Inhibition of GABA_A receptors in intestinal stem cells prevents chemoradiotherapy-induced intestinal toxicity

This study demonstrates that GABA regulates intestinal stem cell apoptosis through its A receptor in chemoradiotherapy-induced intestinal injury. FDA-approved GABA(A)R antagonist flumazenil may be a promising drug for reducing the gastrointestinal side effects brought by chemoradiotherapy. Lethal intestinal tissue toxicity is a common side effect and a dose-limiting factor in chemoradiotherapy. Chemoradiotherapy can trigger DNA damage and induce P53-dependent apoptosis in LGR5(+) intestinal stem cells (ISCs). Gamma-aminobutyric acid (GABA) and its A receptors (GABA(A)R) are present in the gastrointestinal tract. However, the functioning of the GABAergic system in ISCs is poorly defined. We found that GABA(A)R alpha 1 (GABRA1) levels increased in the murine intestine after chemoradiotherapy. GABRA1 depletion in LGR5(+) ISCs protected the intestine from chemoradiotherapy-induced P53-dependent apoptosis and prolonged animal survival. The administration of bicuculline, a GABA(A)R antagonist, prevented chemoradiotherapy-induced ISC loss and intestinal damage without reducing the chemoradiosensitivity of tumors. Mechanistically, it was associated with the reduction of reactive oxygen species-induced DNA damage via the L-type voltage-dependent Ca2+ channels. Notably, flumazenil, a GABA(A)R antagonist approved by the U.S. Food and Drug Administration, rescued human colonic organoids from chemoradiotherapy-induced toxicity. Therefore, flumazenil may be a promising drug for reducing the gastrointestinal side effects of chemoradiotherapy.