Deer antler regeneration: a stem cell-based epimorphic process

Periodontal ligament stem cells modulate root resorption of human primary teeth via Runx2 regulating RANKL/OPG system

Physiological primary teeth exfoliation is a normal phenomenon during teeth development. However, retained primary teeth can often be observed in the patients with cleidocranial dysplasia (CCD) caused by mutation of Runx2. The potential regulative mechanism is still unknown. In the present study, periodontal ligament stem cells (PDLSCs) were derived from different resorbed stages of primary teeth and permanent teeth from normal patients and primary teeth from CCD patient. The proliferative, osteogenic and osteoclast-inductive capacities of PDLSCs from each group were detected. We demonstrated here that the proliferative ability of PDLSCs was reduced while the osteogenic and the osteoclast-inductive capacity of PDLSCs were enhanced during root resorption. The results also showed that PDLSCs from permanent teeth and CCD patient expressed low level of Runx2 and RANKL while high level of OPG. However, expression of Runx2 and RANKL were increased while expression of OPG was decreased in PDLSCs derived from resorbed teeth. Furthermore, Runx2 regulating the expression of RANKL and OPG and the osteoclast-inductive capacity of PDLSCs were confirmed by gain or loss of function assay. These data suggest that PDLSCs promote osteoclast differentiation via Runx2 upregulating RANKL and downregulating OPG, leading to enhanced root resorption that results in physiological exfoliation of primary teeth.

Antleroma in a Free-ranging White-tailed Deer (Odocoileus virginianus)

A 2-year-old male free-ranging white-tailed deer ( Odocoileus virginianus) was diagnosed with bilateral expansile tumors of antler origin. The deer was found dead by a landowner in High Springs, Florida. Two roughly spherical, multilobular, broad-based, bony, velvet-covered masses originated from each antler pedicle. These masses replaced or displaced many of the bones and soft tissues of the skull and extended through the left cribriform plate and the right petrous temporal bone, compressing portions of the brain. Microscopically, the masses closely resembled normal-growing antler, containing all the elements thereof but with areas of necrosis and hemorrhage suggestive of ischemi or trauma. Tumorlike outgrowths termed antleromas have been described in free-ranging and captive cervids and typically are associated with disruptions in the seasonal rise and fall of circulating testosterone necessary for normal antler growth, casting, and regeneration.

Phenotypic differences in white-tailed deer antlerogenic progenitor cells and marrow-derived mesenchymal stromal cells

Deer antlers are bony appendages that are annually cast and rapidly regrown in a seasonal process coupled to the reproductive cycle. Due to the uniqueness of this process among mammals, we reasoned that a fundamental characterization of antler progenitor cell behavior may provide insights that could lead to improved strategies for promoting bone repair. In this study, we investigated whether white-tailed deer antlerogenic progenitor cells (APC) conform to basic criteria defining mesenchymal stromal cells (MSC). In addition, we tested the effects of the artificial glucocorticoid dexamethasone (DEX) on osteogenic and chondrogenic differentiation as well as the degree of apoptosis during the latter. Comparisons were made to animal-matched marrow-derived MSC. APC and MSC generated similar numbers of colonies. APC cultures expanded less rapidly overall but experienced population recovery at later time points. In contrast to MSC, APC did not display adipogenic in vitro differentiation capacity. Under osteogenic culture conditions, APC and MSC exhibited different patterns of alkaline phosphatase activity over time. DEX increased APC alkaline phosphatase activity only initially but consistently led to decreased activity in MSC. APC and MSC in osteogenic culture underwent different time and DEX-dependent patterns of mineralization, yet APC and MSC achieved similar levels of mineral accrual in an ectopic ossicle model. During chondrogenic differentiation, APC exhibited high levels of apoptosis without a reduction in cell density. DEX decreased proteoglycan production and increased apoptosis in chondrogenic APC cultures but had the opposite effects in MSC. Our results suggest that APC and MSC proliferation and differentiation differ in their dependence on time, factors, and milieu. Antler tip APC may be more lineage-restricted osteo/chondroprogenitors with distinctly different responses to apoptotic and glucocorticoid stimuli.

Reprogramming cells and tissue patterning via bioelectrical pathways: molecular mechanisms and biomedical opportunities

Transformative impact in regenerative medicine requires more than the reprogramming of individual cells: advances in repair strategies for birth defects or injuries, tumor normalization, and the construction of bioengineered organs and tissues all require the ability to control large-scale anatomical shape. Much recent work has focused on the transcriptional and biochemical regulation of cell behavior and morphogenesis. However, exciting new data reveal that bioelectrical properties of cells and their microenvironment exert a profound influence on cell differentiation, proliferation, and migration. Ion channels and pumps expressed in all cells, not just excitable nerve and muscle, establish resting potentials that vary across tissues and change with significant developmental events. Most importantly, the spatiotemporal gradients of these endogenous transmembrane voltage potentials (Vmem ) serve as instructive patterning cues for large-scale anatomy, providing organ identity, positional information, and prepattern template cues for morphogenesis. New genetic and pharmacological techniques for molecular modulation of bioelectric gradients in vivo have revealed the ability to initiate complex organogenesis, change tissue identity, and trigger regeneration of whole vertebrate appendages. A large segment of the spatial information processing that orchestrates individual cells' programs toward the anatomical needs of the host organism is electrical; this blurs the line between memory and decision-making in neural networks and morphogenesis in nonneural tissues. Advances in cracking this bioelectric code will enable the rational reprogramming of shape in whole tissues and organs, revolutionizing regenerative medicine, developmental biology, and synthetic bioengineering.

Scalable production of controllable dermal papilla spheroids on PVA surfaces and the effects of spheroid size on hair follicle regeneration

Organ size and numbers are vital issues in bioengineering for hair follicle (HF) regeneration. Murine HF dermal papilla (DP) cells are able to induce HF neogenesis when transplanted as aggregates. However, how the preparation of murine and human DP aggregates affects HF inductivity and the size of regenerated HF is yet to be determined. Here we report a scalable method for production of controllable human and rat DP spheroids in general labs for reproducible experiments. Compared with more hydrophobic polyethylene and poly(ethylene-co-vinyl alcohol), DP cells are poorly adhesive to hydrophilic polyvinyl alcohol (PVA). Seeded in PVA-coated 96-welled commercial PCR tube arrays, DP cells quickly aggregate into single spheroids with progressive compaction. Varying seeded cell numbers and culture periods enables us to control the size and cell number of the spheroids. The spheroids obtained have high viability and preserve DP characters. A proof of principle experiment was conducted to examine the size effect on the efficiency and efficacy of HF regeneration. We found that both human and rat DP spheroids are able to induce HF neogenesis and larger DP spheroids exhibit higher HF inductivity. However, the average diameter of regenerated hair fiber did not significantly change with the increasing size of transplanted DP spheroids. The result suggests that an appropriate size of DP spheroid is essential for HF inductivity, but its size cannot be directly translated to a thicker regenerated hair. Our results also have implications on the efficiency and efficacy in the regeneration of other epithelial organs.