Changes in the Proliferative Program Limit Astrocyte Homeostasis in the Aged Post-Traumatic Murine Cerebral Cortex.

Aging leads to adverse outcomes after traumatic brain injury. The mechanisms underlying these defects, however, are not yet clear. In this study, we found that astrocytes in the aged post-traumatic cerebral cortex develop a significantly reduced proliferative response, resulting in reduced astrocyte numbers in the penumbra. Moreover, experiments of reactive astrocytes in vitro reveal that their diminished proliferation is due to an age-related switch in the division mode with reduced cell-cycle re-entry rather than changes in cell-cycle length. Notably, reactive astrocytes in vivo and in vitro become refractory to stimuli increasing their proliferation during aging, such as Sonic hedgehog signaling. These data demonstrate for the first time that age-dependent, most likely intrinsic changes in the proliferative program of reactive astrocytes result in their severely hampered proliferative response to traumatic injury thereby affecting astrocyte homeostasis.

Influence of the duration of ischemia and reperfusion on infarct volume and microvascular damage in mice.

OBJECTIVES: Focal cerebral ischemia is responsible for alterations of vascular permeability, and the loss of microvascular integrity is a primary source of subsequent hemorrhages. We evaluated the influence of different durations of ischemia and reperfusion on infarction size and microvascular damage after focal cerebral ischemia in the mouse. METHODS: C57BL/6 mice (n=39) were subjected to focal cerebral ischemia (I) and reperfusion (R). Consecutive brain sections were analysed for infarction volumes (Nissl-staining) and for collagen type IV (immunohistochemistry and western blot). RESULTS: Infarction size (percentage of the infarction volume versus ipsilateral hemisphere) increased with total time of ischemia and reperfusion: 19+/-2% (I3R0), 30+/-2% (I3R3), 36+/-4% (I3R12), 41+/-4% (I1R24), 45+/-6% (I2R24) and 58+/-2% (I3R24). The ischemic hemispheres showed a significant progressive reduction of collagen type IV positive vessels (ischemic versus non-ischemic contralateral area): 90+/-3% (I3R0), 88+/-1% (I3R3), 82+/-3% (I3R12), 85+/-3% (I1R24), 79+/-3% (I2R24), 72+/-2% (I3R24). CONCLUSIONS: Both prolonged ischemia and reperfusion lead to an increased infarction volume, as well as progressive microvascular damage.

ACE inhibition reduces activity of the plasminogen/plasmin and MMP systems in the brain of spontaneous hypertensive stroke-prone rats.

The spontaneously hypertensive stroke-prone rat (SHR-SP) is an experimental model of malignant hypertension which lead to secondary alterations of the extracellular matrix. Our aim was to determine ACE-inhibitor related changes of proteases involved in the reconstruction of the extracellular matrix in the brain. Twelve SHR-SP rats were randomized into two groups. Each group was treated with either an antihypertensive dose of ramipril or placebo for 6 months. Brain tissue plasminogen activator (t-PA) and urokinase (u-PA) were quantified by using casein-dependent plasminogen zymography, matrix metalloproteinase (MMP)-2 and MMP-9, by MMP-zymography, and tissue inhibitor of MMP (TIMP)-1 and -2, by reverse zymography. The amounts of u-PA, t-PA, and MMPs were significantly reduced in animals treated with ACE inhibitor. Plasminogen zymography showed a 39% reduction of u-PA in the basal ganglia (p < 0.0001); t-PA expression was reduced by 26% in the cortex and by 33% in the basal ganglia (p < 0.0001). MMP-2 expression was reduced by 15% in the cortex (p < 0.05) and by 10% in the basal ganglia (p < 0.05); MMP-9 expression significantly decreased by 37% in the cortex and by 25% in the basal ganglia (p < 0.0001 each). No differences were observed in the amount of TIMP-1 or TIMP-2. These findings provide new insights into the biochemical mechanisms underlying extracellular matrix proliferation and its modulation by ACE inhibitors. Therapeutic alterations that influence the proteolytic systems might prove important in the prevention of extracellular matrix accumulation and secondary microvascular vessel wall changes.

Mild to moderate hypothermia prevents microvascular basal lamina antigen loss in experimental focal cerebral ischemia.

BACKGROUND AND PURPOSE: Microvascular basal lamina damage occurs after cerebral ischemia and is important for the development of hemorrhage. The aim of this study was to determine whether hypothermia could maintain microvascular integrity in ischemic stroke. METHODS: Using the suture model, we subjected 12 rats to 3 hours of focal ischemia and 24 hours of reperfusion. Six rats received postischemic normothermia (37 degrees C) and 6 received hypothermia (32 degrees C to 34 degrees C) for the reperfusion period; a group of 6 sham-operated animals without ischemia was used as control. Collagen type IV and hemoglobin were measured by Western blot analysis, matrix metalloproteinase (MMP)-2 and MMP-9 by gelatin zymography, and urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA) by plasminogen-casein zymography. RESULTS: Hypothermia reduced basal lamina collagen type IV loss: 87+/-16% (hypothermia) versus 43+/-4% (normothermia) in basal ganglia and 74+/-16% versus 64+/-4% in cortex; hypothermia reduced hemorrhage from 431+/-65% (normothermia) to 241+/-28% (basal ganglia) (P<0.05). Hypothermia also reduced MMP-2, MMP-9, uPA, and tPA (basal ganglia: MMP-2: 71+/-20% [hypothermia] versus 109+/-3% [normothermia]; MMP-9: 38+/-12% versus 115+/-4%; uPA activity: 310+/-86% versus 1019+/-22%; tPA activity: 61+/-17% versus 111+/-13%; cortex: MMP-2: 53+/-6% versus 116+/-1%; MMP-9: 16+/-4% versus 123+/-3%; uPA: 180+/-27% versus 176+/-10%; tPA: 91+/-15% versus 101+/-8%; each difference: P<0.001) (nonischemic control side=100%). CONCLUSIONS: Hypothermia maintains microvascular integrity and reduces hemorrhage and the activities of MMP-2, MMP-9, uPA, and tPA.

Microvascular basal lamina injury after experimental focal cerebral ischemia and reperfusion in the rat.

To define the location and extent of microvascular damage of the basal lamina after cerebral ischemia and reperfusion in rats, the authors subjected animals (n = 16) to 3 hours of focal cerebral ischemia and 24 hours of reperfusion using the suture middle cerebral artery occlusion model; sham-operated animals served as controls (n = 6). The Western blot technique was used to define the collagen type IV protein content in various brain regions, whereas immunohistochemistry identified microvascular basal lamina loss (anticollagen type IV staining). The extent of damage was quantified by automatic morphometric video-imaging analysis. Statistical analysis was based on the Mann-Whitney test and the paired Student's t-test. The ischemic hemisphere showed a reduction of the collagen type IV protein content after ischemia and reperfusion in the Western blot (reduction compared with the nonischemic side: total hemisphere, 33% +/- 6%; basal ganglia, 25% +/- 7%; cortex 49% +/- 4%; P < 0.01) [corrected]. There was also a decrease in the number of cerebral microvessels between the ischemic and nonischemic hemispheres (20% +/- 2%), cortical (8% +/- 3%), and basal ganglia areas (31% +/- 3%) (P < 0.001). Besides a reduction of the vessel number, there was also a loss in basal lamina antigen-positive stained area in ischemic areas (hemisphere, 16% +/- 3%; cortex, 14% +/- 3%; basal ganglia, 21% +/- 4%; P < 0.01) [corrected]. Cortical areas had a less pronounced basal lamina loss than basal ganglia (P < 0.05). For the first time, microvascular basal lamina damage, indicated by collagen type IV loss, is proven in rats by biochemical and morphometric analysis. These changes are comparable with those found in nonhuman primates. The authors report novel data regarding microvascular ischemic changes in the cortex. These data provide a basis for future experiments to determine the mechanisms of ischemic microvascular damage and to devise new therapeutic strategies.

Recombinant human tissue plasminogen activator protects the basal lamina in experimental focal cerebral ischemia.

While recombinant tissue plasminogen activator (rt-PA) is successfully used in human ischemic stroke, it may also cause hemorrhagic complications. Animal experiments have shown that hemorrhages are related to microvascular basal lamina damage. We investigated the effects of different doses of rt-PA on the brain microvasculature. Experimental cerebral ischemia in rats was induced for 3 h and followed by 24 h reperfusion (suture model). Each group of rats (n = 6) received either treatment (0.9, 9, or 18 mg rt-PA/kg body weight) or saline (control group) at the end of ischemia. The loss of microvascular basal lamina antigen collagen type IV was measured by Western blot of the ischemic and non-ischemic basal ganglia and cortex. Compared with the contralateral non-ischemic area, collagen type IV was significantly reduced in the ischemic area: (basal ganglia/cortex) 43% +/- 9% / 64% +/- 4 %. Low/moderate doses of rt-PA had a protective effect: 0.9 mg 79% +/- 3% / 89% +/- 6%, 9 mg 72% +/- 9%/ 81% +/- 12% (p < 0.05). Higher doses of rt-PA (18 mg) had a similar effect as seen in untreated controls: 57% +/- 11% / 59% +/- 9% (p < 0.05, Anova). MMP-9 and MMP-2, measured by gelatine zymography, steadily increased over higher doses of rt-PA: MMP-9 (basal ganglia/cortex): control 115% +/- 4% / 123% +/- 3% compared with 18 mg rt-PA 146% +/- 5%/ 162% +/- 6% (p < 0.05) and MMP-2: control 109% +/- 4%/ 116% +/- 5% and 18 mg rt-PA 222% +/- 15%/ 252% +/- 2% (p < 0.05). Low to moderate doses of rt-PA protect the microvascular basal lamina, whereas high doses of rt-PA have the opposite effect, probably due to increased coactivation of MMP-2 and MMP-9.

Matrix metalloproteinase induction by EMMPRIN in experimental focal cerebral ischemia.

Focal cerebral ischemia leads to the gradual disruption of the extracellular matrix. A key role in the turnover of the extracellular matrix is played by the system of matrix metalloproteinases (MMPs). In this study we describe changes of the MMP inducer protein (EMMPRIN) following experimental cerebral ischemia (induced for 3 h and followed by 24 h reperfusion, suture model) in rats. Extracellular EMMPRIN was measured by Western blot of the ischemic and nonischemic basal ganglia and cortex separately. Compared with the contralateral nonischemic area, the ischemic hemisphere showed a significant increase in EMMPRIN: basal ganglia, 158% +/- 4% (P < 0.05); cortex, 128% +/- 25% (P < 0.05). Immunohistochemistry was used to localize EMMPRIN on cerebral microvessels. EMMPRIN-positive microvascular structures were quantified by automatic morphometric video-imaging analysis and a significant increase in the number of cerebral microvessels staining positive for EMMPRIN in the ischemic basal ganglia was shown. The significant loss of microvascular basal lamina antigen collagen type IV in ischemic cortex and basal ganglia was calculated by Western blot. Measured by gelatin zymography, we demonstrated an MMP-2 and MMP-9 increase in the ischemic brain regions (P < 0.05). For the first time the MMP activation system EMMPRIN was shown to be relevant in cerebral ischemia. These results raise the possibility that the increased expression of EMMPRIN, the increase in MMPs and the damage of the basal lamina following cerebral ischemia are connected and part of a network of related changes.

Rt-PA causes a significant increase in endogenous u-PA during experimental focal cerebral ischemia.

The aim of this study was to investigate the effects of different doses of exogenous recombinant human tissue plasminogen activator (rt-PA) on the endogenous cerebral plasminogen-plasmin system in focal ischemia in rats. Ischemia was induced using the suture model. Each group of rats (n = 6) received either treatment (0.9, 9 or 18 mg rt-PA/kg body weight) or saline (control group) at the end of ischemia; a sham-operated group was added. The activity of the plasminogen activators was measured by casein-dependent plasminogen zymography. In the cortex urokinase (u-PA) rose from sham (no ischemia), 91 +/- 7% to ischemia, 176 +/- 10% (P < 0.005). Increasing rt-PA doses led to further significant (P < 0.001) cortical u-PA activation which was maximal at 18 mg: 249 +/- 13%. An extreme increase in the u-PA activity was observed in the basal ganglia to 1019 +/- 22% (P < 0.001). This increase was further aggravated by higher rt-PA doses (18 mg, 1236 +/- 15%; P < 0.001). The t-PA level did not change I3R24 during (3 h ischemia followed by reperfusion for 24 h); however, during low and moderate doses of rt-PA, endogenous t-PA was reduced. In conclusion, while ischemia leads to a significant increase in u-PA, mainly in the basal ganglia, t-PA is not altered. Increasing doses of rt-PA lead to a further elevation of u-PA. Thus, u-PA seems to play a major role in the endogenous plasminogen activator system following focal cerebral ischemia.