Transcriptomic profiling reveals distinct modes of aging in the kidney
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ABSTRACT: The kidney is an excellent model for studying organ aging, but little is known about the molecular changes that take place during the aging process. In this article we measured mRNA expression and protein expression in a large cohort of Diversity Outbred mice at 6, 12, and 18 months of age, and studied the relationship between the changes we observe in mRNA and protein expression as a function of age. We observed enrichments of specific pathways including those that were previously observed to have significant changes with age at the mRNA level, and here we also identified enriched pathways at the protein level. Our analysis of the direction of change in mRNA and protein levels with age at the total population level revealed distinct functional groups that have either concordant or discordant changes in expression levels. The age-interactive quantitative trait loci (QTL) analysis of mRNA (eQTL) and protein (pQTL) revealed many distantly regulated loci as opposed to the many locally regulated eQTL and pQTL observed without age-interaction. From this, we found a locus on chromosome 12 and chromosome 15 to regulate many age-interactive eQTL and pQTL respectively. Overall, our findings demonstrate that the changes with age in the kidney at the protein level are distinctly different from the changes at the mRNA level and are not mediated by mRNA expression.
Project description:Background: Previous expression quantitative trait loci (eQTL) studies have identified thousands of genetic variants to be associated with gene expression at the mRNA level in the human liver. However, protein expression often correlates poorly with mRNA levels. Thus, protein quantitative trait loci (pQTL) study is required to identify genetics variants that regulate protein expression in human livers. Results: We conducted a genome-wide pQTL study in 287 normal human liver samples and identified 900 local-pQTL variants and 4,026 distant-pQTL variants. We further discovered 53 genome hotspots of pQTL variants. Transcriptional region mapping analysis showed that 1,133 pQTL variants are in transcriptional regulatory regions. Genomic region enrichment analysis of the identified pQTL variants revealed 804 potential regulatory interactions among 595 regulators (e.g. non-coding RNAs) and 394 proteins. Moreover, pQTL variants and trait-variant integration analysis uncovered several novel mechanisms underlying the relationships between protein expression and liver diseases, such as alcohol dependence. Notably, over 2,000 of the identified pQTL variants have not been reported in previous eQTL studies, suggesting extensive involvement of genetic polymorphisms in post-transcriptional regulation of protein expression in human livers. Conclusions: We have partially established protein expression regulation networks in human livers and generated a wealth of pQTL data that could serve as a valuable resource for the scientific community.
Project description:Gene expression varies between individuals and corresponds to a key step linking genotypes to phenotypes. Regulation of transcript and protein abundances can affect the final phenotypes and has been related to many human diseases. However, our knowledge regarding the species-wide genetic control of protein abundance, including its dependency on transcript levels, is very limited. Here, we have determined quantitative proteomes of a large population of 942 diverse natural Saccharomyces cerevisiae yeast isolates. We found that mRNA and protein abundances are weakly correlated at the population gene level (r = 0.165). While the protein co-expression network recapitulates the major biological functions, differential expression patterns reveal proteomic signatures related to specific populations, mainly domesticated. Most importantly, comprehensive genetic association analyses highlight that genetic variants associated with variation in protein (pQTL) and transcript (eQTL) levels poorly overlap (3.6%), with mostly common local QTL. Our results demonstrate that transcriptome and proteome are clearly two distinct layers of regulation, governed by distinct genetic bases in natural populations, and therefore highlight the importance of integrating these different levels of gene expression to better understand the genotype-phenotype relationship. This submission contains the raw files for the wild isolates collection, the library used for the analysis and the corresponding DIA-NN report and associated files.
Project description:Genetic variation governs protein expression through both transcriptional and post-transcriptional processes. To investigate this relationship, we combined a multiplexed, mass spectrometry-based method for protein quantification with an emerging mouse model harboring extensive genetic variation from 8 founder strains. We collected genome-wide mRNA and protein profiling measurements to link genetic variation to protein expression differences in livers from 192 diversity outcross mice. We observed nearly 3,700 protein-level quantitative trait loci (pQTL) with an equal proportion of proteins regulated directly by their cognate mRNA as uncoupled from their transcript. Our analysis reveals an extensive array of at least five models for genetic variant control of protein abundance including direct protein-to-protein associations that act to achieve stoichiometric balance of functionally related enzymes and subunits of multimeric complexes.
Project description:Genetic variation governs protein expression through both transcriptional and post-transcriptional processes. To investigate this relationship, we combined a multiplexed, mass spectrometry-based method for protein quantification with an emerging mouse model harboring extensive genetic variation from 8 founder strains. We collected genome-wide mRNA and protein profiling measurements to link genetic variation to protein expression differences in livers from 192 diversity outcross mice. We observed nearly 3,700 protein-level quantitative trait loci (pQTL) with an equal proportion of proteins regulated directly by their cognate mRNA as uncoupled from their transcript. Our analysis reveals an extensive array of at least five models for genetic variant control of protein abundance including direct protein-to-protein associations that act to achieve stoichiometric balance of functionally related enzymes and subunits of multimeric complexes.
Project description:The kidney is an excellent model for studying organ aging. Kidney function shows steady decline with age and is easy to assay using urine or blood samples. However, little is known about the molecular changes that take place in the kidney during the aging process. In order to better understand the molecular changes that occur with age, we measured mRNA and protein levels in 188 genetically diverse mice at ages 6, 12, and 18 months. We observed distinctive change in mRNA and protein levels as a function of age. Changes in both mRNA and protein are associated with increased immune infiltration and decreases in mitochondrial function. Proteins show a greater extent of change and reveal changes in a wide array of biological processes including unique, organ-specific features of aging in kidney. Most importantly, we observed functionally important age-related changes in protein that occur in the absence of corresponding changes in mRNA. Our findings suggest that mRNA profiling alone provides an incomplete picture of molecular aging in the kidney and that examination of changes in proteins is essential to understand aging processes that are not transcriptionally regulated.
Project description:The mammalian liver plays an essential role in maintaining metabolic homeostasis in response to fasting and feeding. Additionally, the liver exhibits sex dimorphism and zonation. To investigate how these factors interact, we performed RNA-seq and proteomics on periportal and pericentral hepatocytes isolated from male and female mice under fed and starved conditions. We developed a classification system to assess protein-mRNA relationship and found that most zonation genes showed strong concordance between mRNA and protein. Classical growth hormone regulated sex-biased genes also exhibited concordance, while a significant subset of sex genes showed protein-level bias without corresponding mRNA differences. Transition between feeding and starvation triggered widespread changes in mRNA expression alongside rapid modulation of functional de novo lipogenesis. However, key lipogenic enzymes—such as ACC, ACLY, and FAS —showed little to no corresponding change at the protein level. To facilitate further exploration of these findings, we developed Discorda, a web-based database for interactive data analysis. Our findings reinforce the principle that mRNA changes do not reliably predict corresponding protein levels (and vice versa), particularly in the context of sex and acute metabolic regulation.
Project description:Intron retention (IR) may affect gene expression and protein functions during development and age-onset diseases. However, it remains unclear if IR undergoes spatial or temporal changes during different stages of ageing or neurodegenerative disorders like Alzheimer’s disease (AD). By profiling mRNA species across different ages of Drosophila heads, we observed significant increase in the level of IR of many conserved genes as animals aged. Interestingly, distinct sets of genes are affected at different stages of adult fly life with IR occurring at several AD-associated genes in old adult. This suggests that alteration of proper protein functions by IR during ageing may lead to AD pathogenesis. Consistent with this notion, analyses of healthy human ageing brains and different AD datasets revealed similar increased aberrant IR activities in many AD-curated genes. Taken together, our data suggest that increase IR during ageing may be the driver for late-onset sporadic AD.
Project description:We used microarrays and a previously established linkage map to localize the genetic determinants of brain gene expression for a backcross family of lake whitefish species pairs (Coregonus sp.). Our goals were to elucidate the genomic distribution and sex-specificity of brain expression QTL (eQTL) and to determine the extent to which genes controlling transcriptional variation may underlie adaptive divergence in the recently evolved dwarf (limnetic) and normal (benthic) whitefish. We observed a sex-bias in transcriptional genetic architecture, with more eQTL observed in males, as well as divergence in genome location of eQTL between sexes. Hotspots of nonrandom aggregations of up to 32 eQTL in one location were observed. We identified candidate genes for species pair divergence involved with energetic metabolism, protein synthesis, and neural development based on co-localization of eQTL for these genes with eight previously identified adaptive phenotypic QTL and four previously identified outlier loci from a genome scan in natural populations. 88% of eQTL-phenotypic QTL co-localization involved growth rate and condition factor QTL, two traits central to adaptive divergence between whitefish species pairs. Hotspots co-localized with phenotypic QTL in several cases, revealing possible locations where master regulatory genes, such as a zinc finger protein in one case, control gene expression directly related to adaptive phenotypic divergence. We observed little evidence of co-localization of brain eQTL with behavioral QTL, which provides insight on the genes identified by behavioral QTL studies. These results extend to the transcriptome level previous work illustrating that selection has shaped recent parallel divergence between dwarf and normal lake whitefish species pairs and that metabolic, more than morphological differences appear to play a key role in this divergence. Keywords: eQTL mapping, gene expression, linkage mapping, adaptive radiation, Coregonus, microarrays
Project description:To gain a comprehensive systems-level understanding of cellular phenotypes, it is critical to characterize the relationship between the dynamic transcriptome and proteome during environmental perturbations. Previous comparisons have shown a lack of correlation between mRNA and protein level measurements suggesting a predominant role for post-transcriptional regulation in mediating cellular environmental responses. To investigate the extent of post-transcriptional regulation, we have analyzed transcriptome and proteome level changes over a 13-hour 28-point time course during transitions between oxic and anoxic physiologies of Halobacterium. Integrated computational analyses of these data show that temporally shifting mRNA and protein profiles relative to one another significantly increases the mRNA/protein correlation. Although time lags for unrelated genes vary widely, we observe similar temporal lags between the transcription and translation of functionally related genes. In contrast, no significant temporal separation was observed within the transcript profiles. Taken together, these data suggest that while there is indeed a direct correlation between many corresponding changes at mRNA and protein levels, translational delay may be the predominant mechanism for the temporal regulation of protein abundance during physiological oxic/anoxic transitions in Halobacterium. The approach and algorithms delineated in this study provide a framework for incorporating the temporal dimension of information processing across many different layers of gene regulation. Keywords: time course
Project description:We used microarrays and a previously established linkage map to localize the genetic determinants of brain gene expression for a backcross family of lake whitefish species pairs (Coregonus sp.). Our goals were to elucidate the genomic distribution and sex-specificity of brain expression QTL (eQTL) and to determine the extent to which genes controlling transcriptional variation may underlie adaptive divergence in the recently evolved dwarf (limnetic) and normal (benthic) whitefish. We observed a sex-bias in transcriptional genetic architecture, with more eQTL observed in males, as well as divergence in genome location of eQTL between sexes. Hotspots of nonrandom aggregations of up to 32 eQTL in one location were observed. We identified candidate genes for species pair divergence involved with energetic metabolism, protein synthesis, and neural development based on co-localization of eQTL for these genes with eight previously identified adaptive phenotypic QTL and four previously identified outlier loci from a genome scan in natural populations. 88% of eQTL-phenotypic QTL co-localization involved growth rate and condition factor QTL, two traits central to adaptive divergence between whitefish species pairs. Hotspots co-localized with phenotypic QTL in several cases, revealing possible locations where master regulatory genes, such as a zinc finger protein in one case, control gene expression directly related to adaptive phenotypic divergence. We observed little evidence of co-localization of brain eQTL with behavioral QTL, which provides insight on the genes identified by behavioral QTL studies. These results extend to the transcriptome level previous work illustrating that selection has shaped recent parallel divergence between dwarf and normal lake whitefish species pairs and that metabolic, more than morphological differences appear to play a key role in this divergence. Keywords: eQTL mapping, gene expression, linkage mapping, adaptive radiation, Coregonus, microarrays The objective of this study was to elucidate the genomic distribution and sex-specificity of brain eQTL in dwarf and normal lake whitefish. Dissected brain tissue (250-350 mg) was sampled for 55 individuals from a hybrid x dwarf backcross mapping family. We used a loop design (YANG and SPEED 2002; CHURCHILL 2002) to maximize the number of sampled meioses. Each of 55 samples was technically replicated on two distinct slides, while performing dye swapping (Cy3 and Alexa) to estimate the dye intensity variation bias. After correcting for local background, raw intensity values were both log2 transformed and normalized using the regional LOWESS method implemented in the R/MANOVA software (KERR et al. 2000). We used a previously generated linkage map based on the same backcross individuals for which gene expression was measured. eQTL mapping was performed with QTL Cartographer.