OBJECTIVE

In the hypothalamic arcuate nucleus (ARC), orexigenic agouti-related peptide (AgRP) neurons regulate feeding behavior and energy homeostasis, functions connected to bone metabolism. The 3-phosphoinositide-dependent protein kinase-1 (PDK1) serves as a major signaling molecule particularly for leptin and insulin in AgRP neurons. We asked whether PDK1 in AGRP neurons also contributes to bone metabolism.

METHODS

We generated AgRP neuron-specific PDK1 knockout ( ) mice and those with additional AgRP neuron-specific expression of transactivation-defective FoxO1 (). Bone metabolism in KO and WT mice was analyzed by quantitative computed tomography (QCT), bone histomorphometry, measurement of plasma biomarkers, and qPCR analysis of peptides.

RESULTS

In female mice aged 6 weeks, compared with Cre mice, both stature and femur length were shorter while body weight was unchanged. Cortical bone mineral density (BMD) and cancellous BMD in the femur decreased, and bone formation was delayed. Furthermore, plasma GH and IGF-1 levels were reduced in parallel with decreased mRNA expressions for GH in pituitary and GHRH in ARC. Osteoblast activity was suppressed and osteoclast activity was enhanced. These changes in stature, BMD and GH level were rescued in mice, suggesting that the bone abnormalities and impaired GH release were mediated by enhanced Foxo1 due to deletion of PDK1.

CONCLUSIONS

This study reveals a novel role of PDK1-Foxo1 pathway of AgRP neurons in controlling bone metabolism primarily via GHRH-GH-IGF-1 axis.