Dysregulated miRNA biogenesis downstream of cellular stress and ALS-causing mutations: a new mechanism for ALS.

Interest in RNA dysfunction in amyotrophic lateral sclerosis (ALS) recently aroused upon discovering causative mutations in RNA-binding protein genes. Here, we show that extensive down-regulation of miRNA levels is a common molecular denominator for multiple forms of human ALS. We further demonstrate that pathogenic ALS-causing mutations are sufficient to inhibit miRNA biogenesis at the Dicing step. Abnormalities of the stress response are involved in the pathogenesis of neurodegeneration, including ALS. Accordingly, we describe a novel mechanism for modulating microRNA biogenesis under stress, involving stress granule formation and re-organization of DICER and AGO2 protein interactions with their partners. In line with this observation, enhancing DICER activity by a small molecule, enoxacin, is beneficial for neuromuscular function in two independent ALS mouse models. Characterizing miRNA biogenesis downstream of the stress response ties seemingly disparate pathways in neurodegeneration and further suggests that DICER and miRNAs affect neuronal integrity and are possible therapeutic targets.

Presenilin 2 influences miR146 level and activity in microglia.

Microglia, the resident innate immune cells of the CNS, are the primary defenders against microbes and critical to CNS remodeling. Dysregulation of microglial behavior can lead to unchecked pro-inflammatory activity and subsequent neurodegeneration. The molecular mechanisms leading to chronic inflammation and microglial dysfunction in neurodegenerative diseases are not well-understood. It is known that patients with Presenilin 2 (PS2) mutations develop autosomal dominant Alzheimer disease. We have shown that a lack of normal PS2 function is associated with exaggerated microglia pro-inflammatory responses in vitro. To identify pathways by which PS2 regulates microglia and determine how PS2 dysfunction may lead to altered inflammatory pathways, we pursued an unbiased array approach to assess differential expression of microRNAs between murine PS2 knockout (KO) and wild-type microglia. We identified miR146, a negative regulator of monocyte pro-inflammatory response, as constitutively down-regulated in PS2 KO microglia. Consistent with a state of miR146 suppression, we found that PS2 KO microglia express higher levels of the miR146 target protein interleukin-1 receptor-associated kinase-1, and have increased NFκB transcriptional activity. We hypothesize that PS2 impacts microglial responses through modulation of miR146a. PS2 dysfunction, through aging or mutation, may contribute to neurodegeneration by influencing the pro-inflammatory behavior of microglia. Presenilin 2 (PS2), a membrane associated protease, has been implicated in the pathogenesis of Alzheimer disease. We have previously shown that PS2 plays an important role in curbing the proinflammatory response in microglia. Here, we report the novel finding that PS2 participates in maintaining the basal and cytokine induced expression of the innate immunity regulating microRNA, miR146. These data suggest one mechanism by which PS2 works to reign in proinflammatory microglial behavior and that PS2 dysfunction or deficiency could thus result in unchecked proinflammatory activation contributing to neurodegeneration.

Spatial distribution of insulin-like growth factor binding protein-2 following hypoxic-ischemic injury.

BACKGROUND: Insulin-like growth factor binding protein-2 (IGFBP-2) regulates the bioavailability, transportation, and localization of insulin-like growth factor-I (IGF-I), an effective neuroprotectant in animal stroke models especially when administered intranasally. Therefore, determining IGFBP-2's endogenous distribution in the normal and ischemic brain is essential in maximizing the neuroprotective potential of the intranasal IGF-I treatment approach. However, current data on IGFBP-2 is limited to mRNA and in situ hybridization studies. The purpose of this study was to determine if there are any changes in IGFBP-2 protein levels and distribution in ischemic brain and also to determine if IGFBPs play a role in the transportation of intranasally administered IGF-I into the brain. RESULTS: Using an in vitro approach, we show that ischemia causes changes in the distribution of IGFBP-2 in primary cortical neurons and astrocytes. In addition, we show using the transient middle cerebral artery occlusion (MCAO) model in mice that there is a significant increase in IGFBP-2 levels in the stroke penumbra and core after 72 h. This correlated with an overall increase in IGF-I after stroke, with the highest levels of IGF-I in the stroke core after 72 h. Brain sections from stroke mice indicate that neurons and astrocytes located in the penumbra both have increased expression of IGFBP-2, however, IGFBP-2 was not detected in microglia. We used binding competition studies to show that intranasally administered exogenous IGF-I uptake into the brain is not receptor mediated and is likely facilitated by IGFBPs. CONCLUSIONS: The change in protein levels indicates that IGFBP-2 plays an IGF-I-dependent and -independent role in the brain's acute (neuroprotection) and chronic (tissue remodeling) response to hypoxic-ischemic injury. Competition studies indicate that IGFBPs may have a role in rapid transportation of exogenous IGF-I from the nasal tissue to the site of injury.

The blood-spinal cord barrier: morphology and clinical implications.

The blood-spinal cord barrier (BSCB) is the functional equivalent of the blood-brain barrier (BBB) in the sense of providing a specialized microenvironment for the cellular constituents of the spinal cord. Even if intuitively the BSCB could be considered as the morphological extension of the BBB into the spinal cord, evidence suggests that this is not so. The BSCB shares the same principal building blocks with the BBB; nevertheless, it seems that morphological and functional differences may exist between them. Dysfunction of the BSCB plays a fundamental role in the etiology or progression of several pathological conditions of the spinal cord, such as spinal cord injury, amyotrophic lateral sclerosis, and radiation-induced myelopathy. This review summarizes current knowledge of the morphology of the BSCB, the methodology of studying the BSCB, and the potential role of BSCB dysfunction in selected disorders of the spinal cord, and finally summarizes therapeutic approaches to the BSCB.

IGF-I regulated phosphorylation and translocation of PDK-1 in neurons.

3'-phosphoinositide-dependent protein kinase-1 (PDK-1) is a crucial serine/threonine kinase in the insulin-like growth factor-I (IGF-I)/AKT signaling pathway, but its function and localization in the nervous system has not been fully characterized. In this study, we compared the localization of PDK-1 in adult neurons and non-neuronal PC-3 cells. We showed that PC-3 cells expressed phosphorylated and nonphosphorylated PDK-1 in the cytoplasm and nucleoplasm. In contrast, neuronal PDK-1 was located in the nucleoplasm and the phosphorylated form was located along the perinuclear region. Furthermore, we found that IGF-I transiently increased phosphorylation of neuronal PDK-1, resulting in its translocation to other cellular compartments. Our findings suggest that IGF-I may regulate neuronal PDK-1 differently than in non-neuronal cells, which may indicate a novel role for PDK-1 in IGF-I-mediated neuroprotective signaling.