Oligomers of mutant glial fibrillary acidic protein (GFAP) Inhibit the proteasome system in alexander disease astrocytes, and the small heat shock protein alphaB-crystallin reverses the inhibition

Heat shock proteins in the retina: Focus on HSP70 and alpha crystallins in ganglion cell survival

Heat shock proteins (HSPs) belong to a superfamily of stress proteins that are critical constituents of a complex defense mechanism that enhances cell survival under adverse environmental conditions. Cell protective roles of HSPs are related to their chaperone functions, antiapoptotic and antinecrotic effects. HSPs' anti-apoptotic and cytoprotective characteristics, their ability to protect cells from a variety of stressful stimuli, and the possibility of their pharmacological induction in cells under pathological stress make these proteins an attractive therapeutic target for various neurodegenerative diseases; these include Alzheimer's, Parkinson's, Huntington's, prion disease, and others. This review discusses the possible roles of HSPs, particularly HSP70 and small HSPs (alpha A and alpha B crystallins) in enhancing the survival of retinal ganglion cells (RGCs) in optic neuropathies such as glaucoma, which is characterized by progressive loss of vision caused by degeneration of RGCs and their axons in the optic nerve. Studies in animal models of RGC degeneration induced by ocular hypertension, optic nerve crush and axotomy show that upregulation of HSP70 expression by hyperthermia, zinc, geranyl-geranyl acetone, 17-AAG (a HSP90 inhibitor), or through transfection of retinal cells with AAV2-HSP70 effectively supports the survival of injured RGCs. RGCs survival was also stimulated by overexpression of alpha A and alpha B crystallins. These findings provide support for translating the HSP70- and alpha crystallin-based cell survival strategy into therapy to protect and rescue injured RGCs from degeneration associated with glaucomatous and other optic neuropathies.

Lithium Decreases Glial Fibrillary Acidic Protein in a Mouse Model of Alexander Disease

Alexander disease is a fatal neurodegenerative disease caused by mutations in the astrocyte intermediate filament glial fibrillary acidic protein (GFAP). The disease is characterized by elevated levels of GFAP and the formation of protein aggregates, known as Rosenthal fibers, within astrocytes. Lithium has previously been shown to decrease protein aggregates by increasing the autophagy pathway for protein degradation. In addition, lithium has also been reported to decrease activation of the transcription factor STAT3, which is a regulator of GFAP transcription and astrogliogenesis. Here we tested whether lithium treatment would decrease levels of GFAP in a mouse model of Alexander disease. Mice with the Gfap-R236H point mutation were fed lithium food pellets for 4 to 8 weeks. Four weeks of treatment with LiCl at 0.5% in food pellets decreased GFAP protein and transcripts in several brain regions, although with mild side effects and some mortality. Extending the duration of treatment to 8 weeks resulted in higher mortality, and again with a decrease in GFAP in the surviving animals. Indicators of autophagy, such as LC3, were not increased, suggesting that lithium may decrease levels of GFAP through other pathways. Lithium reduced the levels of phosphorylated STAT3, suggesting this as one pathway mediating the effects on GFAP. In conclusion, lithium has the potential to decrease GFAP levels in Alexander disease, but with a narrow therapeutic window separating efficacy and toxicity.

Small heat shock proteins: Role in cellular functions and pathology

Small heat shock proteins (sHsps) are conserved across species and are important in stress tolerance. Many sHsps exhibit chaperone-like activity in preventing aggregation of target proteins, keeping them in a folding-competent state and refolding them by themselves or in concert with other ATP-dependent chaperones. Mutations in human sHsps result in myopathies, neuropathies and cataract. Their expression is modulated in diseases such as Alzheimer's, Parkinson's and cancer. Their ability to bind Cu2+, and suppress generation of reactive oxygen species (ROS) may have implications in Cu2+-homeostasis and neurodegenerative diseases. Circulating αB-crystallin and Hsp27 in the plasma may exhibit immunomodulatory and anti-inflammatory functions. αB-crystallin and Hsp20 exhitbit anti-platelet aggregation: these beneficial effects indicate their use as potential therapeutic agents. sHsps have roles in differentiation, proteasomal degradation, autophagy and development. sHsps exhibit a robust anti-apoptotic property, involving several stages of mitochondrial-mediated, extrinsic apoptotic as well as pro-survival pathways. Dynamic N- and C-termini and oligomeric assemblies of αB-crystallin and Hsp27 are important factors for their functions. We propose a "dynamic partitioning hypothesis" for the promiscuous interactions and pleotropic functions exhibited by sHsps. Stress tolerance and anti-apoptotic properties of sHsps have both beneficial and deleterious consequences in human health and diseases. Conditional and targeted modulation of their expression and/or activity could be used as strategies in treating several human disorders. The review attempts to provide a critical overview of sHsps and their divergent roles in cellular processes particularly in the context of human health and disease.

The ubiquitin proteasome system in glia and its role in neurodegenerative diseases

The ubiquitin proteasome system (UPS) is crucial for intracellular protein homeostasis and for degradation of aberrant and damaged proteins. The accumulation of ubiquitinated proteins is a hallmark of many neurodegenerative diseases, including amyotrophic lateral sclerosis, Alzheimer’s, Parkinson’s, and Huntington’s disease, leading to the hypothesis that proteasomal impairment is contributing to these diseases. So far, most research related to the UPS in neurodegenerative diseases has been focused on neurons, while glial cells have been largely disregarded in this respect. However, glial cells are essential for proper neuronal function and adopt a reactive phenotype in neurodegenerative diseases, thereby contributing to an inflammatory response. This process is called reactive gliosis, which in turn affects UPS function in glial cells. In many neurodegenerative diseases, mostly neurons show accumulation and aggregation of ubiquitinated proteins, suggesting that glial cells may be better equipped to maintain proper protein homeostasis. During an inflammatory reaction, the immunoproteasome is induced in glia, which may contribute to a more efficient degradation of disease-related proteins. Here we review the role of the UPS in glial cells in various neurodegenerative diseases, and we discuss how studying glial cell function might provide essential information in unraveling mechanisms of neurodegenerative diseases.

Post-translational modifications of intermediate filament proteins: mechanisms and functions

Intermediate filaments (IFs) are cytoskeletal and nucleoskeletal structures that provide mechanical and stress-coping resilience to cells, contribute to subcellular and tissue-specific biological functions, and facilitate intracellular communication. IFs, including nuclear lamins and those in the cytoplasm (keratins, vimentin, desmin, neurofilaments and glial fibrillary acidic protein, among others), are functionally regulated by post-translational modifications (PTMs). Proteomic advances highlight the enormous complexity and regulatory potential of IF protein PTMs, which include phosphorylation, glycosylation, sumoylation, acetylation and prenylation, with novel modifications becoming increasingly appreciated. Future studies will need to characterize their on-off mechanisms, crosstalk and utility as biomarkers and targets for diseases involving the IF cytoskeleton.

Emerging role of autophagy in pediatric neurodegenerative and neurometabolic diseases

Pediatric neurodegenerative diseases are a heterogeneous group of diseases that result from specific genetic and biochemical defects. In recent years, studies have revealed a wide spectrum of abnormal cellular functions that include impaired proteolysis, abnormal lipid trafficking, accumulation of lysosomal content, and mitochondrial dysfunction. Within neurons, elaborated degradation pathways such as the ubiquitin-proteasome system and the autophagy-lysosomal pathway are critical for maintaining homeostasis and normal cell function. Recent evidence suggests a pivotal role for autophagy in major adult and pediatric neurodegenerative diseases. We herein review genetic, pathological, and molecular evidence for the emerging link between autophagy dysfunction and lysosomal storage disorders such as Niemann-Pick type C, progressive myoclonic epilepsies such as Lafora disease, and leukodystrophies such as Alexander disease. We also discuss the recent discovery of genetically deranged autophagy in Vici syndrome, a multisystem disorder, and the implications for the role of autophagy in development and disease. Deciphering the exact mechanism by which autophagy contributes to disease pathology may open novel therapeutic avenues to treat neurodegeneration. To this end, an outlook on novel therapeutic approaches targeting autophagy concludes this review.

Caspase cleavage of GFAP produces an assembly-compromised proteolytic fragment that promotes filament aggregation

IF (intermediate filament) proteins can be cleaved by caspases to generate proapoptotic fragments as shown for desmin. These fragments can also cause filament aggregation. The hypothesis is that disease-causing mutations in IF proteins and their subsequent characteristic histopathological aggregates could involve caspases. GFAP (glial fibrillary acidic protein), a closely related IF protein expressed mainly in astrocytes, is also a putative caspase substrate. Mutations in GFAP cause AxD (Alexander disease). The overexpression of wild-type or mutant GFAP promotes cytoplasmic aggregate formation, with caspase activation and GFAP proteolysis. In this study, we report that GFAP is cleaved specifically by caspase 6 at VELD²²⁵ in its L12 linker domain in vitro. Caspase cleavage of GFAP at Asp²²⁵ produces two major cleavage products. While the C-GFAP (C-terminal GFAP) is unable to assemble into filaments, the N-GFAP (N-terminal GFAP) forms filamentous structures that are variable in width and prone to aggregation. The effect of N-GFAP is dominant, thus affecting normal filament assembly in a way that promotes filament aggregation. Transient transfection of N-GFAP into a human astrocytoma cell line induces the formation of cytoplasmic aggregates, which also disrupt the endogenous GFAP networks. In addition, we generated a neo-epitope antibody that recognizes caspase-cleaved but not the intact GFAP. Using this antibody, we demonstrate the presence of the caspase-generated GFAP fragment in transfected cells expressing a disease-causing mutant GFAP and in two mouse models of AxD. These findings suggest that caspase-mediated GFAP proteolysis may be a common event in the context of both the GFAP mutation and excess.

Effects of a polymorphism in the GFAP promoter on the age of onset and ambulatory disability in late-onset Alexander disease

Alexander disease (AxD) is a rare neurodegenerative disorder. Most patients with AxD have a de novo dominant missense mutation in the glial fibrillary acidic protein (GFAP) gene. Patients with late-onset AxD exhibit a more variable onset and severity than patients with early-onset AxD, suggesting the existence of factors that modify the clinical phenotype of late-onset AxD. A -250-bp C/A single-nucleotide polymorphism (SNP) of the GFAP promoter (rs2070935) in the activator protein-1 binding site is a candidate factor for modification of the clinical phenotype. We analyzed the SNP in 10 patients with late-onset AxD and evaluated the effects of the SNP on the clinical course of late-onset AxD. Three of four cases with the C/C genotype lost the ability to walk in their 30s or 40s, whereas all six cases with the other genotypes retained the ability to walk throughout their 30s. The age of onset in patients with the C/C genotype was significantly earlier than in patients with the other genotypes (P<0.05). A more severe phenotype was observed in the patient in whom the C allele of rs2070935 was in cis with the GFAP mutation compared with the patient in whom the C allele of rs2070935 was in trans with the GFAP mutation. Our investigation revealed the possibility that the C/C genotype at rs2070935 of the GFAP promoter in late-onset AxD was associated with an earlier onset and a more rapid progression of ambulatory disability compared with the other genotypes.

Phenotypic conversions of "protoplasmic" to "reactive" astrocytes in Alexander disease

Alexander Disease (AxD) is a primary disorder of astrocytes, caused by heterozygous mutations in GFAP, which encodes the major astrocyte intermediate filament protein, glial fibrillary acidic protein (GFAP). Astrocytes in AxD display hypertrophy, massive increases in GFAP, and the accumulation of Rosenthal fibers, cytoplasmic protein inclusions containing GFAP, and small heat shock proteins. To study the effects of GFAP mutations on astrocyte morphology and physiology, we have examined hippocampal astrocytes in three mouse models of AxD, a transgenic line (GFAP(Tg)) in which the normal human GFAP is expressed in several copies, a knock-in line (Gfap(+/R236H)) in which one of the Gfap genes bears an R236H mutation, and a mouse derived from the mating of these two lines (GFAP(Tg); Gfap(+/R236H)). We report changes in astrocyte phenotype in all lines, with the most severe in the GFAP(Tg);Gfap(+/R236H), resulting in the conversion of protoplasmic astrocytes to cells that have lost their bushy-like morphology because of a reduction of distal fine processes, and become multinucleated and hypertrophic. Astrocytes activate the mTOR cascade, acquire CD44, and lose GLT-1. The altered astrocytes display a microheterogeneity in phenotypes, even neighboring cells. Astrocytes also show diminished glutamate transporter current, are significantly depolarized, and not coupled to adjacent astrocytes. Thus, the accumulation of GFAP in the AxD mouse astrocytes initiates a conversion of normal, protoplasmic astrocytes to astrocytes that display severely "reactive" characteristics, many of which may be detrimental to neighboring neurons and oligodendrocytes.

ASTROCYTES: EMERGING STARS IN LEUKODYSTROPHY PATHOGENESIS

Astrocytes are the predominant glial cell population in the central nervous system (CNS). Once considered only passive scaffolding elements, astrocytes are now recognised as cells playing essential roles in CNS development and function. They control extracellular water and ion homeostasis, provide substrates for energy metabolism, and regulate neurogenesis, myelination and synaptic transmission. Due to these multiple activities astrocytes have been implicated in almost all brain pathologies, contributing to various aspects of disease initiation, progression and resolution. Evidence is emerging that astrocyte dysfunction can be the direct cause of neurodegeneration, as shown in Alexander's disease where myelin degeneration is caused by mutations in the gene encoding the astrocyte-specific cytoskeleton protein glial fibrillary acidic protein. Recent studies point to a primary role for astrocytes in the pathogenesis of other genetic leukodystrophies such as megalencephalic leukoencephalopathy with subcortical cysts and vanishing white matter disease. The aim of this review is to summarize current knowledge of the pathophysiological role of astrocytes focusing on their contribution to the development of the above mentioned leukodystrophies and on new perspectives for the treatment of neurological disorders.

Alzheimer disease periventricular white matter lesions exhibit specific proteomic profile alterations

The white matter (WM) represents approximately half the cerebrum volume and is profoundly affected in Alzheimer's disease (AD). However, both the WM responses to AD as well as potential influences of this compartment to dementia pathogenesis remain comparatively neglected. Neuroimaging studies have revealed WM alterations are commonly associated with AD and renewed interest in examining the pathologic basis and importance of these changes. In AD subjects, immunohistochemistry and electron microscopy revealed changes in astrocyte morphology and myelin loss as well as up to 30% axonal loss in areas of WM rarefaction when measured against non-demented control (NDC) tissue. Comparative proteomic analyses were performed on pooled samples of periventricular WM (PVWM) obtained from AD (n=4) and NDC (n=5) subjects with both groups having a mean age of death of 86 years. All subjects had an apolipoprotein E ε3/3 genotype with the exception of one NDC subject who was ε2/3. Urea-detergent homogenates were analyzed using two different separation techniques: 2-dimensional isoelectric focusing/reverse-phase chromatography and 2-dimensional difference gel electrophoresis (2D-DIGE). Proteins with different expression levels between the 2 diagnostic groups were identified using MALDI-Tof/Tof mass spectrometry. In addition, Western blots were used to quantify proteins of interest in individual AD and NDC cases. Our proteomic studies revealed that when WM protein pools were loaded at equal amounts of total protein for comparative analyses, there were quantitative differences between the 2 groups. Molecules related to cytoskeleton maintenance, calcium metabolism and cellular survival such as glial fibrillary acidic protein, vimentin, tropomyosin, collapsin response mediator protein-2, calmodulin, S100-P, annexin A1, α-internexin, α- and β-synuclein, α-B-crystalline, fascin-1, ubiquitin carboxyl-terminal esterase and thymosine were altered between AD and NDC pools. Our experiments suggest that WM activities become globally impaired during the course of AD with significant morphological, biochemical and functional consequential implications for gray matter function and cognitive deficits. These observations may endorse the hypothesis that WM dysfunction is not only a consequence of AD pathology, but that it may precipitate and/or potentiate AD dementia.

Ceftriaxone for Alexander's Disease: A Four-Year Follow-Up

In 2010, we reported the successful clinical outcome related to a 20-month course of intravenous, cyclical ceftriaxone, in a patient with adult-onset Alexander's disease. We now provide evidence that the progression of the patient's signs/symptoms was halted and reversed with a 4-year-long extension of the trial.The patient's clinical signs/symptoms were evaluated before the start and every 6 months for 6 years. For the early 2 years, without therapy, and for the following 4 years, after intravenous ceftriaxone 2 g daily, for 3 weeks monthly during the initial 4 months, then for 15 days monthly.Gait ataxia and dysarthria were assessed clinically on a 0 to 4 scale. Palatal myoclonus and nystagmus/oscillopsia were monitored by videotape and a self-evaluation scale. The degree of disability, measured by a modified Rankin scale, and the brain MRI were periodically evaluated.Before ceftriaxone therapy, in a 2-year period, gait ataxia and dysarthria worsened from mild to marked, palatal myoclonus spread from the soft palate to lower facial muscles, and the patient complained of oscillopsia. After 4 years of ceftriaxone therapy, gait ataxia and dysarthria improved, from marked to mild at clinical rating scales. The palatal myoclonus was undetectable; the patient did not complained of oscillopsia and declared a progressively better quality of life. Ceftriaxone was safe.This case report provides Class IV evidence that intravenous cycles of ceftriaxone may halt and/or reverse the progression of neurodegeneration in patients with adult-onset Alexander's disease and may significantly improve their quality of life.

Replacement of charged and polar residues in the coiled-coiled interface of huntingtin-interacting protein 1 (HIP1) causes aggregation and cell death

HIP1 crystal structures solved in our laboratory revealed abnormalities in the coiled-coil region, suggesting intrinsic plasticity. To test this, specific amino acids in the coiled-coil were mutated. The apparent thermal stability of HIP1 was altered when Thr528 and Glu531 were replaced by leucine, and was enhanced when Lys510 was also mutated. In cells, HIP1 mutant expression produced aggregation. MTS and flow cytometry indicate a correlation between aggregated HIP1 and enhanced cell death. These data support the idea that flexibility of the HIP1 coiled-coil domain is important for normal function and may lead to new insights into Huntington's disease.

Alpha B-crystallin improved survival of retinal ganglion cells in a rat model of acute ocular hypertension

Increased endogenous αB-crystallin protein levels have been shown to reduce cell apoptosis, although the effects of exogenous αB-crystallin protein remain poorly understood. The present study established an acute ocular hypertension model in the right eye of Sprague-Dawley rats. Fluorogold retrograde tracing and immunofluorescence methods showed that the number of retinal ganglion cells decreased in the right eyes and caspase-3 expression increased following acute ocular hypertension. Intravitreal injection of αB-crystallin in the right eye increased the number of retinal ganglion cells and reduced caspase-3 expression. Results demonstrated that exogenous αB-crystallin protein inhibited caspase-3 expression and improved retinal ganglion cell survival following acute ocular hypertension.

Small heat shock proteins and the cytoskeleton: an essential interplay for cell integrity?

The cytoskeleton is a highly complex network of three major intracellular filaments, microfilaments (MFs), microtubules (MTs) and intermediate filaments (IFs). This network plays a key role in the control of cell shape, division, functions and interactions in animal organs and tissues. Dysregulation of the network can contribute to numerous human diseases. Although small HSPs (sHSPs) and in particular HSP27 (HSPB1) or αB-crystallin (HSPB5) display a wide range of cellular properties, they are mostly known for their ability to protect cells under stress conditions. Mutations in some sHSPs have been found to affect their ability to interact with cytoskeleton proteins, leading to IF aggregation phenotypes that mimick diseases related to disorders in IF proteins (i.e. desmin, vimentin and neuro-filaments). The aim of this review is to discuss new findings that point towards the possible involvement of IFs in the cytoprotective functions of sHSPs, both in physiological and pathological settings, including the likelihood that sHSPs such as HSPB1 may play a role during epithelial-to-mesenchymal transition (EMT) during fibrosis or cancer progression. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.

Genetic ablation of Nrf2/antioxidant response pathway in Alexander disease mice reduces hippocampal gliosis but does not impact survival

In Alexander disease (AxD) the presence of mutant glial fibrillary acidic protein (GFAP), the major intermediate filament of astrocytes, triggers protein aggregation, with marked induction of a stress response mediated by the transcription factor, Nrf2. To clarify the role of Nrf2 in AxD, we have crossed Gfap mutant and transgenic mouse models into an Nrf2 null background. Deletion of Nrf2 eliminates the phase II stress response normally present in mouse models of AxD, but causes no change in body weight or lifespan, even in a severe lethal model. AxD astrocytes without Nrf2 retain features of reactivity, such as expression of the endothelin-B receptor, but have lower Gfap levels, a decrease in p62 protein and reduced iron accumulation, particularly in hippocampus. Microglial activation, indicated by Iba1 expression, is also diminished. Although the Nrf2 response is generally considered beneficial, these results show that in the context of AxD, loss of the antioxidant pathway has no obvious negative effects, while actually decreasing Gfap accumulation and pathology. Given the attention Nrf2 is receiving as a potential therapeutic target in AxD and other neurodegenerative diseases, it will be interesting to see whether induction of Nrf2, beyond the endogenous response, is beneficial or not in these same models.

Neurological diseases as primary gliopathies: a reassessment of neurocentrism

Diseases of the human brain are almost universally attributed to malfunction or loss of nerve cells. However, a considerable amount of work has, during the last decade, expanded our view on the role of astrocytes in CNS (central nervous system), and this analysis suggests that astrocytes contribute to both initiation and propagation of many (if not all) neurological diseases. Astrocytes provide metabolic and trophic support to neurons and oligodendrocytes. Here, we shall endeavour a broad overviewing of the progress in the field and forward the idea that loss of homoeostatic astroglial function leads to an acute loss of neurons in the setting of acute insults such as ischaemia, whereas more subtle dysfunction of astrocytes over periods of months to years contributes to epilepsy and to progressive loss of neurons in neurodegenerative diseases. The majority of therapeutic drugs currently in clinical use target neuronal receptors, channels or transporters. Future therapeutic efforts may benefit by a stronger focus on the supportive homoeostatic functions of astrocytes.

Lopinavir up-regulates expression of the antiviral protein ribonuclease L in human papillomavirus-positive cervical carcinoma cells

BACKGROUND

We have previously shown that the HIV protease inhibitor lopinavir has selective toxicity against human papillomavirus (HPV)-positive cervical carcinoma cells via an unknown mechanism.

METHODS

SiHa cervical carcinoma cells were stably transfected with the proteasome sensor vector pZsProSensor-1 to confirm lopinavir inhibits the proteasome in these cells. The Panorama Xpress profiler 725 antibody array was then used to analyse specific changes in protein expression in lopinavir-treated versus control untreated SiHa cells followed by PCR and western blotting. Colorimetric growth assays of lopinavir-treated E6/E7 immortalised versus control human keratinocytes were performed. Targeted small interfering RNA gene silencing followed by growth assay comparison of lopinavir-treated/untreated SiHa cells was also used.

RESULTS

Lopinavir induced an increase in the fluorescence of pZsProSensor-1 transfected SiHa cells, indicative of proteasomal inhibition. Ribonuclease L (RNASEL) protein was shown to be up-regulated in lopinavir-treated SiHa cells, which was confirmed by PCR and western blot. Targeted silencing of RNASEL reduced the sensitivity of SiHa cells to lopinavir. Selective toxicity against E6/E7 immortalised keratinocytes versus control cells was also seen with lopinavir and was associated with up-regulated RNASEL expression.

CONCLUSIONS

These data are consistent with the toxicity of lopinavir against HPV-positive cervical carcinoma cells being related to its ability to block viral proteasome activation and induce an up-regulation of the antiviral protein RNASEL. This is supported by the drug's selective toxicity and up-regulation of RNASEL in E6/E7 immortalised keratinocytes combined with the increased resistance to lopinavir observed in SiHa cells following silencing of RNASEL gene expression.

Protein misfolding and oxidative stress promote glial-mediated neurodegeneration in an Alexander disease model

Although alterations in glial structure and function commonly accompany death of neurons in neurodegenerative diseases, the role glia play in modulating neuronal loss is poorly understood. We have created a model of Alexander disease in Drosophila by expressing disease-linked mutant versions of glial fibrillary acidic protein (GFAP) in fly glia. We find aggregation of mutant human GFAP into inclusions bearing the hallmarks of authentic Rosenthal fibers. We also observe significant toxicity of mutant human GFAP to glia, which is mediated by protein aggregation and oxidative stress. Both protein aggregation and oxidative stress contribute to activation of a robust autophagic response in glia. Toxicity of mutant GFAP to glial cells induces a non-cell-autonomous stress response and subsequent apoptosis in neurons, which is dependent on glial glutamate transport. Our findings thus establish a simple genetic model of Alexander disease and further identify cellular pathways critical for glial-induced neurodegeneration.

Phosphoproteomic analysis reveals site-specific changes in GFAP and NDRG2 phosphorylation in frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is a progressive neurodegenerative disease characterized by behavioral abnormalities, personality changes, language dysfunction, and can co-occur with the development of motor neuron disease. One major pathological form of FTLD is characterized by intracellular deposition of ubiquitinated and phosphorylated TAR DNA binding protein-43 (TDP-43), suggesting that dysregulation in phosphorylation events may contribute to disease progression. However, to date systematic analysis of the phosphoproteome in FTLD brains has not been reported. In this study, we employed immobilized metal affinity chromatography (IMAC) followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) to identify phosphopeptides from FTLD and age-matched control post-mortem human brain tissue. Using this approach, we identified 786 phosphopeptides in frontal cortex (control and FTLD), in which the population of phosphopeptides represented approximately 50% of the total peptides analyzed. Label-free quantification using spectral counts revealed six proteins with significant changes in the FTLD phosphoproteome. N-myc-Downstream regulated gene 2 (NDRG2) and glial fibrillary acidic protein (GFAP) had an increased number of phosphospectra in FTLD, whereas microtubule associated protein 1A (MAP1A), reticulon 4 (RTN4; also referred to as neurite outgrowth inhibitor (Nogo)), protein kinase C gamma (PRKCG), and heat shock protein 90 kDa alpha, class A member 1(HSP90AA1) had significantly fewer phosphospectra compared to control brain. To validate these differences, we examined NDRG2 phosphorylation in FTLD brain by immunoblot analyses, and using a phosphoserine-13 (pSer13) GFAP monoclonal antibody we show an increase in pSer13 GFAP levels by immunoblot concomitant with increased overall GFAP levels in FTLD cases. These data highlight the utility of combining proteomic and phosphoproteomic strategies to characterize post-mortem human brain tissue.

Strategies for treatment in Alexander disease

Alexander disease is a rare and generally fatal disorder of the CNS, originally classified among the leukodystrophies because of the prominent myelin deficits found in young patients. The most common form of this disease affects infants, who often have profound mental retardation and a variety of developmental delays, but later onset forms also occur, sometimes with little or no white matter pathology at all. The pathological hallmark of Alexander disease is the inclusion body, known as Rosenthal fiber, within the cell bodies and processes of astrocytes. Recent genetic studies identified heterozygous missense mutations in glial fibrillary acidic protein (GFAP), the major intermediate filament protein in astrocytes, as the cause of nearly all cases of Alexander disease. These studies have transformed our view of this disorder and opened new directions for investigation and clinical practice, particularly with respect to diagnosis. Mechanisms by which expression of mutant forms of glial fibrillary acidic protein (GFAP) lead to the pleiotropic manifestations of disease (afflicting cell types beyond the ones expressing the mutant gene) are slowly coming into focus. Ideas are beginning to emerge that suggest several compelling therapeutic targets for interventions that might slow or arrest the evolution of the disease. This review will outline the rationale for pursuing these strategies, and highlight some of the critical issues that must be addressed in the planning of future clinical trials.