PPP2R2B CAG repeat length in the Han Chinese in Taiwan: Association analyses in neurological and psychiatric disorders and potential functional implications

Association between MAPK and PI3K/Akt signaling pathway-related gene polymorphisms and migraine

BACKGROUND

The causes of migraine remain unclear. Evidence suggests that the MAPK and PI3K/Akt signaling pathways play a role in migraine pathogenesis. However, studies on genetic polymorphisms in the two pathways associated with migraine are still limited.

METHODS

This study included 226 migraineurs and 452 age- and sex-matched nonmigraine control individuals. Genotyping of 31 Single Nucleotide Polymorphisms (SNPs) in 21 genes was performed. The relationship between migraine and gene polymorphisms was analyzed by using logistic regression. SNP-SNP interactions were examined by a generalized multifactor dimension reduction (GMDR) approach. The possible role of SNPs was evaluated with gene expression data from the GTEx database.

RESULTS

The RASGRP2-rs2230414 GT genotype was associated with decreased migraine risk compared with the wild-type GG genotype [ORadj (95% CI): 0.674(0.458-0.989)]. PIK3R1-rs3730089 was associated with migraine in the recessive model [ORadj (95% CI): 1.446(1.004-2.083)]. The CACNA1H-rs61734410 CT genotype was associated with migraine risk [ORadj (95% CI): 1.561(1.068-2.281)]. One significant two-way SNP-SNP interaction was found (PRKCA rs2228945-BDNF rs6265) (p = 0.0107). Significant eQTL and sQTL signals were observed for the SNP rs2230414.

CONCLUSIONS

This is the first study to systematically reveal significant associations between MAPK and PI3K/Akt signaling pathway-related gene polymorphisms and migraine risk.

Tremor-associated short tandem repeat intermediate and pathogenic expansions in familial essential tremor

There is an obvious clinical-pathological overlap between essential tremor and some known tremor-associated short tandem repeat expansion disorders. The aim is to analyse whether these short tandem repeat genes, including ATXN1, ATXN2, ATXN3, CACNA1A, ATXN7, ATXN8OS, ATXN10, PPP2R2B, TBP, BEAN1, NOP56, DAB1, ATN1, SADM12 and FMR1, are associated with familial essential tremor patients. Genetic analysis of repeat sizes in tremor-associated short tandem repeat expansions was performed in a large cohort of 515 familial essential tremor probands and 300 controls. The demographic and clinical features among carriers of pathogenic expansions, intermediate repeats and non-carriers were compared. A total of 18 out of 515 (18/515, 3.7%) patients were found to have repeats expansions, including 12 cases (12/515, 2.5%) with intermediate repeat expansions (one ATXN1, eight TBP, two FMR1, one ATN1), and six cases (6/515, 1.2%) with pathogenic expansions (one ATXN1, one ATXN2, one ATXN8OS, one PPP2R2B, one FMR1, one SAMD12). There were no statistically significant differences in intermediate repeats compared to healthy controls. Furthermore, there were no significant differences in demographics and clinical features among individuals with pathogenic expansions, intermediate repeat expansions carriers and non-carriers. Our study indicates that the intermediate repeat expansion in tremor-associated short tandem repeat expansions does not pose an increased risk for essential tremor, and rare pathogenic expansion carriers have been found in the familial essential tremor cohort. The diagnosis of essential tremor based solely on clinical symptoms remains a challenge in distinguishing it from known short tandem repeat expansions diseases with overlapping clinical-pathological features.

CUL4B mutations impair human cortical neurogenesis through PP2A-dependent inhibition of AKT and ERK

Mutation in CUL4B gene is one of the most common causes for X-linked intellectual disability (XLID). CUL4B is the scaffold protein in CUL4B-RING ubiquitin ligase (CRL4B) complex. While the roles of CUL4B in cancer progression and some developmental processes like adipogenesis, osteogenesis, and spermatogenesis have been studied, the mechanisms underlying the neurological disorders in patients with CUL4B mutations are poorly understood. Here, using 2D neuronal culture and cerebral organoids generated from the patient-derived induced pluripotent stem cells and their isogenic controls, we demonstrate that CUL4B is required to prevent premature cell cycle exit and precocious neuronal differentiation of neural progenitor cells. Moreover, loss-of-function mutations of CUL4B lead to increased synapse formation and enhanced neuronal excitability. Mechanistically, CRL4B complex represses transcription of PPP2R2B and PPP2R2C genes, which encode two isoforms of the regulatory subunit of protein phosphatase 2 A (PP2A) complex, through catalyzing monoubiquitination of H2AK119 in their promoter regions. CUL4B mutations result in upregulated PP2A activity, which causes inhibition of AKT and ERK, leading to premature cell cycle exit. Activation of AKT and ERK or inhibition of PP2A activity in CUL4B mutant organoids rescues the neurogenesis defect. Our work unveils an essential role of CUL4B in human cortical development.

Early-onset familial essential tremor is associated with nucleotide expansions of spinocerebellar ataxia in China

BACKGROUND

Essential tremor (ET) is a neurological disease characterized by action tremor in upper arms. Although its high heritability and prevalence worldwide, its etiology and association with other diseases are still unknown.

METHOD

We investigated 10 common spinocerebellar ataxias (SCAs), including SCA1, SCA2, SCA3, SCA6, SCA7, SCA8, SCA12, SCA17, SCA36, dentatorubral-pallidoluysian atrophy (DRPLA) in 92 early-onset familial ET pedigrees in China collected from 2016 to 2022.

RESULT

We found one SCA12 proband carried 51 CAG repeats within PPP2R2B gene and one SCA3 proband with intermediate CAG repeats (55) with ATXN3 gene. The other 90 ET probands all had normal repeat expansions.

CONCLUSION

Tremor can be the initial phenotype of certain SCA. For early-onset, familial ET patients, careful physical examinations are needed before genetic SCA screening.

Deletion or inhibition of prolyl oligopeptidase blocks lithium-induced phosphorylation of GSK3b and Akt by activation of protein phosphatase 2A

Alterations in prolyl oligopeptidase (PREP) activity have been connected, for example, with bipolar and major depressive disorder, and several studies have reported that lack or inhibition of PREP blocks the effects of lithium on inositol 1,4,5-triphosphate (IP₃ ) levels. However, the impact of PREP modulation on other intracellular targets of lithium, such as glycogen synthase kinase 3 beta (GSK3b) or protein kinase B (Akt), has not been studied. We recently found that PREP regulates protein phosphatase 2A (PP2A), and because GSK3b and Akt are PP2A substrates, we studied if PREP-related lithium insensitivity is dependent on PP2A. To assess this, HEK-293 and SH-SY5Y cells with PREP deletion or PREP inhibition (KYP-2047) were exposed to lithium, and thereafter, the phosphorylation levels of GSK3b and Akt were measured by Western blot. As expected, PREP deletion and inhibition blocked the lithium-induced phosphorylation on GSK3b and Akt in both cell lines. When lithium exposure was combined with okadaic acid, a PP2A inhibitor, KYP-2047 did not have effect on lithium-induced GSK3b and Akt phosphorylation. Therefore, we conclude that PREP deletion or inhibition blocks the intracellular effects of lithium on GSK3b and Akt via PP2A activation.

STRs: Ancient Architectures of the Genome beyond the Sequence

Short tandem repeats (STRs) are commonly defined as short runs of repetitive nucleotides, consisting of tandemly repeating 2-6- bp motif units, which are ubiquitously distributed throughout genomes. Functional STRs are polymorphic in the population, and their variations influence gene expression, which subsequently may result in pathogenic phenotypes. To understand STR phenotypic effects and their functional roles, we describe four different mutational mechanisms including the unequal crossing-over model, gene conversion, retrotransposition mechanism and replication slippage. Due to the multi-allelic nature, small length, abundance, high variability, codominant inheritance, nearly neutral evolution, extensive genome coverage and simple assaying of STRs, these markers are widely used in various types of biological research, including population genetics studies, genome mapping, molecular epidemiology, paternity analysis and gene flow studies. In this review, we focus on the current knowledge regarding STR genomic distribution, function, mutation and applications.

Genetic Risk Factors for Essential Tremor: A Review

Highlights

In the current review, we thoroughly reviewed 74 identified articles regarding genes and genetic loci that confer susceptibility to ET. Over 50 genes/genetic loci have been examined for possible association with ET, but consistent results failed to be reported raising the need for collaborative multiethnic studies.

Background:

Essential tremor (ET) is a common movement disorder, which is mainly characterized by bilateral tremor (postural and/or kinetic) in the upper limbs, with other parts of the body possibly involved. While the pathophysiology of ET is still unclear, there is accumulating evidence indicating that genetic variability may be heavily involved in ET pathogenesis. This review focuses on the role of genetic risk factors in ET susceptibility.

Methods:

The PubMed database was searched for articles written in English, for studies with humans with ET, controls without ET, and genetic variants. The terms “essential tremor” and “polymorphism” (as free words) were used during search. We also performed meta-analyses for the most examined genetic variants.

Results:

Seventy four articles concerning LINGO1, LINGO2, LINGO4, SLC1A2, STK32B, PPARGC1A, CTNNA3, DRD3, ALAD, VDR, HMOX1, HMOX2, LRRK1,LRRK2, GBA, SNCA, MAPT, FUS, CYPsIL17A, IL1B, NOS1, ADH1B, TREM2, RIT2, HNMT, MTHFR, PPP2R2B, GSTP1, PON1, GABA receptors and GABA transporter, HS1BP3, ADH2, hSKCa3 and CACNL1A4 genes, and ETM genetic loci were included in the current review. Results from meta-analyses revealed a marginal association for the STK32B rs10937625 and a marginal trend for association (in sensitivity analysis) for the LINGO1 rs9652490, with ET.

Discussion:

Quite a few variants have been examined for their possible association with ET. LINGO1 rs9652490 and STK32B rs10937625 appear to influence, to some extent, ET susceptibility. However, the conflicting results and the lack of replication for many candidate genes raise the need for collaborative multiethnic studies.

PPP2R2B hypermethylation causes acquired apoptosis deficiency in systemic autoimmune diseases

Chronic inflammation causes target organ damage in patients with systemic autoimmune diseases. The factors that allow this protracted response are poorly understood. We analyzed the transcriptional regulation of PPP2R2B (B55ß), a molecule necessary for the termination of the immune response, in patients with autoimmune diseases. Altered expression of B55ß conditioned resistance to cytokine withdrawal-induced death (CWID) in patients with autoimmune diseases. The impaired upregulation of B55ß was caused by inflammation-driven hypermethylation of specific cytosines located within a regulatory element of PPP2R2B preventing CTCF binding. This phenotype could be induced in healthy T cells by exposure to TNF-α. Our results reveal a gene whose expression is affected by an acquired defect, through an epigenetic mechanism, in the setting of systemic autoimmunity. Because failure to remove activated T cells through CWID could contribute to autoimmune pathology, this mechanism illustrates a vicious cycle through which autoimmune inflammation contributes to its own perpetuation.

Neuropathology and Cellular Pathogenesis of Spinocerebellar Ataxia Type 12

OBJECTIVE

SCA12 is a progressive autosomal-dominant disorder, caused by a CAG/CTG repeat expansion in PPP2R2B on chromosome 5q32, and characterized by tremor, gait ataxia, hyperreflexia, dysmetria, abnormal eye movements, anxiety, depression, and sometimes cognitive impairment. Neuroimaging has demonstrated cerebellar and cortical atrophy. We now present the neuropathology of the first autopsied SCA12 brain and utilize cell models to characterize potential mechanisms of SCA12 neurodegeneration.

METHODS

A fixed SCA12 brain was examined using gross, microscopic, and immunohistochemical methods. The effect of the repeat expansion on PPP2R2B Bβ1 expression was examined in multiple cell types by transient transfection of constructs containing the PPP2R2B Bβ1 promoter region attached to a luciferase reporter. The neurotoxic effect of PPP2R2B overexpression was examined in transfected rat primary neurons.

RESULTS

Neuropathological investigation revealed enlarged ventricles, marked cerebral cortical atrophy and Purkinje cell loss, less-prominent cerebellar and pontine atrophy, and neuronal intranuclear ubiquitin-positive inclusions, consistent with Marinesco bodies, which did not stain for long polyglutamine tracts, alpha-synuclein, tau, or transactive response DNA-binding protein 43. Reporter assays demonstrated that the region of PPP2R2B containing the repeat functions as a promoter, and that promoter activity increases with longer repeat length and is dependent on cell type, repeat sequence, and sequence flanking the repeat. Overexpression of PPP2R2B in primary cortical neurons disrupted normal morphology.

CONCLUSIONS

SCA12 involves extensive, but selective, neurodegeneration distinct from Alzheimer's disease, synucleinopathies, tauopathies, and glutamine expansion diseases. SCA12 neuropathology may arise from the neurotoxic effect of repeat-expansion-induced overexpression of PPP2R2B.

Identification of two inherited copy number variants in a male with autism supports two-hit and compound heterozygosity models of autism

Autism is a childhood-onset neurodevelopmental disorder with complex genetic mechanism underlying its etiology. Recent studies revealed that a few single de novo copy number variants of genomic DNA (copy number variants [CNVs]) are pathogenic and causal in some sporadic cases, adding support to the hypothesis that some sporadic autism might be caused by single rare mutation with large clinical effect. In this study, we report the detection of two novel private CNVs simultaneously in a male patient with autism. These two CNVs include a microduplication of ~4.5 Mb at chromosome 4q12-13.1 that was transmitted from his mother and a microdeletion of ~1.8 Mb at 5q32 that was transmitted from his father. Several genes such as LPHN3, POU4F3, SH3RF2, and TCERG1 mapped to these two regions have psychiatric implications. However, the parents had only mild degree of attention deficit symptoms but did not demonstrate any obvious autistic symptoms or psychopathology. Our findings indicate that each of these two CNVs alone may not be pathogenic enough to cause clinical symptoms in their respective carriers, and hence they can be transmitted within each individual family. However, concomitant presence of these two CNVs might result in the clinical phenotypes of the affected patient reported here. Thus, our report of this family may represent an example to show that two hits of CNV and the presence of compound heterozygosity might be important mechanisms underlying the pathogenesis of autism.

Identification and functional analysis of variant haplotypes in the 5'-flanking region of protein phosphatase 2A-Bδ gene

Serine-threonine protein phosphatase 2A (PP2A) is a trimeric holoenzyme that plays an integral role in the regulation of cell growth, differentiation, and apoptosis. The substrate specificity and (sub)cellular localization of the PP2A holoenzymes are highly regulated by interaction with a family of regulatory B subunits (PP2A-Bs). The regulatory subunit PP2A-B/PR55δ (PP2A-Bδ) is involving in the dephosphorylation of PP2A substrates and is crucial for controlling entry into and exit from mitosis. The molecular mechanisms involved in the regulation of expression of PP2A-Bδ gene (PPP2R2D) remain largely unknown. To explore genetic variations in the 5′-flanking region of PPP2R2D gene as well as their frequent haplotypes in the Han Chinese population and determine whether such variations have an impact on transcriptional activity, DNA samples were collected from 70 healthy Chinese donors and sequenced for identifying genetic variants in the 5′-flanking region of PPP2R2D. Four genetic variants were identified in the 1836 bp 5′-flanking region of PPP2R2D. Linkage disequilibrium (LD) patterns and haplotype profiles were constructed for the genetic variants. Using serially truncated human PPP2R2D promoter luciferase constructs, we found that a 601 bp (−540 nt to +61 nt) fragment constitutes the core promoter region. The subcloning of individual 5′-flanking fragment revealed the existence of three haplotypes in the distal promoter of PPP2R2D. The luciferase reporter assay showed that different haplotypes exhibited distinct promoter activities. The EMSA revealed that the −462 G>A variant influences DNA-protein interactions involving the nuclear factor 1 (NF1). In vitro reporter gene assay indicated that cotransfection of NF1/B expression plasmid could positively regulate the activity of PPP2R2D proximal promoter. Introduction of exogenous NF1/B expression plasmid further confirmed that the NF1 involves in the regulation of PPP2R2D gene expression. Our findings suggest that functional genetic variants and their haplotypes in the 5′-flanking region of PPP2R2D are critical for transcriptional regulation of PP2A-Bδ.

Role of the CCAAT-binding protein NFY in SCA17 pathogenesis

Spinocerebellar ataxia 17 (SCA17) is caused by expansion of the polyglutamine (polyQ) tract in human TATA-box binding protein (TBP) that is ubiquitously expressed in both central nervous system and peripheral tissues. The spectrum of SCA17 clinical presentation is broad. The precise pathogenic mechanism in SCA17 remains unclear. Previously proteomics study using a cellular model of SCA17 has revealed reduced expression of heat shock 70 kDa protein 5 (HSPA5) and heat shock 70 kDa protein 8 (HSPA8), suggesting that impaired protein folding may contribute to the cell dysfunction of SCA17 (Lee et al., 2009). In lymphoblastoid cells, HSPA5 and HSPA8 expression levels in cells with mutant TBP were also significantly lower than that of the control cells (Chen et al., 2010). As nuclear transcription factor Y (NFY) has been reported to regulate HSPA5 transcription, we focused on if NFY activity and HSPA5 expression in SCA17 cells are altered. Here, we show that TBP interacts with NFY subunit A (NFYA) in HEK-293 cells and NFYA incorporated into mutant TBP aggregates. In both HEK-293 and SH-SY5Y cells expressing TBP/Q(61~79), the level of soluble NFYA was significantly reduced. In vitro binding assay revealed that the interaction between TBP and NFYA is direct. HSPA5 luciferase reporter assay and endogenous HSPA5 expression analysis in NFYA cDNA and siRNA transfection cells further clarified the important role of NFYA in regulating HSPA5 transcription. In SCA17 cells, HSPA5 promoter activity was activated as a compensatory response before aggregate formation. NFYA dysfunction was indicated in SCA17 cells as HSPA5 promoter activity reduced along with TBP aggregate formation. Because essential roles of HSPA5 in protection from neuronal apoptosis have been shown in a mouse model, NFYA could be a target of mutant TBP in SCA17.

Protein phosphatases and Alzheimer's disease

Alzheimer's Disease (AD) is characterized by progressive loss of cognitive function, linked to marked neuronal loss. Pathological hallmarks of the disease are the accumulation of the amyloid-β (Aβ) peptide in the form of amyloid plaques and the intracellular formation of neurofibrillary tangles (NFTs). Accumulating evidence supports a key role for protein phosphorylation in both the normal and pathological actions of Aβ as well as the formation of NFTs. NFTs contain hyperphosphorylated forms of the microtubule-binding protein tau, and phosphorylation of tau by several different kinases leads to its aggregation. The protein kinases involved in the generation and/or actions of tau or Aβ are viable drug targets to prevent or alleviate AD pathology. However, it has also been recognized that the protein phosphatases that reverse the actions of these protein kinases are equally important. Here, we review recent advances in our understanding of serine/threonine and tyrosine protein phosphatases in the pathology of AD.

Mitochondrial dysfunction and oxidative stress contribute to the pathogenesis of spinocerebellar ataxia type 12 (SCA12)

Spinal cerebellar ataxia type 12 (SCA12) has been attributed to the elevated expression of ppp2r2b. To better elucidate the pathomechanism of the neuronal disorder and to search for a pharmacological treatment, Drosophila models of SCA12 were generated by overexpression of a human ppp2r2b and its Drosophila homolog tws. Ectopic expression of ppp2r2b or tws caused various pathological features, including neurodegeneration, apoptosis, and shortened life span. More detailed analysis revealed that elevated ppp2r2b and tws induced fission of mitochondria accompanied by increases in cytosolic reactive oxygen species (ROS), cytochrome c, and caspase 3 activity. Transmission electron microscopy revealed that fragmented mitochondria with disrupted cristae were engulfed by autophagosomes in photoreceptor neurons of flies overexpressing tws. Additionally, transgenic flies were more susceptible to oxidative injury induced by paraquat. By contrast, ectopic Drosophila Sod2 expression and antioxidant treatment reduced ROS and caspase 3 activity and extended the life span of the SCA12 fly model. In summary, our study demonstrates that oxidative stress induced by mitochondrial dysfunction plays a causal role in SCA12, and reduction of ROS is a potential therapeutic intervention for this neuropathy.

Drosophila notal bristle as a novel assessment tool for pathogenic study of Tau toxicity and screening of therapeutic compounds

To elucidate the Tau gain-of-toxicity functional mechanism and to search for potential treatments, we overexpressed human Tau variants (hTau) in the dorsal mesothorax (notum) of Drosophila. Overexpression of Tau variants caused loss of notal bristles, and the phenotype was used for evaluating toxicity of ectopic Tau. The bristle loss phenotype was found to be highly associated with the toxicity of hyperphosphoryled Tau in flies. We have shown that the bristle loss phenotype can be rescued either by reducing Glycogen synthase kinase 3beta (GSK3beta)/Shaggy (Sgg) activity or overexpressing Bbeta2 regulatory subunits of PP2A. Elevated expression of the Drosophila Bbeta2 homolog, Twins (Tws), also alleviated neuritic dystrophy of the dorsal arborization (da) neuron caused by Tau aggregation. Additionally, lowering endogenous Tau dosage was beneficial as it ameliorated the bristle loss phenotype. Finally, the bristle loss phenotype was used to evaluate the efficacy of potential therapeutic compounds. The GSK3beta inhibitor, alsterpaullone, was found to suppress toxicity of Tau in a concentration-dependent manner. The notum of Drosophila, thus, provides a new tool and insights into Tau-induced toxicity. It could also potentially assist in screening new drugs for possible therapeutic intervention.