Suppression of apoptosis, crypt hyperplasia, and altered differentiation in the colonic epithelia of bak-null mice.

Area of Science:

• Cell biology
• Gastroenterology
• Cancer research

Background:

• The BCL-2 protein family regulates cell fate, with antiapoptotic members like BCL-2 and BCL-W promoting gastrointestinal epithelial cell survival.
• A proapoptotic member of the BCL-2 family with significant gastrointestinal effects had not been identified.
• This study investigates intestinal epithelial apoptosis in mice lacking the Bak protein (bak-null mice).

Purpose of the Study:

• To identify a proapoptotic BCL-2 family member impacting the gastrointestinal tract.
• To investigate the role of Bak in intestinal epithelial apoptosis and colonic carcinogenesis.

Main Methods:

• Assessed apoptosis, mitosis, cell composition, and cell number in the small intestinal and colonic epithelia of bak-null and wild-type mice.
• Induced apoptosis using gamma-irradiation or azoxymethane (AOM).
• Induced aberrant crypt foci (ACF) using AOM.

Main Results:

• Bak-null mice showed reduced spontaneous colonic apoptosis, increased crypt cell number, and elevated mitotic index.
• Colonic crypts in bak-null mice had more goblet cells and fewer endocrine cells compared to wild-type.
• Bak-null mice exhibited fewer apoptotic cells after irradiation/AOM and increased AOM-induced colonic ACF.

Conclusions:

• Bak regulates spontaneous and damage-induced apoptosis in the colon, preventing crypt hyperplasia.
• Bak deletion alters colonic proliferation and differentiation.
• Loss of Bak increases susceptibility to colonic carcinogenesis.