Molecularly defined cortical astroglia subpopulation modulates neurons via secretion of Norrin.

Despite expanding knowledge regarding the role of astroglia in regulating neuronal function, little is known about regional or functional subgroups of brain astroglia and how they may interact with neurons. We use an astroglia-specific promoter fragment in transgenic mice to identify an anatomically defined subset of adult gray matter astroglia. Using transcriptomic and histological analyses, we generate a combinatorial profile for the in vivo identification and characterization of this astroglia subpopulation. These astroglia are enriched in mouse cortical layer V; express distinct molecular markers, including Norrin and leucine-rich repeat-containing G-protein-coupled receptor 6 (LGR6), with corresponding layer-specific neuronal ligands; are found in the human cortex; and modulate neuronal activity. Astrocytic Norrin appears to regulate dendrites and spines; its loss, as occurring in Norrie disease, contributes to cortical dendritic spine loss. These studies provide evidence that human and rodent astroglia subtypes are regionally and functionally distinct, can regulate local neuronal dendrite and synaptic spine development, and contribute to disease.

Mutant Huntingtin Disrupts the Nuclear Pore Complex.

Huntington's disease (HD) is caused by an expanded CAG repeat in the Huntingtin (HTT) gene. The mechanism(s) by which mutant HTT (mHTT) causes disease is unclear. Nucleocytoplasmic transport, the trafficking of macromolecules between the nucleus and cytoplasm, is tightly regulated by nuclear pore complexes (NPCs) made up of nucleoporins (NUPs). Previous studies offered clues that mHTT may disrupt nucleocytoplasmic transport and a mutation of an NUP can cause HD-like pathology. Therefore, we evaluated the NPC and nucleocytoplasmic transport in multiple models of HD, including mouse and fly models, neurons transfected with mHTT, HD iPSC-derived neurons, and human HD brain regions. These studies revealed severe mislocalization and aggregation of NUPs and defective nucleocytoplasmic transport. HD repeat-associated non-ATG (RAN) translation proteins also disrupted nucleocytoplasmic transport. Additionally, overexpression of NUPs and treatment with drugs that prevent aberrant NUP biology also mitigated this transport defect and neurotoxicity, providing future novel therapy targets.

c9orf72 Disease-Related Foci Are Each Composed of One Mutant Expanded Repeat RNA.

The chromosome 9 open reading frame 72 (c9orf72) gene contains a hexanucleotide (GGGGCC) repeat expansion responsible for many cases of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The mutant intronic RNA forms "foci" within nuclei, but the connection between transcript expression, foci, and biochemical disease mechanisms is unclear. Knowing the absolute numbers of cellular RNAs, in any system, is important for understanding the molecular mechanisms of natural physiology, disease, and drug action. Absolute numbers, however, are rarely determined, and this absence is a major impediment to understanding complex systems. Using quantitative methods, we demonstrate that foci are single RNA molecules. Most cells have no foci while 1%-2% have more than ten. Knowing the number of disease-causing molecules may contribute to understanding ALS and FTD pathology and successful drug discovery. More broadly, our data suggest that small numbers of RNA molecules may have a sizable impact on disease.

Generation of GFAP::GFP astrocyte reporter lines from human adult fibroblast-derived iPS cells using zinc-finger nuclease technology.

Astrocytes are instrumental to major brain functions, including metabolic support, extracellular ion regulation, the shaping of excitatory signaling events and maintenance of synaptic glutamate homeostasis. Astrocyte dysfunction contributes to numerous developmental, psychiatric and neurodegenerative disorders. The generation of adult human fibroblast-derived induced pluripotent stem cells (iPSCs) has provided novel opportunities to study mechanisms of astrocyte dysfunction in human-derived cells. To overcome the difficulties of cell type heterogeneity during the differentiation process from iPSCs to astroglial cells (iPS astrocytes), we generated homogenous populations of iPS astrocytes using zinc-finger nuclease (ZFN) technology. Enhanced green fluorescent protein (eGFP) driven by the astrocyte-specific glial fibrillary acidic protein (GFAP) promoter was inserted into the safe harbor adeno-associated virus integration site 1 (AAVS1) locus in disease and control-derived iPSCs. Astrocyte populations were enriched using Fluorescence Activated Cell Sorting (FACS) and after enrichment more than 99% of iPS astrocytes expressed mature astrocyte markers including GFAP, S100ß, NFIA and ALDH1L1. In addition, mature pure GFP-iPS astrocytes exhibited a well-described functional astrocytic activity in vitro characterized by neuron-dependent regulation of glutamate transporters to regulate extracellular glutamate concentrations. Engraftment of GFP-iPS astrocytes into rat spinal cord grey matter confirmed in vivo cell survival and continued astrocytic maturation. In conclusion, the generation of GFAP::GFP-iPS astrocytes provides a powerful in vitro and in vivo tool for studying astrocyte biology and astrocyte-driven disease pathogenesis and therapy.

Overview of current and alternative therapies for idiopathic membranous nephropathy.

Membranous nephropathy is one of the leading causes of nephrotic syndrome in adults, which is characterized by edema, hypoalbuminemia, hyperlipidemia, lipiduria, and proteinuria. Determination of idiopathic membranous nephropathy (IMN) disease progression risk is important for guiding initial therapy, with immunosuppressive therapy being reserved for high-risk patients. Because IMN may spontaneously remit in approximately 30% of patients, it is important to carefully select which patients should begin immunosuppressive therapy so as to maximize clinical benefit while limiting toxicity. An observation period of at least 6 months with conservative management that includes the use of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers is recommended. Initial treatment in high-risk IMN is a 6-month course of alternating steroids and alkylating agents. Calcineurin inhibitors (CNIs) represent an alternative first-line therapeutic option for high-risk patients who refuse treatment with steroid or alkylating agent therapy or for whom these treatments are contraindicated. Additional options are essential for patients with IMN who fail to adequately respond to initial therapies or who cannot use recommended therapies due to contraindications or intolerance, risks associated with repetitive dosing with alkylating agents, or potential exacerbation of impaired renal function with CNIs. While evidence for the use of alternative therapies in IMN is modest at best, our review summarizes the available literature for rituximab, mycophenolate mofetil, adrenocorticotropic hormone, intravenous immunoglobulin, and azathioprine. Rituximab has generally demonstrated beneficial outcomes with limited toxicity. Evidence supports a role for mycophenolate mofetil, although the evidence is of low quality and limited duration. Results from ongoing studies are required before adrenocorticotropic hormone can be recommended as therapy for treatment-resistant patients. Intravenous immunoglobulin and azathioprine are unlikely to have a role in IMN. With the advent of new tools and biomarkers measuring disease activity combined with new data regarding possible treatment options, the management and prognosis of IMN are likely to improve.

RNA toxicity from the ALS/FTD C9ORF72 expansion is mitigated by antisense intervention.

A hexanucleotide GGGGCC repeat expansion in the noncoding region of the C9ORF72 gene is the most common genetic abnormality in familial and sporadic amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The function of the C9ORF72 protein is unknown, as is the mechanism by which the repeat expansion could cause disease. Induced pluripotent stem cell (iPSC)-differentiated neurons from C9ORF72 ALS patients revealed disease-specific (1) intranuclear GGGGCCexp RNA foci, (2) dysregulated gene expression, (3) sequestration of GGGGCCexp RNA binding protein ADARB2, and (4) susceptibility to excitotoxicity. These pathological and pathogenic characteristics were confirmed in ALS brain and were mitigated with antisense oligonucleotide (ASO) therapeutics to the C9ORF72 transcript or repeat expansion despite the presence of repeat-associated non-ATG translation (RAN) products. These data indicate a toxic RNA gain-of-function mechanism as a cause of C9ORF72 ALS and provide candidate antisense therapeutics and candidate human pharmacodynamic markers for therapy.

Role of interleukin-1 inhibitors in the management of gout.

Interleukin-1 (IL-1) inhibitors potentially have a role as antiinflammatory agents in refractory gout or for patients who are unable to tolerate conventional therapy, such as nonsteroidal antiinflammatory drugs (NSAIDs), colchicine, or glucocorticoids, for acute attacks. Additionally, IL-1 inhibitors may also help patients with polyarticular and tophaceous gout by making them less vulnerable to breakthrough attacks during initiation of chronic urate-lowering treatment, the mainstay of gout therapy. Because evidence highlights the role of proinflammatory cytokine IL-1 in the inflammation process during an acute gouty attack, IL-1 inhibitors are used to modulate the pathogenesis of a variety of autoinflammatory diseases, providing support for its potential role in the inflammatory process of gout. After NSAIDs, colchicine, and steroids, IL-1 inhibitors are beneficial as fourth-line therapy for acute gout attacks due to their high cost and limited clinical experience. The IL-1 inhibitors used in gout are anakinra, canakinumab, and rilonacept. Based on published evidence, anakinra has limited support in the form of anecdotal case reports to justify its use for treating gout. Canakinumab's toxic profile in clinical trials precludes its use in treating patients for gout, and rilonacept shows promise with a few well-designed studies to support its use in gout patients initiating urate-lowering treatment. When combined with current traditional therapies, these newer agents present clinicians and patients with more potential treatment options in the difficult-to-treat gout population.

Specification of neural cell fate and regulation of neural stem cell proliferation by microRNAs.

In the approximately 20 years since microRNAs (miRNAs) were first characterized, they have been shown to play important roles in diverse physiologic functions, particularly those requiring coordinated changes in networks of signaling pathways. The ability of miRNAs to silence expression of multiple gene targets hints at complex connections that research has only begun to elucidate. The nervous system, particularly the brain, and its progenitor cells offer opportunities to examine miRNA function due to the myriad different cell types, numerous functionally distinct regions, and fluidly dynamic connections between them. This review aims to summarize current understanding of miRNA regulation in neurodevelopment, beginning with miRNAs that establish a general neural fate in cells. Particular attention is given to miR-124, the most abundant brain-specific miRNA, along with its key regulators and targets as an example of the potentially far-reaching effects of miRNAs. These modulators and mediators enable miRNAs to subtly calibrate cellular proliferation and differentiation. To better understand their mechanisms of action, miRNA profiles in distinct populations and regions of cells have been examined as well as miRNAs that regulate proliferation of stem cells, a process marked by dramatic morphological shifts in response to temporally subtle and refined shifts in gene expression. To tease out the complex interactions of miRNAs and stem cells more accurately, future studies will require more sensitive methods of assessing miRNA expression and more rigorous models of miRNA pathways. Thorough characterization of similarities and differences in specific miRNAs' effects in different species is vital to developing better disease models and therapeutics using miRNAs.