Objective-MicroRNAs (miRNAs) regulate gene expression and have many roles in the brain, but a role in oligodendrocyte (OL) function has not been demonstrated.Methods-A Dicer floxed conditional allele was crossed with the proteolipid protein promoterdriven inducible Cre allele to generate inducible, OL-specific Dicer-floxed mice. Results-OL-specificDicer mutants show demyelination, oxidative damage, inflammatory astrocytosis and microgliosis in the brain, and eventually neuronal degeneration and shorter lifespan. miR-219 and its target ELOVL7 (elongation of very long chain fatty acids protein 7) were identified as the main molecular components that are involved in the development of the phenotype in these mice. Overexpressing ELOVL7 results in lipid accumulation, which is suppressed by miR-219 cooverexpression. In Dicer mutant brain, excess lipids accumulate in myelin-rich brain regions, and the peroxisomal β-oxidation activity is dramatically reduced. Interpretation-PostnatalDicer ablation in mature OLs results in inflammatory neuronal degeneration through increased demyelination, lipid accumulation, and peroxisomal and oxidative damage, and therefore indicates that miRNAs play an essential role in the maintenance of lipids and redox homeostasis in mature OLs that are necessary for supporting axonal integrity as well as the formation of compact myelin.Dicer is essential for generation of functional micro-RNAS (miRNAs), and Dicer knockout is embryonic lethal at E7.5. 1 Using a floxed conditional Dicer allele crossed with various tissuespecific Cre alleles, Dicer-mediated miRNAs have been demonstrated to regulate the development of skin progenitors, immune cells, limb outgrowth, chondrocytes, lung, retina, and various neurons.2 -8 It has been estimated that 70% of miRNAs are expressed in the brain, 9 ,10 but little is known about the functions of these brain-specific/enriched miRNAs. Oligodendrocytes (OLs) are glial cells of the central nervous system (CNS) that synthesize myelin, the multilamellar membrane ensheathing axons. Myelin is required for the saltatory conduction of neuronal action potentials and for the maintenance of axonal integrity. Myelin also increases electrical resistance across the cell membrane to prevent the electrical current

Hypoxia-inducible factor 1alpha (HIF1alpha) is a critical transcriptional factor for inducing tumor metastasis, and stabilized under hypoxia but degraded by von Hippel-Lindau protein (pVHL) under normoxia. For the maximal degradation of HIF1alpha, it must be exported to the cytoplasm via an unidentified transporter. Here, we demonstrate that vitamin D3 up-regulated protein 1 (VDUP1) associates with the beta-domain of pVHL and enhances the interaction between pVHL and HIF1alpha to promote the nuclear export and degradation of HIF1alpha hypoxia-independently. Blocking of VDUP1 translocation either by leptomycin B or by nuclear export signal mutation inhibited the nuclear export of pVHL/HIF1alpha and relieved the destabilization of HIF1alpha. VDUP1 suppressed cell invasiveness and tumor metastasis, which were also recovered by blocking of nuclear export. Taken together, these findings indicate that VDUP1 is a novel tumor suppressor which mediates the nuclear export of pVHL/HIF1alpha complex to destabilize HIF1alpha.

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Globoid cell leukodystrophy (GLD, Krabbe disease) is due to autosomal recessive mutations in the lysosomal enzyme galactosylceramidase (GALC). Many GLD patients develop infantile-onset of progressive neurologic deterioration and death by 2 years of age, whereas others have a later-onset, milder disease. Cord blood transplant slows disease progression much more effectively when performed presymptomatically, highlighting the importance of early diagnosis. Current diagnosis is based on reduced GALC activity, DNA sequence, and clinical examination. However, presymptomatic diagnosis is hampered by imperfect genotype-GALC activity-phenotype correlations. In addition, three polymorphisms in the GALC gene are variably associated with disease mutations and have unknown effects on GALC activity and disease outcome. Here, we study mutations that cause infantile or later-onset GLD, and show that GALC activity is significantly lower in infantile versus later-onset mutants when measured in the lysosomal fraction, but not in whole-cell lysates. In parallel, infantile-onset mutant GALCs showed reduced trafficking to lysosomes and processing than later-onset mutant GALCs. Finally, the cis-polymorphisms also affected trafficking to the lysosome and processing of GALC. These differences potentially explain why the activity of different mutations appears similar in whole-cell extracts from lymphocytes, and suggest that measure of GALC activity in lysosomes may better predict the onset and severity of disease for a given GLD genotype.

Krabbe disease (KD) is caused by a deficiency of galactosylceramidase (GALC), which induces demyelination and neurodegeneration due to accumulation of cytotoxic psychosine. Hematopoietic stem cell transplantation (HSCT) improves clinical outcomes in KD patients only if delivered pre-symptomatically. Here, we hypothesize that the restricted temporal efficacy of HSCT reflects a requirement for GALC in early brain development. Using a novel Galc floxed allele, we induce ubiquitous GALC ablation (Galc-iKO) at various postnatal timepoints and identify a critical period of vulnerability to GALC ablation between P4-6 in mice. Early Galc-iKO induction causes a worse KD phenotype, higher psychosine levels in the rodent brainstem and spinal cord, and a significantly shorter life-span of the mice. Intriguingly, GALC expression peaks during this critical developmental period in mice. Further analysis of this mouse model reveals a cell autonomous role for GALC in the development and maturation of immature T-box-brain-1 positive brainstem neurons. These data identify a perinatal developmental period, in which neuronal GALC expression influences brainstem development that is critical for KD pathogenesis.

Oligodendrocytes generate large amounts of myelin by extension of their cell membranes. Though lipid is the major component of myelin, detailed lipid metabolism in the maintenance of myelin is not understood. We reported previously that miR-32 might be involved in myelin maintenance (Shin et al., 2009). Here we demonstrate a novel role for miR-32 in oligodendrocyte function and development through the regulation of SLC45A3 (solute carrier family 45, member 3) and other downstream targets such as CLDN-11. miR-32 is highly expressed in the myelin-enriched regions of the brain and mature oligodendrocytes, and it promotes myelin protein expression. We found that miR-32 directly regulates the expression of SLC45A3 by binding to the complementary sequence on the 3’UTR of cldn11 and slc45a3. As a myelin-enriched putative sugar transporter, SLC45A3 enhances intracellular glucose levels and the synthesis of long-chain fatty acids. Therefore, overexpression of SLC45A3 triggers neutral lipid accumulation. Interestingly, both overexpression and suppression of SLC45A3 reduces myelin protein expression in mature oligodendrocytes and alters oligodendrocyte morphology, indicating that tight regulation of SLC45A3 expression is necessary for the proper maintenance of myelin proteins and structure. Taken together, our data suggest that miR-32 and its downstream target SLC45A3 play important roles in myelin maintenance by modulating glucose and lipid metabolism and myelin protein expression in oligodendrocytes.

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