WHIM Syndrome-linked CXCR4 mutations drive osteoporosis by mitigating the osteogenic specification of skeletal stromal cells

Abstract

WHIM Syndrome (WS) is a rare immunodeficiency caused by gain-of-function CXCR4 mutations. Here we report for the first time a substantial decrease in bone mineral density in 25% of WS patients and bone defects leading to osteoporosis in a WS mouse model. Reduction in bone content involved impaired CXCR4 desensitization that disrupts cell cycle progression and osteogenic specification of mouse bone marrow (BM)-residing skeletal stromal/stem cells (SSCs). This was also evidenced in BM stromal cells from WS patients. Consistent with this, chronic treatment with the CXCR4 antagonist AMD3100 normalized in vitro osteogenic fate of mutant SSCs and reversed in vivo loss in skeletal cells, thus demonstrating that proper CXCR4 desensitization is required for the osteogenic specification of BM SSCs. Our study provides novel mechanistic insights into how CXCR4 signaling regulates the osteogenic fate of BM SSCs.