A hierarchical vascularized engineered bone inspired by intramembranous ossification for mandibular regeneration

Mandibular defects caused by injuries,tumors,and infections are common and can severely affect mandibular function and the patient's appearance.However,mandible reconstruction with a mandibular bionic structure remains challenging.Inspired by the process of intramembranous ossification in mandibular development,a hierarchical vascularized engineered bone consisting of angiogenesis and osteogenesis modules has been produced.Moreover,the hierarchical vascular network and bone structure generated by these hierarchical vascularized engineered bone modules match the particular anatomical structure of the mandible.The ultra-tough polyion complex has been used as the basic scaffold for hierarchical vascularized engineered bone for ensuring better reconstruction of mandible function.According to the results of in vivo experiments,the bone regenerated using hierarchical vascularized engineered bone is similar to the natural mandibular bone in terms of morphology and genomics.The sonic hedgehog signaling pathway is specifically activated in hierarchical vascularized engineered bone,indicating that the new bone in hierarchical vascularized engineered bone underwent a process of intramembranous ossification identical to that of mandible development.Thus,hierarchical vascularized engineered bone has a high potential for clinical application in mandibular defect reconstruction.Moreover,the concept based on developmental processes and bionic structures provides an effective strategy for tissue regeneration.

Emerging structures and dynamic mechanisms ofγ-secretase for Alzheimer’s disease

γ-Secretase,called“the proteasome of the membrane,”is a membrane-embedded protease complex that cleaves 150+peptide substrates with central roles in biology and medicine,including amyloid precursor protein and the Notch family of cell-surface receptors.Mutations inγ-secretase and amyloid precursor protein lead to early-onset familial Alzheimer’s disease.γ-Secretase has thus served as a critical drug target for treating familial Alzheimer’s disease and the more common late-onset Alzheimer’s disease as well.However,critical gaps remain in understanding the mechanisms of processive proteolysis of substrates,the effects of familial Alzheimer’s disease mutations,and allosteric modulation of substrate cleavage byγ-secretase.In this review,we focus on recent studies of structural dynamic mechanisms ofγ-secretase.Different mechanisms,including the“Fit-Stay-Trim,”“Sliding-Unwinding,”and“Tilting-Unwinding,”have been proposed for substrate proteolysis of amyloid precursor protein byγ-secretase based on all-atom molecular dynamics simulations.While an incorrect registry of the Notch1 substrate was identified in the cryo-electron microscopy structure of Notch1-boundγ-secretase,molecular dynamics simulations on a resolved model of Notch1-boundγ-secretase that was reconstructed using the amyloid precursor protein-boundγ-secretase as a template successfully capturedγ-secretase activation for proper cleavages of both wildtype and mutant Notch,being consistent with biochemical experimental findings.The approach could be potentially applied to decipher the processing mechanisms of various substrates byγ-secretase.In addition,controversy over the effects of familial Alzheimer’s disease mutations,particularly the issue of whether they stabilize or destabilizeγ-secretase-substrate complexes,is discussed.Finally,an outlook is provided for future studies ofγ-secretase,including pathways of substrate binding and product release,effects of modulators on familial Alzheimer’s disease mutations of theγ-secretase-substrate complexes.Comprehensive understanding of the functional mechanisms ofγ-secretase will greatly facilitate the rational design of effective drug molecules for treating familial Alzheimer’s disease and perhaps Alzheimer’s disease in general.

Maternal hyperthyroidism increases the synthesis activity and the osteogenic markers expression of calvarial osteoblasts from offspring in a murine model

To evaluate the characteristics and synthesis activity of osteoblasts extracted from the calvaria of offspring of rats exposed to maternal hyperthyroidism.Twelve adult Wistar rats were divided into two groups,one control and one treated with daily administration of L-thyroxine by an orogastric tube(50μg/animal/day)during pregnancy.Three days after delivery and confirmation of the mothers’hyperthyroidism,the offspring were euthanized for the extraction of osteoblasts from the calvaria.At 7,14,and 21 days,proliferation activity was assessed using MTT assay,while alkaline phosphatase(ALP)activity was assessed by the BCIP/NBT method.At 21 days,the total area of the mineralized matrix stained by von Kossa was evaluated by morphometry.The expression of gene transcripts for Runx2,Bmp2,Fgfr1,collagen type 1(Col1),osteocalcin(Oc),and osteopontin(Op)were evaluated by real-time RT-PCR.Means were compared using the Student’s t-test.FA activity was significantly higher at 14 and 21 days in cultures of osteoblasts extracted from offspring exposed to maternal hyperthyroidism,while MTT conversion was significantly lower at 21 days in this group.Osteoblast cultures of neonates exposed to maternal hyperthyroidism also showed a larger total area of mineralized matrix and greater expression of gene transcripts for Oc and Op.Maternal hyperthyroidism increases the activity of matrix synthesis,alkaline phosphatase activity,and expression of gene transcripts for osteocalcin and osteopontin in the osteoblasts,extracted from the calvaria of the offspring,which may be one of the mechanisms of premature fusion of cranial sutures.

The role of vascular endothelial growth factor in ossification

Osteogenesis and angiogenesis are two closely correlated processes during bone growth, development, remodelling and repair. Vascular endothelial growth factor （VEGF） is an essential mediator during the process of angiogenesis. Based on an extensive literature search, which was carried out using the PubMed database and the keywords of osteogenesis, VEGF, endochondral ossification and intramembranous ossification, this manuscript reviews the role of VEGF in ossification, with emphasis on its effect in endochondral and intramembranous ossification. Osteogenesis and angiogenesis are closely correlated processes. VEGF acts as an essential mediator durin~ these processes. It not only functions in bone an^io^enesis but also in various aspects of bone develooment.

Molecular mechanisms of intermuscular bone development in fish:a review

Intermuscular bones(IBs)are slender linear bones embedded in muscle,which ossify from tendons through a process of intramembranous ossification,and only exist in basal teleosts.IBs are essential for fish swimming,but they present a choking risk during human consumption,especially in children,which can lead to commercial risks that have a negative impact on the aquaculture of these fish.In this review,we discuss the morphogenesis and functions of IBs,including their underlying molecular mechanisms,as well as the advantages and disadvantages of different methods for IB studies and techniques for breeding and generating IB-free fish lines.This review reveals that the many key genes involved in tendon development,osteoblast differentiation,and bone formation,e.g.,scxa,msxC,sost,twist,bmps,and osterix,also play roles in IB development.Thus,this paper provides useful information for the breeding of new fish strains without IBs via genome editing and artificial selection.