Normal hematopoiesis and inflammatory responses despite discrete signaling defects in Gα15 knockout mice

Gα15 activates phospholipase Cβ in response to the greatest variety of agonist-stimulated heptahelical receptors among the four Gq class G-protein α subunits expressed in mammals. Gα15 is primarily expressed in hematopoietic cells in fetal and adult mice. We disrupted the Gα15 gene by homologous recombination in embryonic stem cells to identify its biological functions. Surprisingly, hematopoiesis was normal in Gα15(-/-) mice, Gα15(- /-) Gαq(-/-) double-knockout mice (which express only Gα11 in most hematopoietic cells), and Gα11(-/-) mice, suggesting functional redundancy in Gq class signaling. Inflammatory challenges, including thioglycolate- induced peritonitis and infection with Trichinella spiralis, stimulated similar responses in Gα15(-/-) adults and wild-type siblings. Agonist- stimulated Ca²⁺ release from intracellular stores was assayed to identify signaling defects in primary cultures of thioglycolate-elicited macrophages isolated from Gα15(-/-) mice. C5a-stimulated phosphoinositide accumulation and Ca²⁺ release was significantly reduced in Gα15(-/-) macrophages. Ca²⁺ signaling was abolished only in mutant cells pretreated with pertussis toxin, suggesting that the C5a receptor couples to both Gα15 and Gαi in vivo. Signaling evoked by other receptors coupled by Gq class α subunits appeared normal in Gα15(-/-) macrophages. Despite discrete signaling defects, compensation by coexpressed Gq and/or Gi class α subunits may suppress abnormalities in Gα15-deficient mice.