Genetic architecture of protein expression and its regulation in the mouse brain

Background Natural variation in protein expression is common in all organisms and contributes to phenotypic differences among individuals. While variation in gene expression at the transcript level has been extensively investigated, the genetic mechanisms underlying variation in protein expression have lagged considerably behind. Here we investigate genetic architecture of protein expression by profiling a deep mouse brain proteome of two inbred strains, C57BL/6 J (B6) and DBA/2 J (D2), and their reciprocal F1 hybrids using two-dimensional liquid chromatography coupled with tandem mass spectrometry (LC/LC-MS/MS) technology. Results By comparing protein expression levels in the four mouse strains, we observed 329 statistically significant differentially expressed proteins between the two parental strains and characterized the genetic basis of protein expression. We further applied a proteogenomic approach to detect variant peptides and define protein allele-specific expression (pASE), identifying 33 variant peptides with cis-effects and 17 variant peptides showing trans-effects. Comparison of regulation at transcript and protein levels show a significant divergence. Conclusions The results provide a comprehensive analysis of genetic architecture of protein expression and the contribution of cis- and trans-acting regulatory differences to protein expression.

Integrative analysis of proteome-wide association and transcriptome-wide association study identifies candidate brain proteins associated with insomnia

Great progress has been made in identifying risk loci for insomnia by genome-wide association studies (GWAS) analysis, but its association with human brain proteome is unclear. Two insomnia GWAS summary datasets were derived from deCODE (n = 113,006) and 23andMe (n = 1,331,010). Two human brain proteomic datasets were obtained from ROS/MAP and Banner, and two reference datasets were obtained from brain RNA-seq (CBR) and RNA-seq splicing (CBRS). Proteome-wide association study (PWAS) was first used to detect brain proteins associated with insomnia at the translation level. Transcriptome-wide association study (TWAS) was then used to verify the results at the DNA level. Finally, brain imaging GWAS was used to explore the brain functional areas related to the identified brain proteins and genes in insomnia. PWAS identified 4 and 1 common proteins shared by two human brain proteomic datasets in insomnia GWAS dataset 1 and 2, such as ME1 (PDataset1−Banner−full=1.08×10−2, PDataset1−ROS/MAP−full=8.21×10−3). Further TWAS identified 5 and 1 candidate genes shared by the two reference expression profiles in dataset 1 and 2, like ICA1L (PDataset2−CBR=3.01×10−2, PDataset2−CBRS=3.24×10−2). CAMLG was observed to associate with insomnia in both PWAS (PDataset2−ROS/MAP=2.94×10−2) and TWAS (PDataset2−CBR=1.11×10−2). Comparing the results of PWAS and TWAS, there are 9 common proteins and genes shared by both two datasets, such as INPP4A. Brain imaging analysis found that insomnia associated proteins and genes were functionally related to cortex. Our results may reinforce the understanding of the etiology and pathophysiology of insomnia and provide promising brain protein targets for further therapeutic and mechanistic studies.

A Proteome-Wide Association Study Identified Candidate Human Brain Proteins Associated with Coffee Consumption

Background Increasing evidence suggests the association between caffeine and the brain and nervous system. However, there is limited research on the genetic associations between coffee consumption subtypes and brain proteome, plasma proteomes, and peripheral metabolites. Methods First, proteome-wide association study (PWAS) of coffee consumption subtypes was performed by integrating two independent genome-wide association study (GWAS) datasets (91,462–502,650 subjects) with two reference human brain proteomes (ROS/MAP and Banner), by using the FUSION pipeline. Second, transcriptome-wide association study (TWAS) analysis of coffee consumption subtypes was conducted by integrating the two gene expression weight references (RNAseq and splicing) of brain RNA-seq and the two GWAS datasets (91,462–502,650 subjects) of coffee consumption subtypes. Finally, we used the LD Score Regression (LDSC) analysis to evaluate the genetic correlations of coffee consumption subtypes with plasma proteomes and peripheral metabolites. Results For the traits related to coffee consumption, we identified 3 common PWAS proteins, such as MADD (P PWAS−Banner−dis=0.0114, P PWAS−ROS/MAP−rep =0.0489). In addition, 11 common TWAS genes were found in two cohorts, such as ARPC2 (P TWAS−splicing−dis =2063×10− 12, P TWAS−splicing−dis =1.25×10− 10, P TWAS−splicing−dis =1.24e-08, P TWAS−splicing−rep =3.25×10− 9 and P TWAS−splicing−rep =3.42×10− 13). Importantly, we have identified 8 common genes between PWAS and TWAS, such as ALDH2 (P PWAS−banner−rep =1.22×10− 22, PTWAS− splicing−dis = 4.54×10− 92). For the LDSC analysis of human plasma proteome, we identified 11 plasma proteins, such as CHL1 (P dis = 0.0151, P rep =0.0438). For the LDSC analysis of blood metabolites, 5 metabolites have been found, such as myo-inositol (P dis = 0.0073, P dis = 0.0152, P dis =0.0414, P rep =0.0216). Conclusions We identified several brain proteins and genes associated with coffee consumption subtypes. In addition, we also detected several candidate plasma proteins and metabolites related to these subtypes.

Molecular Effects of Pteryxin and Scopoletin in the 5xFAD Alzheimer’s Disease Mouse Model

Background: Alzheimer’s disease (AD) is one of the most prevalent diseases with rapidly increasing numbers, but there is still no medication to treat or stop the disease. Previous data on coumarins suggests that scopoletin may have potential benefits in AD. Objective: Evaluate the therapeutic potential of the coumarins with natural origin - scopoletin and pteryxin in a 5xFAD mouse model of AD Methods: Both compounds were administered at two doses to 12-month-old mice, which represent severe AD pathology. The effects of coumarins were assessed on cognition in mouse experiments. Changes in the overall brain proteome were evaluated using LC-MS/MS analyses. Results: The Morris water maze test implicated that a higher dose of pteryxin (16 mg/kg) significantly improved learning, and the proteome analysis showed pronounced changes of specific proteins upon pteryxin administration. The amyloid-β precursor protein, glial fibrillary acid protein, and apolipoprotein E protein which are highly associated with AD, were among the differentially expressed proteins at the higher dose of the pteryxin. Conclusion: Overall, pteryxin may be evaluated further as a disease-modifying agent in AD pathology in the late stages of AD.

Proteomic Analysis of Hydromethylthionine in the Line 66 Model of Frontotemporal Dementia Demonstrates Actions on Tau-Dependent and Tau-Independent Networks

Abnormal aggregation of tau is the pathological hallmark of tauopathies including frontotemporal dementia (FTD). We have generated tau-transgenic mice that express the aggregation-prone P301S human tau (line 66). These mice present with early-onset, high tau load in brain and FTD-like behavioural deficiencies. Several of these behavioural phenotypes and tau pathology are reversed by treatment with hydromethylthionine but key pathways underlying these corrections remain elusive. In two proteomic experiments, line 66 mice were compared with wild-type mice and then vehicle and hydromethylthionine treatments of line 66 mice were compared. The brain proteome was investigated using two-dimensional electrophoresis and mass spectrometry to identify protein networks and pathways that were altered due to tau overexpression or modified by hydromethylthionine treatment. Overexpression of mutant tau induced metabolic/mitochondrial dysfunction, changes in synaptic transmission and in stress responses, and these functions were recovered by hydromethylthionine. Other pathways, such as NRF2, oxidative phosphorylation and protein ubiquitination were activated by hydromethylthionine, presumably independent of its function as a tau aggregation inhibitor. Our results suggest that hydromethylthionine recovers cellular activity in both a tau-dependent and a tau-independent fashion that could lead to a wide-spread improvement of homeostatic function in the FTD brain.

Neuronal Nsun2 deficiency produces tRNA epitranscriptomic alterations and proteomic shifts impacting synaptic signaling and behavior

Epitranscriptomic mechanisms linking tRNA function and the brain proteome to cognition and complex behaviors are not well described. Here, we report bi-directional changes in depression-related behaviors after genetic disruption of neuronal tRNA cytosine methylation, including conditional ablation and transgene-derived overexpression of Nsun2 in the mouse prefrontal cortex (PFC). Neuronal Nsun2-deficiency was associated with a decrease in tRNA m5C levels, resulting in deficits in expression of 70% of tRNAGly isodecoders. Altogether, 1488/5820 proteins changed upon neuronal Nsun2-deficiency, in conjunction with glycine codon-specific defects in translational efficiencies. Loss of Gly-rich proteins critical for glutamatergic neurotransmission was associated with impaired synaptic signaling at PFC pyramidal neurons and defective contextual fear memory. Changes in the neuronal translatome were also associated with a 146% increase in glycine biosynthesis. These findings highlight the methylation sensitivity of glycinergic tRNAs in the adult PFC. Furthermore, they link synaptic plasticity and complex behaviors to epitranscriptomic modifications of cognate tRNAs and the proteomic homeostasis associated with specific amino acids.

A proteomic network approach resolves stage-specific molecular phenotypes in chronic traumatic encephalopathy

Background There is an association between repetitive head injury (RHI) and a pathologic diagnosis of chronic traumatic encephalopathy (CTE) characterized by the aggregation of proteins including tau. The underlying molecular events that cause these abnormal protein accumulations remain unclear. Here, we hypothesized that identifying the human brain proteome from serial CTE stages (CTE I-IV) would provide critical new insights into CTE pathogenesis. Brain samples from frontotemporal lobar degeneration due to microtubule associated protein tau (FTLD-MAPT) mutations were also included as a distinct tauopathy phenotype for comparison. Methods Isobaric tandem mass tagged labeling and mass spectrometry (TMT-MS) followed by integrated differential and co-expression analysis (i.e., weighted gene co-expression network analysis (WGCNA)) was used to define modules of highly correlated proteins associated with clinical and pathological phenotypes in control (n = 23), CTE (n = 43), and FTLD-MAPT (n = 12) post-mortem cortical tissues. We also compared these findings to network analysis of AD brain. Results We identified over 6000 unique proteins across all four CTE stages which sorted into 28 WGCNA modules. Consistent with Alzheimer’s disease, specific modules demonstrated reduced neuronal protein levels, suggesting a neurodegeneration phenotype, while other modules were increased, including proteins associated with inflammation and glial cell proliferation. Notably, unique CTE-specific modules demonstrated prominent enrichment of immunoglobulins, including IGHM and IGLL5, and extracellular matrix (ECM) proteins as well as progressive protein changes with increasing CTE pathologic stage. Finally, aggregate cell subtype (i.e., neurons, microglia, astrocytes) protein abundance levels in CTE cases were similar in expression to AD, but at intermediate levels between controls and the more exaggerated phenotype of FTLD-MAPT, especially in astrocytes. Conclusions Overall, we identified thousands of protein changes in CTE postmortem brain and demonstrated that CTE has a pattern of neurodegeneration in neuronal-synaptic and inflammation modules similar to AD. We also identified unique CTE progressive changes, including the enrichment of immunoglobulins and ECM proteins even in early CTE stages. Early and sustained changes in astrocyte modules were also observed. Overall, the prominent overlap with FTLD-MAPT cases confirmed that CTE is on the tauopathy continuum and identified CTE stage specific molecular phenotypes that provide novel insights into disease pathogenesis.

Genetic Architecture of Protein Expression and its Regulation in the Mouse Brain

Background Natural variation in protein expression is common in all organisms and contributes to phenotypic differences among individuals. While variation in gene expression at the transcript level has been extensively investigated, the genetic mechanisms underlying variation in protein expression have lagged considerably behind. Here we investigate genetic architecture of protein expression by profiling a deep mouse brain proteome of two inbred strains, C57BL/6J (B6) and DBA/2J (D2), and their reciprocal F1 hybrids using two-dimensional liquid chromatography coupled with tandem mass spectrometry (LC/LC-MS/MS) technology. Results By comparing protein expression levels in the four mouse strains, we observed 329 statistically significant differentially expressed proteins between the two parental strains and identified four common inheritance patterns, including 1,133 dominant, 980 additive, 63 over- and 62 under-dominant expression. We further applied the proteogenomic approach to detect variant peptides and define protein allele-specific expression (pASE), identifying 33 variant peptides with cis‐effects and 17 variant peptides showing trans‐effects. Comparison of regulation at transcript and protein levels show a significant divergence. Conclusions The results provide a comprehensive analysis of genetic architecture of protein expression and the contribution of cis- and trans‐acting regulatory differences to protein expression.