Trauma-Induced Astrocyte Swelling/Brain Edema: Role of NKCC

描述（由申请人提供）： 脑水肿和颅内压增高是脑外伤（TBI）发病和死亡的主要原因。细胞毒性水肿（细胞内肿胀，主要在星形胶质细胞中）是TBI后早期脑水肿的主要组成部分。令人惊讶的是，对其机制知之甚少，其治疗仍然是一个治疗挑战。细胞肿胀代表细胞由于各种离子转运系统（ITS）功能障碍而不能调节其自身体积。在TBI中，似乎对星形胶质细胞肿胀有显著贡献的一个ITS是Na+-K+-2Cl-协同转运蛋白（NKCC）。我们的假设提出，创伤触发了各种“因子”的激活，这些“因子”随后会聚以激活NKCC，最终导致星形胶质细胞肿胀/脑水肿。在这些“因子”中，包括氧化/亚硝化应激（ONS）、促分裂原活化蛋白激酶（MAPK）和转录因子核因子-κ B（NF-κ B）。目的#1将检查NKCC在体外创伤后星形胶质细胞肿胀中的参与以及表征NKCC蛋白质改变（氧化、硝化、磷酸化和蛋白质表达的变化）。目的#2将研究各种创伤相关“因子”（ONS、MAPK和NF-jB）促成NKCC改变的机制。目的#3将检查NKCC激活中潜在的神经元-星形胶质细胞相互作用。这些研究将应用来自创伤神经元的条件培养基（CM），并确定其对创伤星形胶质细胞中NKCC活性和细胞体积的影响。如果这些研究表明来自创伤神经元的CM加剧创伤星形胶质细胞中的星形胶质细胞肿胀，则将检查ONS、MAPK、NF-κ B在NKCC活化中的作用（如目标#2中所述）。我们还将研究谷氨酸和K+的参与，因为已知这些药物会引起星形胶质细胞肿胀，并且在创伤后也会由神经元释放。目的#4将在大鼠中进行TBI相关脑水肿的体内机制和治疗研究。机制部分将（a）检查TBI后磷酸化NKCC 1（NKCC 1的活性形式）的免疫组织化学分布，并确定NKCC 1是否在星形胶质细胞中过表达;和（B）确定“因子”阻断剂是否减少磷酸化NKCC 1的这种过表达。治疗部分将检查NKCC抑制剂布美他尼对创伤性脑水肿的影响。我们期望从这些研究中获得的知识将产生关于创伤后星形胶质细胞肿胀原因的重要机制信息，这些信息应有助于识别旨在减少创伤性脑损伤背景下发生的细胞毒性脑水肿的治疗药物。 公共卫生相关性： 脑水肿是与创伤性脑损伤（TBI）相关的危及生命的并发症。损伤早期的水肿主要是由于星形胶质细胞肿胀而引起的细胞毒性。目前尚无有效的治疗TBI脑水肿的方法。我们建议研究创伤激活的各种致肿因子对星形胶质细胞肿胀/脑水肿的作用，以及它们在体内的治疗效果。

DESCRIPTION (provided by applicant): Abstract Brain edema and associated increase in intracranial pressure are major causes of morbidity and mortality in traumatic brain injury (TBI). Cytotoxic edema (intracellular swelling, chiefly in astrocytes) represents a major component of the brain edema in the early phase following TBI. Surprisingly, little is known about its mechanisms, and its treatment remains a therapeutic challenge. Cell swelling represents a failure of the cell to regulate its own volume as a consequence of a dysfunction in various ion transporting systems (ITSs). One ITS which appears to significantly contribute to the astrocyte swelling in TBI is the Na+-K+-2Cl- cotransporter (NKCC). Our hypothesis proposes that trauma triggers the activation of various "factors" that subsequently converge to activate NKCC, ultimately resulting in astrocyte swelling/brain edema. Among these "factors", include oxidative/nitrosative stress (ONS), mitogen-activated protein kinases (MAPKs), and the transcription factor nuclear factor-kappaB (NF-jB). Aim #1 will examine the involvement of NKCC in the astrocytic swelling post in vitro trauma as well as characterize NKCC protein alterations (oxidation, nitration, phosphorylation and changes in protein expression). Aim #2 will investigate mechanisms by which various trauma-associated "factors" (ONS, MAPKs and NF-jB) contribute to alterations in NKCC. Aim #3 will examine potential neuronal- astroglial interactions in the activation of NKCC. These studies will apply conditioned media (CM) from traumatized neurons and determine their effect on NKCC activity and cell volume in traumatized astrocytes. Should such studies indicate that CM from traumatized neurons exacerbate astrocyte swelling in traumatized astrocytes, the role of ONS, MAPKs, NF-jB in the activation of NKCC will be examined (as in Aim #2). We will also examine the involvement of glutamate, as well as K+, as these agents are known to cause astrocyte swelling and are also released by neurons following trauma. Aim #4 will perform in vivo mechanistic and therapeutic investigations in TBI-associated brain edema in rats. The mechanistic component will (a) examine the immunohistochemical distribution of phosphorylated NKCC1 (active form of NKCC1) post TBI and determine whether NKCC1 is overexpressed in astrocytes; and (b) determine whether "factor" blockers diminish such overexpression of phosphorylated NKCC1. The therapeutic component will examine the effect of the NKCC inhibitor bumetanide on traumatic brain edema. We expect that knowledge garnered from these studies will yield vital mechanistic information on the cause of astrocyte swelling post trauma that should facilitate the identification of therapeutic agents aimed at bringing about a reduction in the cytotoxic brain edema occurring in the setting of traumatic brain injury. PUBLIC HEALTH RELEVANCE: Project Narrative Brain edema is a life threatening complication associated with traumatic brain injury (TBI). Such edema in the early phase of injury is predominantly cytotoxic due to swelling of astrocytes. There is no effective therapy currently available of brain edema in TBI. We propose to examine the role of various swelling causing factors activated by trauma on astrocyte swelling/brain edema, as well as their therapeutic efficacy in vivo.