1. ¹Department of Anesthesia and Perioperative Care, Center for Cerebrovascular Research, University of California, San Francisco, California, USA
2. ²Cardiovascular Research Institute, University of California, San Francisco, California, USA
3. ³Department of Neurological Surgery, University of California, San Francisco, California, USA
4. ⁴Department of Neurology, University of California, San Francisco, California, USA

Correspondence: Dr G-Y Yang, Department of Anesthesia and Perioperative Care, 1001 Potrero Ave, Room 3C-38, San Francisco, California 94110, USA. E-mail: gyyang@anesthesia.ucsf.edu

Received 16 November 2006; Revised 10 January 2007; Accepted 26 January 2007; Published online 28 March 2007.

Abstract

To explore the role of neutrophil-derived matrix metalloproteinases (MMPs) during angiogenesis in the brain, we hypothesized that transient neutrophil depletion attenuates the angiogenic response to focal hyperstimulation with vascular endothelial growth factor (VEGF). Brain focal angiogenesis was achieved using an adeno-associated virus delivered VEGF (AAV-VEGF) gene transfer in the mature mouse. Four groups of mice underwent AAV vector injection in the brain parenchyma: (1) AAV-LacZ; (2) AAV-VEGF; (3) AAV-VEGF plus anti-polymorphonuclear (PMN) antibody; and (4) AAV-VEGF plus serum. Animals in groups 3 and 4 underwent 4 days of PMN antibody or serum treatment before transfection; treatment was sustained for an additional 14 days. Anti-PMN treatment decreased circulating neutrophils to 9% of baseline (P<0.001). Microvessels in the AAV-VEGF-group increased 25% compared with the AAV-lacZ-transduced group (25615 versus 20816; P<0.05). Anti-PMN treatment attenuated the increase to 10% compared with control serum treatment (23416 versus 25522; P<0.05). Similarly, compared with control serum treatment, anti-PMN treatment also reduced MMP-9 by 50% (20.9 versus 41.4; P<0.05) and MPO expression by 25% (20.8 versus 30.9; P<0.05); MMP-9 activity correlated with MPO expression (R²=0.8, P<0.05). Our study demonstrated that transient depletion of neutrophils suppressed VEGF-induced angiogenesis, indicating that circulating neutrophils contribute to VEGF-induced focal angiogenesis. In addition, brain MMP-9 activity was attenuated after neutrophil depletion, suggesting that neutrophil is an important source of MMP-9.