Quantitative trait loci analysis of tail tendon break time in mice of C57BL/6J and DBA/2J lineage

Strategic outline of interventions targeting extracellular matrix for promoting healthy longevity

The extracellular matrix (ECM), composed of interlinked proteins outside of cells, is an important component of the human body that helps maintain tissue architecture and cellular homeostasis. As people age, the ECM undergoes changes that can lead to age-related morbidity and mortality. Despite its importance, ECM aging remains understudied in the field of geroscience. In this review, we discuss the core concepts of ECM integrity, outline the age-related challenges and subsequent pathologies and diseases, summarize diagnostic methods detecting a faulty ECM, and provide strategies targeting ECM homeostasis. To conceptualize this, we built a technology research tree to hierarchically visualize possible research sequences for studying ECM aging. This strategic framework will hopefully facilitate the development of future research on interventions to restore ECM integrity, which could potentially lead to the development of new drugs or therapeutic interventions promoting health during aging.

Tendon and multiomics: advantages, advances, and opportunities

Tendons heal by fibrosis, which hinders function and increases re-injury risk. Yet the biology that leads to degeneration and regeneration of tendons is not completely understood. Improved understanding of the metabolic nuances that cause diverse outcomes in tendinopathies is required to solve these problems. 'Omics methods are increasingly used to characterize phenotypes in tissues. Multiomics integrates 'omic datasets to identify coherent relationships and provide insight into differences in molecular and metabolic pathways between anatomic locations, and disease stages. This work reviews the current literature pertaining to multiomics in tendon and the potential of these platforms to improve tendon regeneration. We assessed the literature and identified areas where 'omics platforms contribute to the field: (1) Tendon biology where their hierarchical complexity and demographic factors are studied. (2) Tendon degeneration and healing, where comparisons across tendon pathologies are analyzed. (3) The in vitro engineered tendon phenotype, where we compare the engineered phenotype to relevant native tissues. (4) Finally, we review regenerative and therapeutic approaches. We identified gaps in current knowledge and opportunities for future study: (1) The need to increase the diversity of human subjects and cell sources. (2) Opportunities to improve understanding of tendon heterogeneity. (3) The need to use these improvements to inform new engineered and regenerative therapeutic approaches. (4) The need to increase understanding of the development of tendon pathology. Together, the expanding use of various 'omics platforms and data analysis resulting from these platforms could substantially contribute to major advances in the tendon tissue engineering and regenerative medicine field.

Body weight and high-fat diet are associated with epigenetic aging in female members of the BXD murine family

DNA methylation (DNAm) is shaped by genetic and environmental factors and modulated by aging. Here, we examine interrelations between epigenetic aging, body weight (BW), and life span in 12 isogenic strains from the BXD family of mice that exhibit over twofold variation in longevity. Genome-wide DNAm was assayed in 70 liver specimens from predominantly female cases, 6-25 months old, that were maintained on normal chow or high-fat diet (HFD). We defined subsets of CpG regions associated with age, BW at young adulthood, and strain-by-diet-dependent life span. These age-associated differentially methylated CpG regions (age-DMRs) featured distinct genomic characteristics, with DNAm gains over time occurring in sites such as promoters and exons that have high CpG density and low average methylation. CpG regions associated with BW were enriched in introns, tended to have lower methylation in mice with higher BW, and were inversely correlated with gene expression (i.e., higher mRNA levels in mice with higher BW). CpG regions associated with life span were linked to genes involved in life span modulation, including the telomerase reverse transcriptase gene, Tert, which had both lower methylation and higher expression in long-lived strains. An epigenetic clock defined from age-DMRs revealed accelerated aging in mice belonging to strains with shorter life spans. Both higher BW and the HFD were associated with accelerated epigenetic aging. Our results highlight the age-accelerating effect of heavier BW. Furthermore, we demonstrate that the measure of epigenetic aging derived from age-DMRs can predict genotype and diet-induced differences in life span among female BXD members.

Genetic cartography of longevity in humans and mice: Current landscape and horizons

Aging is a complex and highly variable process. Heritability of longevity among humans and other species is low, and this finding has given rise to the idea that it may be futile to search for DNA variants that modulate aging. We argue that the problem in mapping longevity genes is mainly one of low power and the genetic and environmental complexity of aging. In this review we highlight progress made in mapping genes and molecular networks associated with longevity, paying special attention to work in mice and humans. We summarize 40 years of linkage studies using murine cohorts and 15 years of studies in human populations that have exploited candidate gene and genome-wide association methods. A small but growing number of gene variants contribute to known longevity mechanisms, but a much larger set have unknown functions. We outline these and other challenges and suggest some possible solutions, including more intense collaboration between research communities that use model organisms and human cohorts. Once hundreds of gene variants have been linked to differences in longevity in mammals, it will become feasible to systematically explore gene-by-environmental interactions, dissect mechanisms with more assurance, and evaluate the roles of epistasis and epigenetics in aging. A deeper understanding of complex networks-genetic, cellular, physiological, and social-should position us well to improve healthspan.

Profiling DNA methylation differences between inbred mouse strains on the Illumina Human Infinium MethylationEPIC microarray

The Illumina Infinium MethylationEPIC provides an efficient platform for profiling DNA methylation in humans at over 850,000 CpGs. Model organisms such as mice do not currently benefit from an equivalent array. Here we used this array to measure DNA methylation in mice. We defined probes targeting conserved regions and performed differential methylation analysis and compared between the array-based assay and affinity-based DNA sequencing of methyl-CpGs (MBD-seq) and reduced representation bisulfite sequencing. Mouse samples consisted of 11 liver DNA from two strains, C57BL/6J (B6) and DBA/2J (D2), that varied widely in age. Linear regression was applied to detect differential methylation. In total, 13,665 probes (1.6% of total probes) aligned to conserved CpGs. Beta-values (β-value) for these probes showed a distribution similar to that in humans. Overall, there was high concordance in methylation signal between the EPIC array and MBD-seq (Pearson correlation r = 0.70, p-value < 0.0001). However, the EPIC probes had higher quantitative sensitivity at CpGs that are hypo- (β-value < 0.3) or hypermethylated (β-value > 0.7). In terms of differential methylation, no EPIC probe detected a significant difference between age groups at a Benjamini-Hochberg threshold of 10%, and the MBD-seq performed better at detecting age-dependent change in methylation. However, the top most significant probe for age (cg13269407; uncorrected p-value = 1.8 x 10-5) is part of the clock CpGs used to estimate the human epigenetic age. For strain, 219 EPIC probes detected significant differential methylation (FDR cutoff 10%) with ~80% CpGs associated with higher methylation in D2. This higher methylation profile in D2 compared to B6 was also replicated by the MBD-seq data. To summarize, we found only a small subset of EPIC probes that target conserved sites. However, for this small subset the array provides a reliable assay of DNA methylation and can be effectively used to measure differential methylation in mice.

Tendon injury and repair - A perspective on the basic mechanisms of tendon disease and future clinical therapy

Tendon is an intricately organized connective tissue that efficiently transfers muscle force to the bony skeleton. Its structure, function, and physiology reflect the extreme, repetitive mechanical stresses that tendon tissues bear. These mechanical demands also lie beneath high clinical rates of tendon disorders, and present daunting challenges for clinical treatment of these ailments. This article aims to provide perspective on the most urgent frontiers of tendon research and therapeutic development. We start by broadly introducing essential elements of current understanding about tendon structure, function, physiology, damage, and repair. We then introduce and describe a novel paradigm explaining tendon disease progression from initial accumulation of damage in the tendon core to eventual vascular recruitment from the surrounding synovial tissues. We conclude with a perspective on the important role that biomaterials will play in translating research discoveries to the patient.

STATEMENT OF SIGNIFICANCE

Tendon and ligament problems represent the most frequent musculoskeletal complaints for which patients seek medical attention. Current therapeutic options for addressing tendon disorders are often ineffective, and the need for improved understanding of tendon physiology is urgent. This perspective article summarizes essential elements of our current knowledge on tendon structure, function, physiology, damage, and repair. It also describes a novel framework to understand tendon physiology and pathophysiology that may be useful in pushing the field forward.

Age-associated proinflammatory secretory phenotype in vascular smooth muscle cells from the non-human primate Macaca mulatta: reversal by resveratrol treatment

There is increasing evidence that age-associated chronic low-grade inflammation promotes the development of both large-vessel disease (myocardial infarction, stroke, peripheral arterial disease) and small-vessel pathologies (including vascular cognitive impairment) in older persons. However, the source of age-related chronic vascular inflammation remains unclear. To test the hypothesis that cell-autonomous mechanisms contribute to the proinflammatory changes in vascular phenotype that accompanies advancing age, we analyzed the cytokine secretion profile of primary vascular smooth muscle cells (VSMCs) derived from young (∼13 years old) and aged (∼21 years old) Macaca mulatta. Aged VSMCs cultured in the absence of systemic factors exhibited significantly increased secretion of interleukin-1β, MCP-1, and tumor necrosis factorα compared with young control cells. Secretion of interleukin-6 also tended to increase in aged VSMCs. This age-associated proinflammatory shift in the cellular secretory phenotype was associated with an increased mitochondrial O(2)(-) production and nuclear factor κ-light-chain-enhancer of activated B cells activation. Treatment of aged VSMCs with a physiologically relevant concentration of resveratrol (1 μM) exerted significant anti-inflammatory effects, reversing aging-induced alterations in the cellular cytokine secretion profile and inhibiting nuclear factor κ-light-chain-enhancer of activated B cells. Resveratrol also attenuated mitochondrial O(2)(-) production and upregulated the transcriptional activity of Nrf2 in aged VSMCs. Thus, in non-human primates, cell-autonomous activation of nuclear factor κ-light-chain-enhancer of activated B cells and expression of an inflammatory secretome likely contribute to vascular inflammation in aging. Resveratrol treatment prevents the proinflammatory properties of the aged VSMC secretome, an effect that likely contributes to the demonstrated vasoprotective action of resveratrol in animal models of aging.

Growth hormone and IGF-1 deficiency exacerbate high-fat diet-induced endothelial impairment in obese Lewis dwarf rats: implications for vascular aging

Previous studies suggest that the age-related decline in circulating growth hormone (GH) and insulin-like growth factor-1 (IGF-1) levels significantly contribute to vascular dysfunction in aging by impairing cellular oxidative stress resistance pathways. Obesity in elderly individuals is increasing at alarming rates, and there is evidence suggesting that elderly individuals are more vulnerable to the deleterious cardiovascular effects of obesity than younger individuals. However, the specific mechanisms through which aging, GH/IGF-1 deficiency, and obesity interact to promote the development of cardiovascular disease remain unclear. To test the hypothesis that low circulating GH/IGF-1 levels exacerbate the pro-oxidant and proinflammatory vascular effects of obesity, GH/IGF-1-deficient Lewis dwarf rats and heterozygous control rats were fed either a standard diet or a high-fat diet (HFD) for 7 months. Feeding an HFD resulted in similar relative weight gains and increases in body fat content in Lewis dwarf rats and control rats. HFD-fed Lewis dwarf rats exhibited a relative increase in blood glucose levels, lower insulin, and impaired glucose tolerance as compared with HFD-fed control rats. Analysis of serum cytokine expression signatures indicated that chronic GH/IGF-1 deficiency exacerbates HFD-induced inflammation. GH/IGF-1 deficiency also exacerbated HFD-induced endothelial dysfunction, oxidative stress, and expression of inflammatory markers (tumor necrosis factor-α, ICAM-1) in aortas of Lewis dwarf rats. Overall, our results are consistent with the available clinical and experimental evidence suggesting that GH/IGF-1 deficiency renders the cardiovascular system more vulnerable to the deleterious effects of obesity.