Disturbed ATP and AMPK homeostasis in an Ank F377del mouse model for craniometaphyseal dysplasia.

UNLABELLED: Craniometaphyseal dysplasia (CMD) is a rare genetic disorder characterized by hyperostosis of craniofacial bones and flared metaphyses of long bones. Mutations in ANKH (mouse orthologue ANK), a transmembrane protein mediating ATP and citrate efflux, cause the autosomal dominant form of CMD. How ANK mutations in CMD affect ATP/citrate homeostasis and downstream targets remains unknown. We determined that cellular ATP export, intracellular ATP levels, and plasma citric acid were significantly reduced in ANK F377del knock-in ( Ank KI/KI ) mice. Enrichment and pathway analyses of the plasma metabolome suggested the involvement of the citric acid cycle. It is known that AMPK is phosphorylated and activated when ATP is low. Phospho-AMPK was significantly upregulated in fusing Ank KI/KI osteoclasts, major contributors to CMD. AMPK inhibitor treatment only during the fusion stage of osteoclasts significantly restored dysfunctional Ank KI/KI osteoclasts, partly by modulating actin structures. Systemic administration of the AMPK inhibitor SBI-0206965 improved the positioning of cervical loops of incisors but failed to correct other skeletal abnormalities in Ank KI/KI mice. Limitations of systemic administration of SBI-0206965 include its off-target effects on other cell types and the inability to inhibit AMPK only on fusing osteoclasts. Nonetheless, this proof-of-principle study reveals an important role of the ATP-AMPK axis in CMD pathogenesis.

TAKE-HOME MESSAGE: Suppression of increased activation of AMPK restores the function of osteoclasts, suggesting that abnormal energy metabolism is an integral component of the disease phenotype in CMD.