Activation of guanylate cyclase C signaling pathway protects intestinal epithelial cells from acute radiation-induced apoptosis

• Published in: American journal of physiology: Gastrointestinal and liver physiology 2009-04, Vol.296 (4), p.G740-G749
• Main Authors: Garin-Laflam, M P, Steinbrecher, K A, Rudolph, J A, Mao, J, Cohen, M B
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis; Apoptosis - radiation effects; Cell growth; Cells; Cyclic GMP - metabolism; Epithelial Cells - drug effects; Epithelial Cells - radiation effects; Female; Gamma Rays - adverse effects; Guanylate Cyclase - genetics; Guanylate Cyclase - metabolism; Hormones; Immunohistochemistry; In Situ Nick-End Labeling; Intestinal Mucosa - cytology; Intestinal Mucosa - drug effects; Intestinal Mucosa - radiation effects; Male; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Mice, Knockout; Mucosal Biology; Natriuretic Peptides - genetics; Natriuretic Peptides - metabolism; Peptides; Radiation; Receptors, Enterotoxin; Receptors, Guanylate Cyclase-Coupled; Receptors, Peptide - genetics; Receptors, Peptide - metabolism; Rodents; Signal Transduction - physiology; Specific Pathogen-Free Organisms
• ISSN: 0193-1857; 1522-1547
• DOI: 10.1152/ajpgi.90268.2008

Uroguanylin (UGN) is a peptide hormone that binds to and activates the intestinal epithelial cell (IEC) transmembrane receptor guanylate cyclase C (GC-C), which in turn increases intracellular cGMP. Gene targeting of murine UGN or GC-C results in significantly lower levels of cGMP in IECs. On the basis of effects of cGMP in nonintestinal systems, we hypothesized that loss of GC-C activation would increase intestinal epithelial apoptosis following radiation-induced injury. We first compared apoptosis from the proximal jejunum of C57BL/6 wild-type (WT) and GC-C knockout (KO) mice 3 h after they received 5 Gy of gamma-irradiation. We then investigated whether supplementation via intraperitoneal injection of 1 mM 8BrcGMP would mitigate radiation-induced apoptosis in these experimental animals. Identical experiments were performed in BALB/c UGN WT and KO mice. Apoptosis was assessed by quantitating morphological indications of cell death, terminal dUTP nick-end labeling, and cleaved caspase 3 immunohistochemistry. Both UGN KO and GC-C KO mice were more susceptible than their WT littermates in this in vivo model of apoptotic injury. Furthermore, cGMP supplementation in both GC-C and UGN KO animals ameliorated radiation-induced apoptosis. Neither WT strain demonstrated significant alteration in apoptotic susceptibility as a result of cGMP supplementation before radiation injury. These in vivo findings demonstrate increased radiosensitivity of IECs in UGN and GC-C KO mice and a role for cGMP as a primary downstream mediator of GC-C activation in the protection of these IECs from radiation-induced apoptosis.