Cellular Behaviors of Perivascular Fibroblasts in Cerebral Ischemia

恢复脑功能对促进中风后患者的康复至关重要。大脑中的缺血事件限制了氧气和营养的供应，导致神经细胞死亡和强烈的炎症反应。随着坏死组织的清除，损伤经历了伤口愈合过程，最终导致纤维性瘢痕的形成。纤维性瘢痕阻碍神经元再生，从而影响受损组织的恢复和功能。促进中风后纤维化瘢痕形成的细胞类型还知之甚少。解决这些知识差距将使我们能够识别促纤维化细胞类型，并更好地为测试导致中枢神经系统损伤后纤维化的机制做好准备。了解中风的这些重要方面可以为开发旨在限制中风后瘢痕形成和支持神经元再生的治疗方法提供潜力。最近的研究证实，表达PDGFRβ的细胞是中枢神经系统损伤后潜在的促纤维化细胞类型。然而，表达PDGFRβ的细胞的身份尚不清楚。强有力的证据表明，表达PDGFRβ的血管周围成纤维细胞(PVF)是纤维性瘢痕的主要贡献者。另一方面，PDGFRβ+周细胞也被认为可以促进纤维性瘢痕的形成。然而，周细胞通常对缺氧和炎症敏感，并可能在中枢神经系统损伤后发生凋亡。基于此，我假设血管周围成纤维细胞是脑中血管周围细胞的一种独特的群体，并对脑缺血后的纤维性瘢痕起重要作用。使用体内双光子显微镜同时观察周细胞和室旁组织，我将在两个不同的目标上测试这一假说。在目标1中，我将研究PVF与沿脑血管网络的周细胞的拓扑关系，确定其形态特征，并测试PVF在健康大脑中对血管稳定性的作用。在目标2中，我将描述脑缺血后PVF和周细胞的细胞行为，以确定哪种细胞类型对纤维性瘢痕有实质性影响。我还将从药理上抑制PDGF信号，以确定这一途径是否在脑缺血时PVF的激活中发挥重要作用。总之，这些研究将有助于阐明动物中风后促纤维细胞的类型，并确定PVF是否对健康大脑中的血管稳定性很重要。

Regaining brain function is crucial to improve patient recovery following stroke. An ischemic event in the brain limits oxygen and nutrient supply resulting in neuronal cell death and a robust inflammatory response. Following clearance of the necrotic tissue the lesion undergoes a wound healing processes ultimately resulting in the formation of a fibrotic scar. The fibrotic scar impedes neuronal regeneration thus impacting recovery and function of the damaged tissue. The contributing cell types that promote fibrotic scar formation following stroke are poorly understood. Addressing these gaps in knowledge will allow us to identify the pro-fibrotic cell types and better poise us for testing mechanisms that contribute to fibrosis following CNS injury. Understanding these important aspects of stroke could provide a potential for developing therapeutics aimed at limiting scar formation and supporting neuronal regeneration following stroke. Recent studies have identified Pdgfrβ-expressing cells as the potential pro-fibrotic cell type following CNS injury. The identity of the Pdgfrβ-expressing cells, however, is not clear. Strong evidence points to Pdgfrβ- expressing perivascular fibroblasts (PVFs) as major contributors to the fibrotic scar. On the other hand, Pdgfrβ+ pericytes are also suggested to promote fibrotic scar formation. However, pericytes are generally sensitive to hypoxia and inflammation and likely undergo apoptosis following CNS injury. Based on this, I hypothesize that perivascular fibroblasts are a unique population of perivascular cells in the brain and significantly contribute to the fibrotic scar following cerebral ischemia. Using in vivo two-photon microscopy to simultaneously visualize pericytes and PVFs I will test this hypothesis in two distinct aims. In Aim 1, I will study the topological relation of PVFs to pericytes along the cerebrovascular network, define their morphological characteristics, and test the role of PVFs in vascular stability in the healthy brain. In Aim 2, I will characterize the cellular behaviors of PVFs and pericytes following cerebral ischemia to determine which cell type substantially contributes to the fibrotic scar. I will also pharmacologically inhibit PDGF signaling to determine if this pathway plays a significant role in the activation of PVFs during cerebral ischemia. Together these studies will help to elucidate the pro-fibrotic cell type following stroke in animals and determine if PVFs are important for vascular stability in the healthy brain.