Abstract 3153: Endoglin Deficiency in Bone Marrow is Sufficient to Cause Vascular Dysplasia in the Adult Mouse Brain After VEGF Stimulation

Background and Objective: We have previously demonstrated that VEGF overexpression in the brain of adult Eng+/- mice causes vascular abnormalities. We also found that bone marrow-derived cells (BMDCs) home to vascular endothelial growth factor (VEGF)-induced angiogenic foci in the adult mouse brain and contribute to angiogenesis. Impaired angiogenesis in infarcted myocardium of Eng+/- mice was rescued using treatment with healthy human BMDCs but not with BMDCs from Hereditary Hemorrhagic Telangiectasia (HHT1) patients carrying ENG mutations. We hypothesized that ENG-haploinsufficiency in BMDCs can cause cerebrovascular dysplasia in the adult mouse after VEGF stimulation. Methods: WT or Eng+/- BM (2×106 cells) were transplanted to lethally irradiated C57BL/6 recipient mice (8-10 weeks old) via tail vein injection. After 4 weeks of BM transplantation, adeno-associated viral vector expressing VEGF (AAV-VEGF, 2×109 genome copies) was stereotactically injected into the basal ganglia. Brain sections were collected at 4 weeks after virus injection. The vascular density (vessels per 20× objective field) and dysplasia index (number of vessels >15µm in diameter per 200 vessels) were quantified on lectin-stained brain sections. Results: To examine the angiogenic response to VEGF, the vascular density around the AAV-VEGF injection site was analyzed. The mean vascular density increased in all mice with VEGF stimulation. Mice transplanted with Eng+/- BM showed less vascular density compared to mice transplanted with WT BM. The mean vascular densities were167 ± 21 (Eng+/-BM, n=4) and 202 ± 15 (WT BM, n=5) (P<0.01). Further, mice with WT BM had angiogenesis with normal vascular morphology. In contrast, mice with Eng+/- BM had markedly enlarged and dysmorphic vessels. To assess the degree of the dysplastic response, dysplasia index was analyzed. Mice with Eng+/- BM had several fold-higher dysplasia index than mice with WT BM: 2.6 ± 1.4 (Eng+/- BM) versus 0.7 ± 0.4 (WT BM) (P<0.01). Conclusions: In the adult mouse after VEGF stimulation, ENG-deficiency in BM (1) caused a 17% reduction in brain angiogenic response, and (2) increased cerebrovascular dysplasia, compared to control animals. These data support the possibility that cerebrovascular malformations resulting from VEGF stimulation with ENG-haploinsufficiency is attributable to impaired cell-autonomous monocyte/macrophage function, in contrast to the view that ENG dysfunction is primarily an endothelial phenomenon.