SHIP1 Restrains Hypoxia/Reoxygenation-Induced Cytokine Secretion in Mouse Bone Marrow-Derived Mast Cells

Mast cells (MCs) are widely distributed sentinel cells of the myeloid lineage with substantial migratory capacity. Their activation is initiated by receptor-mediated signaling and culminates in the release of prestored mediators and cytokine secretion, processes tightly controlled by the lipid phosphatase SH2-containing inositol 5'-phosphatase 1 (SHIP1). Although MCs frequently reside within hypoxic microenvironments, the impact of hypoxia/reoxygenation on their activation remains elusive. Here we investigated the hypoxia tolerance of MCs and assessed whether hypoxia (≤1% O₂) or subsequent reoxygenation (21% O₂) induces degranulation and/or cytokine production. We further assessed the role of SHIP1 in posthypoxic MC activation. Primary mouse bone marrow-derived MCs (BMMCs) from wildtype and Ship1^-/-mice were subjected to defined periods of hypoxia and subsequent reoxygenation to meticulously analyze their viability, metabolic activity, degranulation, and cytokine secretion. BMMCs were much more resilient to hypoxia than other primary murine cell types, such as microglia, astrocytes, and fibroblasts. A 3 h hypoxic exposure induced sufficient hypoxia-inducible factor-1α (HIF-1α) and its downstream effectors carbonic anhydrase IX and glucose transporter 1, with higher baseline expression in Ship1^-/- BMMCs. Hypoxia increased secretion of IL-6 and TNF-α, but failed to trigger degranulation, even in Ship1^-/- cells. Reoxygenation after 3 h of hypoxia further amplified cytokine secretion and HIF-1α response. Our data indicate that hypoxia activates BMMCs, causing enhanced cytokine secretion and HIF-1α pathway engagement. SHIP1 restrains hypoxia/reoxygenation-driven cytokine release, implicating PI3K/AKT signaling in this regulatory pathway. Recognizing this regulatory checkpoint may inform future efforts to modulate MC-driven cytokine responses in ischemia-reperfusion and other hypoxic inflammatory settings.