A Single-Year Cosmic Ray Event at 5410 BCE Registered in 14C of Tree Rings

The annual 14C data in tree rings is an outstanding proxy for uncovering extreme solar energetic particle (SEP) events in the past. Signatures of extreme SEP events have been reported in 774/775 CE, 992/993 CE, and ∼660 BCE. Here, we report another rapid increase of 14C concentration in tree rings from California, Switzerland, and Finland around 5410 BCE. These 14C data series show a significant increase of ∼6‰ in 5411-5410 BCE. The signature of 14C variation is very similar to the confirmed three SEP events and points to an extreme short-term flux of cosmic ray radiation into the atmosphere. The rapid 14C increase in 5411/5410 BCE rings occurred during a period of high solar activity and 60 years after a grand 14C excursion during 5481-5471 BCE. The similarity of our 14C data to previous events suggests that the origin of the 5410 BCE event is an extreme SEP event.

Age-related dysfunction of the autophago-lysosomal pathway in human endothelial cells

Senescent cells, which are cells in a post-proliferative state, show an increased number of dysfunctional mitochondria and oxidatively damaged and aggregated proteins. The mitochondrial-lysosomal axis theory of aging proposes that the autophago-lysosomal system is unable to cope with the rising amount of damaged organelles and proteins. We used human umbilical vein endothelial cells (HUVEC) as in vitro model system to determine which part/s of the autophago-lysosomal pathway become deficient by aging. Senescent HUVEC contained a much larger population of autophagosomes and lysosomes compared to young cells. Transcriptome analysis comparing young and old cells demonstrated several age-related changes of autophagy gene expression. One reason for the observed increase of autophagosomes was an impairment of the autophagic flux in senescent cells due to reduced V-ATPase activity required for acidification of the lysosomes and thus functionality of lysosomal hydrolases. The hypothesis that reduced mitochondrial ATP production underlies low V-ATPase activity was supported by addition of exogenous ATP. This procedure rescued the lysosomal acidification and restored the autophagic flux. Thus, we propose impaired lysosomal acidification due to ATP shortage which may result from mitochondrial dysfunction as a mechanism underlying the accumulation of dysfunctional cellular constituents during aging.

Polymorphism in Tmem132d regulates expression and anxiety-related behavior through binding of RNA polymerase II complex

TMEM132D is a candidate gene, where risk genotypes have been associated with anxiety severity along with higher mRNA expression in the frontal cortex of panic disorder patients. Concurrently, in a high (HAB) and low (LAB) trait anxiety mouse model, Tmem132d was found to show increased expression in the anterior cingulate cortex (aCC) of HAB as compared to LAB mice. To understand the molecular underpinnings underlying the differential expression, we sequenced the gene and found two single-nucleotide polymorphisms (SNPs) in the promoter differing between both lines which could explain the observed mRNA expression profiles using gene reporter assays. In addition, there was no difference in basal DNA methylation in the CpG Island that encompasses the HAB vs. LAB Tmem132d promoter region. Furthermore, we found significantly higher binding of RNA polymerase II (POLR2A) to the proximal HAB-specific SNP (rs233264624) than the corresponding LAB locus in an oligonucleotide pull-down assay, suggesting increased transcription. Virus mediated overexpression of Tmem132d in the aCC of C57BL/6 J mice could confirm its role in mediating an anxiogenic phenotype. To model gene-environmental interactions, HAB mice exposed to enriched environment (HAB-EE) responded with decreased anxiety levels but, had enhanced Tmem132d mRNA expression as compared to standard-housed HAB (HAB-SH) mice. While LAB mice subjected to unpredictable chronic mild stress (LAB-UCMS) exhibited higher anxiety levels and had lower mRNA expression compared to standard-housed LAB (LAB-SH) mice. Chromatin immunoprecipitation revealed significantly higher binding of POLR2A to rs233264624 in HAB-EE, while LAB-UCMS had lower POLR2A binding at this locus, thus explaining the enhanced or attenuated expression of Tmem132d compared to their respective SH controls. To further investigate gene-environment interactions, DNA methylation was assessed using Illumina 450 K BeadChip in 74 panic disorder patients. Significant methylation differences were observed in two CpGs (cg26322591 and cg03283235) located in TMEM132D depending on the number of positive life events supporting the results of an influence of positive environmental cues on regulation of Tmem132d expression in mice.

Blood RNA biomarkers in prodromal PARK4 and rapid eye movement sleep behavior disorder show role of complexin 1 loss for risk of Parkinson's disease

Parkinson's disease (PD) is a frequent neurodegenerative process in old age. Accumulation and aggregation of the lipid-binding SNARE complex component α-synuclein (SNCA) underlies this vulnerability and defines stages of disease progression. Determinants of SNCA levels and mechanisms of SNCA neurotoxicity have been intensely investigated. In view of the physiological roles of SNCA in blood to modulate vesicle release, we studied blood samples from a new large pedigree with SNCA gene duplication (PARK4 mutation) to identify effects of SNCA gain of function as potential disease biomarkers. Downregulation of complexin 1 (CPLX1) mRNA was correlated with genotype, but the expression of other Parkinson's disease genes was not. In global RNA-seq profiling of blood from presymptomatic PARK4 indviduals, bioinformatics detected significant upregulations for platelet activation, hemostasis, lipoproteins, endocytosis, lysosome, cytokine, Toll-like receptor signaling and extracellular pathways. In PARK4 platelets, stimulus-triggered degranulation was impaired. Strong SPP1, GZMH and PLTP mRNA upregulations were validated in PARK4. When analysing individuals with rapid eye movement sleep behavior disorder, the most specific known prodromal stage of general PD, only blood CPLX1 levels were altered. Validation experiments confirmed an inverse mutual regulation of SNCA and CPLX1 mRNA levels. In the 3'-UTR of the CPLX1 gene we identified a single nucleotide polymorphism that is significantly associated with PD risk. In summary, our data define CPLX1 as a PD risk factor and provide functional insights into the role and regulation of blood SNCA levels. The new blood biomarkers of PARK4 in this Turkish family might become useful for PD prediction.

Age-Related Changes of 14-3-3 Isoforms in Midbrain of A53T-SNCA Overexpressing Mice

BACKGROUND

Parkinson's disease (PD) is characterized by loss of midbrain dopaminergic neurons, which are affected by cytoplasmic inclusions, named Lewy pathology. The main component is alpha-synuclein (SNCA), a protein modulating SNARE-complex dependent neurotransmission. SNCA mutations trigger dominantly inherited PD variants and sporadic cases of PD via aggregation and transmission. SNCA and isoforms of the 14-3-3 family show sequence homology, protein interaction and joint aggregation, so 14-3-3 s may be key molecules of pathogenesis.

OBJECTIVE

We aimed to identify the relevant isoforms in midbrain and to distinguish for the first time the changes that occur very early versus those that progress with pathology.

METHODS

We assessed expression of the 14-3-3 family with quantitative RT-PCR and immunoblots of differential solubility fractions in mice with A53T-SNCA overexpression longitudinally at different ages.

RESULTS

Transcript levels showed reductions at age 3 months with increases at later ages for the beta, eta and zeta isoforms. Protein levels at age 3 months exhibited a concordant reduction only for beta, while increased insolubility was observed for epsilon and zeta. At age 18 months only the reduction of 14-3-3 beta protein remained significant. Thus, the toxic gain-of-function of alpha-synuclein leads to early transitory alterations of several 14-3-3 isoforms. When the levels of soluble 14-3-3 proteins become apparently normal during later life, increasing amounts of beta, eta and zeta mRNA are produced, possibly to compensate for protein insolubility and aggregation in a SNCA/14-3-3 complex.

CONCLUSIONS

These data may contribute to identify key molecular events that reflect Parkinson's disease risk and progression.

Loss of lysosome-associated membrane protein 3 (LAMP3) enhances cellular vulnerability against proteasomal inhibition

The family of lysosome-associated membrane proteins (LAMP) includes the ubiquitously expressed LAMP1 and LAMP2, which account for half of the proteins in the lysosomal membrane. Another member of the LAMP family is LAMP3, which is expressed only in certain cell types and differentiation stages. LAMP3 expression is linked with poor prognosis of certain cancers, and the locus where it is encoded was identified as a risk factor for Parkinson's disease (PD). Here, we investigated the role of LAMP3 in the two main cellular degradation pathways, the proteasome and autophagy. LAMP3 mRNA was not detected in mouse models of PD or in the brain of human patients. However, it was strongly induced upon proteasomal inhibition in the neuroblastoma cell line SH-SY5Y. Induction of LAMP3 mRNA following proteasomal inhibition was dependent on UPR transcription factor ATF4 signaling and induced autophagic flux. Prevention of LAMP3 induction enhanced apoptotic cell death. In summary, these data demonstrate that LAMP3 regulation as part of the UPR contributes to protein degradation and cell survival during proteasomal dysfunction. This link between autophagy and the proteasome may be of special importance for the treatment of tumor cells with proteasomal inhibitors.

Potentiation of neurotoxicity in double-mutant mice with Pink1 ablation and A53T-SNCA overexpression

The common age-related neurodegeneration of Parkinson's disease can result from dominant causes like increased dosage of vesicle-associated alpha-synuclein (SNCA) or recessive causes like deficiency of mitophagy factor PINK1. Interactions between these triggers and their convergence onto shared pathways are crucial, but currently conflicting evidence exists. Here, we crossed previously characterized mice with A53T-SNCA overexpression and with Pink1 deletion to generate double mutants (DMs). We studied their lifespan and behavior, histological and molecular anomalies at late and early ages. DM animals showed potentiated phenotypes in comparison with both single mutants (SMs), with reduced survival and strongly reduced spontaneous movements from the age of 3 months onwards. In contrast to SMs, a quarter of DM animals manifested progressive paralysis at ages >1 year and exhibited protein aggregates immunopositive for pSer129-SNCA, p62 and ubiquitin in spinal cord and basal brain. Brain proteome quantifications of ubiquitination sites documented altered degradation of SNCA and the DNA-damage marker H2AX at the age of 18 months. Global brain transcriptome profiles and qPCR validation experiments identified many consistent transcriptional dysregulations already at the age of 6 weeks, which were absent from SMs. The observed downregulations for Dapk1, Dcaf17, Rab42 and the novel SNCA-marker Lect1 as well as the upregulations for Dctn5, Mrpl9, Tmem181a, Xaf1 and H2afx reflect changes in ubiquitination, mitochondrial/synaptic/microtubular/cell adhesion dynamics and DNA damage. Thus, our study confirmed that SNCA-triggered neurotoxicity is exacerbated by the absence of PINK1 and identified a novel molecular signature that is detectable early in the course of this double pathology.

Complexin-1 and Foxp1 Expression Changes Are Novel Brain Effects of Alpha-Synuclein Pathology

As the second most frequent neurodegenerative disorder of the aging population, Parkinson’s disease (PD) is characterized by progressive deficits in spontaneous movement, atrophy of dopaminergic midbrain neurons and aggregation of the protein alpha-synuclein (SNCA). To elucidate molecular events before irreversible cell death, we studied synucleinopathy-induced expression changes in mouse brain and identified 49 midbrain/brainstem-specific transcriptional dysregulations. In particular complexin-1 (Cplx1), Rabl2a and 14-3-3epsilon (Ywhae) downregulation, as well as upregulation of the midbrain-specific factor forkhead box P1 (Foxp1) and of Rabgef1, were interesting as early mRNA level effects of alpha-synuclein triggered pathology. The protein levels of complexin-1 were elevated in midbrain/brainstem tissue of mice with A53T-SNCA overexpression and of mice with SNCA-knockout. The response of CPLX1 and Foxp1 levels to SNCA deficiency supports the notion that these factors are regulated by altered physiological function of alpha-synuclein. Thus, their analysis might be useful in PD stages before the advent of Lewy pathology. Because both alpha-synuclein and complexin-1 modulate vesicle release, our findings support presynaptic dysfunction as an early event in PD pathology.