CTBP1 and osteoporosis: Norepinephrine is the main neurotransmitter of sympathetic nerves[93] and is involved in the regulation of bone homeostasis.[94] MicroRNA‐21 was upregulated in osteoblasts due to the activation of β adrenergic receptors (βARs) and stimulates osteoclasts via exosomal transport to induce osteoporosis.[95, 96] Hence, the dysregulation of sympathetic activity in TBI may contribute to bone loss.