfusion-Wxed on days 1, 2, 3 and 4 after ligature of the right ureter. Starting from 1 day of UUO an increasing expression of alpha-smooth muscle actin ( SMA) in resident Wbroblasts was revealed by immunoXuorescence and conWrmed by the observation of bundles of microWlaments and webs of intermediate Wlaments in the electron microscope. Inversely, there was a decreased expression of 5Ј-nucleotidase (5ЈNT), a marker of renal cortical Wbroblasts. The RER became more voluminous, suggesting an increased synthesis of matrix. Intercellular junctions, a characteristic feature of myoWbroblasts, became more frequent. The mitotic activity in Wbroblasts was strongly increased. Renal tubules underwent severe regressive changes but the cells retained their epithelial characteristics and there was no sign of EMT. In conclusion, after ureter ligature, resident peritubular Wbroblasts proliferated and they showed progressive alterations, suggesting a transformation in myoWbroblasts. Thus the resident Wbroblasts likely play a central role in Wbrosis in that model.

Renal fibrosis is attenuated by targeted disruption of K Ca 3.1 potassium channels

“…This indicates that loss of K Ca 3.1 likely constrains proliferation of renal (myo)fibroblasts in a profibrotic setting, thus resulting in fewer matrix-producing cells. As shown previously, fibroblasts from fibrotic kidneys are characterized by an enhanced proliferative activity and matrix synthesis capacity (7,8). However, it should be noted that activated resident interstitial fibroblasts may not be the only cells participating in extracellular matrix production.…”

“…For instance, there have been reports that transformed tubular epithelial and endothelial cells as well as bone marrow-derived cells may potentially constitute a part of this cell population in the diseased kidney (3,4). However, ample evidence suggests that resident interstitial fibroblasts represent a significant, if not major, source of (myo)fibroblast recruitment (5)(6)(7)(8). Hence, suppression of fibroblast proliferation in the injured kidney may diminish the number of scar tissue generating cells and could thus yield an option to halt progression of renal fibrosis.…”

Pericytes and Perivascular Fibroblasts Are the Primary Source of Collagen-Producing Cells in Obstructive Fibrosis of the Kidney

“…13 In this context it is worth noting that several recent studies have also implicated an endogenous 'fibroblast' in the normal kidney as a precursor to the myofibroblast, though none has used kinetic modeling or genetic fate mapping. [32][33][34] The fact that pericytes are a major source of myofibroblasts serves to readjust the focus of fibrosis research to the vasculature. Rather than epithelial injury serving as the driving force for fibrosis, our studies lead one to speculate that in fact vascular injury or vascular factors are the most likely triggers for pericyte migration and differentiation into myofibroblasts.…”

Immunophenotypical Characterization of Macrophages in Rat Bleomycin-Induced Scleroderma

“…ED1 (Millipore, Bedford, Massachusetts; 1:500) labels CD68-expressing macrophages, 3 ED2 (AbD Serotec, Oxford, UK; 1:500) is used to identify CD163-expressing macrophages, 32 and OX6 (AbD Serotec; 1:500) recognizes MHC class II molecules in rats. 31 Myofibroblasts were identified using an antibody to a-smooth muscle actin (a-SMA) (clone IA4; DAKO, Carpinteria, California; 1:200). An antibody to galectin-3 (polyclonal; sc-20157; Santa Cruz Biotechnology, Santa Cruz, California; 1:500), which may be associated with the production of fibrogenic proteins by macrophages, was also applied.…”

“…32 OX6 labels MHC class II molecules in antigenpresenting cells. 31 Besides these grouping, currently, macrophages appearing in lesions are classified as classically activated M1 (proinflammatory) and alternatively activated M2 (reparative) macrophages. 23,38 Macrophage properties influencing scleroderma formation have not been fully clarified.…”