Engineering scarless repair of flexor tendon injuries

抽象的。手部II区的屈肌腱损伤容易导致粘连减弱，这是一种疤痕组织。 这会阻碍屈肌腱的滑动，严重损害手的功能。目前没有 预防或解决肌腱粘连的药物治疗，肌腱粘连仍在高达 30%的屈肌腱修复，尽管手术技术和术后康复有所进步。 因此，对屈肌腱瘢痕病因学的机械学理解有一个尚未得到满足的需求，这可能 导致了新疗法的确定。在上一个资助期，我们确定了中断 Smad3基因敲除小鼠中典型的转化生长因子-β信号减少了屈肌腱粘连，但也减少了 修复组织的抗拉强度。然而，转化生长因子-β对激活腱膜的不同作用 和腱内纤维化仍不清楚，可能是识别新的促纤维细胞和 分子机制。为了解决这一知识差距，我们将首先利用他莫昔芬诱导基因 基因缺失小鼠模型研究腱周膜组织中典型的转化生长因子-β信号缺失的影响 与第二区屈肌腱粘连的腱内成纤维细胞相比(Aim1)。朝向确定 下游的纤维化信号介质，我们证明了转化生长因子-β上调了蛋白水解酶- 抑制物，纤溶酶原激活物抑制物1(PAI-1)，它抑制纤溶酶介导的基质金属蛋白酶的激活。 此外，我们还证明了PAI-1功能的丧失使转化生长因子-β1对蛋白酶(纤溶酶)的抑制无效 和基质金属蛋白酶)活性，而不降低细胞增殖。因此，我们假设PAI-1活性不会影响 细胞增殖和屈肌腱愈合，但抑制蛋白酶(纤溶酶和基质金属蛋白酶)活性导致 重塑受损，粘连增加。这一假说将在目标2中通过测试屈肌来检验。 PAI-1功能丧失和功能恢复的小鼠模型的肌腱愈合。总体而言，我们的数据表明 在负重肌腱中，直接靶向转化生长因子-β可能在治疗上是站不住脚的，因为它是二分的 作用，包括不可或缺的PAI-1激活细胞增殖和基质的非依赖性作用 愈合所必需的合成，以及通过规范诱导抑制蛋白酶活性的致病作用 PAI-1。因此，我们假设，PAI-1的局部治疗抑制，无论其细胞来源如何，都将 在不影响修复强度的情况下改善肌腱粘连。在目标3中，我们将检验这一假设 通过优化和研究创新的纳米颗粒介导的siRNA递送系统的有效性 抗PAI-1在野生型小鼠II区屈肌腱损伤中的作用。拟议的研究将阐明 规范的转化生长因子-β信号差异性激活腱周围成纤维细胞导致 外源性纤维化(目标1)，证明典型的转化生长因子-β诱导PAI-1导致纤维化 黏附(目标2)，并建立局部的、瞬时的纳米颗粒介导的siRNA传递以抑制PAI-1 作为一种平移的、维持力量的、抗粘连的屈肌腱修复疗法(目标3)。

Abstract. Flexor tendon injuries in zone II of the hand are prone to debilitating adhesions, a form of scar tissue that obstructs gliding of the flexor tendons, severely impairing hand function. There are presently no pharmacologic treatments for the prevention or resolution of tendon adhesions, which still occur in as high as 30% of flexor tendon repairs, despite advances in surgical techniques and post-operative rehabilitation. Therefore, there is an unmet need for a mechanistic understanding of scar etiology in flexor tendons that could lead to the identification of new therapies. In the previous funding period, we established that disruption of canonical TGF-beta signaling in Smad3 knockout mice reduced flexor tendon adhesions but also reduced the tensile strength of the repair tissue. However, the differential effects of TGF-beta on activating peritendinous and intratendinous fibrosis remain unknown, and could be key to identifying novel profibrotic cellular and molecular mechanisms. To address this gap in knowledge, we will first utilize tamoxifen inducible gene deletion mouse models to investigate the effects of loss of canonical TGF-beta signaling in peritendinous versus intratendinous fibroblasts on zone II flexor tendon adhesions (Aim1). Towards the identification of downstream signaling mediators of fibrosis, we demonstrated that TGF-beta upregulates the protease- suppressor, plasminogen activator inhibitor 1 (PAI-1), which inhibits plasmin-mediated MMP activation. Furthermore, we demonstrated that PAI-1 loss of function nullifies TGF-beta1 inhibition of protease (plasmin and MMP) activity, without reducing cell proliferation. Thus, we hypothesize that PAI-1 activity does not affect cell proliferation and flexor tendon healing, but inhibits protease (plasmin and MMP) activity leading to impaired remodeling and increased adhesions. This hypothesis will be tested in Aim 2 by examining flexor tendon healing in mouse models of PAI- 1 loss- and gain-of-function. Collectively, our data suggest that targeting TGF-beta directly might be therapeutically untenable in load-bearing tendons due to its dichotomous effects, which include the indispensible PAI-1-independent effect of activating cell proliferation and matrix synthesis necessary for healing, and the pathogenic effect of inhibiting protease activity via canonical induction of PAI-1. Thus, we hypothesize that localized therapeutic inhibition of PAI-1, irrespective of its cell source, will ameliorate tendon adhesions without adversely affecting repair strength. In Aim 3, we will test this hypothesis by optimizing and investigating the efficacy of an innovative nanoparticle-mediated siRNA delivery system against PAI-1 in zone II flexor tendon injuries in wild type mice. The proposed studies will elucidate the mechanisms by which canonical TGF-beta signaling differentially activates peritendinous fibroblasts leading to extrinsic fibrosis (Aim 1), demonstrate that canonical TGF-beta induction of PAI-1 precipitates fibrotic adhesions (Aim 2), and establish localized, transient nanoparticle-mediated delivery of siRNA to inhibit PAI-1 as a translational, strength-sustaining, anti-adhesion therapy for flexor tendon repair (Aim 3).