Mast cells are required for the development of renal fibrosis in the rodent unilateral ureteral obstruction model

Abstract

Mast cells are associated with inflammation and fibrosis. Whether they protect against or contribute to renal fibrosis is unclear. Based on our previous findings that mast cells can express and secrete active renin, and that angiotensin (ANG II) is profibrotic, we hypothesized that mast cells play a critical role in tubulointerstitial fibrosis. We tested this hypothesis in the 14-day unilateral ureteral obstruction (UUO) model in rats and mast cell-deficient (MCD) mice (WBB6F1-W/Wv) and their congenic controls (CC). In the 14-day UUO rat kidney, mast cell number is increased and they express active renin. Stabilizing mast cells in vivo with administration of cromolyn sodium attenuated the development of tubulointerstitial fibrosis, which was confirmed by measuring newly synthesized pepsin-soluble collagen and blind scoring of fixed trichrome-stained kidney sections accompanied by spectral analysis. Fibrosis was absent in UUO kidneys from MCD mice unlike that observed in the CC mice. Losartan treatment reduced the fibrosis in the CC UUO kidneys. The effects of mast cell degranulation and renin release were tested in the isolated, perfused kidney preparation. Mast cell degranulation led to renin-dependent protracted flow recovery. This demonstrates that mast cell renin is active in situ and the ensuing ANG II can modulate intrarenal vascular resistance in the UUO kidney. Collectively, the data demonstrate that mast cells are critical to the development of renal fibrosis in the 14-day UUO kidney. Since renin is present in human kidney mast cells, our work identifies potential targets in the treatment of renal fibrosis.

Mast Cells: A Pivotal Role in Pulmonary Fibrosis

“…To strengthen this finding, trichrome-stained lung sections were also analyzed computationally using an algorithm that spectrally separates blue (collagen) from red (cytosol) stained areas of each slide as previously described (Veerappan et al, 2011). The ratios of the average blue (collagen) stained areas to the average total tissue areas (blue + red [cytosol] areas) of the mouse lung are shown in Figure 2C.…”

“…Masson's Trichrome staining was performed using a kit (Richard-Allen Scientific) or Gomori's trichrome reagents using a dilution of Weigert's hematoxylin at 1:10 as previously described (Veerappan et al, 2011).…”

“…The same trichrome-stained slides underwent spectral analysis as previously described (Veerappan et al, 2011). Brightfield spectral analysis was performed blind.…”

“…Stained tissue sections were imaged by capturing adjacent, nonoverlapping, fields using a 10 · objective lens and the SPOT Insight 2 camera with its accompanying software. For each animal, sections spanning the lung were imaged, and the total area of collagen staining was divided by the total area of tissue imaged (Veerappan et al, 2011).…”

“…Immunocytochemistry was performed as previously described (Silver et al, 2004;Veerappan et al, 2008Veerappan et al, , 2011. Primary antibodies used were goat anti-AT 1 R (1:50) and rabbit anti-H 1 R antibodies (1:50) (SCBT).…”