Sexually dimorphic effects of prenatal alcohol exposure on the murine skeleton

Background

Prenatal alcohol exposure (PAE) can result in lifelong disabilities known as foetal alcohol spectrum disorder (FASD) and is associated with childhood growth deficiencies and increased bone fracture risk. However, the effects of PAE on the adult skeleton remain unclear and any potential sexual dimorphism is undetermined. Therefore, we utilised a murine model to examine sex differences with PAE on in vitro bone formation, and in the juvenile and adult skeleton.

Methods

Pregnant C57BL/6J female mice received 5% ethanol in their drinking water during gestation. Primary calvarial osteoblasts were isolated from neonatal offspring and mineralised bone nodule formation and gene expression assessed. Skeletal phenotyping of 4- and 12-week-old male and female offspring was conducted by micro-computed tomography (µCT), 3-point bending, growth plate analyses, and histology.

Results

Osteoblasts from male and female PAE mice displayed reduced bone formation, compared to control (≤30%). Bglap and Ahsg were upregulated with PAE in both sexes compared to control, whereas Vegfa , Bmp6 , Tgfbr1 and Flt1 were downregulated in PAE male osteoblasts only. In 12-week-old mice, µCT analysis revealed a sex and exposure interaction across several trabecular bone parameters. PAE was detrimental to the trabecular compartment in male mice compared to control, yet PAE females were unaffected. Both male and female mice had significant reductions in cortical parameters with PAE. Whilst male mice were negatively affected along the tibia length, females were only distally affected. Posterior cortical porosity was increased in PAE females only. Mechanical testing revealed PAE males had significantly reduced bone stiffness compared to controls; maximum load and yield was reduced in both sexes. PAE had no effect on total body weight or tibial bone length in either sex. However, total growth plate width in male PAE mice compared to control was reduced, whilst female PAE mice were unaffected. 4-week-old mice did not display the altered skeletal phenotype with PAE observed in 12-week-old animals.

Conclusions

Evidence herein suggests for the first time that PAE exerts divergent sex effects on the skeleton, possibly influenced by underlying sex specific transcriptional mechanisms of osteoblasts. Establishing these sex differences will support future policies and clinical management of FASD.

Plain English summary

Prenatal alcohol exposure (PAE) can lead to a set of lifelong cognitive, behavioural, and physical disabilities known as foetal alcohol spectrum disorder (FASD). FASD is a significant burden on healthcare, justice and education systems, which is set to worsen with rising alcohol consumption rates. FASD children have an increased risk of long bone fracture and adolescents are smaller in stature. However, sex differences and the long-term effects of PAE on the skeleton have not been investigated and was the aim of this study. Using a mouse model of PAE, we examined the function and gene expression of bone-forming cells (osteoblasts). We then analysed the skeletons of male and female mice at 12-weeks-old (adult) and 4-weeks-old (juvenile). PAE reduced osteoblast bone formation in both sexes, compared to control. Differential gene expression was predominantly observed in PAE males and largely involved genes related to blood vessel formation. High resolution x-ray imaging (micro-CT) revealed PAE had a detrimental effect on the inner trabecular bone component in 12-week-old male mice only. Analysis of the outer cortical bone revealed that whilst both male and female PAE mice were negatively affected, anatomical variations were observed. Mechanical testing also revealed differences in bone strength in PAE mice, compared to control. Interestingly, 4-week-old mice did not possess these sex differences observed in our PAE model at 12 weeks of age. Our data suggest PAE has detrimental and yet sex-dependent effects on the skeleton. Establishing these sex differences will support future policies and clinical management of FASD.

Highlights

• Primary calvarial osteoblasts isolated from male and female PAE mice displayed reduced mineralised bone nodule formation and differential gene expression compared to control.

• PAE had a detrimental effect on trabecular bone parameters in 12-week-old male mice only.

• PAE leads to spatial variation in cortical bone parameters and geometry, with male mice negatively affected along the tibia length and female mice only affected at the distal end.

• Mechanical testing revealed PAE male mice had significantly reduced bone stiffness compared to controls; PAE in both sexes reduced maximum load and yield.

• 4-week-old mice did not display the altered skeletal phenotype with PAE observed in 12-week-old animals.