Hypoxia Response Element-Regulated MMP-9 Promotes Neurological Recovery via Glial Scar Degradation and Angiogenesis in Delayed Stroke

Abstract

Matrix metalloproteinase 9 (MMP-9) plays a beneficial role in the delayed phase of middle cerebral artery occlusion (MCAO). However, the mechanism is obscure. Here, we constructed hypoxia response element (HRE)-regulated MMP-9 to explore its effect on glial scars and neurogenesis in delayed ischemic stroke. Adult male Institute of Cancer Research (ICR) mice underwent MCAO and received a stereotactic injection of lentivirus carrying HRE-MMP-9 or normal saline (NS)/lentivirus-GFP 7 days after ischemia. We found that HRE-MMP-9 improved neurological outcomes, reduced ischemia-induced brain atrophy, and degraded glial scars (p < 0.05). Furthermore, HRE-MMP-9 increased the number of microvessels in the peri-infarct area (p < 0.001), which may have been due to the accumulation of endogenous endothelial progenitor cells (EPCs) in the peri-infarct area after glial scar degradation. Finally, HRE-MMP-9 increased the number of bromodeoxyuridine-positive (BrdU⁺)/NeuN⁺ cells and the expression of PSD-95 in the peri-infarct area (p < 0.01). These changes could be blocked by vascular endothelial growth factor receptor 2 (VEGFR2) inhibitor SU5416 and MMP-9 inhibitor 2-[[(4-phenoxyphenyl)sulfonyl]methyl]-thiirane (SB-3CT). Our results provided a novel mechanism by which glial scar degradation and vascular endothelial growth factor (VEGF)/VEGFR2-dependent angiogenesis may be key procedures for neurological recovery in delayed ischemic stroke after HRE-MMP-9 treatment. Therefore, HRE-MMP-9 overexpression in the delayed ischemic brain is a promising approach for neurological recovery.

Keywords: HRE-MMP-9; angiogenesis; glial scar; neurogenesis; stroke.

Figure 1

MMP-9 Overexpression Reduced Atrophy Volume and Improved Neurobehavioral Outcomes in the Delayed Phase of tMCAO Mice (A) Diagram of experimental design. Virus inj., virus stereotactic injection; SB, SB-3CT i.p. injection; SU, SU5416 i.p. injection. Animal-sacrificing time points were 3 or 5 weeks after tMCAO. (B) Photograph showing brain sections in four groups with cresyl violet staining for atrophy volume at 3 weeks after tMCAO; the dashed line shows the original size of the ischemic brain side. (C) The bar graph shows statistical data on the atrophy volume at 3 and 5 weeks after tMCAO, respectively. N = 8 mice per group. (D) Atrophy volume of the whole brain in the NS-, GFP-, MMP-9-, and SB-3CT-treated groups of mice. (E) mNSS was performed separately to evaluate the outcomes 1–5 weeks after ischemia in the four groups (N = 16 mice per group from baseline to 3 weeks; eight mice per group at 5 weeks). Data are mean ± SD. The M(IQR) of the non-normal-distributed NS group in mNSS of 2W was 5. *p < 0.05, **p < 0.01, and ***p < 0.001. NS, normal saline; GFP, Lenti-HRE-GFP; MMP-9, Lenti-HRE-MMP9; SB, Lenti-HRE-MMP9 plus SB-3CT.

Figure 2

MMP-9 Degraded the Glial Scar and Extracellular Matrix in the Delayed Phase of tMCAO Mice (A) GFAP fluorescence staining for astrocytes was performed in the NS-, GFP-, MMP-9-, and SB-3CT-treated groups 5 weeks after tMCAO (left panel scale bar, 500 μm; other four panels, 100 μm). p, peri-infarct; GS, glial scar; C, ischemic core. (B) Bar graphs show the maximal scar thickness per field (N = 6 mice per group). (C) Bar graphs show the scar areas per field (N = 6 mice per group). (D) Schematic diagram illustrates the glial scar (green area) and represents the photographed region (red square). (E) Photographs present GFAP (green) double stained with CSPG, NG2, and Laminin (red) in four groups. Scale bar, 100 μm. (F) Quantifications of immunofluorescence intensity for CSPG, NG2, and Laminin in the four groups (fluorescence intensity in each group was normalized to the NS group, N = 5 mice per group). (G–I) Western blots for CSPG (G), NG2 (H), and Laminin (I) and their quantifications in the four groups (corrected by actin as well as normalized to the NS mean value, N = 3 mice per group). Data are mean ± SD. *p < 0.05, **p < 0.01, and ***p < 0.001. NS, normal saline; GFP, Lenti-HRE-GFP; MMP-9, Lenti-HRE-MMP9; SB, Lenti-HRE-MMP9 plus SB-3CT. All green GFAP was stained by Alex 647-conjugated secondary antibodies followed by pseudo-color processing.

Figure 3

MMP-9 Attenuated Astrocyte Activation In Vivo (A) Locations of central and peri-scar by GFAP (green) immunostaining at 5 weeks after tMCAO. Scale bar, 100 μm. Magnified photographs of GFAP⁺ cell morphology in the central and peri-scar of the four groups. Scale bar, 10 μm. (B) Quantifications for the length of the longest process per astrocyte (N = 6 mice per group). (C) Quantifications for the number of processes per astrocyte in the peri-scar region (N = 6 mice per group). (D) Photographs show astrocyte proliferation in vivo (Ki-67, red; GFAP, green; DAPI, blue); left panel scale bar, 50 μm; right panel, 10 μm. (E) Quantifications of astrocyte proliferation per field in each group, N = 6 mice per group. (F) Quantifications of Ki-67-positive cells and doublecortin-positive cells per field in each group, N = 6 mice per group. Data are mean ± SD. *p < 0.05, **p < 0.01, and ***p < 0.001. n.s., no significance; NS, normal saline; GFP, Lenti-HRE-GFP; MMP-9, Lenti-HRE-MMP9; SB, Lenti-HRE-MMP9 plus SB-3CT. All green GFAP was stained by Alex 647-conjugated secondary antibodies followed by pseudo-color processing.

Figure 4

MMP-9 Inhibited Hypoxic Astrocyte Migration In Vitro (A) Representative picture of the relative location of the glial scar (red) and lentivirus transduction (green) 5 weeks after tMCAO. p, peri-infarct; GS, glial scar; C, core; AS, astrocytes. Scale bar, 100 μm. (B) The protocol for astrocyte migration assay in vitro. (C) Representative images of migrated astrocytes in transwells in each group. Scale bar, 100 μm. (D) Quantifications of migrated cell numbers per field in each group (N = 3 per group). Data are mean ± SD. *p < 0.05, **p < 0.01, and ***p < 0.001. n.s., no significance; NS, normal saline; GFP, Lenti-HRE-GFP; MMP-9, Lenti-HRE-MMP-9; SB, Lenti-HRE-MMP-9 plus SB-3CT.

Figure 5

MMP-9 Promoted Angiogenesis in the Peri-infarct Area after tMCAO (A and B) CD31 immunostaining of brain slices (A) and quantifications of vessel numbers (B) in NS-, GFP-, MMP-9-, and SB-3CT-treated mice at 3 and 5 weeks after tMCAO. Scale bar, 100 μm (N = 6 mice per group). (C and D) Representative images of lectin and BrdU double staining for proliferating vessels (C) and quantification of the BrdU⁺/lectin⁺ cell number per field in each group (D). Scale bar, 20 μm (N = 6 mice per group). Data are mean ± SD. ***p < 0.001. NS, normal saline; GFP, Lenti-HRE-GFP; MMP-9, Lenti-HRE-MMP9; SB, Lenti-HRE-MMP9 plus SB-3CT.

Figure 6

MMP-9 Promoted Neurogenesis and Synaptogenesis, Depending on Angiogenesis in the Peri-infarct Area after tMCAO (A) Representative images of BrdU/NeuN double staining for neo-neurons (upper panel) and Lectin/GFAP double staining for vessels (lower panel) in the peri-infarct area 3 weeks after tMCAO. (B and C) Quantifications of BrdU⁺/NeuN⁺ cell (B) and Lectin⁺ vessel (C) number per field in NS-, GFP-, MMP-9-, SB-3CT-, and SU5416-treated mice at 3 weeks after tMCAO. Scale bar, 30 μm in BrdU and NeuN images and 50 μm in Lectin and GFAP images (N = 6 mice per group). (D and E) Western blot for PSD 95, Synaptophysin, VEGF, and VEGFR2 (D) and their quantifications (E) in NS-, GFP-, MMP-9-, SB-3CT-, and SU5416-treated mice at 3 weeks after tMCAO (N = 3 mice per group). (F) Quantitative of RT-PCR analysis of the expression of PSD 95 and synaptophysin in NS-, GFP-, MMP-9-, SB-3CT-, and SU-treated mice. Values were normalized to GAPDH (N = 3 mice per group). Data are mean ± SD. *p < 0.05, **p < 0.01, and ***p < 0.001. NS, normal saline; GFP, Lenti-HRE-GFP; MMP-9, Lenti-HRE-MMP-9; SB, Lenti-HRE-MMP-9 plus SB-3CT; SU, Lenti-HRE-MMP-9 plus SU5416.

Figure 7

Improvement of Neurobehavioral Outcomes by MMP-9 Was Dependent on Angiogenesis (A) Photograph showing brain sections in three groups with cresyl violet staining for atrophy volume. The dashed line shows the original size of the ischemic brain side. (B) Bar graph showing statistical data on the atrophy volume at 3 weeks after tMCAO. N = 6 mice per group. (C and D) Atrophy volume was shown in the whole brain (C), and the mNSS (D) was performed separately to evaluate the outcomes 1–3 weeks after ischemia in the three groups (N = 6 per group from baseline to 3 weeks). Data are the mean ± SD. *p < 0.05, **p < 0.01. MMP-9, Lenti-HRE-MMP9; SU alone, SU5416; MMP9+SU, Lenti-HRE-MMP9 plus SU5416.

Figure 8

Illustrative Model of the Beneficial Role of HRE-MMP-9 in the Delayed Phase of tMCAO Illustrative model in the brain of NS/GFP (A), MMP-9 (B), SB (C), and SU (D) mice after ischemia. (A) Glial scar formed after tMCAO; few vessels and neurons were left in the peri-infarct area. (B) HRE-MMP-9 overexpression induced glial scar degradation; then, more EPCs migrated to the peri-infarct area. Both EPCs and MMP-9 contribute to angiogenesis via the VEGF/VEGFR2 signaling pathway in the injury site, and neovascularization promoted neurogenesis and synaptogenesis after ischemic injury. (C) SB-3CT inhibited glial scar degradation induced by MMP-9; few vessels and neurons were found in the peri-infarct area. (D) VEGFR2 inhibitor (SU5416) prevented neovascularization after glial scar degradation; few vessels and neurons were found in the peri-infarct area. NS, normal saline; GFP, Lenti-HRE-GFP; MMP-9, Lenti-HRE-MMP-9; SB, Lenti-HRE-MMP9 plus SB-3CT; SU, Lenti-HRE-MMP9 plus SU5416.