Endothelial Convergence Mechanisms of Blood–Brain Barrier Disruption across Infectious, Proteopathic, and Environmental Insults

Abstract

혈액-뇌 장벽(Blood-Brain Barrier, BBB)은 뇌 미세혈관 내피세포, 주변세포, 기저막, 그리고 성상교세포 말단부로 구성된 선택적 투과성 인터페이스로서, 뇌 조직의 항상성 유지에 핵심적인 역할을 담당합니다. 본 연구에서는 PM2.5, 나노플라스틱, SARS-CoV-2와 같은 이질적 스트레스 요인들이 BBB에 미치는 영향을 체계적으로 분석하여, 이들이 공통적으로 유발하는 초기 손상 패턴을 규명하고자 하였습니다. 연구 결과, 세 가지 노출 모델 모두에서 혈관 구조는 대체로 보존되었으나 기능적 선택성과 관류 조절 능력이 감소하는 공통된 양상이 관찰되었습니다. 특히 주목할 점은 AQP4 단백질의 총량은 정상 수준을 유지했음에도 불구하고, 혈관 주변부에서의 극성 분포가 현저히 손상되어 수분 수송 시스템의 조직화가 붕괴되었다는 것입니다. 또한 내피세포에서는 미토콘드리아 기능 이상과 산화 스트레스를 포함한 대사적 스트레스 징후가 확인되었으며, 신경세포 손상은 주로 에너지 요구도가 높은 수상돌기 부위에 집중되었습니다. 각 노출 유형별로는 독특한 특성도 나타났습니다. PM2.5 모델에서는 혈관 수축과 혈류 감소가 주된 변화였으며, 나노플라스틱 노출 시에는 밀착연접은 상대적으로 정상이었으나 eNOS 발현 감소와 지질 소포 형성이 관찰되어 세포경유 수송 경로의 활성화 가능성을 시사했습니다. SARS-CoV-2 감염 모델에서는 내피세포 주변에서 바이러스 단백질이 검출되었고, 혈관 구조는 유지되었으나 초기부터 AQP4 극성 손실이 발생했습니다. 중요한 발견 중 하나는 BBB 기능 저하로 인해 유입된 피브리노겐이 미세아교세포를 활성화시켜 AKT 경로 활성화, 해당작용으로의 대사 전환, TNF-α 생산 증가를 유도한다는 점입니다. 이는 주요 혈관 손상이나 직접적인 신경세포 감염 없이도 신경염증 반응이 유발될 수 있음을 보여줍니다. 본 연구는 다양한 환경적, 감염성 노출에 대해 BBB 기능 장애가 공통적인 초기 반응으로 나타남을 제시합니다. 이러한 발견은 성상교세포 말단부의 AQP4-칼모듈린 축 조절, 내피세포 미토콘드리아 지원, eNOS 기능 향상 등을 포함한 통합적 치료 전략 개발의 근거를 제공하며, 조기 진단을 위한 바이오마커 개발에도 중요한 시사점을 제공합니다. |The blood-brain barrier (BBB) is a selective, dynamic interface formed by brain microvascular endothelial cells, pericytes, basement membranes, and astrocytic endfeet. It regulates paracellular and transcellular flux through junctions and transport systems, maintains ionic and osmotic balance, and coordinates perivascular water exchange via AQP4 at astrocyte endfeet. Small functional shifts at this interface can occur before obvious structural loss and can organize downstream tissue response. Against this background, the central question here is whether these heterogeneous stressors—PM2.5, nanoplastics, and viruses—share a common early pattern of disruption in the BBB, specifically characterized by reduced functional selectivity and flow control, the loss of AQP4 polarity, and a microglial state tilted toward inflammatory cytokine output. To keep all comparisons on common terms, a fixed set of readouts was used, parenchymal fibrinogen/IgG access indicators, AQP4 polarity, energetic stress and mitophagy markers, neuronal compartment integrity across dendritic, axonal, and somatic markers. All measurements were then paired with endothelial and microglial assays to keep the interpretation vessel-proximal and highly relevant to the local environment. Similar barrier problems were observed in all tested models. The capillary structure was mostly intact, major vessel loss was not detected. This suggests that the problem is not structural damage but rather reduced transport function. AQP4 protein amount was almost normal, but its polarity was disrupted. This indicates that the water transport system around vessels was disorganized, rather than astrocyte death. The endothelial cells showed signs of metabolic stress, including mitochondrial dysfunction and oxidative stress. Neurons showed damage mainly in dendrites, which is consistent with higher energy demands in these areas located near the compromised BBB. Each exposure type showed some unique features. In the PM2.5 model, mainly vascular changes were observed. The vessel structure remained, but vessels became narrower. Less tracer and IgG were detected inside vessels, and metabolic stress markers were found. These findings suggest reduced blood flow and altered nitric oxide signaling. In the nanoplastic exposure model, the tight junctions appeared relatively normal. However, eNOS expression was reduced. Lipid droplets were also observed, which might indicate transcellular transport pathway activation. Some large molecules could cross the barrier, possibly through transcellular routes rather than between cells. For the SARS-CoV-2 model (intranasal infection was used to mimic household exposure), viral proteins were found near or inside CD31-positive endothelial cells. Some serum proteins leaked into brain tissue, but the vessel structure stayed intact. AQP4 polarity was disrupted early in infection. The effect of BBB changes on microglial activation was examined next. Since even small barrier changes can allow fibrinogen to enter brain tissue, its effect on microglial activation was tested. When primary microglia were cultured with fibrinogen in normal serum conditions, fibrinogen uptake and AKT pathway activation were observed. A shift to glycolysis and increased TNF-alpha production were also detected. In animal models, fibrinogen and TNF-alpha were observed near blood vessels, confirming these in vitro findings. This demonstrates that BBB leakage allows fibrinogen to activate microglia and cause neuronal stress, even without major vascular damage or direct neuronal infection. These findings indicate that BBB dysfunction occurs as an early, functional impairment across different environmental and infectious exposures. The consistent pattern—preserved vascular structure with reduced perfusion capacity, AQP4 polarity loss, and dendrite-focused neuronal damage—suggests common underlying mechanisms despite diverse stressors. A key therapeutic target emerges at the astrocyte endfoot, where AQP4 polarity depends on calmodulin-dependent cues. Modulation of the AQP4-calmodulin axis through astrocyte-targeted calmodulin tuning, support of the endfoot anchoring complex, and prevention of kinase-mediated AQP4 internalization could restore perivascular water handling without increasing bulk permeability. Additional intervention points include endothelial mitochondrial support and eNOS enhancement to improve selectivity, regulation of vesicular routing when junctions remain intact, and modulation of microglial AKT-proximal signaling to limit fibrinogen recognition. For clinical translation, biomarkers should report early functional changes: BBB selectivity on preserved CD31 architecture, AQP4 polarity as an organizational metric, endothelial energetic stress and NO tone, and microglial TNF-skewed microdomains. This biomarker-target pairing framework prioritizes early stabilization of perfusion-glymphatic coupling and gliovascular support, providing a unified approach to diverse neurological challenges involving BBB compromise. Keywords: Neurovascular–glymphatic dysfunction, Blood–brain barrier (BBB), Mitochondrial, Fibrinogen, Environmental exposures