Versican Deficiency Significantly Reduces Lung Inflammatory Response Induced by Polyinosine-Polycytidylic Acid Stimulation

Abstract

Edited by Gerald W. HartViral infection is an exacerbating factor contributing to chronic airway diseases, such as asthma, via mechanisms that are still unclear. Polyinosine-polycytidylic acid (poly(I:C)), a Toll-like receptor 3 (TLR3) agonist used as a mimetic to study viral infection, has been shown to elicit inflammatory responses in lungs and to exacerbate pulmonary allergic reactions in animal models. Previously, we have shown that poly(I:C) stimulates lung fibroblasts to accumulate an extracellular matrix (ECM), enriched in hyaluronan (HA) and its binding partner versican, which promotes monocyte adhesion. In the current study, we aimed to determine the in vivo role of versican in mediating inflammatory responses in poly(I:C)-induced lung inflammation using a tamoxifen-inducible versican-deficient mouse model (Vcan ؊/؊ mice). In C57Bl/6 mice, poly(I:C) instillation significantly increased accumulation of versican and HA, especially in the perivascular and peribronchial regions, which were enriched in infiltrating leukocytes. In contrast, versican-deficient (Vcan ؊/؊ ) lungs did not exhibit increases in versican or HA in these regions and had strikingly reduced numbers of leukocytes in the bronchoalveolar lavage fluid and lower expression of inflammatory chemokines and cytokines. Poly(I:C) stimulation of lung fibroblasts isolated from control mice generated HA-enriched cable structures in the ECM, providing a substrate for monocytic cells in vitro, whereas lung fibroblasts from Vcan ؊/؊ mice did not. Moreover, increases in proinflammatory cytokine expression were also greatly attenuated in the Vcan ؊/؊ lung fibroblasts. These findings provide strong evidence that versican is a critical inflammatory mediator during poly(I:C)-induced acute lung injury and, in association with HA, generates an ECM that promotes leukocyte infiltration and adhesion.

Versican—A Critical Extracellular Matrix Regulator of Immunity and Inflammation

“…Versican is essential during development (76,77) and it is now becoming apparent that it is an important component of the tissue inflammation caused by infection and tissue injury (10). Versican accumulates as part of the early inflammatory response in a number of human diseases often associated with the invasion of leukocytes including those in the vascular system (10,40,(78)(79)(80)(81)(82)(83)(84), lung (5,6,60,77,(85)(86)(87)(88)(89), brain and spinal cord (53,(90)(91)(92), intestine (93)(94)(95)(96), heart (97), liver (63), skin (98,99), eye (100, 101), pancreatic islets (102), and many different forms of cancer [reviewed in (103)(104)(105)]. The accumulation of versican in these tissues is usually associated with other ECM components that bind versican, such as hyaluronan (106,107), link protein, TSG-6, IαI, and CD44 (95, 96, 108-111) (Figure 1).…”

“…LPS and poly I:C, two TLR agonists, stimulate versican expression in both murine bone marrow-derived macrophages and alveolar macrophages in vitro (87) and in murine alveolar macrophages as well as in stromal cells in vivo (60,88). To determine the role of versican derived from macrophages in the innate immune response in vivo, we developed two models of conditional versican deficiency by floxing exon 4 of the versican gene.…”

“…To determine the role of versican derived from macrophages in the innate immune response in vivo, we developed two models of conditional versican deficiency by floxing exon 4 of the versican gene. LysM/Vcan −/− mice have constitutive myeloid cell-specific versican deficiency (60), and R26R ert2 Cre + /Vcan −/− mice, when treated with tamoxifen, are globally deficient in versican (88). In vitro studies with macrophages from LysM/Vcan −/− mice indicate that versican is important for production of type I IFNs and IL-10 by macrophages in response to poly I:C. This is supported by in vivo studies with LysM/Vcan −/− mice which indicate that myeloid-derived versican restrains recruitment of inflammatory cells into lungs and promotes production of the key anti-inflammatory cytokines, IFN-β and IL-10, in the pulmonary response to poly I:C. In contrast, in vivo studies with R26R ert2 Cre + /Vcan −/− mice suggest that stromal-derived versican promotes pulmonary inflammatory cell recruitment in response to poly I:C. When considered in tandem, these results identify versican derived from macrophages as an immunomodulatory molecule with anti-inflammatory properties whereas versican derived from stromal cells has proinflammatory properties.…”

“…Some of the factors that determine the pro-or anti-inflammatory properties of versican include cellular source, surface receptors, signaling pathways affected, nature of the binding partners that associate with versican and/or whether versican is intact or degraded. It should also be noted that reducing versican by genetic manipulation or other means frequently reduces the accumulation of hyaluronan (88) raising some question as to whether the opposing inflammatory properties of versican may be governed by hyaluronan?…”

Proteoglycans as Immunomodulators of the Innate Immune Response to Lung Infection

“…3). 19,[28][29][30] Whether the increases in versican expression in response to these and other inflamma-tory agonists are selective as in the case of LPSinduced inflammation is yet to be determined.…”