HLA Class I Molecules Partner with Integrin β ₄ to Stimulate Endothelial Cell Proliferation and Migration

Abstract

Among transplant recipients, those who produce antibodies against the donor's human leukocyte antigens (HLAs) are at higher risk for antibody-mediated rejection and transplant vasculopathy, which is a progressive, vasculo-occlusive disease that results in ischemic injury and deterioration of organ function. Antibodies against HLA class I (HLA-I) molecules are thought to contribute to transplant vasculopathy by triggering signals that elicit the activation and proliferation of endothelial cells. Here, we demonstrate a molecular association between HLA-I and the integrin β4 subunit after the stimulation of endothelial cells with HLA-I–specific antibodies. Knockdown of integrin β4 in these cells abrogated the ability of HLA-I to stimulate the phosphorylation of the kinases Akt, extracellular signal–regulated kinase (ERK), and Src, as well as cellular proliferation. Similarly, reducing the abundance of HLA-I suppressed integrin β4–mediated phosphorylation of ERK and the migration of endothelial cells on laminin-5, a component of the extracellular matrix. These results indicate a mutual dependency between HLA-I and the integrin β4 subunit to stimulate the proliferation and migration of endothelial cells, which may be important in promoting transplant vasculopathy and tumor angiogenesis.

A Key Role for Matrix Metalloproteinases and Neutral Sphingomyelinase-2 in Transplant Vasculopathy Triggered by Anti-HLA Antibody

“…26 -28,37 Moreover, the concomitant inhibition of anti-HLA mAb-induced MMP2 activation, mitogenic signaling, SMC proliferation, and neointimal hyperplasia by the MMP inhibitor Ro28-2653 is consistent with recent observational studies from Lutz et al, 24 Tsukioka et al, 25 and Hariya et al, 26 suggesting a strong association between MMP2 and transplant vasculopathy. These data and reports from Reed et al [11][12][13][14]35 indicate that multiple signaling pathways act together to trigger the mitogenic effect mediated by W6/32 mAbs. Note that the anti-HLA mAb concentration used in our experiments for triggering SMC proliferation was lower than that used by Reed, 35 but the dose-response curve showed that the W6/32 mAb concentration used here induces a proliferation in SMCs similar to that obtained with higher dose ( Figure IV in the online-only Data Supplement).…”

“…9 -11 HLA alloantibodies have been implicated in chronic allograft rejection and vascular cell proliferation, [13][14][15]17 but thus far their mechanism of action is only partly understood. [13][14][15] The rationale of this study came from our previous work on the stress-induced sphingomyelin/ceramide pathway, which indicated a role for MMPs (namely, MT1-MMP and MMP2) and nSMase2 in stress-induced SMC proliferation. 19,20 We hypothesized that this signaling may also be triggered by anti-HLA mAbs, which behave like stress-inducing agents.…”

“…9 -12 Anti-HLA antibodies trigger the production of growth factors and inflammatory cytokines (fibroblast growth factor, interferon, tumor necrosis factor-␣ [TNF-␣]), the expression of antiapoptotic members of the Bcl-2 family, and activation of signaling pathways involved in the migration and proliferation of vascular cells. [11][12][13][14][15] Moreover, the proinflammatory environment elicited by immune system activation is able to dedifferentiate SMCs that acquire a synthetic phenotype and produce cytokines and extracellular matrix. 16 On the basis of the response of vascular cells to anti-HLA monoclonal antibody (mAb) W6/32 reported by Reed et al, [11][12][13][14] we recently developed an original model of human mesenteric arteries grafted into severe combined immunodeficiency (SCID)/beige mice, in which passive transfer of W6/32 mAb toward HLA class I provokes transplant vasculopathy in the absence of cellular immunity.…”

“…[11][12][13][14][15] Moreover, the proinflammatory environment elicited by immune system activation is able to dedifferentiate SMCs that acquire a synthetic phenotype and produce cytokines and extracellular matrix. 16 On the basis of the response of vascular cells to anti-HLA monoclonal antibody (mAb) W6/32 reported by Reed et al, [11][12][13][14] we recently developed an original model of human mesenteric arteries grafted into severe combined immunodeficiency (SCID)/beige mice, in which passive transfer of W6/32 mAb toward HLA class I provokes transplant vasculopathy in the absence of cellular immunity. 17 The sphingomyelin/ceramide signaling pathway is involved in various stress-induced responses 18 and plays a role in the mitogenic response of vascular SMCs to TNF-␣, oxidized low-density lipoprotein, and H 2 O 2 .…”

Complement—here, there and everywhere, but what about the transplanted organ?

“…It is postulated that TG is the consequence of continuous peritubular glomerulitis and capillaritis or that low levels of DSA and complement are present in the graft, but current assays are unable to measure them [95]. There are also reports of endothelial cell and smooth muscle cell activation by DSAs alone in in-vitro studies thereby suggesting complement-independent mechanisms may contribute to chronic endothelial cell damage [96,97]. The treatment and prevention of CAMR therefore continues to be a challenge.…”