Mechanism of diminished granulopoiesis in AK2-deficient hematopoietic stem and progenitor cells. ATP, adenosine triphosphate; ADP, adenosine diphosphate; AMPK, AMP-activated kinase; mTOR, mammalian target of rapamycin; IMP, inosine monophosphate; NAD⁺, nicotinamide adenine dinucleotide.