Extracellular calcium-sensing receptor/PTH knockout mice colons have increased Wnt/β-catenin signaling, reduced non-canonical Wnt signaling, and increased susceptibility to azoxymethane-induced aberrant crypt foci

Epidemiological evidence suggests increased dietary calcium and dairy products reduce the onset of colon cancer. To understand a role of the colonic extracellular calcium-sensing receptor (CaSR) in calcium-mediated chemoprevention of colon cancer, we induced formation of aberrant crypt foci (ACF) caused by azoxymethane (AOM) injection in 'rescued' CaSR - /PTH - (C - /P - ) double knockout colons compared with colons from control CaSR + /PTH + (C + /P +) mice. C - /P - colonic epithelia had increased Wnt/beta-catenin signaling as evidenced by 3-8-fold increases in Wnt3a, CyclinD1, and MMP-7 proteins compared with C + /P + colonic epithelia. The C - /P - colonic epithelia had reduced Wnt5a and Ror2, and a three-fold increase in TNFR1 compared with C + /P + epithelia. The C - /P - colons and small intestine had extensive neutrophil infiltration with myeloperoxidase (MPO) levels 18-fold higher then C + /P + small intestine and colon. Saline-injected C - /P - colons had the same number of ACF/cm(2) as C + /P + colons, which were injected with AOM. However, there were eight times more ACF/cm(2) in the C - /P - injected with AOM compared with C + /P + colons, which received AOM. Together our results suggest both inflammation and Wnt/beta-catenin signaling are increased in the epithelia of 'rescued' CaSR/PTH double knockout colons, and the capacity for non-canonical Wnt signaling through Wnt5a/Ror2 engagement is reduced. The loss of the colonic CaSR increased the number of ACF/cm(2) in response to AOM injection, suggesting colonic CaSR may mediate the chemoprotective effect of increased dietary calcium against colorectal cancer observed in humans. Laboratory Investigation (2013) 93, 520-527; doi:10.1038/labinvest.2013.51; published online 1 April 2013