Cytoglobin, a novel globin, plays an antifibrotic role in the kidney

Abstract

Cytoglobin (Cygb), a novel member of the globin superfamily, is expressed by fibroblasts in various organs. However, its function remains unknown. Because of its localization, we speculated that a biological role of Cygb may be related to fibrogenesis. To clarify the role of Cygb in kidney fibrosis, we employed the remnant kidney model in rats. Immunohistochemical analysis showed an increase in Cygb expression in parallel with disease progression. To investigate the functional consequence of Cygb upregulation, we established transgenic rats overexpressing rat Cygb. Overexpression of Cygb improved histological injury, preserved renal function, and ameliorated fibrosis, as estimated by the accumulation of collagen I and IV as well as Masson trichrome staining. These protective effects of Cygb were associated with a decrease in nitrotyrosine deposition in the kidney and urinary 8-hydroxy-2′-deoxyguanosine (8-OHdG) excretion as a marker of oxidative stress. We also performed in vitro studies utilizing a rat kidney fibroblast cell line transiently overexpressing Cygb, an inducible kidney cell transfected with Cygb, and primary cultured fibroblasts isolated from the kidneys of the transgenic rats. These different experimental systems consistently showed that Cygb inhibited collagen synthesis. Furthermore, mutant disruption of heme in Cygb that impaired its antioxidant properties led to the loss of antifibrotic effects, suggesting that Cygb reduces fibrosis via a radical scavenging function. In conclusion, we showed that Cygb plays an important role in protection of the kidney against fibrosis via the amelioration of oxidative stress both in vitro and in vivo. Cygb might represent a good therapeutic target in chronic kidney disease.

Cytoglobin: biochemical, functional and clinical perspective of the newest member of the globin family

“…Cygb was first identified in hepatic stellate cells in fibrotic liver, and its fibrosis-induced expression correlated with the upregulation of collagen I protein [14]. Upon fibrogenic stimulus, pancreatic stellate cells and renal interstitial cells also expressed higher Cygb level and, simultaneously, synthesised more collagen [73,79]. Moreover, exogenous overexpression of the globin in combination with TGF-b enhanced collagen production in rat fibroblasts in vitro [26].…”

“…It is of note, however, that while Cygb revealed anti-fibrotic properties, its enforced overexpression was also linked to reduced deposition of collagen protein in fibrotic liver [72] and kidney [73]. Also, in vitro data indicate that exogenous Cygb overexpression decreases collagen mRNA and protein in kidney cell lines [73] and collagen mRNA in lung and breast cancer cell lines [80]. Interestingly, Cygb knock-down did not affect collagen expression in kidney cell lines [73].…”

“…In particular, oxidant-treated neuronal cell lines (SH-SY5Y, TE671), primary HSCs and kidney fibroblasts overexpressing Cygb has demonstrated higher survival rates [21,71,72], ability to scavenge reactive oxygen species (ROS) and lipid-derived radicals [21,[71][72][73] and lower DNA damage [21,74]. Moreover, in the remnant kidney fibrosis model, Cygb overexpression in transgenic rats alleviated accumulation of nitrotyrosine and 8-hydroxy-2 0 -deoxyguanosine, the markers of oxidative and nitrosative stress, thus preserving kidney functioning and reducing fibrotic changes [73]. Inversely, in the cells exposed to oxidative stress, Cygb silencing caused higher apoptosis rate, reduced ROS removal [75] and decreased proliferation rate [59,69].…”

“…Cygb has been proposed to act as a putative O 2 donor for collagen hydroxylation reactions or to activate signalling pathways leading to enhanced collagen synthesis [6]. It is of note, however, that while Cygb revealed anti-fibrotic properties, its enforced overexpression was also linked to reduced deposition of collagen protein in fibrotic liver [72] and kidney [73]. Also, in vitro data indicate that exogenous Cygb overexpression decreases collagen mRNA and protein in kidney cell lines [73] and collagen mRNA in lung and breast cancer cell lines [80].…”

Cytoglobin, a Novel Member of the Globin Family, Protects Kidney Fibroblasts against Oxidative Stress under Ischemic Conditions

“…Immunocytochemistry was performed as previously described. 26 In brief, cells were seeded on four-well chamber slides (Lab-Tek; Nalge Nunc International, Rochester, NY), and fixed with iced acetone-methanol (1:1), followed by indirect immunoperoxidase methods using anti-P1 and antivimentin antibody as primary antibodies. In RT-PCR, primary cultured rat vascular smooth muscle cells 27 and primary cultured rat mesangial cells 28 served as controls.…”