A hydride transfer complex reprograms NAD metabolism and bypasses senescence.

Metabolic rewiring and redox balance play pivotal roles in cancer. Cellular senescence is a barrier for tumorigenesis circumvented in cancer cells by poorly understood mechanisms. We report a multi-enzymatic complex that reprograms NAD metabolism by transferring reducing equivalents from NADH to NADP+. This hydride transfer complex (HTC) is assembled by malate dehydrogenase 1, malic enzyme 1, and cytosolic pyruvate carboxylase. HTC is found in phase-separated bodies in the cytosol of cancer or hypoxic cells and can be assembled in vitro with recombinant proteins. HTC is repressed in senescent cells but induced by p53 inactivation. HTC enzymes are highly expressed in mouse and human prostate cancer models, and their inactivation triggers senescence. Exogenous expression of HTC is sufficient to bypass senescence, rescue cells from complex I inhibitors, and cooperate with oncogenic RAS to transform primary cells. Altogether, we provide evidence for a new multi-enzymatic complex that reprograms metabolism and overcomes cellular senescence.

Enriched Graphene Oxide-Polypropylene Suture Threads Buttons Modulate the Inflammatory Pathway Induced by Escherichia coli Lipopolysaccharide.

Graphene oxide (GO), derived from graphene, has remarkable chemical-physical properties such as stability, strength, and thermal or electric conductivity and additionally shows antibacterial and anti-inflammatory properties. The present study aimed to evaluate the anti-inflammatory effects of polypropylene suture threads buttons (PPSTBs), enriched with two different concentrations of GO, in the modulation of the inflammatory pathway TLR4/MyD 88/NFκB p65/NLRP3 induced by the Escherichia coli (E. coli) lipopolysaccharide (LPS-E). The gene and the protein expression of inflammatory markers were evaluated in an in vitro model of primary human gingival fibroblasts (hGFs) by real-time PCR, western blotting, and immunofluorescence analysis. Both GO concentrations used in the polypropylene suture threads buttons-GO constructs (PPSTBs-GO) decreased the expression of inflammatory markers in hGFs treated with LPS-E. The hGFs morphology and adhesion on the PPSTBs-GO constructs were also visualized by inverted light microscopy, scanning electron microscopy (SEM), and real-time PCR. Together, these results suggest that enriched PPSTBs-GO modulates the inflammatory process through TLR4/MyD 88/NFκB p65/NLRP3 pathway.

Dopaminergic neurons establish a distinctive axonal arbor with a majority of non-synaptic terminals.

Chemical neurotransmission typically occurs through synapses. Previous ultrastructural examinations of monoamine neuron axon terminals often failed to identify a pre- and postsynaptic coupling, leading to the concept of "volume" transmission. Whether this results from intrinsic properties of these neurons remains undefined. We find that dopaminergic neurons in vitro establish a distinctive axonal arbor compared to glutamatergic or GABAergic neurons in both size and propensity of terminals to avoid direct contact with target neurons. While most dopaminergic varicosities are active and contain exocytosis proteins like synaptotagmin 1, only ~20% of these are synaptic. The active zone protein bassoon was found to be enriched in dopaminergic terminals that are in proximity to a target cell. Finally, we found that the proteins neurexin-1αSS4- and neuroligin-1A+B play a critical role in the formation of synapses by dopamine (DA) neurons. Our findings suggest that DA neurons are endowed with a distinctive developmental connectivity program.

No endospore formation confirmed in members of the phylum Proteobacteria.

Endospore formation is used by members of the phylum Firmicutes to withstand extreme environmental conditions. Several recent studies have proposed endospore formation in species outside of Firmicutes, particularly in Rhodobacter johrii and Serratia marcescens, members of the phylum Proteobacteria. Here, we aimed to investigate endospore formation in these two species by using advanced imaging and analytical approaches. Examination of the phase-bright structures observed in R. johrii and S. marcescens using cryo-electron tomography failed to identify endospores or stages of endospore formation. We determined that the phase-bright objects in R. johrii cells were triacylglycerol storage granules and those in S. marcescens were aggregates of cellular debris. In addition, R. johrii and S. marcescens containing phase-bright objects do not possess phenotypic and genetic features of endospores, including enhanced resistance to heat, presence of dipicolinic acid, or the presence of many of the genes associated with endospore formation. Our results support the hypothesis that endospore formation is restricted to the phylum Firmicutes.Importance: Bacterial endospore formation is an important process that allows the formation of dormant life forms called spores. As such, organisms able to sporulate can survive harsh environmental conditions for hundreds of years. Here, we follow up on previous claims that two members of Proteobacteria, Serratia marcescens and Rhodobacter johrii, are able to form spores. We conclude that those claims were incorrect and show that the putative spores in R. johrii and S. marcescens are storage granules and cellular debris, respectively. This study concludes that endospore formation is still unique to the phylum Firmicutes.

VirB8 homolog TraE from plasmid pKM101 forms a hexameric ring structure and interacts with the VirB6 homolog TraD.

Type IV secretion systems (T4SSs) are multiprotein assemblies that translocate macromolecules across the cell envelope of bacteria. X-ray crystallographic and electron microscopy (EM) analyses have increasingly provided structural information on individual T4SS components and on the entire complex. As of now, relatively little information has been available on the exact localization of the inner membrane-bound T4SS components, notably the mostly periplasmic VirB8 protein and the very hydrophobic VirB6 protein. We show here that the membrane-bound, full-length version of the VirB8 homolog TraE from the plasmid pKM101 secretion system forms a high-molecular-mass complex that is distinct from the previously characterized periplasmic portion of the protein that forms dimers. Full-length TraE was extracted from the membranes with detergents, and analysis by size-exclusion chromatography, cross-linking, and size exclusion chromatography (SEC) multiangle light scattering (MALS) shows that it forms a high-molecular-mass complex. EM and small-angle X-ray scattering (SAXS) analysis demonstrate that full-length TraE forms a hexameric complex with a central pore. We also overproduced and purified the VirB6 homolog TraD and show by cross-linking, SEC, and EM that it binds to TraE. Our results suggest that TraE and TraD interact at the substrate translocation pore of the secretion system.

Interaction via the N terminus of the type IV secretion system (T4SS) protein VirB6 with VirB10 is required for VirB2 and VirB5 incorporation into T-pili and for T4SS function.

Many bacterial pathogens employ multicomponent protein complexes such as type IV secretion systems (T4SSs) to transfer virulence factors into host cells. Here we studied the interaction between two essential T4SS components: the very hydrophobic inner membrane protein VirB6, which may be a component of the translocation channel, and VirB10, which links the inner and outer bacterial membranes. To map the interaction site between these two T4SS components, we conducted alanine scanning and deleted six-amino acid stretches from the N-terminal periplasmic domain of VirB6 from Brucella suis Using the bacterial two-hybrid system to analyze the effects of these alterations on the VirB6-VirB10 interaction, we identified the amino acid regions 16-21 and 28-33 and Leu-18 in VirB6 as being required for this interaction. SDS-PAGE coupled with Western blotting of cell lysates and native PAGE of detergent-extracted membrane proteins revealed that the corresponding VirB6 residues in Agrobacterium tumefaciens (Phe-20 and amino acids 18-23 and 30-35) modulate the stability of both VirB6 and VirB5. However, the results from immuno-EM and super-resolution microscopy suggested that these regions and residues are not required for membrane association or for polar localization of VirB6. The six-amino acid deletions in the N terminus of VirB6 abolished pilus formation and virulence of A. tumefaciens, and the corresponding deletions in the VirB6 homolog TraD from the plasmid pKM101-T4SS abrogated plasmid transfer. Our results indicate that specific residues of the VirB6 N-terminal domain are required for VirB6 stabilization, its interaction with VirB10, and the incorporation of VirB2 and VirB5 into T-pili.

Axons morphometry in the human spinal cord.

Due to the technical challenges of large-scale microscopy and analysis, to date only limited knowledge has been made available about axon morphometry (diameter, shape, myelin thickness, volume fraction), thereby limiting our understanding of neuronal microstructure and slowing down research on neurodegenerative pathologies. This study addresses this knowledge gap by establishing a state-of-the-art acquisition and analysis framework for mapping axon morphometry, and providing the first comprehensive mapping of axon morphometry in the human spinal cord. We dissected, fixed and stained a human spinal cord with osmium tetroxide, and used a scanning electron microscope to image the entirety of 23 axial slices, covering C1 to L5 spinal levels. An automatic method based on deep learning was then used to segment each axon and myelin sheath to produce maps of axon morphometry. These maps were then registered to a standard spinal cord magnetic resonance imaging (MRI) template. Between 500,000 (lumbar) and 1 million (cervical) myelinated axons were segmented at each level of this human spinal cord. Morphometric features show a large disparity between tracts, but high right-left symmetry. Our results suggest a modality-based organization of the dorsal column in the human, as it has been observed in the rat. The generated axon morphometry template is publicly available at https://osf.io/8k7jr/ and could be used as a reference for quantitative MRI studies. The proposed framework for axon morphometry mapping could be extended to other parts of the central or peripheral nervous system that exhibit coherently-oriented axons.

Cross-Linked Elastin-like Polypeptide Membranes as a Model for Medial Arterial Calcification.

Calcium phosphate minerals deposit on the elastin-rich medial layers of arteries in the majority of seniors, diabetic, and chronic kidney disease patients, causing severe cardiovascular complications. There is no cure for medial calcification, and the mechanism of mineral formation on elastin layers is unknown. Here we propose cross-linked elastin-like polypeptide membranes as models to study medial calcification. Calcium phosphates deposit first on fibers and filaments and then spread to globular structures present in the membranes. Mineral phase evolution analyzed by near-edge X-ray spectroscopy matches that previously observed in a mouse model of medial calcification, showing that this simple system captures some of the key in vivo findings. This work shows how minerals form and evolve upon nucleation on elastin and provides an in vitro model that can be tuned to study hypotheses related to arterial calcification mechanisms and test drugs to stop or revert mineralization.

TDP-43 regulates the alternative splicing of hnRNP A1 to yield an aggregation-prone variant in amyotrophic lateral sclerosis.

See Fratta and Isaacs (doi:10.1093/brain/awy091) for a scientific commentary on this article.The RNA binding proteins TDP-43 (encoded by TARDBP) and hnRNP A1 (HNRNPA1) are each mutated in certain amyotrophic lateral sclerosis cases and are often mislocalized in cytoplasmic aggregates within motor neurons of affected patients. Cytoplasmic inclusions of TDP-43, which are accompanied by a depletion of nuclear TDP-43, are observed in most amyotrophic lateral sclerosis cases and nearly half of frontotemporal dementia cases. Here, we report that TDP-43 binds HNRNPA1 pre-mRNA and modulates its splicing, and that depletion of nuclear TDP-43 results in increased inclusion of a cassette exon in the HNRNPA1 transcript, and consequently elevated protein levels of an isoform containing an elongated prion-like domain, referred to as hnRNP A1B. Combined in vivo and in vitro approaches demonstrated greater fibrillization propensity for hnRNP A1B, which drives protein aggregation and is toxic to cells. Moreover, amyotrophic lateral sclerosis patients with documented TDP-43 pathology showed neuronal hnRNP A1B cytoplasmic accumulation, indicating that TDP-43 mislocalization may contribute to neuronal vulnerability and loss via altered HNRNPA1 pre-mRNA splicing and function. Given that TDP-43 and hnRNP A1 each bind, and thus modulate, a third of the transcriptome, our data suggest a much broader disruption in RNA metabolism than previously considered.

Selective bacterial degradation of the extracellular matrix attaching the gingiva to the tooth.

The junctional epithelium (JE) is a specialized portion of the gingiva that seals off the tooth-supporting tissues from the oral environment. This relationship is achieved via a unique adhesive extracellular matrix that is, in fact, a specialized basal lamina (sBL). Three unique proteins - amelotin (AMTN), odontogenic ameloblast-associated (ODAM), and secretory calcium-binding phosphoprotein proline-glutamine rich 1 (SCPPPQ1) - together with laminin-332 structure the supramolecular organization of this sBL and determine its adhesive capacity. Despite the constant challenge of the JE by the oral microbiome, little is known of the susceptibility of the sBL to bacterial degradation. Assays with trypsin-like proteases, as well as incubation with Porphyromonas gingivalis, Prevotella intermedia, and Treponema denticola, revealed that all constituents, except SCPPPQ1, were rapidly degraded. Porphyromonas gingivalis was also shown to alter the supramolecular network of reconstituted and native sBLs. These results provide evidence that proteolytic enzymes and selected gram-negative periodontopathogenic bacteria can attack this adhesive extracellular matrix, intimating that its degradation could contribute to progression of periodontal diseases.

High-yield production of human Dicer by transfection of human HEK293-EBNA1 cells grown in suspension.

BACKGROUND: Dicer is a 219-kDa protein that plays key roles in gene regulation, particularly as the ribonuclease III enzyme responsible for cleaving precursor miRNA substrates. Its enzymatic activity is highly regulated by protein factors, and this regulation can impact on the levels of miRNAs and modulate the behavior of a cell. To better understand the underlying mechanisms of regulation, detailed enzymatic and structural characterization of Dicer are needed. However, these types of studies generally require several milligrams of recombinant protein, and efficient preparation of such quantities of pure human Dicer remains a challenge. To prepare large quantities of human Dicer, we have optimized transfection in HEK293-6E cells grown in suspension and streamlined a purification procedure. RESULTS: Transfection conditions were first optimized to achieve expression levels between 10 and 18 mg of recombinant Dicer per liter of culture. A three-step purification protocol was then developed that yields 4-9 mg of purified Dicer per liter of culture in a single day. From SEC-MALS/RI analysis and negative stain TEM, we confirmed that the purified protein is monomerically pure ( ≥ 98%) and folds with the characteristic L-shape geometry. Using an electrophoretic mobility shift assay, a dissociation constant (Kd) of 5 nM was measured for Dicer binding to pre-let-7a-1, in agreement with previous reports. However, when probing the cleavage activity of Dicer for pre-let-7a-1, we measured kcat (7.2 ± 0.5 min- 1) and KM (1.2 ± 0.3 µM) values that are much higher than previously reported due to experimental conditions that better respect the steady-state assumption. CONCLUSIONS: The expression and purification protocols described here provide high yields of monomerically pure and active human Dicer. Cleavage studies of a pre-let-7 substrate with this purified Dicer reveal higher kcat and KM values than previously reported and support the current view that conformational changes are associated with substrate binding. Large quantities of highly pure Dicer will be valuable for future biochemical, biophysical and structural investigations of this key protein of the miRNA pathway.

Absence of the dermatan sulfate chain of decorin does not affect mouse development.

BACKGROUND: In vitro studies suggest that the multiple functions of decorin are related to both its core protein and its dermatan sulfate chain. To determine the contribution of the dermatan sulfate chain to the functional properties of decorin in vivo, a mutant mouse whose decorin lacked a dermatan sulfate chain was generated. RESULTS: Homozygous mice expressing only the decorin core protein developed and grew in a similar manner to wild type mice. In both embryonic and postnatal mice, all connective tissues studied, including cartilage, skin and cornea, appeared to be normal upon histological examination, and their collagen fibrils were of normal diameter and organization. In addition, abdominal skin wounds healed in an identical manner in the mutant and wild type mice. CONCLUSIONS: The absence of a dermatan sulfate chain on decorin does not appear to overtly influence its functional properties in vivo.

Influence of periodontal tissue thickness on buccal plate remodelling on immediate implants with xenograft.

AIM: To evaluate the influence of gingival thickness and bone grafting on buccal bone plate remodelling after immediate implant placement in sockets with thin buccal bone, using a flapless approach. MATERIALS AND METHODS: The gingiva of eight dogs was thinned at one side of the mandible, mandibular premolars were extracted without flaps, and four implants were installed on each side at 1.5 mm from the buccal bone. The sites were randomly assigned into: TG (test group) = thin gingiva; TG + GM (TG with grafting material); CG (control group) = normal gingiva; and CG + GM (CG with grafting material). After 12 weeks the dogs were sacrificed and the samples were processed for histological analysis. RESULTS: All animals exhibited a thin buccal bone initially. In all the experimental groups the buccal gap was filled with newly formed bone and the buccal bone level was slightly apical to the implant shoulder. There were no statistically significant differences among the groups for the histomorphometric parameters. CONCLUSIONS: The thickness of the buccal bone was a fundamental factor in buccal bone plate resorption, even with flapless implantation. The gingival thickness or the addition of a biomaterial in the gap did not influence the results.

Histomorphometric analysis of overloading on palatal tooth movement into the maxillary sinus.

INTRODUCTION: Our objective was to evaluate the effect of overloading on the palatal movement of the maxillary molar. METHODS: The maxillary first molars of male C57Bl/6 mice were moved palatally with loads of 10 or 30 g for 14 days, and the amount of tooth movement was longitudinally measured on microcomputed tomography images. Bone remodeling around the molar root with the 30-g load was evaluated at days 3, 5, 7, and 14 after the start of tooth movement using histomorphometry and immunodetection of bone-restricted interferon inducible transmembrane-like protein, a novel marker of active bone formation. RESULTS: In the 10-g load group, the amount of tooth movement increased dramatically between days 5 and 7 and increased gradually thereafter. Tooth movement at days 5 and 7 was significantly lower in the 30-g-load group than in the 10-g load group; however, the total tooth movement at 14 days was similar in the 2 groups. An orthodontic load of 30 g stimulated bone formation on the sinus wall, but bone resorption on the periodontal ligament side was delayed because of hyalinization, which means that strong force application did not accelerate tooth movement. Moreover, some root resorption was induced by the excessive force. CONCLUSIONS: Root penetration into the sinus and bone height reduction do not occur because new bone formation on the maxillary sinus is induced before bone resorption on the periodontal side, even though an excessive orthodontic force is applied. However, an excessive force can induce root resorption.

Osteogenic cell cultures cannot utilize exogenous sources of synthetic polyphosphate for mineralization.

Phosphate is critical for mineralization and deficiencies in the regulation of free phosphate lead to disease. Inorganic polyphosphates (polyPs) may represent a physiological source of phosphate because they can be hydrolyzed by biological phosphatases. To investigate whether exogenous polyP could be utilized for mineral formation, mineralization was evaluated in two osteogenic cell lines, Saos-2 and MC3T3, expressing different levels of tissue non-specific alkaline phosphatase (tnALP). The role of tnALP was further explored by lentiviral-mediated overexpression in MC3T3 cells. When cells were cultured in the presence of three different phosphate sources, there was a strong mineralization response with ß-glycerophosphate (ßGP) and orthophosphate (Pi) but none of the cultures sustained mineralization in the presence of polyP (neither chain length 17-Pi nor 42-Pi). Even in the presence of mineralizing levels of phosphate, low concentrations of polyP (50 µM) were sufficient to inhibit mineral formation. Energy-dispersive X-ray spectroscopy confirmed the presence of apatite-like mineral deposits in MC3T3 cultures supplemented with ßGP, but not in those with polyP. While von Kossa staining was consistent with the presence or absence of mineral, an unusual Alizarin staining was obtained in polyP-treated MC3T3 cultures. This staining pattern combined with low Ca:P ratios suggests the persistence of Ca-polyP complexes, even with high residual ALP activity. In conclusion, under standard culture conditions, exogenous polyP does not promote mineral deposition. This is not due to a lack of active ALP, and unless conditions that favor significant processing of polyP are achieved, its mineral inhibitory capacity predominates.

Characterisation of secretory calcium-binding phosphoprotein-proline-glutamine-rich 1: a novel basal lamina component expressed at cell-tooth interfaces.

Functional genomic screening of the rat enamel organ (EO) has led to the identification of a number of secreted proteins expressed during the maturation stage of amelogenesis, including amelotin (AMTN) and odontogenic ameloblast-associated (ODAM). In this study, we characterise the gene, protein and pattern of expression of a related protein called secretory calcium-binding phosphoprotein-proline-glutamine-rich 1 (SCPPPQ1). The Scpppq1 gene resides within the secretory calcium-binding phosphoprotein (Scpp) cluster. SCPPPQ1 is a highly conserved, 75-residue, secreted protein rich in proline, leucine, glutamine and phenylalanine. In silico data mining has revealed no correlation to any known sequences. Northern blotting of various rat tissues suggests that the expression of Scpppq1 is restricted to tooth and associated tissues. Immunohistochemical analyses show that the protein is expressed during the late maturation stage of amelogenesis and in the junctional epithelium where it localises to an atypical basal lamina at the cell-tooth interface. This discrete localisation suggests that SCPPPQ1, together with AMTN and ODAM, participates in structuring the basal lamina and in mediating attachment of epithelia cells to mineralised tooth surfaces.

Platelet extracellular vesicles preserve lymphatic endothelial cell integrity and enhance lymphatic vessel function.

Lymphatic vessels are essential for preventing the accumulation of harmful components within peripheral tissues, including the artery wall. Various endogenous mechanisms maintain adequate lymphatic function throughout life, with platelets being essential for preserving lymphatic vessel integrity. However, since lymph lacks platelets, their impact on the lymphatic system has long been viewed as restricted to areas where lymphatics intersect with blood vessels. Nevertheless, platelets can also exert long range effects through the release of extracellular vesicles (EVs) upon activation. We observed that platelet EVs (PEVs) are present in lymph, a compartment to which they could transfer regulatory effects of platelets. Here, we report that PEVs in lymph exhibit a distinct signature enabling them to interact with lymphatic endothelial cells (LECs). In vitro experiments show that the internalization of PEVs by LECs maintains their functional integrity. Treatment with PEVs improves lymphatic contraction capacity in atherosclerosis-prone mice. We suggest that boosting lymphatic pumping with exogenous PEVs offers a novel therapeutic approach for chronic inflammatory diseases characterized by defective lymphatics.

A review of phosphate mineral nucleation in biology and geobiology.

Relationships between geological phosphorite deposition and biological apatite nucleation have often been overlooked. However, similarities in biological apatite and phosphorite mineralogy suggest that their chemical formation mechanisms may be similar. This review serves to draw parallels between two newly described phosphorite mineralization processes, and proposes a similar novel mechanism for biologically controlled apatite mineral nucleation. This mechanism integrates polyphosphate biochemistry with crystal nucleation theory. Recently, the roles of polyphosphates in the nucleation of marine phosphorites were discovered. Marine bacteria and diatoms have been shown to store and concentrate inorganic phosphate (Pi) as amorphous, polyphosphate granules. Subsequent release of these P reserves into the local marine environment as Pi results in biologically induced phosphorite nucleation. Pi storage and release through an intracellular polyphosphate intermediate may also occur in mineralizing oral bacteria. Polyphosphates may be associated with biologically controlled apatite nucleation within vertebrates and invertebrates. Historically, biological apatite nucleation has been attributed to either a biochemical increase in local Pi concentration or matrix-mediated apatite nucleation control. This review proposes a mechanism that integrates both theories. Intracellular and extracellular amorphous granules, rich in both calcium and phosphorus, have been observed in apatite-biomineralizing vertebrates, protists, and atremate brachiopods. These granules may represent stores of calcium-polyphosphate. Not unlike phosphorite nucleation by bacteria and diatoms, polyphosphate depolymerization to Pi would be controlled by phosphatase activity. Enzymatic polyphosphate depolymerization would increase apatite saturation to the level required for mineral nucleation, while matrix proteins would simultaneously control the progression of new biological apatite formation.

Expression of odontogenic ameloblast-associated and amelotin proteins in the junctional epithelium.

Two novel proteins - odontogenic ameloblast-associated protein and amelotin - have recently been identified in maturation-stage ameloblasts and in the junctional epithelium. This article reviews the structure and function of the junctional epithelium, the pattern of expression of odontogenic ameloblast-associated and amelotin proteins and the potential involvement of these proteins in the formation and regeneration of the junctional epithelium.

Mechanical stress induces bone formation in the maxillary sinus in a short-term mouse model.

OBJECTIVES: Clinicians occasionally face the challenge of moving a tooth through the maxillary sinus. The objective of this study was to evaluate tissue remodeling during tooth movement into the maxillary sinus, more specifically as regards to bone formation. MATERIALS AND METHODS: The maxillary first molar of 20 male mice was moved toward the palatal side by a nickel-titanium super elastic wire for 1 to 14 days, and the bone remodeling around the root was evaluated using histomorphometry and immunodetection of bone-restricted Ifitm-like (Bril) protein, a novel marker of active bone formation. RESULTS: When mechanical stress was applied to the tooth, the periodontal ligament on the palatal side was immediately compressed to approximately half of its original width by the tipping movement of the tooth. At the same time, osteoblasts deposited new bone on the wall of the maxillary sinus prior to bone resorption by osteoclasts on the periodontal side, as evidenced by the high level of expression of Bril at this site. As a result of these sequential processes, bone on the sinus side maintained a consistent thickness during the entire observation period. No root resorption was observed. CONCLUSIONS: Bone formation on the surface of the maxillary sinus was evoked by mechanotransduction of mechanical stress applied to a tooth over a 2-week period, and was induced ahead of bone resorption on the periodontal ligament side. CLINICAL RELEVANCE: Mechanical stress can be exploited to induce bone formation in the maxillary sinus so that teeth can be moved into the sinus without losing bone or causing root damage.