# A Novel Human Stem Cell Culture Model for Severe Traumatic Brain Injury Reflecting Sexual Dimorphism in Heterotopic Ossification

## TL;DR

This study introduces a new stem cell model to study bone formation after traumatic brain injury, revealing sex differences in bone development and the role of TGF-β1.

## Contribution

A novel stem cell model that demonstrates sexual dimorphism in heterotopic ossification following traumatic brain injury.

## Key findings

- Male stem cells showed higher osteogenic potential when exposed to TBI serum.
- TGF-β1 levels were elevated in male TBI patients and linked to increased bone formation.
- Blocking TGF-β1 reduced bone formation in male cells but not in female cells.

## Abstract

Heterotopic ossification (HO) is a disease characterized by ectopic bone formation, which can occur following severe traumatic brain injury (TBI). However, the underlying mechanisms remain poorly understood. In this study, we established a stem cell model using adipose-derived stem cells (ADSCs) and skeletal stem cells (SSCs) to examine osteogenic factors present in the sera of TBI patients. Incubation of ADSCs and SSCs with osteoinductive medium supplemented with TBI serum significantly enhanced osteogenic differentiation, particularly in male ADSCs and both female and male SSCs, with male SSCs exhibiting the highest osteogenic potential. Furthermore, we identified TGF-β1 as an important factor involved in these osteogenic processes. Elevated levels of TGF-β1 were detected in the serum of male TBI patients 14 days post-injury. Cellular assays revealed a sexual dimorphism in response to TGF-β1 neutralization: osteogenic differentiation in male SSCs was significantly reduced, while no effect was detectable in female SSCs. These findings, together with the rarity of HO in female patients, suggest that TGF-β1 plays a central role in the development of HO in males. Furthermore, this study highlights the importance of considering sex-specific mechanisms in traumatic HO for the development of sex-specific therapy options.