Inositol pyrophosphate profiling reveals regulatory roles of IP6K2-dependent enhanced IP(7) metabolism in the enteric nervous system

Inositol pyrophosphates regulate diverse physiological processes; to better understand their functional roles, assessing their tissue-specific distribution is important. Here, we profiled inositol pyrophosphate levels in mammalian organs using an originally designed liquid chromatography–mass spectrometry (LC-MS) protocol and discovered that the gastrointestinal tract (GIT) contained the highest levels of diphosphoinositol pentakisphosphate (IP(7)) and its precursor inositol hexakisphosphate (IP(6)). Although their absolute levels in the GIT are diet dependent, elevated IP(7) metabolism still exists under dietary regimens devoid of exogenous IP(7). Of the major GIT cells, enteric neurons selectively express the IP(7)-synthesizing enzyme IP6K2. We found that IP6K2-knockout mice exhibited significantly impaired IP(7) metabolism in the various organs including the proximal GIT. In addition, our LC-MS analysis displayed that genetic ablation of IP6K2 significantly impaired IP(7) metabolism in the gut and duodenal muscularis externa containing myenteric plexus. Whole transcriptome analysis of duodenal muscularis externa further suggested that IP6K2 inhibition significantly altered expression levels of the gene sets associated with mature neurons, neural progenitor/stem cells, and glial cells, as well as of certain genes modulating neuronal differentiation and functioning, implying critical roles of the IP6K2-IP(7) axis in developmental and functional regulation of the enteric nervous system. These results collectively reveal an unexpected role of mammalian IP(7)—a highly active IP6K2-IP(7) pathway is conducive to the enteric nervous system.