Aryl hydrocarbon receptor and bilirubin as therapeutic target for ICH

脑出血（ICH）后，血肿成分[红细胞（RBC）， 血红蛋白（Hb）和血红素]，由小胶质细胞/巨噬细胞（MMΦ）是必不可少的去除/解毒的 血肿、炎症消退和恢复脑内稳态以实现最佳神经恢复。 因此，在吞噬毒性血肿成分过程中保护MMΦ免受损伤的策略对于 MMΦ清除脑出血后血肿的有效性。 当从血肿中吞噬RBC/Hb/血红素时，MMΦ表达血红素加氧酶1（HO 1;由 Hmox 1），其分解代谢血红素以在MMΦ内产生大量胆红素（BrB）。一般来说，BrB是一种 有益的和有效的抗氧化剂;然而，当细胞内BrB积累到非常高的浓度， 可能可逆地抑制HO 1活性，从而降低MMΦ'功能，甚至沉淀到生物膜上 或核酸（由于其水溶性差），导致损伤并损害MMΦ'完整性。 在细胞水平上，BrB作为多效性转录因子芳烃的内源性激动剂， 受体（AhR），一种蛋白质，根据先前的研究和我们的初步数据，在 支持MMΦ在血肿清除过程中的完整性和功能，以促进ICH后的脑恢复。 我们的初步研究表明，在小胶质细胞（MΦ）中， 红细胞吞噬作用，激活AhR以促进BrB处理蛋白、配体蛋白 [(LGN/谷胱甘肽S-转移酶），其结合fBrB以增加其细胞溶质溶解度]和多药耐药性 蛋白质1 [（Mrp 1）14，15，其介导BrB从细胞内室流出到细胞外空间]。 如果不能快速清除细胞内积累的fBrB，MΦ就会受到损伤，功能也会降低， 产生大量的促炎因子，可能导致严重的脑损伤。另外我们 建立BrB激活的AhR促进吞噬作用并上调核因子的表达 红细胞2相关因子2（Nrf 2），一种用于血肿解毒的细胞氧化防御的主要调节剂， 和脑出血的潜在治疗靶点。此外，我们确定AhR活性调节RelB核， 易位，表明AhR也可能与RelB相互作用，以反式激活涉及炎症的基因 分辨率最终，使用ICH小鼠模型，我们发现AhR非常有希望的治疗益处 激动剂ITE 19 -21，单独使用，甚至与Nrf 2的激活剂（萝卜硫素，SF）组合使用， 神经学结局和血肿清除。 我们的假设是，在ICH后，在BrB（或其他药物）清除血肿期间，MMΦ中AhR/RelB的激活可能与脑出血有关。 无毒的AhR激活剂）对于保持MMΦ的存活/吞噬功能至关重要， 损伤，保留修复表型，最终导致更有效的MMΦ介导的血肿 ICH后的清除和修复。AhR的激活可能成为脑出血治疗的新靶点。

After intracerebral hemorrhage (ICH), phago(endo)cytosis of hematoma components [erythrocytes (RBC), hemoglobin (Hb) and heme], by microglia/macrophages (MMΦ) is essential for removal/detoxification of the hematoma, resolution of inflammation, and restoration of brain homeostasis for optimal neurological recovery. Thus, strategies for protecting MMΦ from injury during engulfment of toxic hematoma components is critical for the efficiency of MMΦ in clearing the hematoma after ICH. Upon engulfment of RBC/Hb/heme from the hematoma, MMΦ express heme oxygenase 1 (HO1; encoded by Hmox1), which catabolizes heme to produce large amounts of bilirubin (BrB) within MMΦ. Normally BrB is a beneficial and potent antioxidant; however, when intracellular BrB accumulates to very high concentrations, it may reversibly inhibit HO1 activity, thus reducing MMΦ' function and even precipitate onto biological membranes or nucleic acids (due to its poor water solubility), causing injury and compromising MMΦ' integrity. On the cellular level, BrB acts as an endogenous agonist for a pleotropic transcription factor, aryl hydrocarbon receptor (AhR), a protein that, based on prior research and our preliminary data, plays essential roles in supporting MMΦ for their integrity and function during hematoma clearance to enhance brain recovery after ICH. Our preliminary studies established that intracellularly elevated free BrB in microglia (MΦ), during erythrophagocytosis, activates AhR to promote transcription of BrB handling proteins, ligandins [(LGN/glutathione S-transferases), which bind fBrB to increase its cytosol solubility] and multidrug resistance protein 1 [(Mrp1)14, 15, which mediates efflux of BrB from the intracellular compartment to the extracellular space]. Without fast clearance of intracellularly accumulating fBrB, MΦ are injured and function less efficiently, and produce large amount of proinflammatory factors that could cause severe brain damage. In addition, we established that BrB-activated AhR promotes phagocytosis and upregulates the expression of nuclear factor erythroid 2-related factor 2 (Nrf2), a master regulator of cellular oxidative defense for hematoma detoxification, and a potential therapeutic target for ICH. Furthermore, we established that AhR activity regulates RelB nuclear translocation, suggesting that AhR may also interact with RelB to transactivate genes involving inflammation resolution. Ultimately, using the mouse model of ICH, we found very promising therapeutic benefits of AhR agonist ITE19-21, alone and even more so in combination with the activator of Nrf2 (sulforaphane, SF), regarding neurological outcome and hematoma clearance. Our hypothesis is that after ICH, activation of AhR/RelB in MMΦ during hematoma removal by BrB (or other non-toxic AhR activators) is vital for preserving MMΦ' survival/phagocytic functions, avoiding self-inflicted damage, retention of reparative phenotype, ultimately leading to a more efficient MMΦ-mediated hematoma clearance and repair after ICH. Activation of AhR could be a novel therapeutic target for ICH.