Absence of placental growth factor blocks dextran sodium sulfate-induced colonic mucosal angiogenesis, increases mucosal hypoxia and aggravates acute colonic injury

Abstract

Angiogenesis has recently been described as a component of inflammatory bowel disease. Placental growth factor (PlGF), a vascular endothelial growth factor (VEGF) homologue, establishes its angiogenic capacity under pathophysiological conditions. We investigated the function of PlGF in experimental models of acute colitis. Acute colonic damage was induced in PlGF knock-out (-/-) mice and PlGF wild-type (+/+) mice by dextran sodium sulfate (DSS) and trinitrobenzenesulfonic acid (TNBS). The concentrations of PlGF and VEGF were measured in distal colonic lysates using an enzyme-linked immunosorbent assay. Colonic injury was evaluated by assessing colon length, colonocyte apoptosis (by terminal dUTP nick-end labeling), colonic cytokine production and histological score. Infiltration of polymorphonuclear cells was determined by assaying myeloperoxidase (MPO) activity. In a separate experiment, recombinant PlGF was administered to PlGF -/- mice by adenoviral transfer before DSS administration. Mucosal vascularization was quantified by computerized morphometric analysis of CD31-stained distal colonic sections. Colonic mucosal hypoxia was visualized by pimonidazole staining. Both VEGF and PlGF were upregulated during acute colitis. In addition, compared with PlGF +/+ controls, PlGF -/- mice showed a significant increase in weight loss and colonic shortening during both DSS and TNBS colitis. This correlated with enhanced colonocyte apoptosis, elevated colonic cytokine levels and increased histological damage score, but not with enhanced inflammatory cell infiltration (MPO activity). The increased morbidity of PlGF -/- mice during DSS colitis was preventable by adenovirus (Ad)-mediated overexpression of PlGF. After the administration of DSS, strongly reduced mucosal angiogenesis was observed in PlGF -/- mice compared with PlGF +/+ mice. This was associated with an early increase in intestinal epithelial pimonidazole accumulation in PlGF -/- mice, suggesting a function of enhanced epithelial hypoxia in the observed differences between the two groups. In summary, our data show that the absence of PlGF strongly inhibits mucosal intestinal angiogenesis in acute colitis, which is associated with an early increase in intestinal epithelial hypoxia and aggravation of the course of the disease

PlGF: A Multitasking Cytokine with Disease-Restricted Activity

“…In an acute colonic injury model, PlGF deficiency impairs mucosal angiogenesis, aggravates epithelial hypoxia, and worsens the disease outcome (Hindryckx et al 2010). Notably, PlGF gene delivery improves healing of the inflamed colon (Hindryckx et al 2010).…”

Prolyl hydroxylase 3 (PHD3) is essential for hypoxic regulation of neutrophilic inflammation in humans and mice

“…Dextran sulfate sodium-induced (DSS-induced) colitis is an in vivo model of inflammation where neutrophils are prominent and that is associated with a marked degree of tissue hypoxia (35). Using the acute 6-day time point, we determined the number of neutrophils present in the intestinal mucosa using immunohistochemical staining.…”

“…This is important both to rule out altered neutrophil migration (which was not observed in vitro) but also because, in these whole animal knockouts, PHD3 deficiency of resident cells such as epithelial and endothelial cells could have modified neutrophil influx into the lungs. Murine DSS-induced colitis is also recognized to be profoundly hypoxic (35) and can be characterized histologically by neutrophil-predominant inflammation within the intestinal mucosa, although the specific role neutrophils play in the disease pathogenesis is unclear. In keeping with a reduction in neutrophil-dominant pulmonary inflammation and increased neutrophil apoptosis, we again saw a reduction in neutrophil numbers in the intestinal mucosa of Phd3 -/-animals compared with WT controls.…”

The association of alternate VEGF ligands with resistance to anti-VEGF therapy in metastatic colorectal cancer.

“…Preclinical work has suggested that alternate proangiogenic factors may modulate sensitivity to anti-VEGF-A therapy and allow regrowth of tumor-associated vasculature [11][12][13]. Members of the VEGF signaling family aside from VEGF-A have been implicated in angiogenesis, including placental growth factor (PlGF), VEGF-C, and VEGF-D [14,15]. However, the role of alternate VEGF ligands in angiogenesis remains controversial.…”