Variations in fracture healing due to age-dependent changes in the adaptation of immune cells towards the hypoxic environment of the fracture gap

今天，德国大约20%的人年龄在65岁或更高，在接下来的几十年里，这一比例有增加的趋势。到2060年，三分之一的人口年龄将达到65岁或以上。这种人口结构的发展将导致由于骨骼愈合受损或延迟、退行性关节疾病、骨关节病或骨质疏松而进行手术干预(如骨折治疗和关节置换)的发生率增加。因此，我们有无条件的需要更好地认识和了解骨愈合受损或延迟的原因，以便开发早期诊断和有效的治疗方法。骨折愈合的初始炎症阶段对临床预后有重要影响，而为后续阶段设定进程时，初始阶段是诱导血管生成和成骨的阶段。由于免疫抑制或由于衰老相关的免疫衰老而导致的初始炎症阶段的损害会导致骨愈合受损或延迟。我们的数据和其他研究小组的研究支持这样的假设，即骨折愈合的有效性和质量强烈依赖于参与的免疫细胞对骨折间隙中的病理生理低氧环境(&lt；2%O2)的生物能量适应。为了解决这一假设，我们将检查早期骨折血肿(6小时-72小时)的细胞和体液成分及其与患者年龄相关的对免疫细胞功能的影响。此外，我们将分析和量化单核细胞和T细胞在细胞对低氧微环境的生物能量适应中随年龄的变化，重点是低氧介导的低氧诱导因子(HIF)途径。我们假设，随着年龄的增加，细胞对低氧的适应能力降低，从而导致(I)增强的先天和/或适应性效应免疫反应(例如。单核细胞、中性粒细胞和CTL、Th17、Th1)，而(Ii)通过调节性免疫细胞(例如。Treg)已被攻破。因此，我们进一步假设，促进细胞对病理生理缺氧的适应可以使依赖衰老的过度和/或失控的免疫反应正常化。在一种证明原则的方法中，我们的目标是通过使用HIF的化学稳定来迫使老年捐赠者的免疫细胞对低氧的细胞适应。

Today about 20% of the people in Germany are of age 65 or higher with a tendency towards an increasing frequency for the next decades. In 2060 every third will be aged 65 or older. This demographic development will lead to a higher incidence of surgical interventions (such as fracture treatment and arthroplasty) as a result of an impaired or delayed bone healing, a degenerative joint disease, osteoarthrosis or osteoporosis. Therefore, we have an unconditional need to better recognize and understand the cause of an impaired or delayed bone healing in order to develop early diagnosis and an efficient therapy. The initial inflammatory phase of fracture healing is of great importance for clinical outcome while setting the course for the follow-up phases the initial phase is inducing angiogenesis and osteogenesis. Compromising the initial inflammatory phase due to immunosuppression or due to aging-dependent immune senescence results in an impaired or delayed bone healing. Our data and studies from other research groups support the hypothesis that efficacy and quality of fracture healing strongly depends on the bioenergetic adaptation of participating immune cells to the pathophysiological hypoxic environment (<2%O2) in the fracture gap. To address this hypothesis, we will examine cellular and humoral composition of the early fracture hematoma (6h-72h) and its impact on the functionality on immune cells with regard to the age of the patients. Moreover, we will analyze and quantify the age-dependent changes of monocytes and T cells in cellular bioenergetic adaptation towards a hypoxic microenvironment focusing on hypoxia-mediated hypoxia-inducible factor (HIF) pathways. We hypothesize that an increase of age leads to a decrease of cellular adaptation towards hypoxia which results in (i) an augmented innate and/or adaptive effector immune response (in eg. monocytes, neutrophils and CTL, Th17, Th1, respectively) while (ii) control of effector response by regulatory immune cells (eg. Treg) is compromised. Therefore, we further assume that promotion of cellular adaptation towards pathophysiological hypoxia could normalize an aging-dependent excessive and/or deregulated immune response. In a proof-of-principle approach, we aim to force the cellular adaptation towards hypoxia in immune cells of aged donors by using chemical stabilization of HIFs.