STAT3 is critical for skeletal development and bone homeostasis by regulating osteogenesis

Area of Science:

• Genetics and Molecular Biology
• Skeletal Biology
• Developmental Biology

Background:

• Autosomal dominant–hypomorphic interleukin-21 receptor signaling pathway mutations (AD-HIES) often manifest as skeletal deformities.
• Heterozygous loss-of-function mutations in Signal transducer and activator of transcription 3 (STAT3) are the primary cause of AD-HIES.
• The precise mechanisms underlying STAT3-related skeletal defects and available treatments remain limited.

Purpose of the Study:

• To investigate the role of STAT3 in osteoblasts versus osteoclasts in skeletal development.
• To elucidate the molecular mechanisms by which STAT3 influences osteoblast differentiation and bone homeostasis.
• To evaluate STAT3 as a potential therapeutic target for AD-HIES skeletal manifestations.

Main Methods:

• Generation of mice with osteoblast-specific or osteoclast-specific Stat3 deletion.
• Phenotypic analysis of skeletal deformities, including craniofacial structure, bone density, and fracture incidence.
• Molecular analyses to determine the interaction of STAT3 with transcription factors like MSX1 and its effect on downstream targets such as DLX5.

Main Results:

• Osteoblast-specific Stat3 deletion in mice recapitulated AD-HIES-like skeletal defects, including craniofacial malformations, osteoporosis, and fractures.
• STAT3, in conjunction with MSX1, was found to promote osteoblast differentiation by enhancing DLX5 transcription.
• Pharmacological activation of STAT3 partially ameliorated skeletal deformities in heterozygous knockout mice, whereas STAT3 inhibition exacerbated bone loss.

Conclusions:

• STAT3 plays a critical role in osteoblast differentiation and is essential for maintaining skeletal development and bone homeostasis.
• The STAT3-MSX1-DLX5 pathway is a key regulator of osteogenesis.
• Targeting STAT3 activation represents a promising therapeutic strategy for treating skeletal abnormalities in AD-HIES.