Pyruvate Kinase M2 Regulates Apoptosis of Intestinal Epithelial Cells in Crohn's Disease

Pyruvate kinase M2 (PKM2), a key glycolytic enzyme, is involved in multiple cellular processes including apoptosis. Recently increased fecal PKM2 has been found in Crohn's disease (CD), but little is known regarding its function in the pathophysiology of the disease. The intestinal expression of PKM2 and its involvement in CD was investigated. Pyruvate kinase M2 expression in mucosal biopsies from patients with CD and normal controls was detected by immunohistochemistry. A murine model of colitis induced by trinitrobenzenesulphonic acid (TNBS) was established and expression of PKM2, B cell lymphoma-extra large (Bcl-xl), active caspase-3 as well as cleaved poly (ADP-ribose) polymerase (PARP) was examined for association of PKM2 with intestinal epithelial cell (IEC) apoptosis. Furthermore, we treated human IEC line HT-29 by tumor necrosis factor-alpha (TNF-alpha) and used RNA interference to analyze the role of PKM2 in IEC apoptosis. Intestinal expression of PKM2 was higher in patients with CD compared with normal controls mainly locating in IECs. In TNBS-induced colitis, up-regulation of PKM2 was accompanied by the elevated expression of Bcl-xl, active caspase-3, and cleaved PARP. PKM2 was co-localized with active caspase-3 in IECs marked by E-cadherin, suggesting its role in IEC apoptosis. Expression of PKM2 and Bcl-xl in TNF-alpha-induced HT-29 cells was increased, while TNF-alpha had no effect on cellular localization of PKM2. Furthermore, knockdown of PKM2 by siRNA could inhibit expression of Bcl-xl but enhance apoptosis in TNF-alpha-treated HT-29 cells. The up-regulation of PKM2 might protect IECs against apoptosis possibly through Bcl-xl in CD, indicating its important role in the pathophysiology of CD.