Importance of the circadian clock in tendon development. Vertebrate Skeletal Development. Elsevier; 2019. pp. 309-42. [DOI: 10.1016/bs.ctdb.2018.11.004]

Biomodulating healing after arthroscopic rotator cuff repair: the protocol of a randomised proof of concept trial (BIOHACK)

PURPOSE/INTRODUCTION

Over the last decades, there has been increasing interest in biological stimulation or bioaugmentation after rotator cuff repair. So far, there is no consensus on the appropriate composition of biologicals or which patients would benefit most, and moreover, these biologicals are often expensive. However, there are other, non-pharmacological strategies that are also believed to achieve biological stimulation. This randomised controlled trial evaluates the possible cumulative effect of pragmatic application of cryobiomodulation, photobiomodulation and electrobiomodulation-collectively called biomodulation-on the bone-to-tendon healing process after rotator cuff repair.

METHODS

In this randomised, controlled proof of concept study, 146 patients undergoing arthroscopic repair of a full thickness posterosuperior or anterosuperior rotator cuff tear will be 1:1 randomly assigned to either a control group or to the additional biomodulation protocol group. The adjuvant biomodulation protocol consists of seven self-applicable therapies and will be administered during the first 6 weeks after surgery. Primary outcome will be healing of the rotator cuff as evaluated by the Sugaya classification on MRI at 1-year postoperatively.

ETHICS AND DISSEMINATION

This study has been accepted by the National Ethical Review Board CPP Sud-Est IV in France and has been registered at Clinicaltrials.gov. The results of this study will be published in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

NCT04618484.

Circadian Oscillations in Skin and Their Interconnection with the Cycle of Life

Periodically oscillating biological processes, such as circadian rhythms, are carefully concerted events that are only beginning to be understood in the context of tissue pathology and organismal health, as well as the molecular mechanisms underlying these interactions. Recent reports indicate that light can independently entrain peripheral circadian clocks, challenging the currently prevalent hierarchical model. Despite the recent progress that has been made, a comprehensive overview of these periodic processes in skin is lacking in the literature. In this review, molecular circadian clock machinery and the factors that govern it have been highlighted. Circadian rhythm is closely linked to immunological processes and skin homeostasis, and its desynchrony can be linked to the perturbation of the skin. The interplay between circadian rhythm and annual, seasonal oscillations, as well as the impact of these periodic events on the skin, is described. Finally, the changes that occur in the skin over a lifespan are presented. This work encourages further research into the oscillating biological processes occurring in the skin and lays the foundation for future strategies to combat the adverse effects of desynchrony, which would likely have implications in other tissues influenced by periodic oscillatory processes.

miRNAs contributing to the repair of tendon injury

Tendon injury is one of the most common disorders of the musculoskeletal system, with a higher likelihood of occurrence in elderly individuals and athletes. In posthealing tendons, two undesirable consequences, tissue fibrosis and a reduction in mechanical properties, usually occur, resulting in an increased probability of rerupture or reinjury; thus, it is necessary to propose an appropriate treatment. Currently, most methods do not sufficiently modulate the tendon healing process and restore the function and structure of the injured tendon to those of a normal tendon, since there is still inadequate information about the effects of multiple cellular and other relevant signaling pathways on tendon healing and how the expression of their components is regulated. microRNAs are vital targets for promoting tendon repair and can modulate the expression of biological components in signaling pathways involved in various physiological and pathological responses. miRNAs are a type of noncoding ribonucleic acid essential for regulating processes such as cell proliferation, differentiation, migration and apoptosis; inflammatory responses; vascularization; fibrosis; and tissue repair. This article focuses on the biogenesis response of miRNAs while presenting their mechanisms in tendon healing with perspectives and suggestions.

Ultrastructural evidence for telocytes in equine tendon

The three-dimensional ultrastructure of the tendon is complex. Two main cell types are classically supported: elongated tenocytes and ovoid tenoblasts. The existence of resident stem/progenitor cells in human and equine tendons has been demonstrated, but their location and relationship to tenoblasts and tenocytes remain unclear. Hence, in this work, we carried out an ultrastructural study of the equine superficial digital flexor tendon. Although the fine structure of tendons has been previously studied using electron microscopy, the presence of telocytes, a specific type of interstitial cell, has not been described thus far. We show the presence of telocytes in the equine inter-fascicular tendon matrix near blood vessels. These telocytes have characteristic telopodes, which are composed of alternating dilated portions (podoms) and thin segments (podomers). Additionally, we demonstrate the presence of the primary cilium in telocytes and its ability to release exosomes. The location of telocytes is similar to that of tendon stem cells. The telocyte-blood vessel proximity, the presence of primary immotile cilia and the release of exosomes could have special significance for tendon homeostasis.

Tunnels for Protein Export from the Endoplasmic Reticulum

The functions of coat protein complex II (COPII) coats in cargo packaging and the creation of vesicles at the endoplasmic reticulum are conserved in eukaryotic protein secretion. Standard COPII vesicles, however, cannot handle the secretion of metazoan-specific cargoes such as procollagens, apolipoproteins, and mucins. Metazoans have thus evolved modules centered on proteins like TANGO1 (transport and Golgi organization 1) to engage COPII coats and early secretory pathway membranes to engineer a novel mode of cargo export at the endoplasmic reticulum.

Tissue physiology revolving around the clock: circadian rhythms as exemplified by the intervertebral disc

Circadian clocks in the brain and peripheral tissues temporally coordinate local physiology to align with the 24 hours rhythmic environment through light/darkness, rest/activity and feeding/fasting cycles. Circadian disruptions (during ageing, shift work and jet-lag) have been proposed as a risk factor for degeneration and disease of tissues, including the musculoskeletal system. The intervertebral disc (IVD) in the spine separates the bony vertebrae and permits movement of the spinal column. IVD degeneration is highly prevalent among the ageing population and is a leading cause of lower back pain. The IVD is known to experience diurnal changes in loading patterns driven by the circadian rhythm in rest/activity cycles. In recent years, emerging evidence indicates the existence of molecular circadian clocks within the IVD, disruption to which accelerates tissue ageing and predispose animals to IVD degeneration. The cell-intrinsic circadian clocks in the IVD control key aspects of physiology and pathophysiology by rhythmically regulating the expression of ~3.5% of the IVD transcriptome, allowing cells to cope with the drastic biomechanical and chemical changes that occur throughout the day. Indeed, epidemiological studies on long-term shift workers have shown an increased incidence of lower back pain. In this review, we summarise recent findings of circadian rhythms in health and disease, with the IVD as an exemplar tissue system. We focus on rhythmic IVD functions and discuss implications of utilising biological timing mechanisms to improve tissue health and mitigate degeneration. These findings may have broader implications in chronic rheumatic conditions, given the recent findings of musculoskeletal circadian clocks.

Tendon Extracellular Matrix Assembly, Maintenance and Dysregulation Throughout Life

In his Lissner Award medal lecture in 2000, Stephen Cowin asked the question: "How is a tissue built?" It is not a new question, but it remains as relevant today as it did when it was asked 20 years ago. In fact, research on the organization and development of tissue structure has been a primary focus of tendon and ligament research for over two centuries. The tendon extracellular matrix (ECM) is critical to overall tissue function; it gives the tissue its unique mechanical properties, exhibiting complex non-linear responses, viscoelasticity and flow mechanisms, excellent energy storage and fatigue resistance. This matrix also creates a unique microenvironment for resident cells, allowing cells to maintain their phenotype and translate mechanical and chemical signals into biological responses. Importantly, this architecture is constantly remodeled by local cell populations in response to changing biochemical (systemic and local disease or injury) and mechanical (exercise, disuse, and overuse) stimuli. Here, we review the current understanding of matrix remodeling throughout life, focusing on formation and assembly during the postnatal period, maintenance and homeostasis during adulthood, and changes to homeostasis in natural aging. We also discuss advances in model systems and novel tools for studying collagen and non-collagenous matrix remodeling throughout life, and finally conclude by identifying key questions that have yet to be answered.

Promotion of collagen deposition during skin healing through Smad3/mTOR pathway by parathyroid hormone-loaded microneedle

Skin wounds are associated with huge economic and emotional burdens for millions of people annually and are a challenge for health workers worldwide. At present, for skin defects after traumatic accidents, especially large-area skin defects, newly developed strategies such as the use of emerging biomaterials and cell therapy could be considered as options besides classic skin grafts. However, the new strategies have to deal with problems such as immune rejection and high costs for patients. An insufficient understanding of the mechanisms of skin wound healing further hinders the development of innovative treatment approaches. In this study, we developed a parathyroid hormone (PTH)-loaded phase-transition microneedle (PTMN) patch to deliver PTH subcutaneously in an efficient manner and change microneedle patch daily to achieve intermittent and systematic drug administration. By evaluating wound closure, re-epithelialization, collagen deposition, and extracellular matrix (ECM) expression in a Sprague-Dawley rat model of traumatic skin wounds, we demonstrated that intermittent systemic administration of PTH using our PTMN patches accelerated skin wound healing. Further, we demonstrated that the use of the patch may accelerate skin wound healing depending on the activation of the transforming growth factor (TGF)-β/Smad3/mammalian target of rapamycin (mTOR) cascade pathway. Our results suggest that the PTH-loaded PTMN patch may be a novel therapeutic strategy for treating skin wounds.

Rapid Homeostatic Turnover of Embryonic ECM during Tissue Morphogenesis

The extracellular matrix (ECM) is a polymer network hypothesized to form a stable cellular scaffold. While the ECM can undergo acute remodeling during embryogenesis, it is experimentally difficult to determine whether basal turnover is also important. Most studies of homeostatic turnover assume an initial steady-state balance of production and degradation and measure half-life by quantifying the rate of decay after experimental intervention (e.g., pulse labeling). Here, we present an intervention-free approach to mathematically model basal ECM turnover during embryogenesis by exploiting our ability to live image de novo ECM development in Drosophila to quantify production from initiation to homeostasis. This reveals rapid turnover (half-life ∼7–10 h), which we confirmed by in vivo pulse-chase experiments. Moreover, ECM turnover is partially dependent on proteolysis and network interactions, and slowing turnover affects tissue morphogenesis. These data demonstrate that embryonic ECM undergoes constant replacement, which is likely necessary to maintain network plasticity to accommodate growth and morphogenesis.

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Labeled ECM in fly embryos can be examined from initiation to homeostasis

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Quantifying ECM levels to homeostasis allows for modeling of basal turnover rate

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Embryonic ECM has a half-life of ∼10 h, which was confirmed by pulse-chase analysis

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Inhibiting MMPs or ECM interactions alters the basal turnover rate

EGR1 Transcription Factor is a Multifaceted Regulator of Matrix Production in Tendons and Other Connective Tissues

Although the transcription factor EGR1 is known as NGF1-A, TIS8, Krox24, zif/268, and ZENK, it still has many fewer names than biological functions. A broad range of signals induce Egr1 gene expression via numerous regulatory elements identified in the Egr1 promoter. EGR1 is also the target of multiple post-translational modifications, which modulate EGR1 transcriptional activity. Despite the myriad regulators of Egr1 transcription and translation, and the numerous biological functions identified for EGR1, the literature reveals a recurring theme of EGR1 transcriptional activity in connective tissues, regulating genes related to the extracellular matrix. Egr1 is expressed in different connective tissues, such as tendon (a dense connective tissue), cartilage and bone (supportive connective tissues), and adipose tissue (a loose connective tissue). Egr1 is involved in the development, homeostasis, and healing processes of these tissues, mainly via the regulation of extracellular matrix. In addition, Egr1 is often involved in the abnormal production of extracellular matrix in fibrotic conditions, and Egr1 deletion is seen as a target for therapeutic strategies to fight fibrotic conditions. This generic EGR1 function in matrix regulation has little-explored implications but is potentially important for tendon repair.

Age-associated changes in the response of tendon explants to stress deprivation is sex-dependent

Purpose of the Study: The incidence of tendon injuries increases dramatically with age, which presents a major clinical burden. While previous studies have sought to identify age-related changes in extracellular matrix structure and function, few have been able to explain fully why aged tissues are more prone to degeneration and injury. In addition, recent studies have also demonstrated that age-related processes in humans may be sex-dependent, which could be responsible for muddled conclusions in changes with age. In this study, we investigate short-term responses through an ex vivo explant culture model of stress deprivation that specifically questions how age and sex differentially affect the ability of tendons to respond to altered mechanical stimulus.Materials and Methods: We subjected murine flexor explants from young (4 months of age) and aged (22-24 months of age) male and female mice to stress-deprived culture conditions for up to 1 week and investigated changes in viability, cell metabolism and proliferation, matrix biosynthesis and composition, gene expression, and inflammatory responses throughout the culture period.Results and Conclusions: We found that aging did have a significant influence on the response to stress deprivation, demonstrating that aged explants have a less robust response overall with reduced metabolic activity, viability, proliferation, and biosynthesis. However, age-related changes appeared to be sex-dependent. Together, this work demonstrates that the aging process and the subsequent effect of age on the ability of tendons to respond to stress-deprivation are inherently different based on sex, where male explants favor increased activity, apoptosis, and matrix remodeling while female explants favor reduced activity and tissue preservation.

Insulin-like growth factor 1 signaling in tenocytes is required for adult tendon growth

Tenocytes serve to synthesize and maintain collagen fibrils and other extracellular matrix proteins in tendon. Despite the high prevalence of tendon injury, the underlying biologic mechanisms of postnatal tendon growth and repair are not well understood. IGF1 plays an important role in the growth and remodeling of numerous tissues but less is known about IGF1 in tendon. We hypothesized that IGF1 signaling is required for proper tendon growth in response to mechanical loading through regulation of collagen synthesis and cell proliferation. To test this hypothesis, we conditionally deleted the IGF1 receptor (IGF1R) in scleraxis (Scx)-expressing tenocytes using a tamoxifen-inducible Cre-recombinase system and caused tendon growth in adult mice via mechanical overload of the plantaris tendon. Compared with control Scx-expressing IGF1R-positive (Scx:IGF1R⁺) mice, in which IGF1R is present in tenocytes, mice that lacked IGF1R in their tenocytes [Scx-expressing IGF1R-negative (Scx:IGF1R^Δ) mice] demonstrated reduced cell proliferation and smaller tendons in response to mechanical loading. Additionally, we identified that both the PI3K/protein kinase B and ERK pathways are activated downstream of IGF1 and interact in a coordinated manner to regulate cell proliferation and protein synthesis. These studies indicate that IGF1 signaling is required for proper postnatal tendon growth and support the potential use of IGF1 in the treatment of tendon disorders.-Disser, N. P., Sugg, K. B., Talarek, J. R., Sarver, D. C., Rourke, B. J., Mendias, C. L. Insulin-like growth factor 1 signaling in tenocytes is required for adult tendon growth.

Circadian rhythms in skin and other elastic tissues

Circadian rhythms are daily oscillations that, in mammals, are driven by both a master clock, located in the brain, and peripheral clocks in cells and tissues. Approximately 10% of the transcriptome, including extracellular matrix components, is estimated to be under circadian control. Whilst it has been established that certain collagens and extracellular matrix proteases are diurnally regulated (for example in tendon, cartilage and intervertebral disc) the role played by circadian rhythms in mediating elastic fiber homeostasis is poorly understood. Skin, arteries and lungs are dynamic, resilient, elastic fiber-rich organs and tissues. In skin, circadian rhythms influence cell migration and proliferation, wound healing and susceptibility of the tissues to damage (from protease activity, oxidative stress and ultraviolet radiation). In the cardiovascular system, blood pressure and heart rate also follow age-dependent circadian rhythms whilst the lungs exhibit diurnal variations in immune response. In order to better understand these processes it will be necessary to characterise diurnal changes in extracellular matrix biology. In particular, given the sensitivity of peripheral clocks to external factors, the timed delivery of interventions (chronotherapy) has the potential to significantly improve the efficacy of treatments designed to repair and regenerate damaged cutaneous, vascular and pulmonary tissues.