The researchers found a role for citrullic vimentin as a spoilage-related molecular pattern, or DAMP, created by pulmonary macrophages in response to environmental cadmium / carbon black.
Birmingham, Ala. The etiology and causes of acute scarring of the lungs – idiopathic pulmonary fibrosis or IPF – remain unclear.
The research is now published in Transitional Medicine Sciences It demonstrates how cadmium and carbon black can stimulate pulmonary macrophages to produce a modified protein, feminine citrulline, or FEM, leading to lung fibrosis. Researchers from the University of Alabama at Birmingham and three other American universities described a series of mechanical steps in pulmonary macrophages and pulmonary fibroblasts that lead to lung scarring.
One of the enzymes involved in these steps – peptidylarginine deiminase 2, or PAD2 – may be a promising target for mitigating cadmium / black carbon-induced fibrosis, they say. The researchers also reported a potential disease model for pulmonary fibrosis and IPF – the use of cadmium chloride to induce interstitial fibrosis in mice.
The study, led by Vina Anthony, MD, involved patients with IPF, tissue experiments, and mouse models. Anthony is Professor of Environmental Medicine in the Department of Medicine at Abu Dhabi University, and she directs the UAB Super Fund Research Program.
“Altogether, these studies support the role of cit-vim as a spoilage-related molecular pattern, or DAMP, that is generated by pulmonary macrophages in response to environmental exposure to cadmium / carbon black,” Anthony said. Cadmium is a toxic heavy metal known to be a cause of lung fibrosis. Cadmium can absorb on black carbon particles. In the lung, these particles are ingested by macrophages, the guard cells of the guard host of the mammalian lung. Up to two-thirds of IPF patients have a history of smoking, and cigarette smoke contains both cadmium and carbon black. Air pollution from biomass fuels and coal furnaces are also a source of pollutants.
Data from humans
Researchers assessed the accumulation of cadmium and cit-vim in tissues using lung biopsies
Of the 25 people with an IPF – eight have never smoked, 17 smokers – and 14 officers – eight have never smoked and six smokers.
The researchers found that both cadmium and carbon black had a significant accumulation in the lung tissue of IPF patients. Moreover, cadmium concentrations in IPF lung tissue were directly related to cit-vim amounts, and cit-vim amounts were higher in smoked IPF tissue compared to non-smoked IPF tissue. Also, people with IPF had higher plasma cit-vim levels, and these amounts were inversely related to lung function. Pulmonary macrophages from subjects with IPF significantly increased vimentin and cit-vim expression compared to macrophages from controls. Vimentin is a structural protein in animal cells.
Data from human tissue
Using pulmonary macrophages from subjects with IPF, the researchers found that cadmium / carbon black induced by citrullination of vimentin, and cit-vim secretion from pulmonary macrophages was dependent on the activation of two enzymes, Akt1 and PAD2. Citrullination is the binding of the amino acid citrulline to a protein.
Cit-vim isolated and purified from pulmonary macrophages was able to induce atmospheric invasion by primary lung fibroblasts from normal subjects. Cit-vim enhanced the expression of collagen by fibroblasts, and the expression of collagen by pulmonary fibroblasts from IPF subjects was greater. The atmosphere – the 3D spheroids – was derived from normal lung tissue. Fibroblast proliferation and excessive collagen deposition are part of lung scarring in IPF.
DAMPs are particles of damaged or dying cells that trigger an innate immune response to clean up the damage. The researchers demonstrated that cit-vim acted as a DAMP to activate fibroblasts through a receptor signaling similar to the number 4. Activated fibroblasts produced protivyprotic cytokines, which contribute to the pathogenesis of IPF.
Thus, the data emphasize a critical role for pulmonary macrophages in the development of pulmonary fibrosis.
Data from mice
In animals, researchers found that mice treated with cit-vim, but not natural vimentin, independently developed lung fibrosis, with architectural destruction and increased collagen deposition, in a 4-receptor-dependent manner. Wild mice exposed to cadmium / black produced carbon – but not Mutations in mice lacking PAD2 or toll-like receptors 4 – large amounts of cit-vim in plasma and in bronchial lavage fluid, resulting in mice with pulmonary fibrosis.
Anthony said: “This finding is important, because cit-vim is sufficient to elicit fibroblast activation in vitro and elicit professional cytokine / chemokine production and TLR4-dependent pulmonary fibrosis in vivo.
“Our data show that cadmium / carbon black is a risk factor, not only in people with IPF and those who smoke, but also in non-smokers. Higher concentrations of cadmium in non-smoking patients may be caused by exposure to cadmium through food and / or occupation. Or the environment. “
Co-authors with Anthony in the study, “Citrus Vimentin Mediates Progression and Evolution of Pulmonary Fibrosis” are Fu Jun Lee, Rano Sorolia, Huashi Lee, Cheng Wang, Zhang Liu, Tigaswini Kulkarni, Keith Weil and Victor J. Brent Carter, Department of Pulmonology, Allergy and Critical Care, Department of Medicine, Abu Dhabi University. Adriana VF Massicano and Suzanne E. Lapi, Department of Radiology at UAB; James A. Mobley, Department of Surgery at United Arab Emirates University; Santano Mondal and Paul R. Thompson, University of Massachusetts Medical School, Worcester, Massachusetts; Joao A. De Andrade, Vanderbilt University Medical Center, Nashville, Tennessee; Scott A. Conrod, College of Veterinary Medicine, Cornell University, Ithaca, New York; And Muhammad Athar, Department of Dermatology, University of Bahrain.
Support came from NIH grants ES027723, ES029981, ES015981-13, ES030246, HL114470, CA013148 and GM118112; And from the Department of Veterans Affairs, grant 1 I01 CX001715-01.