Evidence for Pipecolate Oxidase in Mediating Protection Against Hydrogen Peroxide Stress. Issue 7 (13th December 2016) - Natarajan, Sathish Kumar
ABSTRACT: Pipecolate, an intermediate of the lysine catabolic pathway, is oxidized to Δ 1 ‐piperideine‐6‐carboxylate (P6C) by the flavoenzymel ‐pipecolate oxidase (PIPOX). P6C spontaneously hydrolyzes to generate α‐aminoadipate semialdehyde, which is then converted into α‐aminoadipate acid by α‐aminoadipatesemialdehyde dehydrogenase.l ‐pipecolate was previously reported to protect mammalian cells against oxidative stress. Here, we examined whether PIPOX is involved in the mechanism of pipecolate stress protection. Knockdown of PIPOX by small interference RNA abolished pipecolate protection against hydrogen peroxide‐induced cell death in HEK293 cells suggesting a critical role for PIPOX. Subcellular fractionation analysis showed that PIPOX is localized in the mitochondria of HEK293 cells consistent with its role in lysine catabolism. Signaling pathways potentially involved in pipecolate protection were explored by treating cells with small molecule inhibitors. Inhibition of both mTORC1 and mTORC2 kinase complexes or inhibition of Akt kinase alone blocked pipecolate protection suggesting the involvement of these signaling pathways. Phosphorylation of the Akt downstream target, forkhead transcription factor O3 (FoxO3), was also significantly increased in cells treated with pipecolate, further implicating Akt in the protective mechanism and revealing FoxO3 inhibition as a potentially key step. The results presented here demonstrate that pipecolate metabolism can influence cell signaling during oxidative stress to promote cell survival and suggest that the mechanism of pipecolate protection parallels that of proline, which is also metabolized in the mitochondria. J. Cell. Biochem. 118: 1678–1688, 2017. © 2016 Wiley Periodicals, Inc. Abstract : We show that pipecolate, which is an intermediate of the lysine catabolic pathway, protects mammalian cells against pathophysiological concentrations of hydrogen peroxide. The mechanism of protection is shown to involve the enzyme pipecolate oxidase, Akt signaling, and FoxO3. These findings contribute important new insights into pipecolate metabolism and expand its role in mediating cell signaling processes.