An injury-responsive mmp14b enhancer is required for heart regeneration.

Mammals have limited capacity for heart regeneration, whereas zebrafish have extraordinary regeneration abilities. During zebrafish heart regeneration, endothelial cells promote cardiomyocyte cell cycle reentry and myocardial repair, but the mechanisms responsible for promoting an injury microenvironment conducive to regeneration remain incompletely defined. Here, we identify the matrix metalloproteinase Mmp14b as an essential regulator of heart regeneration. We identify a TEAD-dependent mmp14b endothelial enhancer induced by heart injury in zebrafish and mice, and we show that the enhancer is required for regeneration, supporting a role for Hippo signaling upstream of mmp14b. Last, we show that MMP-14 function in mice is important for the accumulation of Agrin, an essential regulator of neonatal mouse heart regeneration. These findings reveal mechanisms for extracellular matrix remodeling that promote heart regeneration.

NOTO Transcription Factor Directs Human Induced Pluripotent Stem Cell-Derived Mesendoderm Progenitors to a Notochordal Fate.

The founder cells of the Nucleus pulposus, the centre of the intervertebral disc, originate in the embryonic notochord. After birth, mature notochordal cells (NC) are identified as key regulators of disc homeostasis. Better understanding of their biology has great potential in delaying the onset of disc degeneration or as a regenerative-cell source for disc repair. Using human pluripotent stem cells, we developed a two-step method to generate a stable NC-like population with a distinct molecular signature. Time-course analysis of lineage-specific markers shows that WNT pathway activation and transfection of the notochord-related transcription factor NOTO are sufficient to induce high levels of mesendoderm progenitors and favour their commitment toward the notochordal lineage instead of paraxial and lateral mesodermal or endodermal lineages. This study results in the identification of NOTO-regulated genes including some that are found expressed in human healthy disc tissue and highlights NOTO function in coordinating the gene network to human notochord differentiation.

Venous endothelin modulates responsiveness of cardiac sympathetic axons to arterial semaphorin.

Developing neurons of the peripheral nervous system reach their targets via cues that support directional growth, a process known as axon guidance. In investigating how sympathetic axons reach the heart in mice, we discovered that a combination of guidance cues are employed in sequence to refine axon outgrowth, a process we term second-order guidance. Specifically, endothelin-1 induces sympathetic neurons expressing the receptor Ednra to project to the vena cavae leading to the heart. Endothelin signaling in turn induces expression of the repulsive receptor Plexin-A4, via induction of the transcription factor MEF2C. In the absence of endothelin or plexin signaling, sympathetic neurons misproject to incorrect competing vascular trajectories (the dorsal aorta and intercostal arteries). The same anatomical and physiological consequences occur in Ednra+/-; Plxna4+/- double heterozygotes, genetically confirming functional interaction. Second-order axon guidance therefore multiplexes a smaller number of guidance cues in sequential fashion, allowing precise refinement of axon trajectories.

Ageing in the musculoskeletal system.

The extent of ageing in the musculoskeletal system during the life course affects the quality and length of life. Loss of bone, degraded articular cartilage, and degenerate, narrowed intervertebral discs are primary features of an ageing skeleton, and together they contribute to pain and loss of mobility. This review covers the cellular constituents that make up some key components of the musculoskeletal system and summarizes discussion from the 2015 Aarhus Regenerative Orthopaedic Symposium (AROS) (Regeneration in the Ageing Population) about how each particular cell type alters within the ageing skeletal microenvironment.

Longitudinal Comparison of Enzyme- and Laser-Treated Intervertebral Disc by MRI, X-Ray, and Histological Analyses Reveals Discrepancies in the Progression of Disc Degeneration: A Rabbit Study.

Regenerative medicine is considered an attractive prospect for the treatment of intervertebral disc (IVD) degeneration. To assess the efficacy of the regenerative approach, animal models of IVD degeneration are needed. Among these animal models, chemonucleolysis based on the enzymatic degradation of the Nucleus Pulposus (NP) is often used, but this technique remains far from the natural physiopathological process of IVD degeneration. Recently, we developed an innovative animal model of IVD degeneration based on the use of a laser beam. In the present study, this laser model was compared with the chemonucleolysis model in a longitudinal study in rabbits. The effects of the treatments were studied by MRI (T2-weighted signal intensity (T2wsi)), radiography (IVD height index), and histology (NP area and Boos' scoring). The results showed that both treatments induced a degeneration of the IVD with a decrease in IVD height and T2wsi as well as NP area and an increase in Boos' scoring. The enzyme treatment leads to a rapid and acute process of IVD degeneration. Conversely, laser radiation induced more progressive and less pronounced degeneration. It can be concluded that laser treatment provides an instrumental in vivo model of slowly evolving IVD degenerative disease that can be of preclinical relevance for assessing new prophylactic biological treatments of disc degeneration.

Aarhus Regenerative Orthopaedics Symposium (AROS).

The combination of modern interventional and preventive medicine has led to an epidemic of ageing. While this phenomenon is a positive consequence of an improved lifestyle and achievements in a society, the longer life expectancy is often accompanied by decline in quality of life due to musculoskeletal pain and disability. The Aarhus Regenerative Orthopaedics Symposium (AROS) 2015 was motivated by the need to address regenerative challenges in an ageing population by engaging clinicians, basic scientists, and engineers. In this position paper, we review our contemporary understanding of societal, patient-related, and basic science-related challenges in order to provide a reasoned roadmap for the future to deal with this compelling and urgent healthcare problem.

TGF-ß1 and GDF5 Act Synergistically to Drive the Differentiation of Human Adipose Stromal Cells toward Nucleus Pulposus-like Cells.

Degenerative disc disease (DDD) primarily affects the central part of the intervertebral disc namely the nucleus pulposus (NP). DDD explains about 40% of low back pain and is characterized by massive cellular alterations that ultimately result in the disappearance of resident NP cells. Thus, repopulating the NP with regenerative cells is a promising therapeutic approach and remains a great challenge. The objectives of this study were to evaluate the potential of growth factor-driven protocols to commit human adipose stromal cells (hASCs) toward NP-like cell phenotype and the involvement of Smad proteins in this differentiation process. Here, we demonstrate that the transforming growth factor-ß1 and the growth differentiation factor 5 synergistically drive the nucleopulpogenic differentiation process. The commitment of the hASCs was robust and highly specific as attested by the expression of NP-related genes characteristic of young healthy human NP cells. In addition, the engineered NP-like cells secreted an abundant aggrecan and type II collagen rich extracellular matrix comparable with that of native NP. Furthermore, we demonstrate that these in vitro engineered cells survived, maintained their specialized phenotype and secretory activity after in vivo transplantation in nude mice subcutis. Finally, we provide evidence suggesting that the Smad 2/3 pathway mainly governed the acquisition of the NP cell molecular identity while the Smad1/5/8 pathway controlled the NP cell morphology. This study offers valuable insights for the development of biologically-inspired treatments for DDD by generating adapted and exhaustively characterized autologous regenerative cells.

[Regenerative medicine of the intervertebral disc: from pathophysiology to clinical application]. / Médecine régénératrice du disque intervertébral - De la physiopathologie à l'application clinique.

A large proportion of low back pain may be explained by intervertebral disc (IVD) degeneration. Currently, the process leading to IVD degeneration highlights the pivotal role of IVD cells. The number of these cells drastically decreases and does not support a spontaneous repair of the tissue. In order to counteract IVD degeneration, regenerative medicine, based on a cell supplementation of the damaged tissue is considered as a promising approach. After a description of IVD physiopathology, we will develop the different strategies based on cell therapy and tissue engineering and currently under investigation to improve altered IVD degeneration. Finally, results from the current pre-clinical and clinical studies will be discussed.

Dynamitin affects cell-surface expression of voltage-gated sodium channel Nav1.5.

The major cardiac voltage-gated sodium channel Nav1.5 associates with proteins that regulate its biosynthesis, localization, activity and degradation. Identification of partner proteins is crucial for a better understanding of the channel regulation. Using a yeast two-hybrid screen, we identified dynamitin as a Nav1.5-interacting protein. Dynamitin is part of the microtubule-binding multiprotein complex dynactin. When overexpressed it is a potent inhibitor of dynein/kinesin-mediated transport along the microtubules by disrupting the dynactin complex and dissociating cargoes from microtubules. The use of deletion constructs showed that the C-terminal domain of dynamitin is essential for binding to the first intracellular interdomain of Nav1.5. Co-immunoprecipitation assays confirmed the association between Nav1.5 and dynamitin in mouse heart extracts. Immunostaining experiments showed that dynamitin and Nav1.5 co-localize at intercalated discs of mouse cardiomyocytes. The whole-cell patch-clamp technique was applied to test the functional link between Nav1.5 and dynamitin. Dynamitin overexpression in HEK-293 (human embryonic kidney 293) cells expressing Nav1.5 resulted in a decrease in sodium current density in the membrane with no modification of the channel-gating properties. Biotinylation experiments produced similar information with a reduction in Nav1.5 at the cell surface when dynactin-dependent transport was inhibited. The present study strongly suggests that dynamitin is involved in the regulation of Nav1.5 cell-surface density.

The lumbar intervertebral disc: from embryonic development to degeneration.

Lumbar intervertebral discs (IVDs) are prone to degeneration upon skeletal maturity. In fact, this process could explain approximately 40% of the cases of low back pain in humans. Despite the efficiency of pain-relieving treatments, the scientific community seeks to develop innovative therapeutic approaches that might limit the use of invasive surgical procedures (e.g., spine fusion and arthroplasty). As a prerequisite to the development of these strategies, we must improve our fundamental knowledge regarding IVD pathophysiology. Recently, several studies have demonstrated that there is a singular phenotype associated with Nucleus pulposus (NP) cells, which is distinct from that of articular chondrocytes. In parallel, recent studies concerning the origin and development of NP cells, as well as their role in intervertebral tissue homeostasis, have yielded new insights into the complex mechanisms involved in disc degeneration. This review summarizes our current understanding of IVD physiology and the complex cell-mediated processes that contribute to IVD degeneration. Collectively, these recent advances could inspire the scientific community to explore new biotherapeutic strategies.