Immunocalization of telomerase in cells of lizard tail after amputation suggests cell activation for tail regeneration

Immunolocalization of telomerases in human hairs identifies proliferating cells in the bulb matrix and outer root sheath

Telomerase is present in cells with numerous or even un-limited replicative cycles, and some studies suggest it is a stemness marker. In order to determine whether this is the case for the human hair bulbs, an immunohistochemical and ultrastructural study has been carried out using antibodies against telomerase and PCNA (a cell proliferation marker). The observed labeling is similar for the two antibodies here utilized and is mainly nuclear. More frequent telomerase-positive cells are seen in the matrix epithelium of anagen hair bulbs but sparse labeled cells are also seen in the outer root sheath. In late catagen and also in telogen hair follicles only sparse labeled cells are present in the outer root sheath and few cells also in the secondary germinal epithelium formed at the base of the hair bulb in telogen. Electron microscopic immunogold shows a prevalent nuclear distribution and a lower cytoplasmic distribution in sparse cells of anagen bulb matrix that contain few keratin bundles. The nuclear localization is generally seen over the euchromatin or in areas occupied by more compact chromatin that may indicate an activity of telomerase in chromatin assemblage or dis-assemblage. The study concludes that the localization of telomerase is present in cells undergoing proliferation, namely transit amplifying cells of the outer root sheath that are sparsely detected in the lowermost secondary germinal hair bulb also in telogen.

Spinal ganglia and peripheral nerves innervating the regenerating tail and muscles of lizards

The present review summarizes available information on the contribution of regenerating nerves to the process of regeneration in the tail of lizards. From the last three segments of the spinal cord and ganglia proximal to the regenerating tail, motor, sensory somatic and autonomous nerves regenerate and richly innervate the growing blastema. However, experimental studies have indicated that peripheral nerves are not essential for stimulating the regeneration of the tail that instead is mainly sustained by the interaction of the apical ependyma with the wound epidermis. Ganglion neurons innervating the regenerating blastema increase their size and some satellite cells multiply but no ganglion neurons are regenerated. Numerous Schwann cells proliferate to keep pace with nerve regeneration, and they form myelin starting from 3 to 4 weeks of tail regeneration. The hypertrophic ganglion neurons synthesize growth factors and signaling proteins such as FGFs and Wnts that are transported into the regenerating blastema through the regenerating nerves. Nerves form synaptic-like contacts with mesenchymal cells or fibroblasts at the tip of the regenerating blastema but not synaptic boutons. These terminals may discharge stimulating factors that favor cell proliferation but this is not experimentally demonstrated. Most of the innervation is directed to differentiating muscles where nerve endings form cholinergic motor-plates. Transcriptome data on the regenerating blastema-cone detect up-regulation of various genes coding for ionic channels, neurotransmitter receptors and signaling proteins. The latter suggests that the neurotrophic stimulation may control cell proliferation but is most directed to the functionality of regenerating muscles.

Impact of Cross-Linking of Collagen Matrices on Tissue Regeneration in a Rabbit Calvarial Bone Defect

The cross-linking of collagen matrices (Cl_CM) may provide volume-stable enhanced defect regeneration when compared to non-cross-linked matrices (Ncl_CM). The aim of the present study was to investigate the bone forming potential of collagen matrices (CMs) and the effects of cross-linking CMs in a rabbit calvaria defect model. (1) Empty controls (n = 6), (2) Ncl_CM (n = 8), and (3) Cl_CM (n = 8) were selected to be observed for the healing in 10 mm critical-sized calvarial bone defects. The potential for the bone as well as the connective tissue formation were evaluated by micro-CT and histomorphometry at three months post-surgery. There were no statistically significant differences in terms of new bone volume in the defects between the groups. However, the Cl_CM induced significantly greater fibrous tissue regeneration (5.29 ± 1.57 mm²) when compared to the controls (3.51 ± 0.93 mm²) by histomorphometry. The remnants of collagen fibers with immune cells, including macrophages and giant cells, were occasionally observed in the Cl_CM group but not in the Ncl_CM group. In conclusion, the cross-linking of collagen did not influence the potential for bone formation. Nevertheless, Cl_CM might be advantageous for the maintenance of fibrous tissue volume without disturbing bone formation in the defects.

Collagen-Based Matrices for Osteoconduction: A Preclinical In Vivo Study

The aim of this study was to evaluate the influence of additional hydroxyapatite (HA) in collagen-based matrices (CM) and membrane placement on bone formation in calvarial defects. Critical size defects in the calvaria of 16 New Zealand White Rabbits were randomly treated with CM or mineralized collagen-based matrices (mCM). Half of the sites were covered with a collagen membrane. Animals were euthanized after 12 weeks of healing. The samples were studied by micro-CT and histology. Newly formed lamellar bone was observed in all samples at the periphery of the defect. In the central areas, however, new bone composed of both woven and lamellar bone was embedded in the soft tissue. Samples treated with mCM showed more residual biomaterial and induced more small bony islands in the central areas of the defects than samples with CM. Nevertheless, a complete defect closure was not observed in any of the samples at 12 weeks. Membrane placement resulted in a decrease in bone density and height. Significant differences between the groups were revealed only between CM groups with and without membrane coverage for bone height in the central area of the defect. Neither mineralization of CM nor membrane placement improved the osteogenic capacity in this particular defect. Nevertheless, mineralisation influenced bone density without a membrane placement and bone volume underneath a membrane. CM may be used as a scaffold in bone regeneration procedures, without the need of a membrane coverage. Further preclinical studies are warrant to optimise the potential of mCM.

Appendage Regeneration in Vertebrates: What Makes This Possible?

The ability to regenerate amputated or injured tissues and organs is a fascinating property shared by several invertebrates and, interestingly, some vertebrates. The mechanism of evolutionary loss of regeneration in mammals is not understood, yet from the biomedical and clinical point of view, it would be very beneficial to be able, at least partially, to restore that capability. The current availability of new experimental tools, facilitating the comparative study of models with high regenerative ability, provides a powerful instrument to unveil what is needed for a successful regeneration. The present review provides an updated overview of multiple aspects of appendage regeneration in three vertebrates: lizard, salamander, and zebrafish. The deep investigation of this process points to common mechanisms, including the relevance of Wnt/β-catenin and FGF signaling for the restoration of a functional appendage. We discuss the formation and cellular origin of the blastema and the identification of epigenetic and cellular changes and molecular pathways shared by vertebrates capable of regeneration. Understanding the similarities, being aware of the differences of the processes, during lizard, salamander, and zebrafish regeneration can provide a useful guide for supporting effective regenerative strategies in mammals.

Tissue Integration and Degradation of a Porous Collagen-Based Scaffold Used for Soft Tissue Augmentation

Collagen-based scaffolds hold great potential for tissue engineering, since they closely mimic the extracellular matrix. We investigated tissue integration of an engineered porous collagen-elastin scaffold developed for soft tissue augmentation. After implantation in maxillary submucosal pouches in 6 canines, cell invasion (vimentin), extracellular matrix deposition (collagen type I) and scaffold degradation (cathepsin k, tartrate-resistant acid phosphatase (TRAP), CD86) were (immuno)-histochemically evaluated. Invasion of vimentin⁺ cells (scattered and blood vessels) and collagen type I deposition within the pores started at 7 days. At 15 and 30 days, vimentin⁺ cells were still numerous and collagen type I increasingly filled the pores. Scaffold degradation was characterized by collagen loss mainly occurring around 15 days, a time point when medium-sized multinucleated cells peaked at the scaffold margin with simultaneous labeling for cathepsin k, TRAP, and CD86. Elastin was more resistant to degradation and persisted up to 90 days in form of packages well-integrated in the newly formed soft connective tissue. In conclusion, this collagen-based scaffold maintained long-enough volume stability to allow an influx of blood vessels and vimentin⁺ fibroblasts producing collagen type I, that filled the scaffold pores before major biomaterial degradation and collapse occurred. Cathepsin k, TRAP and CD86 appear to be involved in scaffold degradation.

Tail loss and telomeres: consequences of large-scale tissue regeneration in a terrestrial ectotherm

Large-scale tissue regeneration has potential consequences for telomere length through increases in cell division and changes in metabolism which increase the potential for oxidative stress damage to telomeres. The effects of regeneration on telomere dynamics have been studied in fish and marine invertebrates, but the literature is scarce for terrestrial species. We experimentally induced tail autotomy in a lizard ( Niveoscincus ocellatus) and assessed relative telomere length (RTL) in blood samples before and after partial tail regeneration while concurrently measuring reactive oxygen species (ROS) levels. The change in ROS levels was a significant explanatory variable for the change in RTL over the 60-day experiment. At the average value of ROS change, the mean RTL increased significantly in the control group (intact tails), but there was no such evidence in the regenerating group. By contrast, ROS levels decreased significantly in the regenerating group, but there was no such evidence in the control group. Combined, these results suggest that tail regeneration following autotomy involves a response to oxidative stress and this potentially comes at a cost to telomere repair. This change in telomere maintenance demonstrates a potential long-term cost of tail regeneration beyond the regrowth of tissue itself.

Ectothermic telomeres: it's time they came in from the cold

We review the evolutionary ecology and genetics of telomeres in taxa that cannot elevate their body temperature to a preferred level through metabolism but do so by basking or seeking out a warm environment. This group of organisms contains all living things on earth, apart from birds and mammals. One reason for our interest in this synthetic group is the argument that high, stable body temperature increases the risk of malignant tumours if long, telomerase-restored telomeres make cells 'live forever'. If this holds true, ectotherms should have significantly lower cancer frequencies. We discuss to what degree there is support for this 'anti-cancer' hypothesis in the current literature. Importantly, we suggest that ectothermic taxa, with variation in somatic telomerase expression across tissue and taxa, may hold the key to understanding ongoing selection and evolution of telomerase dynamics in the wild. We further review endotherm-specific effects of growth on telomeres, effects of autotomy ('tail dropping') on telomere attrition, and costs of maintaining sexual displays measured in telomere attrition. Finally, we cover plant ectotherm telomeres and life histories in a separate 'mini review'.This article is part of the theme issue 'Understanding diversity in telomere dynamics'.

Telomere maintenance during anterior regeneration and aging in the freshwater annelid Aeolosoma viride

Aging is a complex process involving declines in various cellular and physical functionalities, including regenerative ability. Telomere maintenance is thought to be necessary for regeneration, and telomere attrition is one mechanism that contributes to aging. However, it is unclear if aging affects regeneration owing to deterioration of telomeric maintenance. We introduce Aeolosoma viride—a freshwater annelid with strong regenerative abilities—as a new model for studying the effects of aging on telomere functions and regeneration. We show that the anterior regenerative ability of A. viride declines with age. We characterized the A. viride telomere sequence as being composed of TTAGGG repeats and identifyied the telomerase gene Avi-tert. In adult A. viride, telomerase was constantly active and telomere lengths were similar among different body sections and stably maintained with age. Notably, we found that regeneration did not result in telomere shortening at regenerating sites. Moreover, transient up-regulation of Avi-tert expression and telomerase activity was observed at regenerating sites, which might promote telomere lengthening to counteract telomere erosion resulting from cell proliferation. Our study suggests that although aging affects A. viride regeneration independent of steady-state telomere length, timely regulation of telomerase functions is critical for the regeneration process in A. viride.