Mechanisms of heterotopic ossification in TMJ

颞下颌关节紊乱病(TMJD)是一种异质性疾病，其特征是剧烈疼痛，对咀嚼功能产生负面影响。在美国，TMJDS影响1000多万人，主要是中年人(20-40岁)，女性的患病率高于男性(NIDCR)。对TMJDS的治疗结果是高度可变的，这可能归因于对潜在致病机制的了解不足。因此，更好地了解TMJD的主要因素和致病机制可能会显著改善治疗和/或手术干预后的结果。虽然关节盘退变在TMJD中的作用已经确定，但对于TMJD中肌腱和肌腱-骨附着受损的功能后果却知之甚少。最近的研究表明，肌腱和肌腱-骨插入发育的缺陷以及对这些组织产生负面影响的细胞信号转导失调可导致TMJ畸形(Roberts等人，2019年)。下颌运动产生的生物力学力由翼肌和咬肌产生，这些力穿过肌腱和肌腱-骨插入并连接到下颌关节突。我们的初步研究表明，由于Fkbp10缺乏导致端肽赖氨酰羟化和交联化受损，导致TMJ异位骨化(HO)，并显著增加出生后小鼠下颌骨的长度和宽度。此外，我们还发现Fkbp10基因缺失会导致TMJ内侧髁突内异位成骨增加，同时在肌腱和肌腱-骨连接部位出现异常的Asma表达细胞。初步数据还显示，pSmad1/5在TMJ的肌腱和肌腱-骨附着中的表达增强，表明BMP信号转导失调。基于这些初步数据，我们将检验TMJ肌腱端肽赖氨酸羟化的改变导致HO和功能缺陷的假说，这是由于依赖于异常的BMP信号的表达ASMA的前体细胞的异常分化所致。具体地说，我们将(目标1)确定受损的I型前胶原端肽赖氨酸羟化和交联在TMJ稳态中的功能后果，(目标2)确定Fkbp10缺失是否触发组织损伤并改变表达ASMA的祖细胞群，以及(目标3)确定药物抑制异常的BMP信号是否可以防止Fkbp10基因缺陷小鼠TMJ中的HO。拟议的研究将为制定竞争性研究人员发起的R01或同等的NIH研究提案提供基础和额外的初步数据。

Temporomandibular joint disorder (TMJD) is a heterogeneous disease which is characterized by severe pain that negatively affects masticatory function. In the United States, TMJDs affect over 10 million individuals predominantly in middle-aged adults (20-40 years-of-age) with a higher prevalence in women than in men (NIDCR). Treatment outcomes for TMJDs are highly variable which may be attributed to the gap in knowledge of the underlying pathogenic mechanisms. Hence, a better understanding of the major contributors and causative mechanisms in TMJD may significantly improve outcome following therapeutic and/or surgical intervention. Whereas the contribution of disc degeneration in TMJD is well established, the functional consequence of impaired tendon and tendon-bone insertion in TMJD is poorly understood. Recent studies have shown that defects in tendon and tendon-bone insertion development as well as dysregulated cell signaling that negatively affect these tissues can cause deformities in TMJ (Roberts et al., 2019). Jaw movement creates biomechanical forces that are generated by the pterygoid and masseter muscles which are transmitted across tendon and tendon-bone insertion and connect to the mandibular condyle. Our preliminary studies have shown that impaired telopeptide lysyl hydroxylation and cross-linking due to Fkbp10- deficiency induces heterotopic ossification (HO) in TMJ and substantially increases mandibular condyle length and width in postnatal mice. In addition, we found that Fkbp10 deletion induces aberrant aSMA-expressing cells in the tendon and tendon-bone insertion concomitant with an increase in ectopic bone formation in the medial condyle of TMJ. Preliminary data also showed enhanced pSmad1/5 expression in the tendon and tendon-bone insertion in TMJ, indicating dysregulated BMP signaling. Based on these preliminary data, we will test the hypothesis that alterations in telopeptide lysyl hydroxylation in tendons of TMJ causes HO and functional defects due to abnormal differentiation of aSMA-expressing progenitor cells that is dependent on aberrant BMP signaling. Specifically, we will (Aim 1) determine the functional consequence of impaired procollagen I telopeptide lysyl hydroxylation and cross-linking in TMJ homeostasis, (Aim 2) determine if Fkbp10 deletion triggers tissue injury and alters aSMA-expressing progenitor cell populations, and (Aim 3) determine if pharmacological inhibition of aberrant BMP signaling can prevent HO in TMJ of Fkbp10-deficient mice. The proposed studies will provide the foundational basis and additional preliminary data to develop a competitive investigator-initiated R01 or equivalent NIH research proposal.