Fibronectin Produced by Cerebral Endothelial and Vascular Smooth Muscle Cells Contributes to Perivascular Extracellular Matrix in Late-Delayed Radiation-Induced Brain Injury

Abstract

Late-delayed radiation-induced brain injury (RIBI) is a major adverse effect of fractionated whole-brain irradiation (fWBI). Characterized by progressive cognitive dysfunction, and associated cerebrovascular and white matter injury, RIBI deleteriously affects quality of life for cancer patients. Despite extensive morphological characterization of the injury, the pathogenesis is unclear, thus limiting the development of effective therapeutics. We previously reported that RIBI is associated with increased gene expression of the extracellular matrix (ECM) protein fibronectin (FN1). We hypothesized that fibronectin contributes to perivascular ECM, which may impair diffusion to the dependent parenchyma, thus contributing to the observed cognitive decline. The goal of this study was to determine the localization of fibronectin in RIBI and further characterize the composition of perivascular ECM, as well as identify the cell of origin for FN1 by in situ hybridization. Briefly, fibronectin localized to the vascular basement membrane of morphologically normal blood vessels from control comparators and animals receiving fWBI, and to the perivascular space of edematous and fibrotic vascular phenotypes of animals receiving fWBI. Additional mild diffuse parenchymal staining in areas of vascular injury suggested blood-brain-barrier disruption and plasma fibronectin extravasation. Perivascular ECM lacked amyloid and contained lesser amounts of collagens I and IV, which localized to the basement membrane. These changes occurred in the absence of alterations in microvascular area fraction or microvessel density. Fibronectin transcripts were rarely expressed in control comparators, and were most strongly induced within cerebrovascular endothelial and vascular smooth muscle cells after fWBI. Our results demonstrate that fibronectin is produced by cerebrovascular endothelial and smooth muscle cells in late-delayed RIBI and contributes to perivascular ECM, which we postulate may contribute to diffusion barrier formation. We propose that pathways that antagonize fibronectin deposition and matrix assembly or enhance degradation may serve as potential therapeutic targets in RIBI.

Non-Human Primates Receiving High-Dose Total-Body Irradiation are at Risk of Developing Cerebrovascular Injury Years Postirradiation

“…Despite previous categorization as ''hemangiomas,'' these focal structural abnormalities are not presumed due to proliferation of endothelium, and in keeping with the International Society for the Study of Vascular Anomalies (ISSVA) classification system, are more correctly classified as ''vascular malformations'' (93). The remaining cerebrovascular lesions observed in this study (perivascular extracellular matrix with acute and chronic hemorrhage) are similar to lesions observed in late-delayed RIBI after fWBI in non-human primates and humans (64,67,68,70,90,94,95). These cases suggest the etiopathogenesis of late-delayed RIBI involves vascular injury characterized by inappropriate remodeling and resultant structural abnormalities.…”

“…However, rodents do not develop white matter necrosis after fractionated whole-brain irradiation (fWBI) (44,(56)(57)(58), and differences in neuroanatomy [(e.g., greater hippocampal relative brain volume, larger gray:white matter ratio) (59-61)] and limited inter-individual genetic variability (62) may limit the translatability of findings. In contrast to rodents, non-human primates have greater neuroanatomic and genomic homology to humans and more fully recapitulate the histopathologic features of late-delayed radiation-induced brain injury (RIBI) after fWBI (e.g., cerebrovascular and white matter injury) (63)(64)(65)(66)(67)(68).…”

The Role of Basement Membranes in Cerebral Amyloid Angiopathy

“…• Brain microvessels (Keable et al, 2016;Andrews et al, 2018;Howe et al, 2018aHowe et al, , 2019 • Astrocytes (Howe et al, 2019) • Endothelial cells (Thomsen et al, 2017a;Andrews et al, 2018) • Meningeal cells (Sievers et al, 1994) • VSMCs (Andrews et al, 2018) Together, the ECM molecules and cellular components at the PVS support tissue homeostasis via a variety of functions in the healthy brain, including maintaining the structural integrity of vessels and permitting the exchange of fluids and solutes between the PVS and the brain parenchyma. In the next section, we will take a detailed look at the molecular and cellular changes that occur within the BM during CAA pathogenesis.…”

Radiation Effects on Brain Extracellular Matrix

“…Long-term effects (6 months) of irradiation of the whole brain of Rhesus macaques (age 6–11 years), which had received 40 Gy (8 fractions of 5 Gy each, twice per week), increased expression of fibronectin 1 (FN1) in brain tissue at mRNA level ( 32 ) and protein content of fibronectin and collagen I (COL1), whereas collagen IV (COL4) protein level was not affected ( 33 ).…”

“…X-ray irradiation of animal brain results in a quick (4–24 h) up-regulation of expression and enzymatic activity of MMPs: MMP2 and MMP9 (for rats, single dose) and MMP2 (for mice, 8 × 5 Gy, twice a week) ( 39 ). Irradiation-induced changes in MMPs expression seem to possess long-term effect—brain tissues of Rhesus macaques irradiated at a similar regimen (8 × 5 Gy, twice a week) demonstrate significantly increased mRNA level for MMP2 ( 32 ) and MMP9 protein content ( 33 ) at 6 months after irradiation.…”