Altered Expression of Angiotensinogen and Mediators of Angiogenesis in Ileal Crohn’s Disease
Background & Aims: Angiotensin II (AII) is a powerful splanchnic vasoconstrictor with pro-inflammatory and pro-fibrotic properties. Angiotensin converting enzyme (ACE) inhibitors and AII Receptor Antagonists (ARBs) are therapeutic in animal models of colitis. The aim of this case-control study is to determine the expression of angiotensinogen and related genes in human ileal Crohn’s disease.
Methods: Using quantitative real-time polymerase chain reaction (RT-PCR), we measured mRNA expression levels of angiotensinogen (AGT), hypoxia inducible factor (HIF)1α and melanoma cell adhesion molecule (MCAM; CD146) in 101 human samples (69 biopsy, 12 resection) from affected ileum (inflamed CD cases, n=36) and unaffected ileum (non-inflamed CD cases, n=45 and controls, n=20). Immunohistochemistry for angiotensinogen was also performed. The study was of case-control design in a tertiary care setting.
Results: Ileal expression of AGT was lower in CD cases compared to controls (p<0.0001), in inflamed CD samples (p=0.017) and current smokers (p=0.02). HIF1α expression was lower in non-inflamed CD biopsy samples than controls (p=0.006). The presence of disease-associated NOD2 variants was associated with increased expression of markers of angiogenesis (HIF1α p=0.009; MCAM p=0.007) in inflamed CD samples. Angiotensinogen immunohistochemical staining supported the quantitative RT-PCR expression findings.
Conclusions: Angiotensinogen expression is down regulated in human ileal CD, particularly in the presence of inflammation and current cigarette smoking, implicating the mesenteric vasculature and mucosal hypoxia as co-factors in ileal CD pathogenesis. A novel reduction in HIF1α expression in non-inflamed ileal mucosa in CD patients was also demonstrated..
Abbrevations: AI: angiotensin I; AII: angiotensin II; ACE: Angiotensin Converting Enzyme; AGT: angiotensinogen; ARB: Angiotensin II receptor Antagonists; AT1: Angiotensin type 1; AT2: Angiotensin type 2: AT-6: Angiotensinogen-6; ATG16L1: Autophagy-related 16-like 1; CD: Crohn’s disease; CTGF: Connective Tissue Growth Factor; ECM: Extracellular matrix; HIF-1: Hypoxia inducible factor-1; IBD: Inflammatory Bowel Disease; IBDU: Inflammatory Bowel Disease, type unclassified; MCAM: Melanoma Cell Adhesion Molecule; mRNA: Messenger RNA; NOD: Nucleotide-binding oligomerisation domain; NF-κB: Nuclear Factor-κB; NSAIDs: Non-Steroidal Anti-Inflammatory Drugs; PCR: Polymerase Chain Reaction; RAAS: Renin-angiotensin-aldosterone system; RT-PCR: Real Time Polymerase Chain Reaction; SNP: Single Nucleotide Polymorphism; TGF-β: Transforming Growth Factor-β; TNBS: Trinitrobenzene sulfonic acid; TNF: Tumour Necrosis Factor; UC: Ulcerative colitis; UPR: Unfolded protein response; VEGF: Vascular Endothelial Growth Factor.