Mutant valosin-containing protein causes a novel type of frontotemporal dementia

Regulated cell death and its role in Alzheimer's disease and amyotrophic lateral sclerosis

Despite considerable research efforts, it is still not clear which mechanisms underlie neuronal cell death in neurodegenerative diseases. During the last 20 years, multiple pathways have been identified that can execute regulated cell death (RCD). Among these RCD pathways, apoptosis, necroptosis, pyroptosis, ferroptosis, autophagy-related cell death, and lysosome-dependent cell death have been intensively investigated. Although RCD consists of numerous individual pathways, multiple common proteins have been identified that allow shifting from one cell death pathway to another. Another layer of complexity is added by mechanisms such as the endosomal machinery, able to regulate the activation of some RCD pathways, preventing cell death. In addition, restricted axonal degeneration and synaptic pruning can occur as a result of RCD activation without loss of the cell body. RCD plays a complex role in neurodegenerative processes, varying across different disorders. It has been shown that RCD is differentially involved in Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS), among the most common neurodegenerative diseases. In AD, neuronal loss is associated with the activation of not only necroptosis, but also pyroptosis. In ALS, on the other hand, motor neuron death is not linked to canonical necroptosis, whereas pyroptosis pathway activation is seen in white matter microglia. Despite these differences in the activation of RCD pathways in AD and ALS, the accumulation of protein aggregates immunoreactive for p62/SQSTM1 (sequestosome 1) is a common event in both diseases and many other neurodegenerative disorders. In this review, we describe the major RCD pathways with clear activation in AD and ALS, the main interactions between these pathways, as well as their differential and similar involvement in these disorders. Finally, we will discuss targeting RCD as an innovative therapeutic concept for neurodegenerative diseases, such as AD and ALS. Considering that the execution of RCD or "cellular suicide" represents the final stage in neurodegeneration, it seems crucial to prevent neuronal death in patients by targeting RCD. This would offer valuable time to address upstream events in the pathological cascade by keeping the neurons alive.

UBXN1 maintains ER proteostasis and represses UPR activation by modulating translation

ER protein homeostasis (proteostasis) is essential for proper folding and maturation of proteins in the secretory pathway. Loss of ER proteostasis can lead to the accumulation of misfolded or aberrant proteins in the ER and triggers the unfolded protein response (UPR). In this study, we find that the p97 adaptor UBXN1 is an important negative regulator of the UPR. Loss of UBXN1 sensitizes cells to ER stress and activates the UPR. This leads to widespread upregulation of the ER stress transcriptional program. Using comparative, quantitative proteomics we show that deletion of UBXN1 results in a significant enrichment of proteins involved in ER-quality control processes including those involved in protein folding and import. Notably, we find that loss of UBXN1 does not perturb p97-dependent ER-associated degradation (ERAD). Our studies indicate that loss of UBXN1 increases translation in both resting and ER-stressed cells. Surprisingly, this process is independent of p97 function. Taken together, our studies have identified a new role for UBXN1 in repressing translation and maintaining ER proteostasis in a p97 independent manner.

Protein disaggregation machineries in the human cytosol

Proteins carry out the vast majority of functions in cells, but can only do so when properly folded. Following stress or mutation, proteins can lose their proper fold, resulting in misfolding, inactivity, and aggregation-posing a threat to cellular health. In order to counteract protein aggregation, cells have evolved a remarkable subset of molecular chaperones, called protein disaggregases, which collaboratively possess the ability to forcibly untangle protein aggregates. Here, we review the different chaperone disaggregation machineries present in the human cytosol and their mechanisms of action. Understanding, how these disaggregases function, is both universally and clinically important, as protein aggregation has been linked to multiple, debilitating neurodegenerative diseases.

Clinical Classification of Variants in the Valosin-Containing Protein Gene Associated With Multisystem Proteinopathy

Background and Objectives

Pathogenic variants in the valosin-containing protein (VCP) gene cause a phenotypically heterogeneous disorder that includes myopathy, motor neuron disease, Paget disease of the bone, frontotemporal dementia, and parkinsonism termed multisystem proteinopathy. This hallmark pleiotropy makes the classification of novel VCP variants challenging. This retrospective study describes and assesses the effect of 19 novel or nonpreviously clinically characterized VCP variants identified in 28 patients (26 unrelated families) in the retrospective VCP International Multicenter Study.

Methods

A 6-item clinical score was developed to evaluate the phenotypic level of evidence to support the pathogenicity of the novel variants. Each item is allocated a value, a score ranging from 0.5 to 5.5 points. A receiver-operating characteristic curve was used to identify a cutoff value of 3 to consider a variant as high likelihood disease associated. The scoring system results were confronted with results of in vitro ATPase activity assays and with in silico analysis.

Results

All variants were missense, except for one small deletion-insertion, 18 led to amino acid changes within the N and D1 domains, and 13 increased the enzymatic activity. The clinical score coincided with the functional studies in 17 of 19 variants and with the in silico analysis in 12 of 19. For 12 variants, the 3 predictive tools agreed, and for 7 variants, the predictive tools disagreed. The pooled data supported the pathogenicity of 13 of 19 novel VCP variants identified in the study.

Discussion

This study provides data to support pathogenicity of 14 of 19 novel VCP variants and provides guidance for clinicians in the evaluation of novel variants in the VCP gene.

Autophagy-related proteins: Potential diagnostic and prognostic biomarkers of aging-related diseases

Autophagy plays a key role in cellular, tissue and organismal homeostasis and in the production of the energy load needed at critical times during development and in response to nutrient shortage. Autophagy is generally considered as a pro-survival mechanism, although its deregulation has been linked to non-apoptotic cell death. Autophagy efficiency declines with age, thus contributing to many different pathophysiological conditions, such as cancer, cardiomyopathy, diabetes, liver disease, autoimmune diseases, infections, and neurodegeneration. Accordingly, it has been proposed that the maintenance of a proper autophagic activity contributes to the extension of the lifespan in different organisms. A better understanding of the interplay between autophagy and risk of age-related pathologies is important to propose nutritional and life-style habits favouring disease prevention as well as possible clinical applications aimed at promoting long-term health.

The AAA+ chaperone VCP disaggregates Tau fibrils and generates aggregate seeds in a cellular system

Amyloid-like aggregates of the microtubule-associated protein Tau are associated with several neurodegenerative disorders including Alzheimer's disease. The existence of cellular machinery for the removal of such aggregates has remained unclear, as specialized disaggregase chaperones are thought to be absent in mammalian cells. Here we show in cell culture and in neurons that the hexameric ATPase valosin-containing protein (VCP) is recruited to ubiquitylated Tau fibrils, resulting in their efficient disaggregation. Aggregate clearance depends on the functional cooperation of VCP with heat shock 70 kDa protein (Hsp70) and the ubiquitin-proteasome machinery. While inhibition of VCP activity stabilizes large Tau aggregates, disaggregation by VCP generates seeding-active Tau species as byproduct. These findings identify VCP as a core component of the machinery for the removal of neurodegenerative disease aggregates and suggest that its activity can be associated with enhanced aggregate spreading in tauopathies.

Genotype-phenotype correlations in valosin-containing protein disease: a retrospective muticentre study

BACKGROUND

Valosin-containing protein (VCP) disease, caused by mutations in the VCP gene, results in myopathy, Paget's disease of bone (PBD) and frontotemporal dementia (FTD). Natural history and genotype-phenotype correlation data are limited. This study characterises patients with mutations in VCP gene and investigates genotype-phenotype correlations.

METHODS

Descriptive retrospective international study collecting clinical and genetic data of patients with mutations in the VCP gene.

RESULTS

Two hundred and fifty-five patients (70.0% males) were included in the study. Mean age was 56.8±9.6 years and mean age of onset 45.6±9.3 years. Mean diagnostic delay was 7.7±6 years. Symmetric lower limb weakness was reported in 50% at onset progressing to generalised muscle weakness. Other common symptoms were ventilatory insufficiency 40.3%, PDB 28.2%, dysautonomia 21.4% and FTD 14.3%. Fifty-seven genetic variants were identified, 18 of these no previously reported. c.464G>A (p.Arg155His) was the most frequent variant, identified in the 28%. Full time wheelchair users accounted for 19.1% with a median time from disease onset to been wheelchair user of 8.5 years. Variant c.463C>T (p.Arg155Cys) showed an earlier onset (37.8±7.6 year) and a higher frequency of axial and upper limb weakness, scapular winging and cognitive impairment. Forced vital capacity (FVC) below 50% was as risk factor for being full-time wheelchair user, while FVC <70% and being a full-time wheelchair user were associated with death.

CONCLUSION

This study expands the knowledge on the phenotypic presentation, natural history, genotype-phenotype correlations and risk factors for disease progression of VCP disease and is useful to improve the care provided to patient with this complex disease.

Valosin Containing Protein (VCP): A Multistep Regulator of Autophagy

Valosin containing protein (VCP) has emerged as a central protein in the regulation of the protein quality control (PQC) system. VCP mutations are causative of multisystem proteinopathies, which include neurodegenerative diseases (NDs), and share various signs of altered proteostasis, mainly associated with autophagy malfunctioning. Autophagy is a complex multistep degradative system essential for the maintenance of cell viability, especially in post-mitotic cells as neurons and differentiated skeletal muscle cells. Interestingly, many studies concerning NDs have focused on autophagy impairment as a pathological mechanism or autophagy activity boosting to rescue the pathological phenotype. The role of VCP in autophagy has been widely debated, but recent findings have defined new mechanisms associated with VCP activity in the regulation of autophagy, showing that VCP is involved in different steps of this pathway. Here we will discuss the multiple activity of VCP in the autophagic pathway underlying its leading role either in physiological or pathological conditions. A better understanding of VCP complexes and mechanisms in regulating autophagy could define the altered mechanisms by which VCP directly or indirectly causes or modulates different human diseases and revealing possible new therapeutic approaches for NDs.

DNA damage in embryonic neural stem cell determines FTLDs' fate via early-stage neuronal necrosis

The early-stage pathologies of frontotemporal lobal degeneration (FTLD) remain largely unknown. In VCP^T262A-KI mice carrying VCP gene mutation linked to FTLD, insufficient DNA damage repair in neural stem/progenitor cells (NSCs) activated DNA-PK and CDK1 that disabled MCM3 essential for the G1/S cell cycle transition. Abnormal neural exit produced neurons carrying over unrepaired DNA damage and induced early-stage transcriptional repression-induced atypical cell death (TRIAD) necrosis accompanied by the specific markers pSer46-MARCKS and YAP. In utero gene therapy expressing normal VCP or non-phosphorylated mutant MCM3 rescued DNA damage, neuronal necrosis, cognitive function, and TDP43 aggregation in adult neurons of VCP^T262A-KI mice, whereas similar therapy in adulthood was less effective. The similar early-stage neuronal necrosis was detected in PGRN^R504X-KI, CHMP2B^Q165X-KI, and TDP^N267S-KI mice, and blocked by embryonic treatment with AAV-non-phospho-MCM3. Moreover, YAP-dependent necrosis occurred in neurons of human FTLD patients, and consistently pSer46-MARCKS was increased in cerebrospinal fluid (CSF) and serum of these patients. Collectively, developmental stress followed by early-stage neuronal necrosis is a potential target for therapeutics and one of the earliest general biomarkers for FTLD.

Autophagy and ALS: mechanistic insights and therapeutic implications

Mechanisms of protein homeostasis are crucial for overseeing the clearance of misfolded and toxic proteins over the lifetime of an organism, thereby ensuring the health of neurons and other cells of the central nervous system. The highly conserved pathway of autophagy is particularly necessary for preventing and counteracting pathogenic insults that may lead to neurodegeneration. In line with this, mutations in genes that encode essential autophagy factors result in impaired autophagy and lead to neurodegenerative conditions such as amyotrophic lateral sclerosis (ALS). However, the mechanistic details underlying the neuroprotective role of autophagy, neuronal resistance to autophagy induction, and the neuron-specific effects of autophagy-impairing mutations remain incompletely defined. Further, the manner and extent to which non-cell autonomous effects of autophagy dysfunction contribute to ALS pathogenesis are not fully understood. Here, we review the current understanding of the interplay between autophagy and ALS pathogenesis by providing an overview of critical steps in the autophagy pathway, with special focus on pivotal factors impaired by ALS-causing mutations, their physiologic effects on autophagy in disease models, and the cell type-specific mechanisms regulating autophagy in non-neuronal cells which, when impaired, can contribute to neurodegeneration. This review thereby provides a framework not only to guide further investigations of neuronal autophagy but also to refine therapeutic strategies for ALS and related neurodegenerative diseases.Abbreviations: ALS: amyotrophic lateral sclerosis; Atg: autophagy-related; CHMP2B: charged multivesicular body protein 2B; DPR: dipeptide repeat; FTD: frontotemporal dementia; iPSC: induced pluripotent stem cell; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; PINK1: PTEN induced kinase 1; RNP: ribonuclear protein; sALS: sporadic ALS; SPHK1: sphingosine kinase 1; TARDBP/TDP-43: TAR DNA binding protein; TBK1: TANK-binding kinase 1; TFEB: transcription factor EB; ULK: unc-51 like autophagy activating kinase; UPR: unfolded protein response; UPS: ubiquitin-proteasome system; VCP: valosin containing protein.

An autopsy report of a familial amyotrophic lateral sclerosis case carrying VCP Arg487His mutation with a unique TDP-43 proteinopathy

We here report an autopsy case of familial amyotrophic lateral sclerosis (ALS) with p.Arg487His mutation in the valosin-containing protein (VCP) gene (VCP), in which upper motor neurons (UMNs) were predominantly involved. Moreover, our patient developed symptoms of frontotemporal dementia later in life and pathologically exhibited numerous phosphorylated transactivation response DNA-binding protein of 43 kDa (p-TDP-43)-positive neuronal cytoplasmic inclusions and short dystrophic neurites with a few lentiform neuronal intranuclear inclusions, sharing the features of frontotemporal lobar degeneration with TDP-43 pathology type A pattern. A review of previous reports of ALS with VCP mutations suggests that our case is unique in terms of its UMN-predominant lesion pattern and distribution of p-TDP-43 pathology. Thus, this case report effectively expands the clinical and pathological phenotype of ALS in patients with a VCP mutation.

Increased Neurofilament Light Chain and YKL-40 CSF Levels in One Japanese IBMPFD Patient With VCP R155C Mutation: A Clinical Case Report With CSF Biomarker Analyses

Inclusion body myopathy (IBM) with Paget's disease of bone (PDB) and frontotemporal dementia (IBMPFD) presents with multiple symptoms and an unknown etiology. Valosin-containing protein (VCP) has been identified as the main causative gene of IBMPFD. However, no studies on neurofilament light chain (NFL) as a cerebrospinal fluid (CSF) marker of axonal neurodegeneration or on YKL-40 as a CSF marker of glial neuroinflammation have been conducted in IBMPFD patients with VCP mutations. A 65-year-old man presented with progressive muscle atrophy and weakness of all limbs, non-fluent aphasia, and changes in personality and behavior. Cerebral MRI revealed bilateral frontal and temporal atrophy. ^99mTc-HMDP bone scintigraphy and pelvic CT revealed remodeling changes and active osteoblastic accumulations in the right medial iliac bone. Muscle biopsy demonstrated multiple rimmed vacuoles in muscle cells with myogenic and neurogenic pathological alterations. After the patient was clinically diagnosed with IBMPFD, DNA analysis of the VCP gene revealed a cytosine (C) to thymine (T) (C→ T) mutation, resulting in an amino acid exchange of arginine to cysteine (p.R155C mutation). The CSF levels of NFL at two time points (12 years apart) were higher than those in non-dementia controls (CTR) and Alzheimer's disease (AD); lower than those in frontotemporal dementia with motor neuron disease (FTD-MND); and comparable to those in patients with behavioral variant frontotemporal dementia (bvFTD), progressive supranuclear palsy (PSP), and corticobasal syndrome (CBS). The CSF levels of YKL-40 were comparable at both time points and higher than those in CTR; lower than those in FTD-MND; and comparable to those in bvFTD, PSP, CBS, and AD. The CSF levels of phosphorylated tau 181 (P-Tau) and total tau (T-Tau) were not significantly different from those in CTR and other neurodegenerative diseases, except those in AD, which were significantly elevated. This is the first report that demonstrates increased NFL and YKL-40 CSF levels in an IBMPFD patient with a VCP mutation (p.R155C); NFL and YKL-40 levels were comparable to those in bvFTD, PSP, CBS, and AD and higher than those in CTR. Our results suggest that IBMPFD neuropathology may involve both axonal neurodegeneration and glial neuroinflammation.

Bridging biophysics and neurology: aberrant phase transitions in neurodegenerative disease

Biomolecular condensation arising through phase transitions has emerged as an essential organizational strategy that governs many aspects of cell biology. In particular, the role of phase transitions in the assembly of large, complex ribonucleoprotein (RNP) granules has become appreciated as an important regulator of RNA metabolism. In parallel, genetic, histopathological and cell and molecular studies have provided evidence that disturbance of phase transitions is an important driver of neurological diseases, notably amyotrophic lateral sclerosis (ALS), but most likely also other diseases. Indeed, our growing knowledge of the biophysics underlying biological phase transitions suggests that this process offers a unifying mechanism to explain the numerous and diverse disturbances in RNA metabolism that have been observed in ALS and some related diseases - specifically, that these diseases are driven by disturbances in the material properties of RNP granules. Here, we review the evidence for this hypothesis, emphasizing the reciprocal roles in which disease-related protein and disease-related RNA can lead to disturbances in the material properties of RNP granules and consequent pathogenesis. Additionally, we review evidence that implicates aberrant phase transitions as a contributing factor to a larger set of neurodegenerative diseases, including frontotemporal dementia, certain repeat expansion diseases and Alzheimer disease.

VCP expression decrease as a biomarker of preclinical and early clinical stages of Parkinson's disease

Valosin-containing human protein (VCP) or p97 performs enzyme functions associated with the maintenance of protein homeostasis and control of protein quality. Disruption of its normal functioning might be associated with the development of Parkinson’s disease (PD). Tissues of mice with toxin-induced presymptomatic and early symptomatic stages of PD, as well as 52 treated and untreated patients with newly diagnosed PD and nine patients with a “predicted” form of PD, were investigated. Significant changes in Vcp gene expression were observed in almost all studied mouse tissues. A significant decrease in VCP expression specific for PD was also detected at both the late preclinical and the early clinical stages of PD in untreated patients. Thus, a decrease in VCP expression is important for changes in the function of the nervous system at early stages of PD. Analysis of changes in VCP expression in all patients with PD and in Vcp in the peripheral blood of mice used as models of PD revealed significant decreases in expression specific for PD. These data suggest that a decrease in the relative levels of VCP mRNA might serve as a biomarker for the development of pathology at the early clinical and preclinical stages of human PD.

The heterozygous R155C VCP mutation: Toxic in humans! Harmless in mice?

Heterozygous missense mutations in the human VCP gene cause inclusion body myopathy associated with Paget disease of bone and fronto-temporal dementia (IBMPFD) and amyotrophic lateral sclerosis (ALS). The exact molecular mechanisms by which VCP mutations cause disease manifestation in different tissues are incompletely understood. In the present study, we report the comprehensive analysis of a newly generated R155C VCP knock-in mouse model, which expresses the ortholog of the second most frequently occurring human pathogenic VCP mutation. Heterozygous R155C VCP knock-in mice showed decreased plasma lactate, serum albumin and total protein concentrations, platelet numbers, and liver to body weight ratios, and increased oxygen consumption and CD8+/Ly6C + T-cell fractions, but none of the typical human IBMPFD or ALS pathologies. Breeding of heterozygous mice did not yield in the generation of homozygous R155C VCP knock-in animals. Immunoblotting showed identical total VCP protein levels in human IBMPFD and murine R155C VCP knock-in tissues as compared to wild-type controls. However, while in human IBMPFD skeletal muscle tissue 70% of the total VCP mRNA was derived from the mutant allele, in R155C VCP knock-in mice only 5% and 7% mutant mRNA were detected in skeletal muscle and brain tissue, respectively. The lack of any obvious IBMPFD or ALS pathology could thus be a consequence of the very low expression of mutant VCP. We conclude that the increased and decreased fractions of the R155C mutant VCP mRNA in man and mice, respectively, are due to missense mutation-induced, divergent alterations in the biological half-life of the human and murine mutant mRNAs. Furthermore, our work suggests that therapy approaches lowering the expression of the mutant VCP mRNA below a critical threshold may ameliorate the intrinsic disease pathology.

The involvement of endoplasmic reticulum formation and protein synthesis efficiency in VCP- and ATL1-related neurological disorders

The endoplasmic reticulum (ER) is the biggest organelle in cells and is involved in versatile cellular processes. Formation and maintenance of ER morphology are regulated by a series of proteins controlling membrane fusion and curvature. At least six different ER morphology regulators have been demonstrated to be involved in neurological disorders-including Valosin-containing protein (VCP), Atlastin-1 (ATL1), Spastin (SPAST), Reticulon 2 (RTN2), Receptor expression enhancing protein 1 (REEP1) and RAB10-suggesting a critical role of ER formation in neuronal activity and function. Among these genes, mutations in VCP gene involve in inclusion body myopathy with Paget disease of bone and frontotemporal dementia (IBMPFD), familial amyotrophic lateral sclerosis (ALS), autism spectrum disorders (ASD), and hereditary spastic paraplegia (HSP). ATL1 is also one of causative genes of HSP. RAB10 is associated with Parkinson's disease (PD). A recent study showed that VCP and ATL1 work together to regulate dendritic spine formation by controlling ER formation and consequent protein synthesis efficiency. RAB10 shares the same function with VCP and ATL1 to control ER formation and protein synthesis efficiency but acts independently. Increased protein synthesis by adding extra leucine to cultured neurons ameliorated dendritic spine deficits caused by VCP and ATL1 deficiencies, strengthening the significance of protein synthesis in VCP- and ATL1-regulated dendritic spine formation. These findings provide new insight into the roles of ER and protein synthesis in controlling dendritic spine formation and suggest a potential etiology of neurodegenerative disorders caused by mutations in VCP, ATL1 and other genes encoding proteins regulating ER formation and morphogenesis.

Frontotemporal dementia

Frontotemporal dementia (FTD) is a neurodegenerative disorder characterized by progressive changes in behavior, personality, and language with involvement of the frontal and temporal regions of the brain. About 40% of FTD cases have a positive family history, and about 10% of these cases are inherited in an autosomal-dominant pattern. These gene defects present with distinct clinical phenotypes. As the diagnosis of FTD becomes more recognizable, it will become increasingly important to keep these gene mutations in mind. In this chapter, we review the genes with known associations to FTD. We discuss protein functions, mutation frequencies, clinical phenotypes, imaging characteristics, and pathology associated with these genes.

Is amyotrophic lateral sclerosis/frontotemporal dementia an autophagy disease?

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are neurodegenerative disorders that share genetic risk factors and pathological hallmarks. Intriguingly, these shared factors result in a high rate of comorbidity of these diseases in patients. Intracellular protein aggregates are a common pathological hallmark of both diseases. Emerging evidence suggests that impaired RNA processing and disrupted protein homeostasis are two major pathogenic pathways for these diseases. Indeed, recent evidence from genetic and cellular studies of the etiology and pathogenesis of ALS-FTD has suggested that defects in autophagy may underlie various aspects of these diseases. In this review, we discuss the link between genetic mutations, autophagy dysfunction, and the pathogenesis of ALS-FTD. Although dysfunction in a variety of cellular pathways can lead to these diseases, we provide evidence that ALS-FTD is, in many cases, an autophagy disease.

Valosin-containing protein (VCP) is a novel IQ motif-containing GTPase activating protein 1 (IQGAP1)-interacting protein

Scaffold proteins play a pivotal role in making protein complexes, and organize binding partners into a functional unit to enhance specific signaling pathways. IQ motif-containing GTPase activating protein 1 (IQGAP1) is an essential protein for spine formation due to its role in scaffolding multiple signal complexes. However, it remains unclear how IQGAP1 interacts within the brain. In the present study, we screened novel IQGAP1-interacting proteins by a proteomic approach. As a novel IQGAP1-interacting protein, we identified valosin-containing protein (VCP) which is a causative gene in patients with inclusion body myopathy with Paget's disease of bone and frontotemporal dementia (IBMPFD). The physiological interaction of IQGAP1 with VCP was confirmed by an immunoprecipitation assay. Both the N-terminal (N-half) and C-terminal (C-half) fragments of IQGAP1 interacted with the N-terminal region of VCP. Co-localization of IQGAP1 and VCP was observed in the growth corn, axonal shaft, cell body, and dendrites in cultured hippocampal neurons at 4 days in vitro (DIV4). In cultured neurons at DIV14, IQGAP1 co-localized with VCP in dendrites. When HEK293T cells were co-transfected with IQGAP1 and VCP, an immunoprecipitation assay revealed that binding of IQGAP1 with disease-related mutant (R155H or A232E) VCP was markedly reduced compared to wild-type (WT) VCP. These results suggest that reduction of IQGAP1 and VCP interaction may be associated with the pathophysiology of IBMPFD.

Loss of TMEM106B Ameliorates Lysosomal and Frontotemporal Dementia-Related Phenotypes in Progranulin-Deficient Mice

Progranulin (GRN) and TMEM106B are associated with several common neurodegenerative disorders including frontotemporal lobar degeneration (FTLD). A TMEM106B variant modifies GRN-associated FTLD risk. However, their functional relationship in vivo and the mechanisms underlying the risk modification remain unclear. Here, using transcriptomic and proteomic analyses with Grn^-/- and Tmem106b^-/- mice, we show that, while multiple lysosomal enzymes are increased in Grn^-/- brain at both transcriptional and protein levels, TMEM106B deficiency causes reduction in several lysosomal enzymes. Remarkably, Tmem106b deletion from Grn^-/- mice normalizes lysosomal protein levels and rescues FTLD-related behavioral abnormalities and retinal degeneration without improving lipofuscin, C1q, and microglial accumulation. Mechanistically, TMEM106B binds vacuolar-ATPase accessory protein 1 (AP1). TMEM106B deficiency reduces vacuolar-ATPase AP1 and V0 subunits, impairing lysosomal acidification and normalizing lysosomal protein levels in Grn^-/- neurons. Thus, Grn and Tmem106b genes have opposite effects on lysosomal enzyme levels, and their interaction determines the extent of neurodegeneration.

Interactions of pathological proteins in neurodegenerative diseases

Neurodegenerative diseases such as Alzheimer's disease (AD), frontotemporal lobar degeneration (FTD), Lewy body disease (LBD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS) have in common that protein aggregates represent pathological hallmark lesions. Amyloid β-protein, τ-protein, α-synuclein, and TDP-43 are the most frequently aggregated proteins in these disorders. Although they are assumed to form disease-characteristic aggregates, such as amyloid plaques and neurofibrillary tangles in AD or Lewy bodies in LBD/PD, they are not restricted to these clinical presentations. They also occur in non-diseased individuals and can co-exist in the same brain without or with a clinical picture of a distinct dementing or movement disorder. In this review, we discuss the co-existence of these pathologies and potential additive effects in the human brain as well as related functional findings on cross-seeding and molecular interactions between these aggregates/proteins. We conclude that there is evidence for interactions at the molecular level as well as for additive effects on brain damage by multiple pathologies occurring in different functionally important neurons. Based upon this information, we hypothesize a cascade of events that may explain general mechanisms in the development of neurodegenerative disorders: (1) distinct lesions are a prerequisite for the development of a distinct disease (e.g., primary age-related tauopathy for AD), (2) disease-specific pathogenic events further trigger the development of a specific disease (e.g., Aβ aggregation in AD that exaggerate further Aβ and AD-related τ pathology), (3) the symptomatic disease manifests, and (4) neurodegenerative co-pathologies may be either purely coincidental or (more likely) have influence on the disease development and/or its clinical presentation.

Myogenic differentiation of VCP disease-induced pluripotent stem cells: A novel platform for drug discovery

Valosin Containing Protein (VCP) disease is an autosomal dominant multisystem proteinopathy caused by mutations in the VCP gene, and is primarily associated with progressive muscle weakness, including atrophy of the pelvic and shoulder girdle muscles. Currently, no treatments are available and cardiac and respiratory failures can lead to mortality at an early age. VCP is an AAA ATPase multifunction complex protein and mutations in the VCP gene resulting in disrupted autophagic clearance. Due to the rarity of the disease, the myopathic nature of the disorder, ethical and practical considerations, VCP disease muscle biopsies are difficult to obtain. Thus, disease-specific human induced pluripotent stem cells (hiPSCs) now provide a valuable resource for the research owing to their renewable and pluripotent nature. In the present study, we report the differentiation and characterization of a VCP disease-specific hiPSCs into precursors expressing myogenic markers including desmin, myogenic factor 5 (MYF5), myosin and heavy chain 2 (MYH2). VCP disease phenotype is characterized by high expression of TAR DNA Binding Protein-43 (TDP-43), ubiquitin (Ub), Light Chain 3-I/II protein (LC3-I/II), and p62/SQSTM1 (p62) protein indicating disruption of the autophagy cascade. Treatment of hiPSC precursors with autophagy stimulators Rapamycin, Perifosine, or AT101 showed reduction in VCP pathology markers TDP-43, LC3-I/II and p62/SQSTM1. Conversely, autophagy inhibitors chloroquine had no beneficial effect, and Spautin-1 or MHY1485 had modest effects. Our results illustrate that hiPSC technology provide a useful platform for a rapid drug discovery and hence constitutes a bridge between clinical and bench research in VCP and related diseases.

Weighted Protein Interaction Network Analysis of Frontotemporal Dementia

The genetic analysis of complex disorders has undoubtedly led to the identification of a wealth of associations between genes and specific traits. However, moving from genetics to biochemistry one gene at a time has, to date, rather proved inefficient and under-powered to comprehensively explain the molecular basis of phenotypes. Here we present a novel approach, weighted protein–protein interaction network analysis (W-PPI-NA), to highlight key functional players within relevant biological processes associated with a given trait. This is exemplified in the current study by applying W-PPI-NA to frontotemporal dementia (FTD): We first built the state of the art FTD protein network (FTD-PN) and then analyzed both its topological and functional features. The FTD-PN resulted from the sum of the individual interactomes built around FTD-spectrum genes, leading to a total of 4198 nodes. Twenty nine of 4198 nodes, called inter-interactome hubs (IIHs), represented those interactors able to bridge over 60% of the individual interactomes. Functional annotation analysis not only reiterated and reinforced previous findings from single genes and gene-coexpression analyses but also indicated a number of novel potential disease related mechanisms, including DNA damage response, gene expression regulation, and cell waste disposal and potential biomarkers or therapeutic targets including EP300. These processes and targets likely represent the functional core impacted in FTD, reflecting the underlying genetic architecture contributing to disease. The approach presented in this study can be applied to other complex traits for which risk-causative genes are known as it provides a promising tool for setting the foundations for collating genomics and wet laboratory data in a bidirectional manner. This is and will be critical to accelerate molecular target prioritization and drug discovery.

Impaired protein degradation in FTLD and related disorders

Impaired protein degradation has been discussed as a cause or consequence of various neurodegenerative diseases, such as Alzheimer's, Parkinson's and Huntington's disease. More recently, evidence accumulated that dysfunctional protein degradation may play a role in frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). Since in almost all neurodegenerative diseases, protein aggregates are disease-defining hallmarks, it is most likely that impaired protein degradation contributes to disease onset and progression. In the majority of FTD cases, the pathological protein aggregates contain either microtubuleassociated protein tau or TAR DNA-binding protein (TDP)-43. Aggregates are also positive for ubiquitin and p62/sequestosome 1 (SQSTM1) indicating that these aggregates are targeted for degradation. FTD-linked mutations in genes encoding three autophagy adaptor proteins, p62/SQSTM1, ubiquilin 2 and optineurin, indicate that impaired autophagy might cause FTD. Furthermore, the strongest evidence for lysosomal impairment in FTD is provided by the progranulin (GRN) gene, which is linked to FTD and neuronal ceroid lipofuscinosis. In this review, we summarize the observations that have been made during the last years linking the accumulation of disease-associated proteins in FTD to impaired protein degradation pathways. In addition, we take resent findings for nucleocytoplasmic transport defects of TDP-43, as discussed for hexanucleotide repeat expansions in C9orf72 into account and provide a hypothesis how the interplay of altered nuclear transport and protein degradation leads to the accumulation of protein deposits.

Mutations in the Human AAA+ Chaperone p97 and Related Diseases

A number of neurodegenerative diseases have been linked to mutations in the human protein p97, an abundant cytosolic AAA⁺ (ATPase associated with various cellular activities) ATPase, that functions in a large number of cellular pathways. With the assistance of a variety of cofactors and adaptor proteins, p97 couples the energy of ATP hydrolysis to conformational changes that are necessary for its function. Disease-linked mutations, which are found at the interface between two main domains of p97, have been shown to alter the function of the protein, although the pathogenic mutations do not appear to alter the structure of individual subunit of p97 or the formation of the hexameric biological unit. While exactly how pathogenic mutations alter the cellular function of p97 remains unknown, functional, biochemical and structural differences between wild-type and pathogenic mutants of p97 are being identified. Here, we summarize recent progress in the study of p97 pathogenic mutants.

IBMPFD Disease-Causing Mutant VCP/p97 Proteins Are Targets of Autophagic-Lysosomal Degradation

The ubiquitin-proteasome system (UPS) degrades soluble proteins and small aggregates, whereas macroautophagy (autophagy herein) eliminates larger protein aggregates, tangles and even whole organelles in a lysosome-dependent manner. VCP/p97 was implicated in both pathways. VCP/p97 mutations cause a rare multisystem disease called IBMPFD (Inclusion Body Myopathy with Paget's Disease and Frontotemporal Dementia). Here, we studied the role IBMPFD-related mutants of VCP/p97 in autophagy. In contrast with the wild-type VCP/p97 protein or R155C or R191Q mutants, the P137L mutant was aggregate-prone. We showed that, unlike commonly studied R155C or R191Q mutants, the P137L mutant protein stimulated both autophagosome and autolysosome formation. Moreover, P137L mutant protein itself was a substrate of autophagy. Starvation- and mTOR inhibition-induced autophagy led to the degradation of the P137L mutant protein, while preserving the wild-type and functional VCP/p97. Strikingly, similar to the P137L mutant, other IBMPFD-related VCP/p97 mutants, namely R93C and G157R mutants induced autophagosome and autolysosome formation; and G157R mutant formed aggregates that could be cleared by autophagy. Therefore, cellular phenotypes caused by P137L mutant expression were not isolated observations, and some other IBMPFD disease-related VCP/p97 mutations could lead to similar outcomes. Our results indicate that cellular mechanisms leading to IBMPFD disease may be various, and underline the importance of studying different disease-associated mutations in order to better understand human pathologies and tailor mutation-specific treatment strategies.

Cardiac-Restricted Expression of VCP/TER94 RNAi or Disease Alleles Perturbs Drosophila Heart Structure and Impairs Function

Valosin-containing protein (VCP) is a highly conserved mechanoenzyme that helps maintain protein homeostasis in all cells and serves specialized functions in distinct cell types. In skeletal muscle, it is critical for myofibrillogenesis and atrophy. However, little is known about VCP’s role(s) in the heart. Its functional diversity is determined by differential binding of distinct cofactors/adapters, which is likely disrupted during disease. VCP mutations cause multisystem proteinopathy (MSP), a pleiotropic degenerative disorder that involves inclusion body myopathy. MSP patients display progressive muscle weakness. They also exhibit cardiomyopathy and die from cardiac and respiratory failure, which are consistent with critical myocardial roles for the enzyme. Nonetheless, efficient models to interrogate VCP in cardiac muscle remain underdeveloped and poorly studied. Here, we investigated the significance of VCP and mutant VCP in the Drosophila heart. Cardiac-restricted RNAi-mediated knockdown of TER94, the Drosophila VCP homolog, severely perturbed myofibrillar organization and heart function in adult flies. Furthermore, expression of MSP disease-causing alleles engendered cardiomyopathy in adults and structural defects in embryonic hearts. Drosophila may therefore serve as a valuable model for examining role(s) of VCP in cardiogenesis and for identifying novel heart-specific VCP interactions, which when disrupted via mutation, contribute to or elicit cardiac pathology.

VCP and ATL1 regulate endoplasmic reticulum and protein synthesis for dendritic spine formation

Imbalanced protein homeostasis, such as excessive protein synthesis and protein aggregation, is a pathogenic hallmark of a range of neurological disorders. Here, using expression of mutant proteins, a knockdown approach and disease mutation knockin mice, we show that VCP (valosin-containing protein), together with its cofactor P47 and the endoplasmic reticulum (ER) morphology regulator ATL1 (Atlastin-1), regulates tubular ER formation and influences the efficiency of protein synthesis to control dendritic spine formation in neurons. Strengthening the significance of protein synthesis in dendritic spinogenesis, the translation blocker cyclohexamide and the mTOR inhibitor rapamycin reduce dendritic spine density, while a leucine supplement that increases protein synthesis ameliorates the dendritic spine defects caused by Vcp and Atl1 deficiencies. Because VCP and ATL1 are the causative genes of several neurodegenerative and neurodevelopmental disorders, we suggest that impaired ER formation and inefficient protein synthesis are significant in the pathogenesis of multiple neurological disorders.

Protein homeostasis is crucial for maintaining a variety of cellular functions. Here the authors show that valosin-containing protein and its cofactors regulate tubular ER formation and protein synthesis efficiency, thereby control dendritic spine formation in neurons.

[A patient with familial amyotrophic lateral sclerosis associated with a new valosin-containing protein (VCP) gene mutation]

In this communication, we report a patient with familial amyotrophic lateral sclerosis (ALS) associated with a familial dyslipidemia. Genetic analysis revealed a novel heterozygous valosin-containing protein (VCP) mutation (c.466G>T (p.G156C)). The other gene analysis also disclosed a known homozygous LCAT mutation (c.101C>T (p.P10L)). VCP gene mutation shown should be responsible for familial ALS because of following reasons. The patient's father also was also affected by ALS. The VCP gene mutation (p.G156C) in the patient was located in the vicinity of a site frequently associated with pathogenic VCP variants. The same amino acid transformation as that of this patient has been reported to be involved in the pathogenesis of inclusion body myopathy with Paget's disease of the bone and frontotemporal dementia. This is the first case report of rare association of ALS with VCP mutation and dyslipidemia with LCAT mutation.

Targeted excision of VCP R155H mutation by Cre-LoxP technology as a promising therapeutic strategy for valosin-containing protein disease

Inclusion body myopathy associated with Paget's disease of the bone and frontotemporal dementia is attributed to mutations in the valosin-containing protein (VCP) gene, mapped to chromosomal region 9p13.3-12. Affected individuals exhibit scapular winging and die from progressive muscle weakness and cardiac and respiratory failure in their 40s to 50s. Mutations in the VCP gene have also been associated with amyotrophic lateral sclerosis in 10-15% of individuals with hereditary inclusion body myopathy and 2-3% of isolated familial amyotrophic lateral sclerosis. Currently, there are no effective treatments for VCP-related myopathy or dementia. To determine the effects of targeted excision of the most common R155H mutation in VCP disease, we generated the Cre-ER™-VCPR155H/+ tamoxifen-inducible model. We administered tamoxifen (0.12 mg/g body weight) or corn oil (vehicle) to the pregnant dams by oral gavage and monitored survival and muscle strength measurements of the pups until 18 months of age. We confirmed efficient removal of exons 4 and 5 and recombination of the mutant/floxed VCP copies by Q-PCR analyses. The activity and specificity of Cre recombinase was confirmed by immunostaining. Herein, we report that Cre-ER™-VCPR155H/+ mice demonstrated improved muscle strength and quadriceps fibers architecture, autophagy signaling pathway, reduced brain neuropathology, decreased apoptosis, and less severe Paget-like bone changes. The Cre-ER™-VCPR155H/+ mouse model provides proof of principle by demonstrating that removal of the mutated exons could be beneficial to patients with VCP-related neurodegenerative diseases, and serves as an excellent platform in understanding the underlying pathophysiological mechanism(s) in the hopes of a promising therapeutic approach.

Rapamycin and chloroquine: the in vitro and in vivo effects of autophagy-modifying drugs show promising results in valosin containing protein multisystem proteinopathy

Mutations in the valosin containing protein (VCP) gene cause hereditary Inclusion body myopathy (hIBM) associated with Paget disease of bone (PDB), frontotemporal dementia (FTD), more recently termed multisystem proteinopathy (MSP). Affected individuals exhibit scapular winging and die from progressive muscle weakness, and cardiac and respiratory failure, typically in their 40s to 50s. Histologically, patients show the presence of rimmed vacuoles and TAR DNA-binding protein 43 (TDP-43)-positive large ubiquitinated inclusion bodies in the muscles. We have generated a VCP^R155H/+ mouse model which recapitulates the disease phenotype and impaired autophagy typically observed in patients with VCP disease. Autophagy-modifying agents, such as rapamycin and chloroquine, at pharmacological doses have previously shown to alter the autophagic flux. Herein, we report results of administration of rapamycin, a specific inhibitor of the mechanistic target of rapamycin (mTOR) signaling pathway, and chloroquine, a lysosomal inhibitor which reverses autophagy by accumulating in lysosomes, responsible for blocking autophagy in 20-month old VCP^R155H/+ mice. Rapamycin-treated mice demonstrated significant improvement in muscle performance, quadriceps histological analysis, and rescue of ubiquitin, and TDP-43 pathology and defective autophagy as indicated by decreased protein expression levels of LC3-I/II, p62/SQSTM1, optineurin and inhibiting the mTORC1 substrates. Conversely, chloroquine-treated VCP^R155H/+ mice revealed progressive muscle weakness, cytoplasmic accumulation of TDP-43, ubiquitin-positive inclusion bodies and increased LC3-I/II, p62/SQSTM1, and optineurin expression levels. Our in vitro patient myoblasts studies treated with rapamycin demonstrated an overall improvement in the autophagy markers. Targeting the mTOR pathway ameliorates an increasing list of disorders, and these findings suggest that VCP disease and related neurodegenerative multisystem proteinopathies can now be included as disorders that can potentially be ameliorated by rapalogs.

Immunoreactivity of valosin-containing protein in sporadic amyotrophic lateral sclerosis and in a case of its novel mutant

Background

Mutations in the valosin-containing protein (VCP) gene were first found to cause inclusion- body myopathy with early-onset Paget disease and frontotemporal dementia (IBMPFD). Mutations in the VCP gene were later reported to occur in familial amyotrophic lateral sclerosis (ALS). But the role of VCP in the neurodegenerative processes that occur in ALS remains unknown. The purpose of the present study was to elucidate the role of VCP in the neurodegeneration seen in sporadic and VCP mutant ALS.

Results

Immunohistochemistry demonstrated that the frequency of distinct VCP-positive nuclei of spinal motor neurons of patients with sporadic ALS (SALS) and the ALS with VCP novel mutation (ALS-VCP, M158V) was increased, compared with that of the control cases. No VCP-positive inclusion bodies were observed in SALS patients, a ALS-VCP patient or in control subjects. Neuropathologic examination of the ALS-VCP case showed loss of motor neurons, the presence of Bunina bodies, and degeneration of the corticospinal tracts. Bunina bodies detected in this case were confirmed to show immunohistochemical and ultrastructural features similar to those previously described. Furthermore, neuronal intracytoplasmic inclusions immunopositive for TAR DNA-binding protein 43 kDa (TDP-43), phosphorylated TDP-43, ubiquitin (Ub), p62, and optineurin were identified in the spinal and medullary motoneurons, but not in the neocortex. Gene analysis of this ALS-VCP patient confirmed the de novo mutation of M158V, which was not found in control cases; and bioinformatics using several in silico analyses showed possible damage to the structure of VCP. Immunocytochemical study of cultured cells showed increased cytoplasmic translocation of TDP-43 in cells transfected with several mutant VCP including our patient’s compared with wild-type VCP.

Conclusion

These findings support the idea that VCP is associated with the pathomechanism of SALS and familial ALS with a VCP mutation, presumably acting through a dominant-negative mechanism.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-014-0172-0) contains supplementary material, which is available to authorized users.

Global gene expression profiling in R155H knock-in murine model of VCP disease

Dominant mutations in the valosin-containing protein (VCP) gene cause inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia, which is characterized by progressive muscle weakness, dysfunction in bone remodeling, and frontotemporal dementia. More recently, VCP has been linked to 2% of familial amyotrophic lateral sclerosis cases. VCP plays a significant role in a plethora of cellular functions including membrane fusion, transcription activation, nuclear envelope reconstruction, postmitotic organelle reassembly, and cell cycle control. To elucidate the pathological mechanisms underlying the VCP disease progression, we have previously generated a VCP(R155H/+) mouse model with the R155H mutation. Histological analyses of mutant muscle showed vacuolization of myofibrils, centrally located nuclei, and disorganized muscle fibers. Global expression profiling of VCP(R155H/+) mice using gene annotations by DAVID identified key dysregulated signaling pathways including genes involved in the physiological system development and function, diseases and disorders, and molecular and cellular functions. There were a total of 212 significantly dysregulated genes, several of which are involved in the regulation of proteasomal function and NF-κB signaling cascade. Findings of the gene expression study were validated by using quantitative reverse transcriptase polymerase chain reaction analyses to test genes involved in various signaling cascades. This investigation reveals the importance of the VCP(R155H/+) mouse model in the understanding of cellular and molecular mechanisms causing VCP-associated neurodegenerative diseases and in the discovery of novel therapeutic advancements and strategies for patients suffering with these debilitating disorders.

Hereditary inclusion-body myopathies

The term hereditary inclusion-body myopathies (HIBMs) defines a group of rare muscle disorders with autosomal recessive or dominant inheritance and presence of muscle fibers with rimmed vacuoles and collection of cytoplasmic or nuclear 15-21 nm diameter tubulofilaments as revealed by muscle biopsy. The most common form of HIBM is due to mutations of the GNE gene that codes for a rate-limiting enzyme in the sialic acid biosynthetic pathway. This results in abnormal sialylation of glycoproteins that possibly leads to muscle fiber degeneration. Mutations of the valosin containing protein are instead responsible for hereditary inclusion-body myopathy with Paget's disease of the bone and frontotemporal dementia (IBMPFD), with these three phenotypic features having a variable penetrance. IBMPFD probably represents a disorder of abnormal cellular trafficking of proteins and maturation of the autophagosome. HIBM with congenital joint contractures and external ophthalmoplegia is due to mutations of the Myosin Heavy Chain IIa gene that exerts a pathogenic effect through interference with filament assembly or functional defects in ATPase activity. This review illustrates the clinical and pathologic characteristics of HIBMs and the main clues available to date concerning the possible pathogenic mechanisms and therapeutic perspectives of these disorders. This article is part of a Special Issue entitled: Neuromuscular Diseases: Pathology and Molecular Pathogenesis.

Psychiatric Presentation of Frontotemporal Dementia Associated with Inclusion Body Myopathy due to the VCP Mutation (R155H) in a French Family

Introduction

Inclusion body myopathy with Paget's disease of the bone and frontotemporal dementia (IBMPFD) is a rare late-onset autosomal dominant disorder due to a mutation of the valosin-containing protein (VCP) gene.

Case Report

We report the case of a patient who developed progressive weakness of the limbs in his fifties, until he was confined to a wheelchair. At that time, he developed acute behavioural changes including irritability, severe anxiety and major depression, which led to him being hospitalised in a psychiatric hospital. He also suffered from aphasia and executive function impairment, which helped us to diagnose a behavioural form of frontotemporal dementia (FTD). The diagnosis of IBMPFD due to a mutation in the VCP gene was confirmed by a genetic study of the VCP gene (R155H mutation).

Discussion

The clinical diagnosis of IBMPFD is suggested by the presence of at least one of three major manifestations as follows: inclusion body myopathy (mean onset at 42 years of age), Paget's disease of the bone and FTD (mean onset at 55 years of age). It is mostly the behavioural form of FTD (behavioural changes, executive dysfunction and aphasia). One interesting finding in our report is the predominance of the psychiatric symptoms at the beginning of the behavioural changes, which led to the diagnosis of FTD. The diagnosis of IBMPFD was confirmed by the genetic study: the R155H mutation found on exon 5 domain CDC48 is the most frequent of the 18 known mutations in the VCP gene.

Exercise training reverses skeletal muscle atrophy in an experimental model of VCP disease

Background

The therapeutic effects of exercise resistance and endurance training in the alleviation of muscle hypertrophy/atrophy should be considered in the management of patients with advanced neuromuscular diseases. Patients with progressive neuromuscular diseases often experience muscle weakness, which negatively impact independence and quality of life levels. Mutations in the valosin containing protein (VCP) gene lead to Inclusion body myopathy associated with Paget's disease of bone and frontotemporal dementia (IBMPFD) and more recently affect 2% of amyotrophic lateral sclerosis (ALS)-diagnosed cases.

Methods/Principle Findings

The present investigation was undertaken to examine the effects of uphill and downhill exercise training on muscle histopathology and the autophagy cascade in an experimental VCP mouse model carrying the R155H mutation. Progressive uphill exercise in VCP^R155H/+ mice revealed significant improvement in muscle strength and performance by grip strength and Rotarod analyses when compared to the sedentary mice. In contrast, mice exercised to run downhill did not show any significant improvement. Histologically, the uphill exercised VCP^R155H/+ mice displayed an improvement in muscle atrophy, and decreased expression levels of ubiquitin, P62/SQSTM1, LC3I/II, and TDP-43 autophagy markers, suggesting an alleviation of disease-induced myopathy phenotypes. There was also an improvement in the Paget-like phenotype.

Conclusions

Collectively, our data highlights that uphill exercise training in VCP^R155H/+ mice did not have any detrimental value to the function of muscle, and may offer effective therapeutic options for patients with VCP-associated diseases.

Genotype-phenotype studies of VCP-associated inclusion body myopathy with Paget disease of bone and/or frontotemporal dementia

Valosin containing protein (VCP) disease associated with inclusion body myopathy, Paget disease of the bone and frontotemporal dementia is a progressive autosomal dominant disorder caused by mutations in Valosin containing protein gene. To establish genotype-phenotype correlations we analyzed clinical and biochemical markers from a database of 190 members in 27 families harboring 10 missense mutations. Individuals were grouped into three categories: symptomatic, presymptomatic carriers and noncarriers. The symptomatic families were further divided into ten groups based on their VCP mutations. There was marked intra and inter-familial variation; and significant genotype-phenotype correlations were difficult to establish because of small numbers. Nevertheless when comparing the two most common mutations, R155C mutation was found to be more severe, with an earlier onset of myopathy and Paget (p = 0.03). Survival analysis of all subjects revealed an average life span after diagnosis of myopathy and Paget of 18 and 19 years respectively, and after dementia only 6 years. R155C had a reduced survival compared to the R155H mutation (p = 0.03).We identified amyotrophic lateral sclerosis (ALS) was diagnosed in 13 individuals (8.9%) and Parkinson's disease in five individuals (3%); however, there was no genotypic correlation. This study represents the largest dataset of patients with VCP disease and expands our understanding of the natural history and provides genotype-phenotype correlations in this unique disease.

A novel VCP mutation as the cause of atypical IBMPFD in a Chinese family

INTRODUCTION

Inclusion-body myopathy (IBM) with Paget's disease of bone (PDB) and frontotemporal dementia (FTD), designated as IBMPFD, is a rare, autosomal dominant disorder (MIM 605382). IBMPFD is caused by mutations in the gene that encode valosin-containing protein (VCP). We investigated a Chinese family in which multiple members were diagnosed with PDB and suffered from weakness of the limbs. However, no members of this family were diagnosed with FTD. We made a preliminary diagnosis of PDB, but failed to identify an SQSTM1 mutation in any of the patients. We used whole-exome sequencing to identify the pathogenic gene mutation affecting the Chinese male proband.

MATERIALS AND METHODS

Altogether, 254 subjects, including one 56-year-old male proband, four affected, related individuals and additional nine family members from a non-consanguineous Chinese family, and 240 healthy donors were recruited and genomic DNA was extracted. All eight exons and the exon-intron boundaries of the SQSTM1 gene were amplified by polymerase chain reaction (PCR) and directly sequenced in five patients (II13, II4, II5, II8, II9). Using whole-exome sequencing, we identified a novel mutation in VCP as the disease-causing mutation. We confirmed the result by sequencing a 500-bp region of the promoter and the coding region of VCP in all 254 of the participants using Sanger sequencing.

RESULTS

No mutation in the SQSTM1 gene was identified in the five patients examined using direct Sanger sequencing. However, through whole-exome sequencing we were able to identify a novel missense mutation in exon 3 of the VCP gene (p.Gly97Glu) in the Chinese male proband. This mutation was confirmed using Sanger sequencing. The proband, four affected individuals and three unaffected individuals carried this mutation. We were able to correctly diagnose the patients with atypical IBMPFD. Structural analysis of the p.Gly97Glu mutation in the VCP protein showed that the affected amino-acid is located in the interface of the protein. This abnormality may therefore interfere with protein function.

CONCLUSIONS

This is the first report of a family from China with IBMPFD. A novel VCP mutation was found as the cause of atypical IBMPFD in a Chinese family. Our findings confirm that VCP gene mutations can be a pathogenic cause of IBMPFD.

[A case of inclusion body myopathy with Paget's disease of bone and frontotemporal dementia (IBMPFD) showing clinical features of motor neuron disease]

Inclusion body myopathy with Paget's disease of bone and frontotemporal dementia (IBMPFD) is caused by mutations in the valosin-containing protein (VCP) gene. Varied clinical features caused by VCP mutations have been reported: these clinical phenotypes include distal myopathy, frontotemporal dementia and amyotrophic lateral sclerosis. We report a 49-year-old woman with 3-year history of progressive proximal limb muscle weakness. Family history was notable for her father with motor neuron disease and an elder brother with a myopathy involving tibialis anterior and quadriceps. Neurological examinations showed proximal muscle atrophy, especially severe atrophy of paravertebral muscles, right-dominant scapular winging, bilateral pyramidal signs and hyperreflexia. Serum CK level was normal and EMG showed chronic neurogenic changes. Muscle imaging (CT) showed adipose tissue replacement of paravertebral muscles and right serratus anterior, and marked atrophy of bilateral trapezius and vastus intermedius muscles. Her lumbar spine X-ray showed an osteosclerotic change in the vertebral body, where an increased uptake of Tc99m was also observed in bone scintigraphy. Although brain MRI was normal, neuropsychological examination showed a mild attention deficit with cognitive impairment. A muscle biopsy specimen revealed scattered fibers with rimmed vacuoles. These findings prompted us to analyze a mutation in the VCP gene. Genomic sequencing of all exons of the gene showed a heterozygous missense mutation in exon 5 (c.1315G>C; p.Ala439Pro).

Heteromeric p97/p97R155C complexes induce dominant negative changes in wild-type and autophagy 9-deficient Dictyostelium strains

Heterozygous mutations in the human VCP (p97) gene cause autosomal-dominant IBMPFD (inclusion body myopathy with early onset Paget's disease of bone and frontotemporal dementia), ALS14 (amyotrophic lateral sclerosis with or without frontotemporal dementia) and HSP (hereditary spastic paraplegia). Most prevalent is the R155C point mutation. We studied the function of p97 in the social amoeba Dictyostelium discoideum and have generated strains that ectopically express wild-type (p97) or mutant p97 (p97(R155C)) fused to RFP in AX2 wild-type and autophagy 9 knock-out (ATG9(KO)) cells. Native gel electrophoresis showed that both p97 and p97(R155C) assemble into hexamers. Co-immunoprecipitation studies revealed that endogenous p97 and p97(R155C)-RFP form heteromers. The mutant strains displayed changes in cell growth, phototaxis, development, proteasomal activity, ubiquitinylated proteins, and ATG8(LC3) indicating mis-regulation of multiple essential cellular processes. Additionally, immunofluorescence analysis revealed an increase of protein aggregates in ATG9(KO)/p97(R155C)-RFP and ATG9(KO) cells. They were positive for ubiquitin in both strains, however, solely immunoreactive for p97 in the ATG9(KO) mutant. A major finding is that the expression of p97(R155C)-RFP in the ATG9(KO) strain partially or fully rescued the pleiotropic phenotype. We also observed dose-dependent effects of p97 on several cellular processes. Based on findings in the single versus the double mutants we propose a novel mode of p97 interaction with the core autophagy protein ATG9 which is based on mutual inhibition.

The homozygote VCP(R¹⁵⁵H/R¹⁵⁵H) mouse model exhibits accelerated human VCP-associated disease pathology

Valosin containing protein (VCP) mutations are the cause of hereditary inclusion body myopathy, Paget's disease of bone, frontotemporal dementia (IBMPFD). VCP gene mutations have also been linked to 2% of isolated familial amyotrophic lateral sclerosis (ALS). VCP is at the intersection of disrupted ubiquitin proteasome and autophagy pathways, mechanisms responsible for the intracellular protein degradation and abnormal pathology seen in muscle, brain and spinal cord. We have developed the homozygous knock-in VCP mouse (VCP(R155H/R155H)) model carrying the common R155H mutations, which develops many clinical features typical of the VCP-associated human diseases. Homozygote VCP(R155H/R155H) mice typically survive less than 21 days, exhibit weakness and myopathic changes on EMG. MicroCT imaging of the bones reveal non-symmetrical radiolucencies of the proximal tibiae and bone, highly suggestive of PDB. The VCP(R155H/R155H) mice manifest prominent muscle, heart, brain and spinal cord pathology, including striking mitochondrial abnormalities, in addition to disrupted autophagy and ubiquitin pathologies. The VCP(R155H/R155H) homozygous mouse thus represents an accelerated model of VCP disease and can be utilized to elucidate the intricate molecular mechanisms involved in the pathogenesis of VCP-associated neurodegenerative diseases and for the development of novel therapeutic strategies.

The genetics and neuropathology of frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is a heterogeneous group of disorders characterized by disturbances of behavior and personality and different types of language impairment with or without concomitant features of motor neuron disease or parkinsonism. FTLD is characterized by atrophy of the frontal and anterior temporal brain lobes. Detailed neuropathological studies have elicited proteinopathies defined by inclusions of hyperphosphorylated microtubule-associated protein tau, TAR DNA-binding protein TDP-43, fused-in-sarcoma or yet unidentified proteins in affected brain regions. Rather than the type of proteinopathy, the site of neurodegeneration correlates relatively well with the clinical presentation of FTLD. Molecular genetic studies identified five disease genes, of which the gene encoding the tau protein (MAPT), the growth factor precursor gene granulin (GRN), and C9orf72 with unknown function are most frequently mutated. Rare mutations were also identified in the genes encoding valosin-containing protein (VCP) and charged multivesicular body protein 2B (CHMP2B). These genes are good markers to distinguish underlying neuropathological phenotypes. Due to the complex landscape of FTLD diseases, combined characterization of clinical, imaging, biological and genetic biomarkers is essential to establish a detailed diagnosis. Although major progress has been made in FTLD research in recent years, further studies are needed to completely map out and correlate the clinical, pathological and genetic entities, and to understand the underlying disease mechanisms. In this review, we summarize the current state of the rapidly progressing field of genetic, neuropathological and clinical research of this intriguing condition.