ACVR1 sensory neuron-specific signaling in neuropathic pain and injury-induced heterotopic ossification

项目总结 衰弱疼痛是组织损伤和神经病变的标志，是一个未得到满足的临床挑战，尤其是在 肌肉骨骼疾病，如异位骨化(HO)。骨科手术后可发生HO 和创伤性损伤，表现为肌肉和结缔组织中的病理性骨形成。然而， 在开发有效的治疗HO或其相关疼痛的方法方面进展甚微。 持续性神经病理性疼痛可由背根感觉神经元伤害性感受器的过度兴奋引起 神经节(DRG)释放神经肽，与免疫细胞相互作用，调节宿主的反应 损伤后对骨骼和肌肉等神经组织造成损伤。骨骼动态平衡和骨质疏松症之间的关键联系 缺乏TRPV1+的小鼠的骨化和骨丢失受损提示神经病理性疼痛 痛觉感受器。尽管HO形成或HO相关疼痛的机制尚不清楚， 对遗传性骨质疏松症HO亚群的研究得出的重要见解 进展(FOP)。FOP通常是由精氨酸206组氨酸功能点突变引起的 BMP I型受体(ACVR1，也称为ALK2)在97%的患者中存在。我们最近发现了一名成年人 在没有炎症性反应的情况下，FOP患者有基线热度和机械过敏 火力爆发。利用FOP患者诱导的多能干细胞来源的伤害性感觉神经元 (ISNS)，我们证明了ACVR1R206H对于神经细胞的超兴奋性是必要和充分的。 伤害性感受器，神经性疼痛的标志。为了确定神经元ACVR1过度活动是否也是 与更常见的神经病理性疼痛情况相关，我们有条件地表达激活Acvr1R206H 非FOP转基因小鼠的感觉神经元。这导致了对机械和 FOP患者的热过敏反应。由于ACVR1在背根节轴索切断后的表达显著增加 我们发现，在由备用神经损伤(SNI)产生的神经病理性疼痛的传统临床前模型中，神经元 鞘内注射α-氨基丁酸抑制损伤诱导的DRG神经元ACVR1信号通路 小分子ACVR1/ALK2激酶抑制剂预防损伤诱导的机械超敏反应 重要的是，逆转了小鼠SNI模型中的持续性疼痛。根据我们的观察，创伤引起的 在临床前FOP小鼠模型中，HO触发了损伤部位大量伤害性感受器的萌发，我们进一步 假设感觉神经元中活跃的ACVR1信号是神经病理性疼痛和 呵呵。总之，旨在阐明活性ACVR1信号下游的机制，即 可能与其他慢性疼痛和肌肉骨骼损伤情况相同；同时开发新的治疗方法 策略，我们将定义感觉神经元特异性ACVR1的分子靶点，这些分子靶点有助于神经病理 疼痛(目标1)；验证抑制外周神经元ACVR1是否降低过敏(目标2)；以及确定 如果感觉神经元特异性ACVR1参与了损伤诱导的HO(目标3)。

PROJECT SUMMARY Debilitating pain, a hallmark of tissue injury and neuropathy, is an unmet clinical challenge particularly in musculoskeletal diseases, such as heterotopic ossification (HO). HO can occur following orthopedic surgery and traumatic injuries, manifests with pathological bone formation in muscle and connective tissues. However, little progress has been made in developing effective treatments for either HO or its associated pain. Persistent neuropathic pain can arise from hyperexcitability of sensory neuron nociceptors in dorsal root ganglia (DRG), which release neuropeptides, interact with immune cells, and modulate the host response after injury to innervated tissues including bone and muscle. A critical link between bone homeostasis and neuropathic pain has been suggested by the impaired ossification and bone loss in mice lacking Trpv1+ nociceptors. Although the mechanisms that underlie HO formation or HO related pain are poorly understood, important insights derive from studies of an hereditary HO subset, namely Fibrodysplasia Ossificans Progressiva (FOP). FOP is commonly caused by an arginine206 to histidine gain-of-function point mutation in the BMP type I receptor (ACVR1, also known as ALK2) in 97% of patients. We recently found that adult patients with FOP have baseline heat and mechanical hypersensitivity, in the absence of an inflammatory flareup. Utilizing FOP patient induced pluripotent stem cell (iPSC)-derived nociceptive sensory neurons (iSNs), we demonstrated that ACVR1R206H is both necessary and sufficient for the hyperexcitability of nociceptors, a hallmark of neuropathic pain. To determine whether neuronal ACVR1 hyperactivity is also relevant to more common neuropathic pain conditions, we conditionally expressed activating Acvr1R206H in sensory neurons of non-FOP transgenic mice. This led to a remarkable recapitulation of the mechanical and heat hypersensitivity in patients with FOP. As Acvr1 expression is profoundly increased in axotomized DRG neurons in a traditional preclinical model of neuropathic pain produced by spared nerve injury (SNI), we found that inhibiting injury-induced active neuronal ACVR1 signaling in the DRG by intrathecal (IT) injections of a small-molecule ACVR1/ALK2 kinase inhibitor prevented injury-induced mechanical hypersensitivity and, most importantly, reversed persistent pain in the mouse SNI model. Based on our observation that trauma-induced HO triggered massive nociceptor sprouting at the injury site in a preclinical mouse model of FOP, we further hypothesize that active ACVR1 signaling in sensory neurons is a critical link between neuropathic pain and HO. Together, aiming to elucidate the mechanisms downstream of active ACVR1 signaling, mechanisms that may be shared by other chronic pain and musculoskeletal injury conditions; while developing new treatment strategies, we will define molecular targets of sensory neuron-specific ACVR1 that contribute to neuropathic pain (Aim 1); validate if inhibiting peripheral neuronal ACVR1 reduces hypersensitivity (Aim 2); and determine if sensory neuron-specific ACVR1 contributes to injury-induced HO (Aim 3).