Longitudinal MRI evaluation of protection against brain damage after transient ischemia in mice deficient in mannose-binding lectin

Abstract

[Objectives]: The complement system has been shown to participate in brain damage after stroke. The complement can be activated through the lectin pathway, which involves mannosebinding lectin (MBL). We recently showed that experimental animals and patients with deficient production of MBL are protected after stroke. Up to two days after brain ischemia, MBLdeficient (MBL-null) mice showed smaller infarct volume and better neurological outcome than the wild type (wt). Here we carried a longitudinal MRI study in wild type and MBL-null mice by examining the progression of the brain lesion up to day 7. We also evaluated the acquired neurological deficit at 1 and 7 days after transient ischemia. [Methods]: Intraluminal middle cerebral artery (MCA) occlusion was induced for 90 min in adult male MBL-null mice of the C57/Bl6 background (n=8) and corresponding wt mice (n=6) under isofluorane anesthesia. Cortical cerebral blood flow (CBF) was recorded with laser Doppler flowmetry (Perimed). Longitudinal MRI scans were performed under isofluorane anaesthesia in a BioSpec 70/30 horizontal animal scanner (Bruker BioSpin, Ettlingen, Germany), equipped with a 12 cm inner diameter actively shielded gradient system (400 mT/m) and a phased array surface coil for mouse brain. MRI studies (Apparent Diffusion Coeficient, ADC, and T2 relaxometry) were performed during MCA occlusion, and at 1 and 7 days post-ischemia. The volume of infarction was measured from the T2 map images. The neurological deficit was assessed with the tape-removal behavioral test that required training the animals before induction of ischemia. [Results]: The mean cortical perfusion during ischemia (expressed as percent of basal preocclusion levels) was similar in the MBL-null group (27±7%) than in the wt group (22±7%). By measuring the volume of infarction at 1 and 7 days in the same animals we showed a significant reduction from day 1 to 7 in both groups. The percentage of infarct volume reduction from day 1 to 7 was 41% (p< 0.01) and 46% (p< 0.05) in wt and MBL-null groups, respectively. MBL-null mice showed significantly smaller infarct volumes that the wt at day 1 (p< 0.05) with a 32% reduction in infarct volume. Likewise, at day 7, infarct volume in MBL-null mice was 38% smaller (p< 0.05) than in the wt, demonstrating that the protection reported before was maintained at day 7. Also, the neurological deficit was significantly attenuated in MBL-null mice versus the wt at day 1 (p< 0.01) and at day 7 (p< 0.05). [Conclusions]: This study shows that protection from transient brain ischemia/reperfusion in MBL-null mice is maintained for 7 days. The results support that MBL negatively contributes to stroke outcome.