IL-13 signaling via IL-13Rα2 triggers TGF-β1-dependent allograft fibrosis

Abstract

BackgroundAllograft fibrosis still remains a critical problem in transplantation, including heart transplantation. The IL-13/TGF-β1 interaction has previously been identified as a key pathway orchestrating fibrosis in different inflammatory immune disorders. Here we investigate if this pathway is also responsible for allograft fibrosis and if interference with the IL-13/TGF-β1 interaction prevents allograft fibrosis.MethodsFVB or control DBA/1 donor hearts were transplanted heterotopically into DBA/1 recipient mice and hearts were explanted at day 60 and 100 post-transplantation. Cardiac tissue was examined by Masson’s trichrome staining and immunohistochemistry for CD4, CD8, CD11b, IL-13, Fas ligand, matrix metalloproteinase (MMP)-1, MMP-13, β2-microglobulin, and Gremlin-1. Graft-infiltrating cells were isolated and analyzed by flow cytometry. IL-13 and TGF-β1 levels were determined by enzyme-linked immunosorbent assay (ELISA) and the amount of collagen was quantified using a Sircol assay; IL-13Rα2 expression was detected by Western blotting. In some experiments IL-13/ TGF-β1 signaling was blocked with specific IL-13Rα2 siRNA. Additionally, a PCR array of RNA isolated from the allografts was performed to analyze expression of multiple genes involved in fibrosis.ResultsBoth groups survived long-term (>100 days). The allogeneic grafts were infiltrated by significantly increased numbers of CD4+ (P <0.0001), CD8+ (P <0.0001), and CD11b+ cells (P = 0.0065) by day 100. Furthermore, elevated IL-13 levels (P = 0.0003) and numbers of infiltrating IL-13+ cells (P = 0.0037), together with an expression of IL-13Rα2, were detected only within allografts. The expression of IL-13 and IL-13Rα2 resulted in significantly increased TGF-β1 levels (P <0.0001), higher numbers of CD11bhighGr1intermediateTGF-β1+ cells, and elevated cardiac collagen deposition (P = 0.0094). The allograft fibrosis found in these experiments was accompanied by upregulation of multiple profibrotic genes, which was confirmed by immunohistochemical stainings of allograft tissue. Blockage of the IL-13/TGF-β1 interaction by IL-13Rα2 siRNA led to lower numbers of CD11bhighGr1intermediateTGF-β1+, CD4+, CD8+, and CD11b+ cells, and prevented collagen deposition (P = 0.0018) within these allografts.ConclusionsIL-13 signaling via IL-13Rα2 induces TGF-β1 and causes allograft fibrosis in a murine model of chronic transplant rejection. Blockage of this IL-13/TGF-β1 interaction by IL-13Rα2 siRNA prevents cardiac allograft fibrosis. Thus, IL-13Rα2 may be exploitable as a future target to reduce allograft fibrosis in organ transplantation.

Diffuse Myocardial Fibrosis in Children After Heart Transplantations

“…Possible etiologies of increased fibrosis in pediatric transplant recipients include factors related to the transplantation surgery, such as ischemia and ischemia-reperfusion injury, donorspecific antibodies, arterial hypertension, CAV, drug toxicity, 29,33 and previous episodes of rejection, although data about the association of rejection and fibrosis are conflicting. 34,35 The reason of fibrosis in the patients studied remains speculative, but could be related to ischemic injury, as interestingly, 2 patients with very short ischemia times had the lowest measures of fibrosis.…”

Strategies targeting the IL-4/IL-13 axes in disease

“…The significant pro-fibrotic role of IL-13 in vivo over IL-4 could be attributed to the signaling mechanism of IL-13Ra2 and/or the involvement of ILC2 which produce IL-13 and IL-5 but not IL-4 [363][364][365]. Moreover, results from several disease models indicate that differences in ligand concentration might also explain the differential activities of IL-4 and IL-13.…”

“…IL-13 plays an intimate role in the activation of TGF-b 1 . IL-13 induces the production of latent TGF-b 1 [363,364]. IL-13 also indirectly activates TGF-b 1 by upregulating LAP-TGF-b 1 complex [367,368].…”

The cytokines of pulmonary fibrosis: Much learned, much more to learn

“…On the other hand, IL-13 first binds to the IL13Ra1 chain, leading to the recruitment of the IL-4Ra chain. Another chain, termed IL-13Ra2, also binds IL-13; there is an ongoing controversy as to whether IL-13Ra2 acts as a decoy receptor attenuating IL-13-driven fibrosis [154,155] or its triggering induces TGF-b, which in turn acts profibrotically [156,157]. Activation of the IL-4R complexes initiates complex intracellular signaling utilizing members of the JAK family of tyrosine kinases, the IRS family of proteins, STAT6, and other intracellular signaling mediators (reviewed in [153]).…”