Effect of Nanoscale Topography of Titanium Implants on Bone Vessel Network,Osteocytes, and Mineral Densities

Background: Chemical and physical properties of an implant surface have a major influence on the structure of peri‐implant bone and thus may influence the clinical performance of the implant. This study aims to evaluate the bone microstructure around implants with and without added nanometer‐sized calcium phosphate particles. Methods: An implant with dual acid‐etched surface (control) and an implant with dual acid‐etched surface and CaP nanoparticles (test) were placed in the posterior maxilla of 15 patients. Bone microstructure was evaluated for osteocyte density (OD), bone vessel volume density (BVVD), and bone mineral density (BMD). Results: BVVD was 1.806 ± 0.05 for test implants and 1.533 ± 0.10 for control implants (P <0.001). BMD_low was 17.4 × 10⁴ µm² for test implants and 15.0 × 10⁴ µm² for control implants (P = 0.025). Results from the BMD_high comparison, test versus control, were not statistically significant (P >0.05). OD was 575.6 ± 63.7 mm² for test implants and 471.2 ± 61.9 mm² for control implants (P <0.001). Conclusions: After 8 weeks of healing, the bone microstructure around test implants appeared to be significantly more organized. Clinical implications of these results include shortened healing time and indication for earlier loading protocols.     

Fossilized cell structures identify an ancient origin for the teleost whole-genome duplication

Teleost fishes comprise one-half of all vertebrate species and possess a duplicated genome. This whole-genome duplication (WGD) occurred on the teleost stem lineage in an ancient common ancestor of all living teleosts and is hypothesized as a trigger of their exceptional evolutionary radiation. Genomic and phylogenetic data indicate that WGD occurred in the Mesozoic after the divergence of teleosts from their closest living relatives but before the origin of the extant teleost groups. However, these approaches cannot pinpoint WGD among the many extinct groups that populate this 50- to 100-million-y lineage, preventing tests of the evolutionary effects of WGD. We infer patterns of genome size evolution in fossil stem-group teleosts using high-resolution synchrotron X-ray tomography to measure the bone cell volumes, which correlate with genome size in living species. Our findings indicate that WGD occurred very early on the teleost stem lineage and that all extinct stem-group teleosts known so far possessed duplicated genomes. WGD therefore predates both the origin of proposed key innovations of the teleost skeleton and the onset of substantial morphological diversification in the clade. Moreover, the early occurrence of WGD allowed considerable time for postduplication reorganization prior to the origin of the teleost crown group. This suggests at most an indirect link between WGD and evolutionary success, with broad implications for the relationship between genomic architecture and large-scale evolutionary patterns in the vertebrate Tree of Life.

Whole-genome duplication (WGD) has occurred independently in multiple lineages of plants, fungi, and animals (1–3). This represents a major change to genomic architecture, with hypothesized impacts on evolutionary diversification (4, 5) caused by the origin of new gene functions from duplicate copies, expanding the genetic toolbox available for evolutionary “tinkering” (6). However, despite its mechanistic plausibility, this hypothesis is so far supported by only limited and contradictory empirical evidence (7–10). Teleost fishes—comprising more than one-half of modern vertebrates—are a key example, with their spectacular variety of form and kind (ranging from eels to seahorses) often viewed as prima facie evidence for the role of WGD in triggering evolutionary diversification (6, 11). Teleosts also show an incredible diversity of genome biology, demonstrating particularly high rates of evolution of protein-coding genes (12) and noncoding elements (13), a broad range of genome sizes including the smallest known in vertebrates (14), and multiple polyploid lineages (15).The genome of all living teleosts derives from an ancient WGD event that occurred before the last common ancestor of modern species (16). Additional duplication events occurred more recently in several teleost subgroups (9, 17) but are not generally proposed as drivers of diversification (9). Studies of the role of WGD in contributing to teleost diversity so far have analyzed the distribution of species richness among extant lineages and morphometric data for fossil phenotypes, with potentially conflicting results: extant teleosts have high rates of lineage diversification compared to other ray-finned fishes (7), but early fossil members of the teleost crown group do not show increased rates of morphological evolution (18).Molecular phylogenetic studies indicate that WGD occurred on the teleost stem lineage: after the divergence of teleosts from their extant sister taxon (Holostei) but before the most recent common ancestor of all living teleosts (19, 20). However, these bounds encompass a large phylogenetic diversity of extinct groups that diverged during an interval of 50 to 100 million y, from the initial origin of the teleost total group by the Triassic (21), up to the first appearance of crown-group teleosts in the Late Jurassic (18, 22). Molecular-clock estimates provide only broad constraints on the precise timing of duplication [316 to 226 Ma (23); ∼310 Ma (24)] and offer no information on its phylogenetic position on the teleost stem lineage. The imprecision of these estimates and the sometimes-considerable incongruence of molecular clocks with the teleost fossil record question the reliability of these inferences in the absence of further evidence.Patterns of genome-size evolution on the teleost stem lineage could provide alternative and independent evidence on the timing and phylogenetic position of the teleost WGD. However, stem lineages, by definition, comprise entirely extinct species that are known only from fossils, for which genomic data are absent. Nevertheless, some information about vertebrate genome size is preserved within fossil bone (25–27). Living organisms show a positive correlation between cell size and genome size (28–30), such that the volumes of bone cell spaces (osteocyte lacunae) allow estimates of genome size. This relationship has been demonstrated in ray-finned fishes, including teleosts, and is predictive for large-scale variation in genome size (31). The precision of this approach is sufficient for inferring the large change (presumably, doubling) of genome size involved in WGD (31). Here, we use this relationship to trace the evolution of genome size in extinct ray-finned fishes using osteocyte lacuna volumes as a proxy for genome size. Our sample includes a broad range of stem- and crown-group teleosts, providing information on patterns of teleost genome-size evolution during the deep evolutionary history of the teleost total group.Three-dimensional measurement of fossil bone cell spaces with μm-scale diameters presents considerable technical challenges. We used propagation phase contrast synchrotron radiation X-ray microcomputed tomography (PPC-SRµCT) to address this, collecting standardized measurements of osteocyte lacuna volumes for 61 fossil ray-finned fish species ranging from 2.5 to 252 million y in age (SI Appendix, section I). This fossil evidence is complemented by data from a previous study including 34 modern ray-finned fish species with known genome sizes (31). Our fossil sample includes all major groups of stem-group teleosts, members of both living and extinct lineages within the teleost crown group, and several nonteleost ray-finned fishes. This sample allows us to estimate relative genome sizes in extinct groups, providing information on the absolute timing and specific phylogenetic position of the teleost WGD as well as the timescale of postduplication reductions in genome size (24). Both statistical analysis and qualitative observations demonstrate the effectiveness of lacuna size for inferring large evolutionary increases in genome size: known polyploid lineages such as catostomids and salmonids, which underwent additional rounds of WGD, both show large osteocyte lacuna volumes compared to their close relatives (31).     

Osteocytes: central conductors of bone biology in normal and pathological conditions

Osteocytes are the most abundant and longest-living cells in the adult skeleton. For a long time, osteocytes were considered static and inactive cells, but in recent years, it has been suggested that they represent the key responder to various stimuli that regulate bone formation and remodelling as well as one of the key endocrine regulators of bone metabolism. Osteocytes respond to mechanical stimuli by producing and secreting several signalling molecules, such as nitric oxide and prostaglandin E(2) , that initiate local bone remodelling. Moreover, they can control bone formation by modulating the WNT signalling pathway, an essential regulator of cell fate and commitment, as they represent the main source of sclerostin, a negative regulator of bone formation. Osteocytes can also act as an endocrine organ by releasing fibroblast growth factor 23 and several other proteins (DMP-1, MEPE, PHEX) that regulate phosphate metabolism. It has been demonstrated that various bone diseases are associated with osteocyte abnormalities, although it is not clear if these changes are the direct cause of the pathology or if they are secondary to the pathological changes in the bone microenvironment. Thus, a better understanding of these cells could offer exciting opportunities for new advances in the prevention and management of different bone diseases.     

Analysis of the Effect of Osteon Diameter on the Potential Relationship of Osteocyte Lacuna Density and Osteon Wall Thickness

An important hypothesis is that the degree of infilling of secondary osteons (Haversian systems) is controlled by the inhibitory effect of osteocytes on osteoblasts, which might be mediated by sclerostin (a glycoprotein produced by osteocytes). Consequently, this inhibition could be proportional to cell number: relatively greater repression is exerted by progressively greater osteocyte density (increased osteocytes correlate with thinner osteon walls). This hypothesis has been examined, but only weakly supported, in sheep ulnae. We looked for this inverse relationship between osteon wall thickness (On.W.Th) and osteocyte lacuna density (Ot.Lc.N/B.Ar) in small and large osteons in human ribs, calcanei of sheep, deer, elk, and horses, and radii and third metacarpals of horses. Analyses involved: (1) all osteons, (2) smaller osteons, either ≤150 μm diameter or less than or equal to the mean diameter, and (3) larger osteons (>mean diameter). Significant, but weak, correlations between Ot.Lc.N/B.Ar and On.W.Th/On.Dm (On.Dm = osteon diameter) were found when considering all osteons in limb bones (r values ?0.16 to ?0.40, P < 0.01; resembling previous results in sheep ulnae: r = ?0.39, P < 0.0001). In larger osteons, these relationships were either not significant (five/seven bone types) or very weak (two/seven bone types). In ribs, a negative relationship was only found in smaller osteons (r = ?0.228, P < 0.01); this inverse relationship in smaller osteons did not occur in elk calcanei. These results do not provide clear or consistent support for the hypothesized inverse relationship. However, correlation analyses may fail to detect osteocyte‐based repression of infilling if the signal is spatially nonuniform (e.g., increased near the central canal). Anat Rec,, 2011. © 2011 Wiley‐Liss, Inc.     

模拟微重力效应对骨细胞SOC通道功能的影响

目的探究模拟微重力效应下骨细胞钙池操纵Ca~(2+)通道(store-operated calcium channels,SOC)的活性变化以及其可能机制,阐明失重性骨丢失的发生机制。方法以小鼠骨细胞(MLO-Y4)为对象,分为回转模拟微重力效应组(simulated microgravity, SM)和正常重力组(control, CON)。分别旋转培养24、48 h后,激光共聚焦显微镜检测毒胡萝卜素引发细胞内质网钙库耗竭后胞内Ca~(2+)浓度水平,以反映SOC通道的活性;免疫荧光染色法观察膜骨架spectrin和内质网膜蛋白IP_3R的分布情况,研究SOC通道功能变化的可能机制。结果在内质网钙库释放Ca~(2+)时期,24、48 h SM组的胞内Ca~(2+)浓度水平与CON组相比均无显著差异,而在胞外Ca~(2+)经SOC通道内流时期,24 h SM组只在前4 min比CON组有显著性下降,48 h SM组在整个时期均比CON组有显著性下降。与CON组相比,SM组膜骨架spectrin向细胞边缘聚集,而ER膜蛋白IP_3R则向ER核被膜区域聚集,且48 h组更为显著。结论模拟微重力效应可抑制骨细胞SOC通道活性。骨细胞膜骨架spectrin以及内质网膜上蛋白IP_3R位置分布变化,可能影响SOC通道激活过程中蛋白间的构象耦合,进而降低骨细胞SOC通道的活性。