Loss of Pericytes in Radiation Necrosis after Glioblastoma Treatments.

Radiation necrosis (RN) in brain tumor patients is often symptomatic, persistent without immediate resolution, and confused with tumor recurrence. Cerebral vascular pericytes are essential for endothelial function, vascular integrity, and angiogenesis. In this study, we showed that the loss of pericytes is involved in the pathogenesis of RN. From a brain tumor tissue repository, we identified three patients since 2011 with pathologically confirmed RN after the standard treatment for glioblastoma (GBM). The RN and their preradiation GBM tissues were serially processed for Western blotting using cell-type-specific antibodies against endothelial (CD31, active RhoA), pericyte [platelet-derived growth factor receptor-beta (PDGFR-β)], alpha-smooth muscle actin (α-SMA), astrocyte (GFAP), myelin sheath protein (MBP), and microglial markers (Iba1). Normal brain tissues from a brain bank were used as normal controls. The expressions of PDGFR-β and α-SMA were remarkably reduced in the RN, compared to those of GBM. However, the levels of CD31 or RhoA were not different between the two groups, which suggest that there was no change in the number of endothelial cells or their cytoskeletal assembly. The RN tissues showed a decreased ratio of pericyte/endothelial markers and an increased level of Iba1 compared to the GBM and even to the normal brain. The levels of GFAP and MBP were not changed in the RN. In the histopathology, the RN tissues showed a loss of markers (PDGFR-β), whereas the GBM tissues had abundant expression of the markers. The loss of pericytes and vascular smooth muscle cells, and the unsupported endothelial cells might be the cause of the leaky blood-brain barrier and tissue necrosis.