SUMMARY Sialic acids (Sias), 9-carbon-backbone sugars, are among the most complex and versatile molecules of life. As terminal residues of glycans on proteins and lipids, Sias are key elements of glycotopes of both cellular and microbial lectins and thus act as important molecular tags in cell recognition and signaling events. Their functions in such interactions can be regulated by post-synthetic modifications, the most common of which is differential Sia-O-acetylation (O-Ac-Sias). The biology of O-Ac-Sias remains mostly unexplored, largely because of limitations associated with their specific in situ detection. Here, we show that dual-function hemagglutinin-esterase envelope proteins of nidoviruses distinguish between a variety of closely related O-Ac-Sias. By using soluble forms of hemagglutinin-esterases as lectins and sialate-O-acetylesterases, we demonstrate differential expression of distinct O-Ac-sialoglycan populations in an organ-, tissue- and cell-specific fashion. Our findings indicate that programmed Sia-O-acetylation/de-O-acetylation may be critical to key aspects of cell development, homeostasis, and/or function.

BackgroundImplant-related infections represent one of the most severe complications in orthopaedics. A fast-resorbable, antibacterial-loaded hydrogel may reduce or prevent bacterial colonization and biofilm formation of implanted biomaterials.Questions/purposesWe asked: (1) Is a fast-resorbable hydrogel able to deliver antibacterial compounds in vitro? (2) Can a hydrogel (alone or antibacterial-loaded) coating on implants reduce bacterial colonization? And (3) is intraoperative coating feasible and resistant to press-fit implant insertion?MethodsWe tested the ability of Disposable Antibacterial Coating (DAC) hydrogel (Novagenit Srl, Mezzolombardo, Italy) to deliver antibacterial agents using spectrophotometry and a microbiologic assay. Antibacterial and antibiofilm activity were determined by broth microdilution and a crystal violet assay, respectively. Coating resistance to press-fit insertion was tested in rabbit tibias and human femurs.ResultsComplete release of all tested antibacterial compounds was observed in less than 96 hours. Bactericidal and antibiofilm effect of DAC hydrogel in combination with various antibacterials was shown in vitro. Approximately 80% of the hydrogel coating was retrieved on the implant after press-fit insertion.ConclusionsImplant coating with an antibacterial-loaded hydrogel reduces bacterial colonization and biofilm formation in vitro.Clinical Relevance A fast-resorbable, antibacterial-loaded hydrogel coating may help prevent implant-related infections in orthopaedics. However, further validation in animal models and properly controlled human studies is required.

The members of Betacoronavirus phylocluster A possess two types of surface projections, one comprised of the spike protein (S) and the other of hemagglutinin-esterase (HE). Purportedly, these viruses bind to O-acetylated sialic acids (O-Ac-Sias) primarily through S, with HE serving merely as receptor-destroying enzyme. Here, we show that, in apparent contrast to human and ungulate host range variants of Betacoronavirus-1, murine coronaviruses actually bind to O-Ac-Sias via HE exclusively. Apparently, expansion of group A betacoronaviruses into new hosts and niches was accompanied by changes in HE ligand and substrate preference and in the roles of HE and S in Sia receptor usage.Receptor specificity is a major viral determinant of host preference, cell tropism, and pathogenesis. In coronaviruses (CoVs) (family Coronaviridae, order Nidovirales), which are enveloped, plus-strand RNA viruses of clinical and veterinary relevance, receptor binding is mediated by the class I fusion spike protein (S). Often, the receptors employed are glycoproteins and virion-receptor binding involves protein-protein interaction. Some CoVs, however, specifically bind to glycans (10,19,26,30,38). For example, members of phylocluster A in the genus Betacoronavirus (previously known as "coronavirus group 2A"; see http://talk.ictvonline.org/media/g/vertebrate -2008/default.aspx for official coronavirus taxonomy) use Oacetylated sialic acid (O-Ac-Sia) either as the primary receptor or as the initial attachment factor. Among them are human coronavirus OC43 (HCoV-OC43), bovine coronavirus (BCoV), and porcine hemagglutinating encephalomyelitis virus (PHEV), which are host range variants of the species Betacoronavirus-1, and mouse hepatitis virus (MHV) (species Murine coronavirus [MuCoV]) (22,28,34,38). Interestingly, these viruses differ from other CoVs in that they code for an additional spike protein species, the hemagglutinin-esterase (HE) (1,3,9,11,17,18). HE possesses sialate-O-acetylesterase receptor-destroying enzyme (RDE) activity (20,29,37,42,43), which allows virions to elute from sialylated surfaces (29,34,38). It may thus facilitate the release of viral progeny from infected cells and provide virions with a means of escape from irreversible attachment to non-cell-associated sialoglycoconjugates and off-target host cells.Remarkably, group A betacoronaviruses differ from each other in their dependency on O-Ac-Sia cell surface expression. For the infection of cultured cells, HCoV-OC43, BCoV, and PHEV critically require 9-O-Ac-Sias as receptor determinants (13, 38), whereas MuCoVs rely exclusively on their primary receptor CAECAM1a (4-6, 39). As a likely reflection of this biological difference, HE expression is dispensable in MHV and rapidly lost during serial passage in vitro (17, 41). Indeed, many MHV laboratory strains, including the best-studied variant MHV-A59, carry a defective HE gene (18). As inferred from phylogenetic analyses, however, the HE gene is preserved in MHV field strains, implying that HE expression does offer a sel...

Bone healing is a complicated process of tissue regeneration that is influenced by multiple biological and biomechanical processes. In a minority of cases, these physiological processes are complicated by issues such as nonunion and/or fracture-related infection (FRI). Based on a select few in vivo experimental animal studies, construct stability is considered an important factor influencing both prevention and treatment of FRI. Stephan Perren played a pivotal role in the evolution of our current understanding of the critical relationship between biomechanics, fracture healing and infection. Furthermore, his concept of strain theory and the process of fracture healing is familiar to several generations of surgeons and has influenced implant development and design for the past 50 years. In this review we describe the role of biomechanical stability on fracture healing, and provide a detailed analysis of the preclinical studies addressing this in the context of FRI. Furthermore, we demonstrate how Perren's concepts of stability are still applied to current surgical techniques to aid in the prevention and treatment of FRI. Finally, we highlight the key knowledge gaps in the underlying basic research literature that need to be addressed as we continue to optimize patient care.

ObjectiveAlthough extracellular matrix (ECM)–derived scaffolds have been extensively studied and applied in a number of clinical applications, the use of ECM as a biomaterial for (osteo)chondral regeneration is less extensively explored. This study aimed at evaluating the chondrogenic potential of cells seeded on cartilage-derived matrix (CDM) scaffolds in vitro.DesignScaffolds were generated from decellularized equine articular cartilage and seeded with either chondrocytes or multipotent stromal cells (MSCs). After 2, 4, and 6 weeks of in vitro culture, CDM constructs were analyzed both histologically (hematoxylin and eosin, Safranin-O, collagen types I and II) and biochemically (glycosaminoglycan [GAG] and DNA content).ResultsAfter 4 weeks, both cell types demonstrated chondrogenic differentiation; however, the MSCs significantly outperformed chondrocytes in producing new GAG-containing cartilaginous matrix.ConclusionThese promising in vitro results underscore the potency of CDM scaffolds in (osteo)chondral defect repair.