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Abstract
Background Transducin-like enhancer of split 1 (TLE1) has been reported as co-repressor of multiple transcriptional factors. The association between TLE1 and the pathogenesis of Crohn’s disease (CD) is obscure. The aim of the study is to identify the expression and function of TLE1 in CD.
Methods TLE1 expression was detected in peripheral blood mononuclear cells (PBMC) and intestinal biopsies (diseased/non-diseased mucosae) in 43 patients with active ulcerative colitis (UC), 40 patients with active CD and 37 healthy controls (HC) by real-time polymerase chain reaction or immunohistochemistry. We transfected TLE1-siRNA into HEK293, SW480 and LoVo cells to inhibit TLE1 expression and then to detect cell apoptosis by FITC Annexin V/PI and Hoechst staining. Apoptosis-related and autophagy-related proteins were tested by Western blot, and co-immunoprecipitation (Co-IP) was conducted to study the interaction of TLE1 and autophagy-related proteins.
Results TLE1 mRNA expression significantly decreased in both PBMC (p=0.030) and intestinal tissues (diseased mucosae: p=0.028; non-diseased mucosae: p=0.031) in active CD compared to HC. Protein expression of TLE1 in active CD’s intestinal biopsies, especially in diseased tissues, was also lower than it in active UC and HC (figure 1). Cell experiments showed that Cleaved caspase-3 and Cleaved caspase-9 was markedly upregulated and cell apoptosis was highly activated after TLE1 silencing. In addition, the decrease of LC3-II/I value and the increase of ATG16L1 degradation were observed, indicating the inhibition of autophagy formation. Co-IP in HEK293 cells revealed the possible direct interaction of TLE1 and ATG16L1/ATG7 proteins.
Staining images and immunohistochemical scores of TLE1 in diseased and non-diseased intestinal mucosae of active Crohn’s disease and ulcerative colitis patients compared to healthy controls
Conclusions There is a significant and specific decrease of TLE1 in active CD. Its low expression promotes cell apoptosis by upregulating Cleaved caspase-3 and Cleaved caspase-9 as well as induces aberrant autophagy by activating ATG16L1 degradation. TLE1 may directly interact with ATG16L1 or ATG7. TLE1 could be promisingly introduced as a new study target in CD pathogenesis and a potential biomarker for CD diagnosis.