PSTPIP1 and pyrin, two key regulators of macrophage differentiation

Monocytes develop from hematopoietic stem cells; migrate into the tissue, where they undergo a stimulation-dependent and tissue specific differentiation into macrophages imprinting specific inflammatory functions. The development of inflammatory functions during differentiation of progenitor cells into macrophages remained incompletely understood.

We intended to identify regulatory factors driving monocyte/macrophage differentiation.

A Genome-wide CRISPR/Cas9 knockout screen (GeCKO) in ER-HoxB8 macrophages was used to identify key drivers of macrophage differentiation which were verified in independent knock-out and knock-in cells. Immunophenotyping was studied by FACS, morphology and migration by fluorescence microscopy, the inflammatory response by ELISA. Transcriptomic data were obtained by next generation mRNA sequencing and validated by quantitative polymerase chain reaction and immunoblotting.

Genome-wide CRISPR/Cas9 knockout screen identified the cytosolic cytoskeleton-associated adaptor molecule PSTPIP1 (proline-serine-threonine phosphatase interacting protein 1) as a regulatory factor of macrophage differentiation. Interestingly, mutations in PSTPIP1 cause autoinflammatory disorders (PAPA syndrome). Deletion of PSTPIP1 resulted in hampered differentiation, decreased inflammatory response, changed morphology, altered cell adhesion and migration properties. PSTPIP1 is a regulator of Pyrin inflammasome activity which drives autoinflammation in familial Mediterranean fever (FMF). Deletion of Pyrin also resulted in a strong alteration of cellular dynamics in macrophages.

PSTPIP1 and Pyrin are crucial factors in macrophage differentiation. Their deletion or mutation resulted in a hampered differentiation of macrophages resulting in strong morphological alterations and impacting phagocyte key functions as adhesion and migration. Impaired differentiation of macrophages may represent a significant factor in the pathophysiology of autoinflammatory diseases like FMF and PAPA.