Nerve growth factor‐mediated regulation of pain signalling and proposed new intervention strategies in clinical pain management

Nerve growth factor (NGF) is the founding member of the neurotrophins family of proteins. It was discovered more than half a century ago through its ability to promote sensory and sympathetic neuronal survival and axonal growth during the development of the peripheral nervous system, and is the paradigmatic target‐derived neurotrophic factor on which the neurotrophic hypothesis is based. Since that time, NGF has also been shown to play a key role in the generation of acute and chronic pain and in hyperalgesia in diverse pain states. NGF is expressed at high levels in damaged or inflamed tissues and facilitates pain transmission by nociceptive neurons through a variety of mechanisms. Genetic mutations in NGF or its tyrosine kinase receptor TrkA, lead to a congenital insensitivity or a decreased ability of humans to perceive pain. The hereditary sensory autonomic neuropathies (HSANs) encompass a spectrum of neuropathies that affect one's ability to perceive sensation. HSAN type IV and HSAN type V are caused by mutations in TrkA and NGF respectively. This review will focus firstly on the biology of NGF and its role in pain modulation. We will review neuropathies and clinical presentations that result from the disruption of NGF signalling in HSAN type IV and HSAN type V and review current advances in developing anti‐NGF therapy for the clinical management of pain.     

Deficient activity of guanine nucleotide regulatory protein in erythrocytes from patients with pseudohypoparathyroidism

The activity in two assay systems of guanine nucleotide regulatory protein was significantly lower in red cells from pseudohypoparathyroid patients compared to that of normal subjects. The results support the hypothesis that deficient activity of the guanine nucleotide regulatory protein is the molecular basis for hormone resistance in this inherited disorder.     

Recruitment and the Role of Nuclear Localization in Polyglutamine-mediated Aggregation

The inherited neurodegenerative diseases caused by an expanded glutamine repeat share the pathologic feature of intranuclear aggregates or inclusions (NI). Here in cell-based studies of the spinocerebellar ataxia type-3 disease protein, ataxin-3, we address two issues central to aggregation: the role of polyglutamine in recruiting proteins into NI and the role of nuclear localization in promoting aggregation. We demonstrate that full-length ataxin-3 is readily recruited from the cytoplasm into NI seeded either by a pathologic ataxin-3 fragment or by a second unrelated glutamine-repeat disease protein, ataxin-1. Experiments with green fluorescence protein/polyglutamine fusion proteins show that a glutamine repeat is sufficient to recruit an otherwise irrelevant protein into NI, and studies of human disease tissue and a Drosophila transgenic model provide evidence that specific glutamine-repeat–containing proteins, including TATA-binding protein and Eyes Absent protein, are recruited into NI in vivo. Finally, we show that nuclear localization promotes aggregation: an ataxin-3 fragment containing a nonpathologic repeat of 27 glutamines forms inclusions only when targeted to the nucleus. Our findings establish the importance of the polyglutamine domain in mediating recruitment and suggest that pathogenesis may be linked in part to the sequestering of glutamine-containing cellular proteins. In addition, we demonstrate that the nuclear environment may be critical for seeding polyglutamine aggregates.     

Commentary: ZFYVE26/SPASTIZIN: A close link between complicated hereditary spastic paraparesis and autophagy

Defective autophagy is associated with neurodegenerative disorders including Alzheimer, Parkinson and Huntington diseases, amyotrophic lateral sclerosis and SCA (spinocerebellar ataxias). Autophagy defects were detected also in SPG49, a complicated form of hereditary spastic paraparesis (cHSP) associated with mutations in the TECPR2 gene, suggesting a role of autophagy also in this heterogeneous group of neurodegenerative diseases. We recently found defective autophagy in SPG15, another HSP subtype associated with mutations in the ZFYVE26/SPG15 gene. Patient-derived cells (fibroblasts/lymphoblasts) carrying different ZFYVE26 mutations show accumulation of immature autophagosomes and increased MAP1LC3B-II and SQSTM1/p62 levels. These findings indicate that ZFYVE26 is a key determinant of autophagosome maturation, which is impaired when the protein is defective or absent. Replication of these findings in primary neurons supports the relevance of defective autophagy in SPG15-related neurodegeneration.     

Further assembly required: construction and dynamics of the endoplasmic reticulum network

The endoplasmic reticulum (ER) is a continuous membrane system comprising the nuclear envelope, ribosome‐studded peripheral sheets and an interconnected network of smooth tubules extending throughout the cell. Although protein biosynthesis, transport and quality control in the ER have been studied extensively, mechanisms underlying the notably diverse architecture of the ER have only emerged recently; this review highlights these new findings and how they relate to ER functional specializations. Several protein families, including reticulons and DP1/REEPs/Yop1, harbour hydrophobic hairpin domains that shape high‐curvature ER tubules and mediate intramembrane protein interactions. Members of the atlastin/RHD3/Sey1 family of dynamin‐related GTPases mediate the formation of three‐way junctions that characterize the tubular ER network, and additional classes of hydrophobic hairpin‐containing ER proteins interact with and remodel the microtubule cytoskeleton. Flat ER sheets have a different complement of proteins implicated in shaping, cisternal stacking and microtubule interactions. Finally, several shaping proteins are mutated in hereditary spastic paraplegias, emphasizing the particular importance of proper ER morphology and distribution for highly polarized cells.     

Mutation and expression analysis of the IDH1, IDH2, DNMT3A, and MYD88 genes in colorectal cancer

Colorectal cancer (CRC) is one of the leading causes of death around the world. Its genetic mechanism was intensively investigated in the past decades with findings of a number of canonical oncogenes and tumor-suppressor genes such as APC, KRAS, and TP53. Recent genome-wide association and sequencing studies have identified a series of promising oncogenes including IDH1, IDH2, DNMT3A, and MYD88 in hematologic malignancies. However, whether these genes are involved in CRC remains unknown. In this study, we screened the hotspot mutations of these four genes in 305 CRC samples from Han Chinese by direct sequencing. mRNA expression levels of these genes were quantified by quantitative real-time PCR (RT-qPCR) in paired cancerous and paracancerous tissues. Association analyses between mRNA expression levels and different cancerous stages were performed. Except for one patient harboring IDH1 mutation p.I99M, we identified no previously reported hotspot mutations in colorectal cancer tissues. mRNA expression levels of IDH1, DNMT3A, and MYD88, but not IDH2, were significantly decreased in the cancerous tissues comparing with the paired paracancerous normal tissues. Taken together, the hotspot mutations of IDH1, IDH2, DNMT3A, and MYD88 gene were absent in CRC. Aberrant mRNA expression of IDH1, DNMT3A, and MYD88 gene might be actively involved in the development of CRC.     

Confirmation of the mitochondrial ND1 gene mutation G3635A as a primary LHON mutation

We report the clinical and genetic characterization of two Chinese LHON families who do not carry the primary LHON-mutations. Mitochondrial genome sequence analysis revealed the presence of a homoplasmic ND1 G3635A mutation in both families. In Family LHON-001, 31 other variants belonging to the East Asian haplogroup R11a were identified and in Family LHON-019, 37 other variants belonging to the East Asian haplogroup D4g were determined. The ND1 G3635A mutation changes the conversed serine¹¹⁰ residue to asparagine. This mutation has been previously described in a single Russian LHON family and has been suggested to contribute to increased LHON expressivity. In addition, a mutation in cytochrome c oxidase subunit II at C7868T (COII/L95F) may act in synergy with G3635A, increasing LHON expressivity in Family LHON-001, which had a higher level of LHON penetrance than Family LHON-019. In summary, the G3635A mutation is confirmed as a rare primary pathogenic mutation for LHON.     

Spastin Couples Microtubule Severing to Membrane Traffic in Completion of Cytokinesis and Secretion

Mutations in the gene encoding the microtubule (MT)-severing protein spastin are the most common cause of hereditary spastic paraplegia, a genetic condition in which axons of the corticospinal tracts degenerate. We show that not only does endogenous spastin colocalize with MTs, but that it is also located on the early secretory pathway, can be recruited to endosomes and is present in the cytokinetic midbody. Spastin has two main isoforms, a 68 kD full-length isoform and a 60 kD short form. These two isoforms preferentially localize to different membrane traffic pathways with 68 kD spastin being principally located at the early secretory pathway, where it regulates endoplasmic reticulum-to-Golgi traffic. Sixty kiloDalton spastin is the major form recruited to endosomes and is also present in the midbody, where its localization requires the endosomal sorting complex required for transport-III-interacting MIT domain. Loss of midbody MTs accompanies the abscission stage of cytokinesis. In cells lacking spastin, a MT disruption event that normally accompanies abscission does not occur and abscission fails. We suggest that this event represents spastin-mediated MT severing. Our results support a model in which membrane traffic and MT regulation are coupled through spastin. This model is relevant in the axon, where there also is co-ordinated MT regulation and membrane traffic.     

Leber's hereditary optic neuropathy is associated with the mitochondrial ND4 G11696A mutation in five Chinese families

We report here the clinical, genetic, and molecular characterization of five Chinese families with Leber's hereditary optic neuropathy (LHON). Clinical and genetic evaluations revealed the variable severity and age-of-onset in visual impairment in these families. Strikingly, there were extremely low penetrances of visual impairment in these Chinese families. Sequence analysis of the complete mitochondrial genomes in these pedigrees showed the distinct sets of mtDNA polymorphism, in addition to the identical ND4 G11696A mutation associated with LHON. Indeed, this mutation is present in homoplasmy only in the maternal lineage of those pedigrees but not other members of these families. In fact, the occurrence of the G11696A mutation in these several genetically unrelated subjects affected by visual impairment strongly indicates that this mutation is involved in the pathogenesis of visual impairment. Furthermore, the N405D in the ND5 and G5820A in the tRNA(Cys), showing high evolutional conservation, may contribute to the phenotypic expression of G11696A mutation in the WZ10 pedigree. However, there was the absence of functionally significant mtDNA mutations in other four Chinese pedigrees carrying the G11696A mutation. Therefore, nuclear modifier gene(s) or environmental factor(s) may play a role in the phenotypic expression of the LHON-associated G11696A mutation in these Chinese pedigrees.