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Exploring Baseline Variations and Mechanical Loading-Induced Bone Formation in Young-Adult and Aging Mice through Proteomics

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Bone mass declines with age, and the anabolic effects of skeletal loading decrease. While much research has focused on gene transcription, how bone ages and loses its mechanoresponsiveness at the protein level remains unclear.

Researchers Christopher J. Chermside-Scabbo, John T. Shuster, Petra Erdmann-Gilmore, Eric Tycksen, Qiang Zhang, R. Reid Townsend, Matthew J. Silva from Washington University School of Medicine and Washington University in St. Louis, MO, share their findings which underscore the need for complementary protein-level assays in skeletal biology research.

On October 12, 2024, their research paper was published as the cover of Aging (listed by MEDLINE/PubMed as “Aging (Albany NY)” and “Aging-US” by Web of Science), Volume 16, Issue 19, entitled, “A proteomics approach to study mouse long bones: examining baseline differences and mechanical loading-induced bone formation in young-adult and old mice.”

THE STUDY

In this study, the tibias of young-adult and old mice were analyzed using proteomics and RNA-seq techniques, while the femurs were examined for age-related changes in bone structure. A total of 1,903 proteins and 16,273 genes were detected through these analyses. Multidimensional scaling demonstrated a clear separation between the young-adult and old samples at both the protein and RNA levels. Furthermore, 93% of the detected proteins were also identifiable by RNA-seq, and the abundance of these shared targets showed a moderately positive correlation. Additionally, differential expression analysis revealed 183 age-related differentially expressed proteins and 2,290 differentially expressed genes between young-adult and old bone samples.

Proteomic and RNA-seq analyses were conducted on paired tibias from young-adult and old mice to study age-related differences and the effects of mechanical loading on bone formation. The results showed distinct differences in protein and gene expression between the two age groups. Many of the significantly upregulated and downregulated proteins and genes in old bone have been associated with bone phenotypes in genome-wide association studies (GWAS). The study also identified age-related differentially expressed proteins and genes involved in bone phenotypes and aging processes. Integrated analysis with GWAS data revealed eight targets that may be relevant to human disease, including Asrgl1 and Timp2. Furthermore, co-expression analysis identified an age-related module indicating baseline differences in TGF-beta and Wnt signaling. Baseline age-related differences in ECM/MMPs and TGF-beta signaling were detected in both the proteome and transcriptome. Following mechanical loading, the proteome showed distinct pathway, protein class, and process enrichments, with temporal differences observed between young-adult and old mice.

Overall, the findings provide valuable insights into the molecular mechanisms underlying age-related changes and the response to mechanical loading in mouse long bones.

DISCUSSION

This study aimed to compare the proteome and transcriptome of tibias from young-adult and old mice under baseline conditions and analyze changes in the bone proteome in response to mechanical loading. The researchers successfully developed a proteomics method to detect protein-level changes in cortical bone and used it to perform proteomic and RNA-seq analyses on tibias from both young-adult and old mice. They observed a moderately positive correlation between the proteome and transcriptome in bone tissue. Age-related differences were detected at both the protein and RNA levels, with altered TGF-beta signaling and changes in extracellular matrix (ECM) and matrix metalloproteinases (MMPs) protein and transcript levels in old bones. The researchers identified Tgfb2 as the most reduced Tgfb transcript in old bone, predominantly expressed by osteocytes. Proteomic analysis of the loading response showed modest changes compared to age-related differences, with fewer protein-level changes in old bones. The findings suggest that proteomics is a valuable tool for studying bone biology and can provide insights into protein-specific changes in aging.

The data obtained from the analysis were subjected to various statistical and data exploration techniques. Differential expression analysis was performed to compare protein abundance between different groups. Total RNA was extracted from the bones using TRIzol, and its integrity and concentration were measured. The bones were also processed for paraffin sectioning and RNA in situ hybridization.

Overall, the study involved the collection and analysis of bone samples from female mice to investigate age-related changes and loading responses in the skeletal system.

Click here to read the full research paper in Aging.

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Aging is indexed by PubMed/Medline (abbreviated as “Aging (Albany NY)”), PubMed Central, Web of Science: Science Citation Index Expanded (abbreviated as “Aging‐US” and listed in the Cell Biology and Geriatrics & Gerontology categories), Scopus (abbreviated as “Aging” and listed in the Cell Biology and Aging categories), Biological Abstracts, BIOSIS Previews, EMBASE, META (Chan Zuckerberg Initiative) (2018-2022), and Dimensions (Digital Science).

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How Single Housing Impacts Growth and Lifespan in African Turquoise Killifish

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“[…] our results suggest that sharing housing with others in early life might influence whole-life attributes, potentially leading to specific life history traits beyond the typical relationship between the growth rate and lifespan.”

In this research, Chika Takahashi, Emiko Okabe, Masanori Nono, Saya Kishimoto, Hideaki Matsui, Tohru Ishitani, Takuya Yamamoto, Masaharu Uno, and Eisuke Nishida from the RIKEN Center for Biosystems Dynamics Research (BDR) in Hyogo, Japan; Brain Research Institute, Niigata University in Niigata, Japan; Research Institute for Microbial Diseases at Osaka University in Osaka, Japan; Kyoto University in Kyoto, Japan; and RIKEN Center for Advanced Intelligence Project (AIP), explored the effects of housing density during the juvenile stage on whole-life traits, including growth, fecundity, and lifespan, in African turquoise killifish. Their research paper was published on the cover of Aging (listed by MEDLINE/PubMed as Aging (Albany NY) and as Aging-US by Web of Science), Volume 16, Issue 18, entitled, “Single housing of juveniles accelerates early-stage growth but extends adult lifespan in African turquoise killifish.”

THE STUDY

A study on African turquoise killifish examined the impact of housing density on juvenile growth. Newly hatched fish were kept in different densities ranging from 1 to 40 fish per tank. It was found that lower housing densities resulted in faster growth, with fish in single housing growing significantly larger than those in group housing. Additionally, single-housed fish reached sexual maturity earlier compared to group-housed fish at higher densities. Comparisons between group-housed and single-housed fish showed that housing conditions in the juvenile stage did not affect the appearance changes during sexual maturation. 

As the fish progressed to middle-aged adults, the rate of increase in body length slowed down, while body weight continued to increase. Differences in body weight between group-housed and single-housed fish persisted into old age, suggesting potential differences in body composition. Surprisingly, single-housed fish had a longer mean adult lifespan compared to group-housed fish, contradicting the commonly held belief that faster growth leads to shorter lifespan. Lower housing densities during the juvenile stage were also found to extend adult lifespan, further challenging the inverse correlation between growth rate and lifespan. These findings suggest that lower housing densities promote accelerated growth in the juvenile stage of African turquoise killifish.

The study also found that single-housed fish had a longer adult lifespan compared to group-housed fish. This led to the suspicion that the egg-laying period of single-housed fish might also be longer. To investigate this, the researchers conducted weekly monitoring of the number of eggs laid until the old adult stage. In group-housed fish, the number of eggs laid was high for the first two weeks, followed by a medium level for the subsequent five weeks, and then decreased. In contrast, single-housed fish showed a medium level of egg-laying for the first nine weeks, followed by a decrease. The cumulative number of live embryos was found to be lower in single-housed fish compared to group-housed fish. These findings suggest that while the number of eggs laid is not very high, single-housed fish have a longer egg-laying period than group-housed fish.

To investigate the potential reasons behind the reduction in offspring number and longer egg-laying period in single-housed fish, the researchers conducted RNA sequencing analysis of testes or ovaries at four life stages. These stages included the onset of sexual maturity, young adult, mature adult, and middle-aged adult. Interestingly, the analysis revealed that single-housed fish showed higher similarity to group-housed fish at earlier life stages compared to group-housed fish at the same life stage. For instance, in the testes, single-housed fish at stage II exhibited the highest similarity to group-housed fish at stage I. Similarly, in the ovaries, single-housed fish at stage II and III showed higher similarity to group-housed fish at stage I. These findings suggest that the rate of gonadal transcriptional change with life stage progression is slower in single-housed fish compared to group-housed fish.

The researchers identified differentially expressed genes (DEGs) between stage I and stage IV in group- and single-housed fish. In the testes, ribosome-related genes and cilium-related genes were highly enriched in DEGs with higher expression in stage I compared to stage IV, suggesting a link between life stage progression, testes development, and spermatogenesis. In the ovaries, growth-related genes and translation-related genes were highly enriched in DEGs with higher expression in stage I compared to stage IV, indicating a link between life stage progression, ovarian development, oogenesis, and aging. Comparing group-housed and single-housed fish at different stages, there were differences in the PC1 values, suggesting that single-housed fish exhibited slower progression of gametogenesis and gonadal maturation relative to life stage progression compared to group-housed fish.

To further investigate this, the researchers focused on specific genes related to spermatogenic differentiation, oocyte development, oocyte construction, and female gonad development. The expression of these genes showed slower changes with life stage progression in single-housed fish compared to group-housed fish in both the testes and ovaries. This suggests that single-housed fish may have slower rates of gametogenesis and gonadal maturation, leading to a lower proportion of mature sperm and oocytes in their gonads. Overall, the results indicate that, at the transcriptional level, the progression of gonadal maturation and ovarian aging is slower in single-housed fish compared to group-housed fish. This slower progression may explain the medium fecundity and extended egg-laying period observed in single-housed fish.

The liver was chosen for analysis as it plays a central role in organismal metabolic processes. Gene expression profiles of the livers were compared between group- and single-housed fish at two different ages: 7 weeks post-hatching (wph) and 14 wph. Surprisingly, despite the 2-week age difference, the correlation coefficients showed that group- and single-housed fish at 14 wph were highly similar. The researchers identified 1588 age-related differentially expressed genes (DEGs) between the two age groups. Hierarchical clustering based on the expression changes of these age-related genes demonstrated that the expression profiles of group- and single-housed fish were similar at 14 wph.

IN CONCLUSION

In summary, juvenile single housing in African turquoise killifish promotes faster growth, longer egg-laying periods, and extended lifespans compared to group housing. These findings challenge traditional assumptions about the relationship between growth and lifespan and shed light on the impact of early-life environmental conditions on overall life history.

Overall, the experiments involved maintaining and rearing the fish, measuring their body length and weight, analyzing RNA sequencing data, measuring lifespan, and counting the number of eggs laid. Statistical analysis was conducted to assess significant differences between groups.

Click here to read the full research paper in Aging.

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Aging is indexed by PubMed/Medline (abbreviated as “Aging (Albany NY)”), PubMed Central, Web of Science: Science Citation Index Expanded (abbreviated as “Aging‐US” and listed in the Cell Biology and Geriatrics & Gerontology categories), Scopus (abbreviated as “Aging” and listed in the Cell Biology and Aging categories), Biological Abstracts, BIOSIS Previews, EMBASE, META (Chan Zuckerberg Initiative) (2018-2022), and Dimensions (Digital Science).

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The Cell Rejuvenation Atlas: Unveiling Rejuvenation Strategies through Network Biology

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Researchers introduce SINGULAR, a cell rejuvenation atlas that provides a unified analysis framework to study the effects of rejuvenation strategies at the single-cell level.

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Researchers Javier Arcos Hodar, Sascha Jung, Mohamed Soudy, Sybille Barvaux, and Antonio del Sol from CIC bioGUNE-BRTA and University of Luxembourg introduce SINGULAR, a cell rejuvenation atlas that provides a unified analysis framework to study the effects of rejuvenation strategies at the single-cell level. On September 9, 2024, their research paper was published on the cover of Aging (listed by MEDLINE/PubMed as “Aging (Albany NY)” and “Aging-US” by Web of Science), Volume 16, Issue 17, entitled, “The cell rejuvenation atlas: leveraging network biology to identify master regulators of rejuvenation strategies.”

THE RESEARCH

Various strategies, including lifestyle changes, gene therapies, and surgical procedures, have shown promise in improving aging markers and increasing lifespan in model organisms. These interventions often have limitations, however, such as not achieving comprehensive functional improvement across tissues or facing challenges in clinical translation. To address these limitations, the researchers characterized and compared rejuvenation interventions at different biological levels. The paper introduces SINGULAR, a cell rejuvenation atlas that provides a unified analysis framework to study the effects of rejuvenation strategies at the single-cell level. By examining gene regulatory networks, intracellular signaling, cell-cell communication, and cellular processes, the atlas identifies master regulators and common targets across immune cells. SINGULAR has the potential to inform future advancements in human age reversal and aid in the selection of drugs that mimic the effects of rejuvenation interventions.

RESULTS

The authors propose a unified multiscale analysis pipeline for characterizing and comparing the effects of rejuvenation interventions. This process begins by filtering low-quality cells, normalizing expression profiles, and identifying optimal cell clustering. The data is then analyzed at various biological levels, including differential gene expression, transcriptional regulatory networks, signaling cascades, and intercellular communication.

Nine previously published single-cell RNA-seq datasets from different rejuvenation interventions were collected and analyzed, revealing technical variability that highlights the need for a standardized data processing pipeline. The analysis showed heterogeneous gene expression responses across different cell types and organs. Systemic interventions had consistent effects on multiple organs, while metformin had minimal impact. Interestingly, exercise produced the largest transcriptional effects in the liver, artery, and spinal cord, even though it primarily targets muscles.

Transcriptional regulatory networks (TRNs) were reconstructed to explore the regulatory mechanisms behind these gene expression changes. The TRNs, which averaged 72 genes, were highly hierarchical, indicating the presence of ‘master regulators’ that explain significant portions of gene expression changes.

To demonstrate the practical application of SINGULAR, the study investigated the identification of drugs that could target transcription factor (TF) master regulators and key signaling molecules. Drug-target relationships from DrugBank were analyzed to find drugs that could activate master regulators or mimic the effects of rejuvenation interventions. Interestingly, only 17 out of 239 TFs could be activated by drugs, primarily nuclear receptors, with notable exceptions like AP-1 complex proteins and Trp53. Some of these drugs, such as Curcumin and Vitamin D3, have shown rejuvenating effects on lifespan in model organisms. Key signaling molecules were found to be more druggable, with several drugs targeting specific molecules, though none targeted both genes.

The study aimed to identify master regulators and their downstream effects in rejuvenation interventions. By simulating the activation of transcription factors (TFs) within the network, the researchers quantified the number of genes regulated by each TF. They discovered 493 TFs with non-zero activity across various conditions, though most acted as master regulators in only a few cases. The study also highlighted key differences between TFs involved in aging-related activity changes and those regulating rejuvenation. Notably, the AP-1 complex, consisting of Fos and Jun, emerged as a common master regulator across multiple interventions. The researchers also identified TFs linked to aging and validated their potential rejuvenating effects experimentally. They also explored crosstalk between TFs and signaling pathways, finding negative enrichment of aging gene sets in several integrated networks. Overall, the findings offer valuable insights into the regulatory mechanisms and potential rejuvenating effects of master regulators and signaling molecules involved in rejuvenation interventions.

CONCLUSION

In conclusion, this study employed a unified analysis pipeline, SINGULAR, to compare the effects and mediators of various rejuvenation interventions. Key master regulators, including Arntl, AP-1 complex proteins, NFE2L2, and MAF, were identified as playing crucial roles in rejuvenation. The analysis revealed distinct differences between aging-related transcriptional changes and rejuvenation regulators. Immune and skin cell types were highlighted as potential intervention targets, with the possibility of additive or synergistic effects by targeting non-overlapping master regulators. Some limitations were noted, such as biases in cell type comparisons, reliance on ligand-receptor interactions for cell-cell communication analysis, and the risk of false negatives in differential expression testing. Despite these limitations, SINGULAR offers valuable insights into rejuvenation mechanisms and the identification of agents for anti-aging strategies. It provides a robust framework for understanding the mechanisms behind various interventions and offers a wide range of potential target genes for a comprehensive anti-aging approach.

Click here to read the full research paper in Aging.

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Aging is indexed by PubMed/Medline (abbreviated as “Aging (Albany NY)”), PubMed Central, Web of Science: Science Citation Index Expanded (abbreviated as “Aging‐US” and listed in the Cell Biology and Geriatrics & Gerontology categories), Scopus (abbreviated as “Aging” and listed in the Cell Biology and Aging categories), Biological Abstracts, BIOSIS Previews, EMBASE, META (Chan Zuckerberg Initiative) (2018-2022), and Dimensions (Digital Science).

Click here to subscribe to Aging publication updates.

For media inquiries, please contact [email protected].

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Unveiling Role of Cytoskeleton in Aging: Insights from Dermal Fibroblast Research

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In this study, researchers reinforce knowledge about an age-related alteration in the synthesis of major proteins linked to the migratory and contractile functions of dermal human fibroblasts.

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Dermal fibroblasts orchestrate the synthesis and degradation of extracellular matrix components, which is crucial for skin homeostasis. Alterations in the expression of components such as collagens and enzymes can lead to reduced mechanical cutaneous tension and impaired skin wound healing during aging.

Researchers Françoise Boismal, Sandy Peltier, Sophie Ly ka so, Guillaume Chevreux, Loïse Blondel, Kévin Serror, Niclas Setterblab, Elina Zuelgaray, David Boccara, Maurice Mimoun, Christelle Guere, Armand Benssussan, Marie Dorr, Gallic Beauchef, Katell Vie, and Laurence Michel from Saint-Louis Hospital, Paris; Paris University, Paris Cité; Jacques-Monod Institute, Paris; and Clarins Laboratories, Pontoise, aimed to better understand the molecular alterations in fibroblasts during aging by comparing secretomic and proteomic signatures of fibroblasts from young (<35years) and aged (>55years) skin donors, in quiescence or TGF-stimulated conditions, using HLPC/MS. 

Their research paper was published on the cover of Aging’s Volume 16, Issue 16, entitled, “Proteomic and secretomic comparison of young and aged dermal fibroblasts highlights cytoskeleton as a key component during aging.”

Dermal fibroblasts were obtained from healthy, sun-protected skin of young (<35 years) and aged (>55 years) healthy women undergoing breast reduction surgery. Peptides were loaded using an online preconcentration method and separated by chromatography. RNA extraction, reverse transcription, quantitative PCR, and blot quantification were performed, along with immunostaining on fibroblasts seeded on culture chamber slides.

To identify key molecules involved in the role of human dermal fibroblasts during wound healing and skin aging, a comparative analysis of the secretome and proteome of 12 fibroblast cultures, freshly isolated from young and mature skin, was conducted using HPLC/MS. This analysis was performed in both quiescence and TGF-β1-treated conditions, without senescence-inducing factors, as described in previously reported aging models. Importantly, the analyses were conducted in the absence of serum in the culture medium 24 hours before and during cell stimulation to avoid serum protein contamination in the secretomic and proteomic assays

This study revealed a significant decrease in fibroblast protein secretion with age, while cytoplasmic protein accumulation increased by over 60%. Proteins related to actin and ECM (extracellular matrix) organization were the two main categories altered during aging. An in-depth analysis of actin-related proteins highlighted the involvement of CFL1, CORO1C, the ARP2/3 complex, FLNB, and ACTC1 in cytoskeleton organization and fibroblast migration. These findings offer potential new targets to slow key features of skin aging.

“Our present data reinforce knowledge about an age-related alteration in the synthesis of major proteins linked to the migratory and contractile functions of dermal human fibroblasts.”

Read the full research paper, published in Aging.

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Aging is an open-access, traditional, peer-reviewed journal that publishes high-impact papers in all fields of aging research. All papers are available to readers (at no cost and free of subscription barriers) in bi-monthly issues at Aging-US.com.

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Aging’s Scientific Integrity Process

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The open-access journal Aging recently launched a new webpage showcasing the full Aging Scientific Integrity Process.

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BUFFALO, NY-November 8, 2022 – Scientific integrity is a crucial component of scholarly publishing for any credible journal. Peer-reviewed, open-access journal Aging (listed as “Aging (Albany NY)” by Medline/PubMed and “Aging-US” by Web of Science) has recently presented its Scientific Integrity process.

Launched in 2009, Aging is an open-access biomedical journal dedicated to publishing high-quality, aging-focused research. Aging publishes papers of general interest and biological significance in all fields of aging research and age-related diseases, including cancer—and now, with a special focus on COVID-19 vulnerability as an age-dependent syndrome. 

Aging has a scientific integrity process to ensure that publications meet a number of scrupulous criteria for authenticity and integrity. Each published paper is thoroughly analyzed by diligent reviewers and services, including multiple in-house developed image forensics softwares. A growing industry of digital technologies, tools and ideas are constantly being added to Aging’s scientific integrity toolbox. 

Aging’s Scientific Integrity process is built upon six critical components:

  1. Easily Accessible Ethics Statements
  2. Devotion to Industry Standards for Scientific Publishing
  3. Rigorous and Insightful Peer Review
  4. Detection and Zero-Tolerance of Plagiarism
  5. Leading-Edge Image Forensics
  6. Post-Publication Investigations (if needed)

You can read about each of these components in greater detail on Aging’s new Scientific Integrity webpage. 

The new webpage also depicts publishing statistics in a detailed graph (below)—showcasing a visual representation of the number of post-publication corrections and retractions by Aging compared to the industry average, between 2010 and 2022. As of September 2022, Aging’s average rate of corrections/retractions since 2009 is a low 2.33%. The industry average correction/retraction rate is 3.80%. 

Image forensics corrections/retractions (published & pending) as a percent of IF-eligible articles in Aging, 2009-2022

Aging’s highly-effective scientific integrity process allows researchers to read, share and cite Aging papers with confidence.

Click here for Aging’s full Scientific Integrity Process.

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