論文

正常脳においてアストロサイトは、ニューロンのための細胞外環境の維持、エネルギー代謝の補助、脳血流調節と多面的に作用している。虚血脳において、その作用は急性期、亜急性期、慢性期のいずれにおいても、ニューロンに対して時に保護的、時に傷害性に作用するため一元的に論じることは難しい。またアストロサイトは成体脳における神経幹細胞の一部である可能性があり、回復期の再生医療を考えるうえでも重要な細胞である。(著者抄録)

The metabolic properties of astroglia differentiated from neurospheres have not been fully assessed. In this study, the glycolytic and oxidative metabolism of glucose in astroglia differentiated from rat tertiary neurospheres (astroglia(NS)) was compared with that in astroglia prepared from the striata of embryonic day 16 rats (astroglia(ST)). In addition to the basal condition, we also investigated energy metabolism under Na+,K+-ATPase activation. Furthermore, the effects of glucose concentration in the culture medium were assessed. No significant differences in 2-deoxy-D-[1-(14)C]glucose phosphorylation were observed between astroglia(NS) and astrogliaST. The rates of L-[U-14C]lactate ([14C]lactate) and D-[U-14C]glucose ([14C]glucose) oxidation were 5.74+/-0.82 and 2.83+/-0.4 pmol/60 min/microg protein, respectively, in astrogliaNS grown in low glucose (2 mM) and 3.01+/-1.03 and 1.77+/-0.23 pmol/60 min/microg protein, respectively, in astrogliaNS grown in high glucose (22 mM). Neither the [14C]lactate nor the [14C]glucose oxidation rates in astrogliaNS were significantly different from those in astrogliaST. D-aspartate (500 microM) significantly increased the [14C]lactate and [14C]glucose oxidation rates by 127% and 62%, respectively, in astrogliaNS grown in low glucose and by 217% and 115%, respectively, in astroglia(NS) grown in high glucose. D-aspartate also increased the oxidation of [14C]lactate and [14C]glucose to 236% and 147% of the control values, respectively, in astrogliaST grown in low glucose and to 174% and 144%, respectively, in astrogliaST grown in high glucose. Rat astroglia differentiated from neurospheres might possess an equivalent capacity for utilizing energy substrates under both basal and activated conditions to that of astroglia prepared from striatum.

メタボリックシンドロームは虚血性脳血管障害の発症リスクを約2倍に増大させる.人種,民族の差異に基づいた適正なカットオフ値による診断をもとに,生活習慣によって生じる軽微なリスクの集積に早期から対処することで脳梗塞や一過性脳虚血発作(TIA)の発症を有効に予防できる可能性が高い.治療には運動と体重減少とともにアンジオテンシンII受容体拮抗薬(ARB)やペルオキシソーム増殖剤応答性受容体(PPAR)α,γアゴニストの適正な選択が必要で,時に複数の薬剤の使用が有効である(著者抄録)

The glucose concentration in the culture medium may affect the energy metabolism of cultured cells. The oxidative metabolism of glucose in astrocytes might also be affected because the glucose concentration (25 mmol/L) of many culture media is higher than the physiological levels (approximately 3 mmol/L). In the present study, we assessed the effects of reducing the glucose concentration in the culture medium on the oxidative metabolism of glucose in cultured rat astroglia by measuring the oxidation rates of L-[U-14C]lactate or D-[U-14C]glucose to 14CO2. The effects of D-aspartate and elevated extracellular K+ levels on oxidative and glycolytic metabolism in astroglia were also investigated. The rates of [14C]lactate and [14C]glucose oxidation in astroglia cultured in a medium containing 2 mmol/L of glucose (astroglia2) were approximately twofold of those in astroglia cultured in a medium containing 22 mmol/L of glucose (astroglia22). D-Aspartate (500 micromol/L) significantly increased [14C]lactate oxidation by 156% in astroglia22 and by 83% in astroglia2. D-[U-14C]glucose oxidation in astroglia22 and astroglia2 was also increased by 94% and 76%, respectively. In contrast, an elevated extracellular K+ concentration (7.4 mmol/L) did not affect glucose and lactate oxidation, although it increased 2-deoxy-D-[1-14C]glucose phosphorylation. Astroglia grown in the physiological glucose concentration are more dependent on the oxidative metabolism of glucose than that in high-glucose concentration. Glucose concentration in culture medium has a strong influence on astrocytic oxidative capacity in vitro.

Neurovascular unit(NVU)とは、ニューロンと血管(内皮細胞、周皮細胞、平滑筋細胞、非細胞性要素として細胞外マトリックスを構成する蛋白とその調節酵素)、両者の橋渡しをするアストロサイトからなる機能的統合体を示す。NVUは脳血管障害急性期の病態をこれらの機能ユニットとして捉えることで、新たな急性期治療戦略を模索するために提唱された。近年NVUは、脳血管障害急性期のみならず、広く中枢神経疾患を理解するためのツールとしても用いられている。(著者抄録)

NVU(Neurovascular Unit)とは脳卒中の病態から治療戦略を構築するための概念的枠組み(conceptual framework)である。NVUには微小血管(毛細血管と細動脈)とニューロン、これらを橋渡しするアストロサイトが含まれる。その血管側では内皮細胞、細胞外マトリクス、アストロサイトの足突起が血液脳関門を形成する。脳血流はニューロンの活動によって増減し、代謝基質としてのグルコース、脂肪酸、アミノ酸はアストロサイトで中間代謝を受け効率よくニューロンに運搬される。NVUの生理的メカニズムの研究は、脳卒中のみならず、神経変性疾患、神経免疫疾患など広く中枢神経疾患を理解するツールとなる。(著者抄録)

Neurovascular unit(NVU)とは、ニューロンと脳微小循環を基盤として脳機能を統合的に捉え、脳虚血病態を理解するためのconceptual frameworkである。主要な構造要素としてニューロン、脳微小血管のほか、両者を橋渡しするアストロサイトが含まれる。血液脳関門(BBB)はNVUの血管側の解剖学的構造に由来するバリア機能であり、脳微小循環から脳実質内への物質移動の制御機構を担う。BBBという透過性の制限を設けることは、脳の保護機構として重要な生体戦略であるが、BBBには必須物質に対する特異的輸送系のほか、safety systemとしてエネルギー代替物質となるモノカルボン酸(乳酸、ケトン体)トランスポーターが存在し、さらに脳実質内には細胞(種)間の合成系と消費系が存在する。NVU構成要素のうちニューロンとアストロサイトに注目し、cellular metabolic compartmentを介したNVU維持機構を論じる。(著者抄録)

We describe the clinical features of limbic encephalitis that developed after palliative spinal cordotomy in 2 patients with malignant thoracic astrocytoma. Both patients showed short-term memory loss, hallucinations of smells and psychiatric symptoms. Brain MRI on T2-weighted and fluid-attenuated inversion recovery sequences revealed high intensity lesions in bilateral temporal lobe areas. We considered that both patients had paraneoplastic limbic encephalitis associated with astrocytoma because of various clinical and radiological features. But the possibility of intracranial dissemination of astrocytoma could not be fully excluded. The differential diagnosis between intracranial dissemination of spinal cord astrocytoma and paraneoplastic limbic encephalitis may be sometimes difficult.

ROS (reactive oxygen species) play an essential role in the pathophysiology of diabetes, stroke and neurodegenerative disorders. Hyperglycaemia associated with diabetes enhances ROS production and causes oxidative stress in vascular endothelial cells, but adverse effects of either acute or chronic high-glucose environments on brain parenchymal cells remain unclear. The PPP (pentose phosphate pathway) and GSH participate in a major defence mechanism against ROS in brain, and we explored the role and regulation of the astroglial PPP in response to acute and chronic high-glucose environments. PPP activity was measured in cultured neurons and astroglia by determining the difference in rate of (14)CO(2) production from [1-(14)C]glucose and [6-(14)C]glucose. ROS production, mainly H(2)O(2), and GSH were also assessed. Acutely elevated glucose concentrations in the culture media increased PPP activity and GSH level in astroglia, decreasing ROS production. Chronically elevated glucose environments also induced PPP activation. Immunohistochemical analyses revealed that chronic high-glucose environments induced ER (endoplasmic reticulum) stress (presumably through increased hexosamine biosynthetic pathway flux). Nuclear translocation of Nrf2 (nuclear factor-erythroid 2 p45 subunit-related factor 2), which regulates G6PDH (glyceraldehyde-6-phosphate dehydrogenase) by enhancing transcription, was also observed in association with BiP (immunoglobulin heavy-chain-binding protein) expression. Acute and chronic high-glucose environments activated the PPP in astroglia, preventing ROS elevation. Therefore a rapid decrease in glucose level seems to enhance ROS toxicity, perhaps contributing to neural damage when insulin levels given to diabetic patients are not properly calibrated and plasma glucose levels are not adequately maintained. These findings may also explain the lack of evidence for clinical benefits from strict glycaemic control during the acute phase of stroke.

Reactive oxygen species (ROS) derived from mitochondria play an essential role in stroke as well as in neurodegenerative disorders. Although hyperglycemia associated with diabetes mellitus is well known to enhance ROS production in vascular endothelial cells, the effects of either acute or chronic high glucose environments on neurons and glial cells remain unclear. Astroglia play a pivotal role in glucose metabolism. Thus, the astroglial metabolic response to high glucose environments is an interesting subject. In particular, the glutathione/pentose phosphate pathway (PPP) system, which is a major defense mechanism against ROS in the brain, contributes to glucose metabolism and is more active in astroglia. We propose that high glucose environments activate PPP through an increased flux to the hexosamine biosynthetic pathway (HBP). HBP is known to induce endoplasmic reticulum (ER) stress under hyperglycemia, resulting in the nuclear translocation of nuclear factor-erythroid-2-related factor 2 (Nrf2), a master regulator of phase 2 detoxifying enzymes including glucose-6-phosphate dehydrogenase that regulates PPP activity, as Nrf2 is reported to be a direct substrate of protein kinase RNA (PKR)-like ER kinase (PERK), a transducer of ER stress. Therefore, the phosphorylation of Nrf2 by hyperglycemia-induced ER stress facilitates Nrf2 translocation through PERK, thus activating the PPP. If acute or chronic hyperglycemia induces PPP activation in astroglia to reduce ROS, reducing the glucose concentration may be accompanied by a risk, which may explain the lack of evidence that strict glycemic control during the acute phase of stroke conveys no beneficial effect.

脳梗塞後の炎症による神経障害のメディエータとして活性酸素種(ROS)と活性窒素種(RNS)は重要であるが、その上流因子であるToll様受容体4(TLR4)の有する神経保護シグナルに注目した。脳梗塞急性期において、TLR4の内因性リガンド刺激は下流シグナルであるNFκB、JAK/STAT、MAPKなどを介してNADPH oxidase、iNOS、炎症性サイトカインを誘導し神経障害を増悪させる。ROS消去にはペントースリン酸経路(PPP)活性の維持が必須であり、アストロサイトは高いPPP活性を有す。PPPの律速酵素G6PDHの転写調節は、グルタチオン合成、グルタチオンペルオキシダーゼなどの酵素を含めて転写因子Nrf2による制御下にある。TLR4リガンドであるリポ多糖(LPS)刺激は、Nrf2依存性にアストロサイトのPPPを活性化し、虚血性神経細胞障害に対する保護作用をもたらす可能性が示された。(著者抄録)