The pathological hallmark of Alzheimer disease is the senile plaque principally composed of tightly aggregated amyloid-␤ fibrils (fA␤), which are thought to be resistant to degradation and clearance. In this study, we explored whether proteases capable of degrading soluble A␤ (sA␤) could degrade fA␤ as well. We demonstrate that matrix metalloproteinase-9 (MMP-9) can degrade fA␤ and that this ability is not shared by other sA␤-degrading enzymes examined, including endothelinconverting enzyme, insulin-degrading enzyme, and neprilysin. fA␤ was decreased in samples incubated with MMP-9 compared with other proteases, assessed using thioflavin-T. Furthermore, fA␤ breakdown with MMP-9 but not with other proteases was demonstrated by transmission electron microscopy. Proteolytic digests of purified fA␤ were analyzed with matrix-assisted laser desorption ionization time-of-flight mass spectrometry to identify sites of A␤ that are cleaved during its degradation. Only MMP-9 digests contained fragments (A␤ 1-20 and A␤ 1-30 ) from fA␤ 1-42 substrate; the corresponding cleavage sites are thought to be important for ␤-pleated sheet formation. To determine whether MMP-9 can degrade plaques formed in vivo, fresh brain slices from aged APP/PS1 mice were incubated with proteases. MMP-9 digestion resulted in a decrease in thioflavin-S (ThS) staining. Consistent with a role for endogenous MMP-9 in this process in vivo, MMP-9 immunoreactivity was detected in astrocytes surrounding amyloid plaques in the brains of aged APP/PS1 and APPsw mice, and increased MMP activity was selectively observed in compact ThS-positive plaques. These findings suggest that MMP-9 can degrade fA␤ and may contribute to ongoing clearance of plaques from amyloid-laden brains.

Recent studies suggest that in humans, DNA sequences responsible for protein coding regions comprise only 2% of the total genome. The rest of the transcripts result in RNA transcripts without protein-coding ability, including long noncoding RNAs (lncRNAs). Different from most members in the lncRNA family, the metastasis-associated lung adenocarcinoma transcript 1 (Malat1) is abundantly expressed and evolutionarily conserved throughout various mammalian species. Malat1 is one of the first identified lncRNAs associated with human disease, and cumulative studies have indicated that Malat1 plays critical roles in the development and progression of various cancers. Malat1 is also actively involved in various physiologic processes, including alternative splicing, epigenetic modification of gene expression, synapse formation, and myogenesis. Furthermore, extensive evidences show that Malat1 plays pivotal roles in multiple pathological conditions as well. In this review, we will summarize latest findings related to the physiologic and pathophysiological processes of Malat1 and discuss its therapeutic potentials.

It has been postulated that the development of amyloid plaques in Alzheimer's disease (AD) may result from an imbalance between the generation and clearance of the amyloid-␤ peptide (A␤). Although familial AD appears to be caused by A␤ overproduction, sporadic AD (the most prevalent form) may result from impairment in clearance. Recent evidence suggests that several proteases may contribute to the degradation of A␤. Furthermore, astrocytes have recently been implicated as a potential cellular mediator of A␤ degradation. In this study, we examined the possibility that matrix metalloproteinases (MMPs), proteases known to be expressed and secreted by astrocytes, could play a role in extracellular A␤ degradation. We found that astrocytes surrounding amyloid plaques showed enhanced expression of MMP-2 and MMP-9 in aged amyloid precursor protein (APP)/presenilin 1 mice. Moreover, astrocyte-conditioned medium (ACM) degraded A␤, lowering levels and producing several fragments after incubation with synthetic human A␤ 1-40 and A␤ 1-42 . This activity was attenuated with specific inhibitors of MMP-2 and -9, as well as in ACM derived from mmp-2 or -9 knock-out (KO) mice. In vivo, significant increases in the steady-state levels of A␤ were found in the brains of mmp-2 and -9 KO mice compared with wild-type controls.

Dysfunction of the microRNA (miR) network has been emerging as a major regulator in neurological diseases. However, little is known about the functional significance of unique miRs in ischemic brain damage. Here, we found that miR-497 is induced in mouse brain after transient middle cerebral artery occlusion (MCAO) and mouse N2A neuroblastoma (N2A) cells after Oxygen-Glucose-Deprivation (OGD). Loss-of-miR-497 function significantly suppresses OGD-induced N2A cell death, whereas gain-of-miR-497 function aggravates OGD-induced neuronal loss. Moreover, miR-497 directly binds to the predicted 3'-UTR target sites of bcl-2/-w genes. Furthermore, knockdown of cerebral miR-497 effectively enhances bcl-2/-w protein levels in the ischemic region, attenuates ischemic brain infarction, and improves neurological outcomes in mice after focal cerebral ischemia. Taken together, our data suggest that miR-497 promotes ischemic neuronal death by negatively regulating anti-apoptotic proteins, bcl-2 and bcl-w. We raise the possibility that this pathway may contribute to the pathogenesis of the ischemic brain injury in stroke.

The study was designed to determine the role of long noncoding RNA (lncRNA), metastasis-associated lung adenocarcinoma transcript 1 (Malat1), in ischemic stroke outcome. Primary mouse brain microvascular endothelial cells (BMECs) were cultured and treated with Malat1 GapmeR before 16 h oxygen and glucose depravation (OGD). Cell death was assayed by LDH and MTT methods. Malat1 knock-out and wild-type mice were subjected to 1 h of middle cerebral artery occlusion (MCAO) and 24 -72 h of reperfusion. To explore the underlying mechanism, apoptotic and inflammatory factors were measured by qPCR, ELISA, and Western blotting. The physical interaction between Malat1 and apoptotic or inflammatory factors was measured by RNA immunoprecipitation. Increased Malat1 levels were found in cultured mouse BMECs after OGD as well as in isolated cerebral microvessels in mice after MCAO. Silencing of Malat1 by Malat1 GapmeR significantly increased OGD-induced cell death and Caspase 3 activity in BMECs. Silencing of Malat1 also significantly aggravated OGD-induced expression of the proapoptotic factor Bim and proinflammatory cytokines MCP-1, IL-6, and E-selectin. Moreover, Malat1 KO mice presented larger brain infarct size, worsened neurological scores, and reduced sensorimotor functions. Consistent with in vitro findings, significantly increased expression of proapoptotic and proinflammatory factors was also found in the cerebral cortex of Malat1 KO mice after ischemic stroke compared with WT controls. Finally, we demonstrated that Malat1 binds to Bim and E-selectin both in vitro and in vivo. Our study suggests that Malat1 plays critical protective roles in ischemic stroke.