A candidate gene for human neurodegenerative disorders: a rat PKC gamma mutation causes a Parkinsonian syndrome

Relationship between sleep quality and gravitational Tolerance

BACKGROUND

The purpose of this study was to investigate the relationship between sleep quality and gravitational tolerance because sleep could directly affect physiological variables of the human body.

METHODS

For the present study, 157 male Korea Air Force Academy cadets were recruited. They were assigned into a gravity (G)-tolerance test pass group (GP, n = 87) and a G-tolerance test fail group (GF, n = 70). All participants were assessed for G-tolerance test and Pittsburgh Sleep Quality Index (PSQI), a self-report questionnaire. Physical fitness test was performed based on the physical fitness test of the Ministry of National Defense of Korea.

RESULTS

Independent t-test showed that PSQI global score (p < 0.001), PSQI sleep quality (p < 0.001), PSQI sleep onset latency (p = 0.009), PSQI sleep disturbance (p < 0.001), and PSQI daytime dysfunction (p < 0.001) were significantly different between the two groups. Participants with PSQI score less than 5 were more likely to have a longer G-tolerance test time (OR = 4.705, 95% CI = 2.00-11.05). Additionally, associations between those with PSQI score less than 5 (OR = 4.567, 95% CI = 1.94-10.74) were after adjusting (< 30 s and ≥ 30 s) for covariates. A negative correlation was found between G-tolerance test time and PSQI global score (p < 0.001). Negative correlations were found among 3 km running, push-up (p < 0.001), and sit-up (p < 0.001). A positive correlation was found between push-up and sit-up (p < 0.001).

CONCLUSION

In conclusion, participants with good sleep quality were 4.705 times more likely to have longer G-tolerance test time. Thus, it is important for aircraft pilots to manage their sleep quality. Pre-pilots should also improve their sleep quality to pass the G-tolerance test.

Parkinsonism in neurodegenerative diseases predominantly presenting with ataxia

The number of molecularly defined degenerative ataxia diseases is rapidly increasing, many of them involving complex multisystemic presentations including parkinsonism. The increasing number of novel ataxia genes -with most of them being ultra-rare - often makes it difficult for clinicians and scientists to identify the molecular diagnosis underlying these ataxia-parkinsonism syndromes. Here we aim to provide an overview on the most frequent diseases and molecular causes underlying ataxia-parkinsonism, focusing both on novel aspects of well-known causes of ataxia-parkinsonism (MSA-C, PSP-C, FXTAS, repeat-expansion spinocerebellar ataxias [SCAs], conventional mutation SCAs) as well as on more recently identified rare genetic causes of ataxia-parkinsonism (AT, POLG, SPG7). We demonstrate that frequency data and phenotype characteristics help to guide diagnostics in patients with unexplained ataxia-parkinsonism, while the newly identified rare genetic causes of ataxia-parkinsonism provide novel insights into molecular key pathways underlying the shared vulnerability of cerebellar and basal ganglia neurons.

Spinocerebellar ataxia type 14 caused by a nonsense mutation in the PRKCG gene

Spinocerebellar ataxia type 14 (SCA14) is an autosomal dominant neurodegenerative disorder characterized by cerebellar ataxia with myoclonus, dystonia, spasticity, and rigidity. Although missense mutations and a deletion mutation have been found in the protein kinase C gamma (PRKCG) gene encoding protein kinase C γ (PKCγ) in SCA14 families, a nonsense mutation has not been reported. The patho-mechanisms underlying SCA14 remain poorly understood. However, gain-of-function mechanisms and loss-of-function mechanisms, but not dominant negative mechanisms, were reported the patho-mechanism of SCA14. We identified the c.226C>T mutation of PRKCG, which caused the p.R76X in PKCγ by whole-exome sequencing in patients presenting cerebellar atrophy with cognitive and hearing impairment. To investigate the patho-mechanism of our case, we studied aggregation formation, cell death, and PKC inhibitory effect by confocal microscopy, western blotting with cleaved caspase 3, and pSer PKC motif antibodies, respectively. PKCγ(R76X)-GFP have aggregations the same as wild-type (WT) PKCγ-GFP. The PKCγ(R76X)-GFP inhibited PKC phosphorylation activity more than GFP alone. It also induced more apoptosis in COS7 and SH-SY5Y cells compared to WT-PKCγ-GFP and GFP. We first reported SCA14 patients with p.R76X in PKCγ who have cerebellar atrophy with cognitive and hearing impairment. Our results suggest that a dominant negative mechanism due to truncated peptides produced by p.R76X may be at least partially responsible for the cerebellar atrophy.

Genotype-phenotype correlations, dystonia and disease progression in spinocerebellar ataxia type 14

Background: Spinocerebellar ataxia type 14 is a rare form of autosomal dominant cerebellar ataxia caused by mutations in protein kinase Cγ gene. Clinically, it presents with a slowly progressive, mainly pure cerebellar ataxia.

Methods: Using next generation sequencing, we screened 194 families with autosomal dominant cerebellar ataxia and normal polyglutamine repeats. In‐depth phenotyping was performed using validated clinical rating scales neuroimaging and electrophysiological investigations.

Results: We identified 25 individuals from 13 families carrying pathogenic mutations in protein kinase Cγ gene. A total of 10 unique protein kinase Cγ gene mutations have been confirmed of which 5 are novel and 5 were previously described. Our data suggest that the age at onset is highly variable; disease course is slowly progressive and rarely associated with severe disability. However, one third of patients presented with a complex ataxia comprising severe focal and/or task‐induced dystonia, peripheral neuropathy, parkinsonism, myoclonus, and pyramidal syndrome. The most complex phenotype is related to a missense mutation in the catalytic domain in exon 11.

Conclusion: We present one of the largest genetically confirmed spinocerebellar ataxia type 14 cohorts contributing novel variants and clinical characterisation. We show that although protein kinase Cγ gene mutations present mainly as slowly progressive pure ataxia, more than a third of cases had a complex phenotype. Overall, our case series extends the phenotype and suggests that protein kinase Cγ gene mutations should be considered in patients with slowly progressive autosomal dominant cerebellar ataxia, particularly when myoclonus, dystonia, or mild cognitive impairment are present in the absence of polyglutamine expansion. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

The role of Pak-interacting exchange factor-β phosphorylation at serines 340 and 583 by PKCγ in dopamine release

Protein kinase C (PKC) has been implicated in the control of neurotransmitter release. The AS/AGU rat, which has a nonsense mutation in PKCγ, shows symptoms of parkinsonian syndrome, including dopamine release impairments in the striatum. Here, we found that the AS/AGU rat is PKCγ-knock-out (KO) and that PKCγ-KO mice showed parkinsonian syndrome. However, the PKCγ substrates responsible for the regulated exocytosis of dopamine in vivo have not yet been elucidated. To identify the PKCγ substrates involved in dopamine release, we used PKCγ-KO mice and a phosphoproteome analysis. We found 10 candidate phosphoproteins that had decreased phosphorylation levels in the striatum of PKCγ-KO mice. We focused on Pak-interacting exchange factor-β (βPIX), a Cdc42/Rac1 guanine nucleotide exchange factor, and found that PKCγ directly phosphorylates βPIX at Ser583 and indirectly at Ser340 in cells. Furthermore, we found that PKC phosphorylated βPIX in vivo. Classical PKC inhibitors and βPIX knock-down (KD) significantly suppressed Ca(2+)-evoked dopamine release in PC12 cells. Wild-type βPIX, and not the βPIX mutants Ser340 Ala or Ser583 Ala, fully rescued the decreased dopamine release by βPIX KD. Double KD of Cdc42 and Rac1 decreased dopamine release from PC12 cells. These findings indicate that the phosphorylation of βPIX at Ser340 and Ser583 has pivotal roles in Ca(2+)-evoked dopamine release in the striatum. Therefore, we propose that PKCγ positively modulates dopamine release through β2PIX phosphorylation. The PKCγ-βPIX-Cdc42/Rac1 phosphorylation axis may provide a new therapeutic target for the treatment of parkinsonian syndrome.

Functional genomics of the rat neuromedin U receptor 1 reveals a naturally occurring deleterious allele

Neuromedin U (NMU) plays an important role in a number of physiological processes, but the relative contribution of its two known receptors, NMUR1 and NMUR2, is still poorly understood. Here we report the existence of a SNP T1022→A (Val341→Glu) in the third exon of the rat Nmur1 gene that leads to an inactive receptor. This SNP is present within the coding region of the highly conserved NPXXY motif found within all class A type G protein-coupled receptors and translates to an NMUR1 receptor that is not expressed on the cell surface. Genetic analysis of the Nmur1 gene in a population of Sprague-Dawley rats revealed that this strain is highly heterogeneous for the inactivating polymorphism. The loss of functional NMUR1 receptors in Sprague-Dawley rats homozygous for the inactive allele was confirmed by radioligand binding studies on native tissue expressing NMUR1. The physiological relevance of this functional genomics finding was examined in two nociceptive response models. The pronociceptive effects of NMU were abolished in rats lacking functional NMUR1 receptors. The existence of naturally occurring NMUR1-deficient rats provides a novel and powerful tool to investigate the physiological role of NMU and its receptors. Furthermore, it highlights the importance of verifying the NMUR1 single nucleotide polymorphism status for rats used in physiological, pharmacological or toxicological studies conducted with NMUR1 modulators.

Functional protein kinase arrays reveal inhibition of p-21-activated kinase 4 by α-synuclein oligomers

There is increasing evidence that aggregation of alpha-synuclein contributes to the functional and structural deterioration in the CNS of Parkinson's disease patients and transgenic animal models. alpha-Synuclein binds to various cellular proteins and aggregated alpha-synuclein species may affect their physiological function. In the present study, we used protein arrays spotted with 178 active human kinases for a large-scale analysis of the effects of recombinant alpha-synuclein on kinase activities. Incubation with globular alpha-synuclein oligomers significantly inhibited autophosphorylation of p21-activated kinase (PAK4) compared to treatment with monomeric alpha-synuclein or beta-synuclein. A concentration-dependent inhibition was also observed in a solution-based kinase assay. To show in vivo relevance, we analyzed brainstem protein extracts from alpha-synuclein (A30P) transgenic mice where accumulation of alpha-synuclein oligomers has been demonstrated. By immunoblotting using a phospho-specific antibody, we detected a significant decline in phosphorylation of LIM kinase 1, a physiological substrate for PAK4. Suppression of PAK activity by amyloid-beta oligomers has been reported in Alzheimer's disease. Thus, PAKs may represent a target for various neurotoxic protein oligomers, and signaling deficits may contribute to the behavioral defects in chronic neurodegenerative diseases.

On autosomal dominant cerebellar ataxia (ADCA) other than polyglutamine diseases, with special reference to chromosome 16q22.1-linked ADCA

Autosomal dominant cerebellar ataxia (ADCA) is a group of heterogeneous conditions. More than 20 genes or gene loci have been identified that are responsible for ADCA. Although expansions of the trinucleotide (CAG) repeat that encode polyglutamine are known to cause some forms of ADCA, growing knowledge about the genetic basis of ADCA indicates that many subtypes of ADCA are caused by mutations other than the CAG repeat/polyglutamine expansion. In this paper, we review ADCA caused by mutations other than polyglutamine expansions (i.e. "non-polyglutamine diseases"). We also describe the neuropathology of chromosome 16q22.1-linked ADCA, which appears to be the most common non-polyglutamine disease in Japan. What we find to be characteristic on the chromosome 16q22.1-linked ADCA brain is the presence of atrophic Purkinje cells surrounded by the formation of amorphous material, the latter composed of the Purkinje cell dendrites stemming from the cell bodies, the presynaptic terminals innervated by certain neurons, and the astroglial processes. Such neuropathological findings seem to be unique for this disease.

New mutations in protein kinase Cgamma associated with spinocerebellar ataxia type 14

Autosomal dominant cerebellar ataxias (ADCA) are a heterogeneous group of neurological disorders. Point mutations in the gene encoding protein kinase Cgamma (PRKCG) are responsible for spinocerebellar ataxia 14 (SCA14). We screened for mutations in the PRKCG gene, in a large series of 284 ADCA index cases, mostly French (n=204) and German (n=48), in whom CAG repeat expansions in the known SCA genes were previously excluded. Six mutations were found that segregated with the disease and were not detected on 560 control chromosomes, including F643L (exon 18), already reported in another French kindred. Five new missense mutations were identified in exons 4 (C114Y/G123R/G123E), 10 (G360S) and 18 (V692G). All but one (V692G) were located in highly conserved regions of the regulatory or catalytic domains of the protein. All six SCA14 families were French and there was no evidence of reduced penetrance. The phenotype consisted in a very slowly progressive cerebellar ataxia with a mean age at onset of 33.5+/-14.2 years (range 15 to 60 years), occasionally associated with executive dysfunction, myoclonus, myorythmia, tremor or decreased vibration sense. SCA14 represented only 1.5% (7/454) of French ADCA families but none of the German families. It should, however, be considered in patients with slowly progressive ADCA, particularly when myoclonus and cognitive impairment are present.

Deficits in the mid-brain raphe nuclei and striatum of the AS/AGU rat, a protein kinase C-γ mutant

The AS/AGU rat carries a recessive mutation (agu) in the gene coding for the gamma isoform of protein kinase C. The rat is characterized by disordered locomotion and progressive dysfunction of the nigrostriatal dopaminergic (DA) system. This dysfunction begins with a failure to release DA within the striatum and culminates in cell loss within the substantia nigra pars compacta. The present study examines another midbrain aminergic system with input to the basal ganglia, the serotonergic (5-HT) raphe-striatal system originating in the dorsal raphe nucleus. By 3 months after birth, there is a very substantial reduction in the extracellular levels of 5-HT in the dorsal caudate-putamen of the mutants compared with controls (c. 70%). This is accompanied by a proportional increase in the levels of the 5-HT metabolite 5-hydroxyindole acetic acid (5-HIAA). At a later age, there are reductions in whole tissue 5-HT (and increases in 5-HIAA) in both the striatum and the region containing the dorsal raphe nucleus, as well as numbers of 5-HT-immunoreactive cells in the dorsal raphe nucleus. The median raphe appears to be unaffected. The results are seen in terms of an initial dysfunction in transmitter release leading to cell death, perhaps through the formation of free radicals or neurotoxins.

Involvement of gamma protein kinase C in estrogen-induced neuroprotection against focal brain ischemia through G protein-coupled estrogen receptor

The neuroprotective effects of estrogen were studied in the ischemic model mice by 90 min transient unilateral middle cerebral artery occlusion (MCAO) followed by 22.5 h reperfusion. The total infarct size in C57BL/6 female mice after MCAO and reperfusion was significantly smaller than that in male mice. Intraperitoneal injection of estrogen after the start of reperfusion significantly reduced the infarct volume in the male mice. However, no significant gender difference was found in total infarct size in gamma protein kinase C (PKC)-knockout mice, suggesting that the neuroprotective effects of estrogen are due to the activation of a specific subtype of PKC, gammaPKC, a neuron-specific PKC subtype, in the brain. We demonstrated that exogenous estrogen-induced neuroprotection was attenuated in gammaPKC-knockout mice. Immunocytochemical study showed that gammaPKC was translocated to nerve fiber-like structures when observed shortly after MCAO and reperfusion. We also visualized the rapid and reversible translocation of gammaPKC-GFP (green fluorescent protein) by estrogen stimulation in living CHO-K1 cells. These results suggest that the activation of gammaPKC through the G-protein-coupled estrogen receptors on the plasma membrane is involved in the estrogen-induced neuroprotection against focal brain ischemia.

Genetic contributions to Parkinson's disease

Sporadic Parkinson's disease (PD) is a common neurodegenerative disorder, characterized by the loss of midbrain dopamine neurons and Lewy body inclusions. It is thought to result from a complex interaction between multiple predisposing genes and environmental influences, although these interactions are still poorly understood. Several causative genes have been identified in different families. Mutations in two genes [alpha-synuclein and nuclear receptor-related 1 (Nurr1)] cause the same pathology, and a third locus on chromosome 2 also causes this pathology. Other familial PD mutations have identified genes involved in the ubiquitin-proteasome system [parkin and ubiquitin C-terminal hydroxylase L1 (UCHL1)], although such cases do not produce Lewy bodies. These studies highlight critical cellular proteins and mechanisms for dopamine neuron survival as disrupted in Parkinson's disease. Understanding the genetic variations impacting on dopamine neurons may illuminate other molecular mechanisms involved. Additional candidate genes involved in dopamine cell survival, dopamine synthesis, metabolism and function, energy supply, oxidative stress, and cellular detoxification have been indicated by transgenic animal models and/or screened in human populations with differing results. Genetic variation in genes known to produce different patterns and types of neurodegeneration that may impact on the function of dopamine neurons are also reviewed. These studies suggest that environment and genetic background are likely to have a significant influence on susceptibility to Parkinson's disease. The identification of multiple genes predisposing to Parkinson's disease will assist in determining the cellular pathway/s leading to the neurodegeneration observed in this disease.

Missense mutations in the regulatory domain of PKC gamma: a new mechanism for dominant nonepisodic cerebellar ataxia

We report a nonepisodic autosomal dominant (AD) spinocerebellar ataxia (SCA) not caused by a nucleotide repeat expansion that is, to our knowledge, the first such SCA. The AD SCAs currently comprise a group of > or =16 genetically distinct neurodegenerative conditions, all characterized by progressive incoordination of gait and limbs and by speech and eye-movement disturbances. Six of the nine SCAs for which the genes are known result from CAG expansions that encode polyglutamine tracts. Noncoding CAG, CTG, and ATTCT expansions are responsible for three other SCAs. Approximately 30% of families with SCA do not have linkage to the known loci. We recently mapped the locus for an AD SCA in a family (AT08) to chromosome 19q13.4-qter. A particularly compelling candidate gene, PRKCG, encodes protein kinase C gamma (PKC gamma), a member of a family of serine/threonine kinases. The entire coding region of PRKCG was sequenced in an affected member of family AT08 and in a group of 39 unrelated patients with ataxia not attributable to trinucleotide expansions. Three different nonconservative missense mutations in highly conserved residues in C1, the cysteine-rich region of the protein, were found in family AT08, another familial case, and a sporadic case. The mutations cosegregated with disease in both families. Structural modeling predicts that two of these amino acid substitutions would severely abrogate the zinc-binding or phorbol ester-binding capabilities of the protein. Immunohistochemical studies on cerebellar tissue from an affected member of family AT08 demonstrated reduced staining for both PKC gamma and ataxin 1 in Purkinje cells, whereas staining for calbindin was preserved. These results strongly support a new mechanism for neuronal cell dysfunction and death in hereditary ataxias and suggest that there may be a common pathway for PKC gamma-related and polyglutamine-related neurodegeneration.

The genetics of Parkinson's disease

The recent identification of several genes and gene loci linked to familial forms of Parkinson's disease (PD) has contributed significantly to our understanding of the genetic contribution in PD. Although the etiology of sporadic PD remains unknown, it is currently assumed that genetic susceptibilities may be involved. The advent of genome-wide scanning techniques has now made it possible to conduct complete genome screens for linkage in PD in multigenerational parkinsonian kindreds. Such studies undoubtedly will be instrumental in establishing the susceptibility genes involved in idiopathic PD. This article reviews the recent advances in the genetics of PD.

Long-term potentiation and adenosine sensitivity are unchanged in the AS/AGU protein kinase Cgamma-deficient rat

The AS/AGU rat is a spontaneously occurring mutation which exhibits locomotor abnormalities, reduced tyrosine hydroxylase levels in substantia nigra and lower extracellular levels of dopamine, making it a valuable model for some human locomotor disorders, and spontaneous chronic degeneration. The molecular defect is an absence of protein kinase Cgamma (PKCgamma), an enzyme suggested to play a role in synaptic plasticity. We have therefore examined long-term potentiation (LTP) in hippocampal slices from the mutant animals compared with the normal control strain of Albino Swiss rat. In the CA1 region, LTP was of the same magnitude in mutant and control animals, and the presynaptic inhibitory effects of adenosine were unchanged in naïve slices or following LTP. Paired-pulse inhibition and facilitation were normal. It is concluded that the absence of PKCgamma in this strain does not modify synaptic plasticity or presynaptic sensitivity to adenosine.