Isoform- And cell type specific roles of glycogen synthase kinase 3 N-terminal serine phosphorylation in liver ischemia reperfusion injury

Glycogen synthase kinase 3 (Gsk3) a and b are both constitutively active and inhibited upon stimulation by N-terminal serine phosphorylation. Although roles of active Gsk3 in liver ischemia reperfusion injury (IRI) have been well appreciated, whether Gsk3 N-terminal serine phosphorylation has any functional significance in the disease process remains unclear. In a murine liver partial warm ischemia model, we studied Gsk3 N-terminal serine mutant knock-in (KI) mice and showed that liver IRI was decreased in Gsk3aS21A but increased in Gsk3bS9A mutant KI mice. Bone marrow chimeric experiments revealed that the Gsk3a, but not b, mutation in liver parenchyma protected from IRI, and both mutations in bone marrow derived cells exacerbated liver injuries. Mechanistically, mutant Gsk3a protected hepatocytes from inflammatory (TNF-a) cell death by the activation of HIV-1 TAT-interactive protein 60 (TIP60) mediated autophagy pathway. The pharmacological inhibition of TIP60 or autophagy diminished the protection of the Gsk3a mutant hepatocytes from inflammatory cell death in vitro and the Gsk3a mutant KI mice from liver IRI in vivo. Thus, Gsk3 N-terminal serine phosphorylation inhibits liver innate immune activation but suppresses hepatocyte autophagy in response to inflammation. Gsk3 aS21, but not bS9, mutation is sufficient to sustain Gsk4 activities in hepatocytes and protect livers from IRI via TIP60 activation.