The African killifish: A short-lived vertebrate model to study the biology of sarcopenia and longevity.

Sarcopenia, the age-related decline in muscle function, places a considerable burden on health-care systems. While the stereotypic hallmarks of sarcopenia are well characterized, their contribution to muscle wasting remains elusive, which is partly due to the limited availability of animal models. Here, we have performed cellular and molecular characterization of skeletal muscle from the African killifish-an extremely short-lived vertebrate-revealing that while many characteristics deteriorate with increasing age, supporting the use of killifish as a model for sarcopenia research, some features surprisingly reverse to an "early-life" state in the extremely old stages. This suggests that in extremely old animals, there may be mechanisms that prevent further deterioration of skeletal muscle, contributing to an extension of life span. In line with this, we report a reduction in mortality rates in extremely old killifish. To identify mechanisms for this phenomenon, we used a systems metabolomics approach, which revealed that during aging there is a striking depletion of triglycerides, mimicking a state of calorie restriction. This results in the activation of mitohormesis, increasing Sirt1 levels, which improves lipid metabolism and maintains nutrient homeostasis in extremely old animals. Pharmacological induction of Sirt1 in aged animals was sufficient to induce a late life-like metabolic profile, supporting its role in life span extension in vertebrate populations that are naturally long-lived. Collectively, our results demonstrate that killifish are not only a novel model to study the biological processes that govern sarcopenia, but they also provide a unique vertebrate system to dissect the regulation of longevity.

Microplastic pollution in the intertidal and subtidal sediments of Vava'u, Tonga.

Plastic pollution research on a global scale intensified considerably in the current decade; however, research efforts in the South Pacific are still lagging. Here, we report on microplastic contamination of intertidal and subtidal sediments in the Vava'u archipelago, Tonga. While providing the first baseline data of its type in Tonga, the study also advances methods and adjusts them for low-budget research. The methods were based on density separation of microplastics from the sediment using CaCl2, a high-density salt which due to its high solubility, low cost and availability. Once separated, microplastics were quantified by microscopic analysis and polymers characterized via FTIR spectroscopy. Microplastics in intertidal and subtidal sediments were found in concentrations of 23.5 ± 1.9 and 15.0 ± 1.9 particles L-1 of sediment, respectively. The dominant type of microplastics in both intertidal (85 %) and subtidal sediments (62 %) were fibres.

Microplastic pollution in the surface waters of Vava'u, Tonga.

Marine plastic pollution, particularly microplastics, has been recognised as a global issue in the recent years, but research efforts in the Pacific are lagging. We carried out research on microplastics contamination of surface waters of the Vava'u archipelago, Tonga. Since microplastics smaller than the standard mesh size (333-335 µm) are readily reported in the literature on microplastics, we used a finer plankton net (100 µm) to determine the proportion of captured microplastics smaller than 300 µm. Isolated microplastics were counted and measured using stereomicroscope with polymer identification performed by FTIR spectroscopy. The analysis revealed high microplastics concentrations (329,299.7 ± 40,994.2 pcs km-2 or 1.05 ± 0.13 pcs m-3). The proportion of particles smaller than 300 µm was 40 %. The predominant type of microplastics in surface waters were small bits of white film, which we associated with cement-filled white bags used to construct docks throughout Vava'u, often heavily eroded.

RGD inhibition of itgb1 ameliorates laminin-α2-deficient zebrafish fibre pathology.

Deficiency of muscle basement membrane (MBM) component laminin-α2 leads to muscular dystrophy congenital type 1A (MDC1A), a currently untreatable myopathy. Laminin--α2 has two main binding partners within the MBM, dystroglycan and integrin. Integrins coordinate both cell adhesion and signalling; however, there is little mechanistic insight into integrin's function at the MBM. In order to study integrin's role in basement membrane development and how this relates to the MBM's capacity to handle force, an itgß1.b-/- zebrafish line was created. Histological examination revealed increased extracellular matrix (ECM) deposition at the MBM in the itgß1.b-/- fish when compared with controls. Surprisingly, both laminin and collagen proteins were found to be increased in expression at the MBM of the itgß1.b-/- larvae when compared with controls. This increase in ECM components resulted in a decrease in myotomal elasticity as determined by novel passive force analyses. To determine if it was possible to control ECM deposition at the MBM by manipulating integrin activity, RGD peptide, a potent inhibitor of integrin-ß1, was injected into a zebrafish model of MDC1A. As postulated an increase in laminin and collagen was observed in the lama2-/- mutant MBM. Importantly, there was also an improvement in fibre stability at the MBM, judged by a reduction in fibre pathology. These results therefore show that blocking ITGß1 signalling increases ECM deposition at the MBM, a process that could be potentially exploited for treatment of MDC1A.

Muscle Stem Cells Undergo Extensive Clonal Drift during Tissue Growth via Meox1-Mediated Induction of G2 Cell-Cycle Arrest.

Organ growth requires a careful balance between stem cell self-renewal and lineage commitment to ensure proper tissue expansion. The cellular and molecular mechanisms that mediate this balance are unresolved in most organs, including skeletal muscle. Here we identify a long-lived stem cell pool that mediates growth of the zebrafish myotome. This population exhibits extensive clonal drift, shifting from random deployment of stem cells during development to reliance on a small number of dominant clones to fuel the vast majority of muscle growth. This clonal drift requires Meox1, a homeobox protein that directly inhibits the cell-cycle checkpoint gene ccnb1. Meox1 initiates G2 cell-cycle arrest within muscle stem cells, and disrupting this G2 arrest causes premature lineage commitment and the resulting defects in muscle growth. These findings reveal that distinct regulatory mechanisms orchestrate stem cell dynamics during organ growth, beyond the G0/G1 cell-cycle inhibition traditionally associated with maintaining tissue-resident stem cells.

Asymmetric division of clonal muscle stem cells coordinates muscle regeneration in vivo.

Skeletal muscle is an example of a tissue that deploys a self-renewing stem cell, the satellite cell, to effect regeneration. Recent in vitro studies have highlighted a role for asymmetric divisions in renewing rare "immortal" stem cells and generating a clonal population of differentiation-competent myoblasts. However, this model currently lacks in vivo validation. We define a zebrafish muscle stem cell population analogous to the mammalian satellite cell and image the entire process of muscle regeneration from injury to fiber replacement in vivo. This analysis reveals complex interactions between satellite cells and both injured and uninjured fibers and provides in vivo evidence for the asymmetric division of satellite cells driving both self-renewal and regeneration via a clonally restricted progenitor pool.

Age-related changes in tissue macrophages precede cardiac functional impairment.

Cardiac tissue macrophages (cTMs) are abundant in the murine heart but the extent to which the cTM phenotype changes with age is unknown. This study characterizes aging-dependent phenotypic changes in cTM subsets. Using theCx3cr1(GFP/+) mouse reporter line where GFP marks cTMs, and the tissue macrophage marker Mrc1, we show that two major cardiac tissue macrophage subsets, Mrc1-GFP(hi) and Mrc1+GFP(hi) cTMs, are present in the young (<10 week old) mouse heart, and a third subset, Mrc1+GFP(lo), comprises ~50% of total Mrc1+ cTMs from 30 weeks of age. Immunostaining and functional assays show that Mrc1+ cTMs are the principal myeloid sentinels in the mouse heart and that they retain proliferative capacity throughout life. Gene expression profiles of the two Mrc1+ subsets also reveal that Mrc1+GFP(lo) cTMs have a decreased number of immune response genes (Cx3cr1, Lpar6, CD9, Cxcr4, Itga6 and Tgfßr1), and an increased number of fibrogenic genes (Ltc4s, Retnla, Fgfr1, Mmp9 and Ccl24), consistent with a potential role for cTMs in cardiac fibrosis. These findings identify early age-dependent gene expression changes in cTMs, with significant implications for cardiac tissue injury responses and aging-associated cardiac fibrosis.