Lymphangiogenesis in Inflammatory Bowel Disease; A New Therapeutic Target?

Abstract

In their study, D' Alessio et al.1 investigated the results of stimulating lymphatic function and adaptive immune response via vascular endothelial growth factor (VEGF)-C/VEGFR3 signaling on various parameters including intestinal inflammation, lymphatic drainage, bacterial antigen clearance, and macrophage (MΦs) activation during gut inflammation. The mechanism through which this pathway acts in disease progression was also evaluated. Initial investigation focused on an examination on lymphangiogenesis in human inflammatory bowel disease (IBD), with an immunohistologic characterization of colonic tissues from IBD patients and controls that were stained with antibodies recognizing podoplanin. The total number of lymphatic vessels (LVs) per field in the lamina propria and submucosa of IBD specimens was significantly increased compared with that of the controls. Moreover, the VEGF-C expression was found to be upregulated in the mucosal extracts of IBD patients (mainly those with ulcerative colitis) and increased VEGFR3+ vessel density in inflamed tissue was noticed. An overexpression of VEGFR3 in IBD human intestinal lymphatic endothelial cells (LECs) was also observed using immunofluorescence. The second part of the study was an investigation of the functional role of the VEGF-C/VEGFR3 pathway by systemic inhibition of VEGFR3 or by delivery of the human lymphangiogenic factor VEGF-C in two models of chronic colitis (dextran sodium sulfate and interleukin-10—knockout) using either a blocking Ab or adenoviral transfer. VEGFR3 protein levels were significantly increased in colonic tissue lysates (mainly in the DDS model) during both acute and chronic intestinal inflammation. The systemic administration of Ad-hVEGF-C improved the chronic intestinal inflammation (as was measured by percentage of body weight, endoscopy and disease activity index) in both animal models of colitis. On the other hand, the anti-VEGFR3 antibody (mF431C1) worsened the clinical course of experimental colitis. Increased VEGFR3+ vessel density in inflamed tissues and increased VEGF-C expression protein levels in extracts from the colons of colitic mice compared to controls were also demonstrated. Treatment with the anti-VEGFR3 Ab mF431C1 was found to reduce the number of LVs per area compared with that in the wild-type control group in both animal models of colitis. LV decrease with anti-VEGFR3 Ab was found to inversely correlate with increased disease activity and increased weight loss, suggesting that lymphangiogenesis per se might be important for the resolution of inflammation. Exacerbation of experimental colitis by VEGFR3 blockade with resultant exacerbation of experimental colitis was associated with decreased afferent lymph flow and inflammatory cell migration to draining nodes. The antigen clearance from the inflamed colon was accelerated by systemic delivery of VEGF-C through MΦ mobilization. MΦ depletion was associated with less protection in VEGF-C-treated mice during chronic experimental colitis. MΦ plasticity and activation was found to be regulated both in vivo and in vitro by the VEGF-C/VEGFR3. Finally, the VEGF-C/VEGFR3 pathway was demonstrated to modulate activation of signal transducer and activator of transcription 6 during experimental colitis and in cultured bone marrow−derived MΦs.