Biology subjects

Waters, S.

Publications and source records attributed to Waters, S..

17 recordsLinked to original sources

bioRxiv2026

Proteolytic control of the SARS-CoV-2 furin cleavage site defines the phenotypic evolution from the pandemic to endemic state

The successive emergence of SARS-CoV-2 variants with altered tissue tropism has progressively decoupled transmissibility from lower respiratory tract pathogenicity. Omicron lineages transmit exceptionally well whilst limiting severe lung disease. Here, we demonstrate that this phenotype has evolved through two temporally distinct tissue-specific proteolytic controls at the Spike (S) furin cleavage site (FCS). At the virion level, cell-type-dependent furin-mediated FCS hyper-cleavage depletes S in lung but not nasal epithelial cells. At the infected cell membrane during cell-cell spread, TMPRSS2 mediates S FCS cleavage but is negatively regulated in the presence of ACE2. Tissue-specific solute carriers SLC6A19 and SLC6A20 sequester ACE2, thereby relieving inhibition of TMPRSS2 and enabling S FCS cleavage during cell-cell spread. Critically, whilst all SARS-CoV-2 lineages benefit from this latter pathway, Omicron variants have evolved exclusive dependence on it, a strategic consolidation that focuses S proteolytic activation to TMPRSS2 alone. The combined outcomes of S protein regulation across viral and cell membranes reveal how tissue-specific proteolytic optimisation drives Omicron's transmission fitness advantage in the upper respiratory tract but at the cost of heavy attenuation in the lower respiratory tract.

microbiology↗

bioRxiv2026

Experimental flowering order shapes priority effects in plant-pollinator interactions

Climate change is disrupting life's seasonal rhythms, altering the timing of key phenophases and reshaping how communities assemble. Beyond shifting flowering times, climate change can modify the extent of floral overlap and the sequence in which species bloom, generating novel assemblages with uncertain consequences for plant-pollinator interactions. Here, we ask whether flowering order generates priority effects in plant-pollinator communities, much like germination order does in plant communities. We tested how flowering order influences bee foraging behaviour and plant reproductive success in two co-flowering species, Hypochaeris radicata and Campanula rotundifolia, using a greenhouse experiment in which we manipulated the sequence of floral availability while allowing bees to forage repeatedly. We quantified changes in visit frequency, interspecific switches, handling time, and seed production. Our findings reveal priority effects in bee foraging that were strong enough to affect plant fitness: both species received more visits when flowering earlier than their co-occurring counterpart, and seed production declined when species flowered later. Overall, our results show that flowering order is an underappreciated driver of plant-pollinator interactions, suggesting that climate-driven phenological shifts could alter priority-effect dynamics with broader implications for community assembly. Key questions remain: How will climate-driven phenological shifts rearrange flowering sequences, and how will these priority effects emerge in more diverse communities in the wild? Our controlled experiment reveals strong flowering-order effects, underscoring the need to evaluate how widespread and impactful such dynamics are under accelerating climate change.

ecology↗

bioRxiv2025

Biomechanics of yawning: insights into cranio-cervical fluid dynamics and kinematic consistency

Yawning is a stereotyped orofacial-respiratory behaviour whose physiological role remains uncertain. Because cerebrospinal fluid (CSF) movement contributes to solute transport and waste removal and is strongly influenced by respiratory pressure dynamics, the study evaluated whether yawning alters neurofluid flow relative to normal and deep breathing, and whether yawning kinematics are reproducible within individuals. In a single MRI session in healthy adults, real-time phase-contrast imaging at the upper cervical level (C3) was combined with mid-sagittal real-time cine imaging to quantify CSF and internal jugular venous flows during normal breathing, forceful oral inspirations (deep breaths), yawns, and stifled yawns, and to derive tongue-motion trajectories. Both deep breaths and yawns increased CSF and venous flow compared with normal breathing; despite similar flow magnitudes, yawns more frequently produced co-directional caudal CSF and jugular outflow during inspiration, whereas deep breaths typically showed counter-directional CSF-venous flow. Yawning kinematics were highly reproducible within individuals across repeated events, indicating a stable motor sequence consistent with brainstem pattern-generator control. These observations show that yawning is not simply an intensified breath but a distinct cardiorespiratory manoeuvre that reorganizes neurofluid flow. The inspiratory alignment of CSF with venous outflow during yawns suggests a transient caudal advection that could influence solute transport and heat exchange within the cranial-cervical system, motivating targeted mechanistic studies with simultaneous airway pressure, thoraco-abdominal motion, and cervical venous pressure measurements.

physiology↗

bioRxiv2025

Phage-encoded sRNA counteracts xenogenic silencing in pathogenic E. coli

Horizontal gene transfer introduces foreign DNA that can disrupt cellular processes and is therefore subject to xenogenic silencing by nucleoid-associated proteins such as H-NS and Hha. In Enterohaemorrhagic Escherichia coli (EHEC), prophages make up a large fraction of the accessory genome and encode many virulence factors, yet to be expressed they must overcome this silencing. We identify a prophage-encoded small RNA (sRNA), HnrS, that functions as an anti-silencing factor by targeting the H-NS paralogue Hha. HnrS is a short (66-nt) sRNA present in multiple copies (up to nine) in EHEC and Enteropathogenic Escherichia coli (EPEC) genomes and is enriched in E. coli strains that carry the locus of enterocyte effacement (LEE). We show that HnrS directly base-pairs with the ribosome-binding site of the hha mRNA, repressing its translation and thereby reducing Hha-enhanced H-NS silencing. This counter-silencing de-represses the LEE type III secretion system and concomitantly represses motility. Transcriptomic profiling further revealed that HnrS indirectly activates genes involved in nitrate/nitrite respiration and nitric oxide resistance, metabolic pathways that contribute to survival in the inflamed gastrointestinal tract. Deletion of hnrS reduced expression of nitrate reductase genes and impaired actin pedestal formation on host epithelial cells. Our results indicate that prophage-encoded, multicopy hnrS provides a counter-silencing mechanism that reduces Hha-H-NS repression at specific virulence loci. This likely enables expression of horizontally acquired genes without broadly disrupting the core H-NS regulon. HnrS illustrates how mobile genetic elements deploy sRNAs to counteract xenogenic silencing and promote virulence gene expression, enhancing colonisation of the host. Importance statementHorizontally acquired genes are often silenced to protect bacterial genomes, but this defence also limits the expression of new traits. We identify a prophage-encoded small RNA, HnrS, that counteracts this restriction by repressing the xenogenic silencer Hha, lifting Hha-H-NS-mediated repression of virulence and metabolic genes. HnrS activates the locus of enterocyte effacement, nitrate/nitrite respiration, and nitric oxide resistance--pathways that help E. coli survive and colonise the inflamed gut. Our findings reveal an RNA-based counter-silencing mechanism encoded by mobile genetic elements, showing how phages can reprogram bacterial regulatory networks to promote adaptation and pathogenicity.

microbiology↗

bioRxiv2025

Replication of SARS-CoV-2 Omicron lineages is defined by TMPRSS2 use in environments where ACE2 is complexed with solute carriers SLC6A19 and SLC6A20.

The Omicron variant of SARS-CoV-2 emerged in late 2021 and since then Omicron subvariants have continued to evolve and dominate globally. The viral S protein evolved towards highly efficient antibody evasion and replicative capacity in the upper respiratory tract resulting in high transmissibility. At the same time, the mutations acquired in the S protein diminish infection of the lung epithelium and pathogenic potential. The changing entry requirements for Omicron sub-lineages that lead to this shift in tropism remain poorly understood. We resolve the changing replication requirements of SARS-CoV-2 to be related to two distinct pools of ACE2. The first pool relates to ACE2s role in the renin angiotensin system (RAS) and this pool can complex with TMPRSS2 (RAS-ACE2). The second pool relates to ACE2s role as a protein solute carrier chaperone than cannot complex with TMPRSS2 (Chaperone ACE2). Here, we demonstrate that pre-Omicron lineages replicate in a TMPRSS2 dependent manner across both ACE2 pools, whilst Omicron lineages can only spread and replicate using chaperone ACE2. This provides a mechanistic basis for the evolving infectivity requirements of SARS-CoV-2 and furthermore provides approaches to track and monitor ACE2 utilizing coronaviruses. Graphical AbstractMechanistic basis for shift in SARS-CoV-2 tropism with the arrival of Omicron. A. Chaperone ACE2 is defined structurally as a heterodimer of dimers with a solute carrier protein-SLC6A19 or SLC6A20. Here this ACE2 structure can exist uncomplexed from TMPRSS2 and enables TMPRSS2 use by both pre-Omicron and Omicron lineages. B. Renin Angiotensin ACE2 is defined by ACE2 with an exposed collectrin-like domain (CLD), which enables binding of TMPRSS2 or ADAM-17. Here ACE2 can form a complex with TMPRSS2 in a manner that allows pre-Omicron but not Omicron lineages to utilize TMPRSS2 to facilitate infection. Here Omicron lineages are heavily attenuated as they cannot use TMPRSS2 to spread. C. to E. Based on single cell profiles, ACE2 can exist as a chaperone with SLC6A20 in C. the Nasal Cavity or D. primarily as RAS-ACE2 in the lung to respond to acute lung injury. E. The largest pool of ACE2 in our body resides within the small intestine on enterocytes and this further facilitates replication in this tissue by pre-Omicron and Omicron lineages. O_FIG O_LINKSMALLFIG WIDTH=198 HEIGHT=200 SRC="FIGDIR/small/663433v1_ufig1.gif" ALT="Figure 1"> View larger version (40K): org.highwire.dtl.DTLVardef@172aa47org.highwire.dtl.DTLVardef@109285eorg.highwire.dtl.DTLVardef@394f8corg.highwire.dtl.DTLVardef@958e31_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2024

Use of Stem Cell-Derived Cardiomyocyte and Nasal Epithelium Models to Establish a Multi-Tissue Model Platform to Validate Repurposed Drugs Against SARS-CoV-2 Infection

The novel coronavirus disease (COVID-19) and any future coronavirus outbreaks will require more affordable, effective and safe treatment options to complement current ones such as Paxlovid. Drug repurposing can be a promising approach if we are able to find a rapid, robust and reliable way to down-select and screen candidates using in silico and in vitro approaches. With repurposed drugs, ex vivo models could offer a rigorous route to human clinical trials with less time invested into nonclinical animal (in vivo) studies. We have previously shown the value of commercially available ex vivo/3D airway and alveolar tissue models, and this paper takes this further by developing and validating human nasal epithelial model and embryonic stem cells derived cardiomyocyte model. Five shortlisted candidates (fluvoxamine, everolimus, pyrimethamine, aprepitant and sirolimus) were successfully compared with three control drugs (remdesivir, molnupiravir, nirmatrelvir) when tested against key variants of the SARS-CoV-2 virus including Delta and Omicron, and we were able to reconfirm our earlier finding that fluvoxamine can induce antiviral efficacy in combination with other drugs. Scalability of this high-throughput screening approach has been demonstrated using a liquid handling robotic platform for future Disease-X outbreaks.

microbiology↗

bioRxiv2023

Functional coherence of the Xist and RSX protein interactomes: X chromosome inactivation marsupials

Long range epigenetic silencing is epitomised by X chromosome inactivation (XCI) in mammals. It is mediated by independently evolved, non-homologous long noncoding RNAs in eutherian and marsupial mammals (XIST and RSX). The Xist interactome, comprising proteins that mediate the silencing process, is well documented in mouse studies. Here we interrogate proteins that interact with RSX using chromatin isolation by RNA purification followed by mass spectrometry (ChIRP-MS) in a marsupial representative, Monodelphis domestica. We identify 135 proteins that interact with RSX, of which 56 have orthologues in the Xist interactome. Remarkably, nearly 90% of the combined Xist and RSX interactomes are within the same protein-protein association network. This network clustered into three major groups with distinctive functional enrichments, including RNA splicing and processing, regulation of translation and ribosomal biogenesis, and epigenetic transcriptional silencing. The proteins of the RSX interactome were enriched for regions of intrinsic disorder in common with the Xist interactome, identifying this as a feature of ribonucleoprotein complexes associated with XCI. We also show that RNAi knockdown of representative RSX interactors, HNRNPK and CKAP4, led to reactivation of transcription from the inactive X chromosome, indicating a role for each in marsupial XCI. Thus, despite the absence of linear sequence homology between Xist and RSX, they exhibit extraordinary functional coherence that indicates potential for post-transcriptional regulation, a feature not previously associated with the molecular machinery of XCI.

genetics↗

bioRxiv2023

Incomplete transcriptional dosage compensation of vertebrate sex chromosomes is balanced by post-transcriptional compensation.

Heteromorphic sex chromosomes (XY or ZW) present problems of gene dosage imbalance between the sexes, and with the autosomes. Mammalian X chromosome inactivation was long thought to imply a critical need for dosage compensation in vertebrates. However, the universal importance of sex chromosome dosage compensation was questioned by mRNA abundance measurements that demonstrated sex chromosome transcripts are neither balanced between the sexes or with autosomes in monotreme mammals or birds. Here, we demonstrate unbalanced mRNA levels of X genes in platypus males and females that correlate with differential loading of histone modifications, and confirm that transcripts of Z genes are unbalanced between males and females also in chicken. However, we found that in both species, median male to female protein abundance ratios were 1:1, implying an additional level of post-transcriptional control. We conclude that parity of sex chromosome output is achieved in birds, as well as all mammal groups, by a combination of transcriptional and post-transcriptional control, consistent with an essential role for sex chromosome dosage compensation in vertebrates.

evolutionary biology↗

bioRxiv2022

Copper chelation inhibits TGF-β pathways and suppresses epithelial-mesenchymal transition in cancer

Copper is a trace element essential to cellular function with elevated levels implicated in cancer progression. Clinical trials using copper chelators are associated with improved patient survival, however, the molecular mechanisms by which copper depletion inhibits tumor progression are poorly understood. This remains a major hurdle to the clinical translation of copper chelators. Epithelial-mesenchymal transition (EMT) is often exploited by malignant cells to promote growth and metastasis. Transforming growth factor (TGF)-{beta} is a master regulator of EMT and facilitates cancer progression through changes in the tumor and its microenvironment. Herein, we report that a reduction of copper with the chelating agent tetraethylenepentamine (TEPA) inhibited EMT in vitro in three diverse cancer cell types; human triple-negative breast cancer (TNBC), neuroblastoma (NB), and diffuse intrinsic pontine glioma (DIPG) cell lines. Single-molecule imaging demonstrated EMT markers including Vimentin, {beta}-catenin, ZEB1, and p-SMAD2 had increased expression with copper treatment and this pro-mesenchymal shift was rescued by the addition of TEPA. Moreover, SNAI1, ZEB1, and p-SMAD2 demonstrated increased accumulation in the cytoplasm after treating with TEPA. Transcriptomic analyses revealed a significant downregulation of the EMT pathway, including canonical (TGF-{beta}/SMAD2&3) and non-canonical (TGF-{beta}/PI3K/AKT and TGF-{beta}/RAS/RAF/MEK/ERK) TGF signaling pathways. Matrix metalloproteinases MMP-9 and MMP-14 proteins which activate latent TGF-{beta} complexes were also downregulated by TEPA treatment. These molecular changes are consistent with reduced plasma levels of TGF-{beta} we observed in cancer models treated with TEPA. Importantly, copper chelation reduced metastasis to the lung in a TNBC orthotopic syngeneic mouse model. Our studies suggest copper chelation therapy can be used to inhibit EMT-induced metastasis by targeting TGF-{beta} signalling. Because on-target anti-TGF-{beta} therapies are failing in the clinic, copper chelation presents itself as a potential therapy for targeting TGF-{beta} in cancer.

cancer biology↗

bioRxiv2022

The metabolic influence of the core ciliate Entodinium caudatum within the rumen microbiome

Protozoa comprise a major fraction of the microbial biomass in the rumen microbiome, of which the entodiniomorphs (order: Entodiniomorphida) and holotrichs (order: Vestibuliferida) are consistently observed to be dominant across a diverse genetic and geographical range of ruminant hosts. Despite the apparent core role that protozoal species exert, their major biological and metabolic contributions to rumen function remain largely undescribed in vivo. Here, we have leveraged (meta)genome-centric metaproteomes from rumen fluid samples originating from both cattle and goats fed diets with varying inclusion levels of lipids and starch, to detail the specific metabolic niches that protozoa occupy in the context of their microbial co-habitants. Initial proteome estimations via total protein counts and label-free quantification highlight that entodiniomorph species Entodinium and Epidinium as well as the holotrichs Dasytricha and Isotricha comprise an extensive fraction of the total rumen metaproteome. Proteomic detection of protozoal metabolism such as hydrogenases (Dasytricha, Isotricha, Epidinium, Enoploplastron), carbohydrate-active enzymes (Epidinium, Diplodinium, Enoploplastron, Polyplastron), microbial predation (Entodinium) and volatile fatty acid production (Entodinium and Epidinium) was observed at increased levels in high methane-emitting animals. Despite certain protozoal species having well-established reputations for digesting starch, they were unexpectedly less detectable in low methane emitting-animals fed high starch diets, which were instead dominated by propionate/succinate-producing bacterial populations suspected of being resistant to predation irrespective of host. Finally, we reaffirmed our abovementioned observations in geographically independent datasets, thus illuminating the substantial metabolic influence that under-explored eukaryotic populations have in the rumen, with greater implications for both digestion and methane metabolism.

microbiology↗

bioRxiv2021

In silico and functional characterisation of an ultra-rare CFTR mutation identifies novel lasso motif interactions regulating channel gating

Characterisation of I37R - a novel mutation in the lasso motif of ABC-transporter CFTR, a chloride channel - was conducted by theratyping using CFTR potentiators which increase channel gating activity and correctors which repair protein trafficking defects. I37R-CFTR function was characterised using intestinal current measurements (ICM) in rectal biopsies, forskolin-induced swelling (FIS) in intestinal organoids and short circuit current measurements (Isc) in organoid-derived monolayers from an individual with I37R/F508del CFTR genotype. We demonstrated that the I37R-CFTR mutation results in a residual function defect amenable to treatment with potentiators and type III, but not to type I, correctors. Molecular dynamics of I37R-CFTR using an extended model of the phosphorylated, ATP-bound human CFTR identified an altered lasso motif conformation which results in an unfavourable strengthening of the interactions between the lasso motif, the regulatory (R) domain and the transmembrane domain two (TMD2). In conclusion, structural and functional characterisation of the I37R-CFTR mutation increases understanding of CFTR channel regulation and provides a potential pathway to access CFTR modulator treatments for individuals with CF caused by ultra-rare CFTR mutations.

molecular biology↗

bioRxiv2021

Molecular dynamics and theratyping in airway and gut organoids reveal R352Q-CFTR conductance defect

A significant challenge to making targeted CFTR modulator therapies accessible to all individuals with cystic fibrosis (CF) are many mutations in the CFTR gene that can cause CF, most of which remain uncharacterized. Here, we characterized the structural and functional defects of the rare CFTR mutation R352Q - with potential role contributing to intrapore chloride ion permeation - in patient-derived cell models of the airway and gut. CFTR function in differentiated nasal epithelial cultures and matched intestinal organoids was assessed using ion transport assay and forskolin-induced swelling (FIS) assay respectively. Two CFTR potentiators (VX-770, GLPG1837) and a corrector (VX-809) were tested. Data from R352Q-CFTR were compared to that of participants with mutations with known impact on CFTR function. R352Q-CFTR has residual CFTR function which was restored to functional CFTR activity by CFTR potentiators but not the corrector. Molecular dynamics (MD) simulations of R352Q-CFTR were carried out which indicated the presence of a chloride conductance defect, with little evidence supporting a gating defect. The combination approach of in vitro patient-derived cell models and in silico MD simulations to characterize rare CFTR mutations can improve the specificity and sensitivity of modulator response predictions and aid in their translational use for CF precision medicine.

molecular biology↗

bioRxiv2021

Remote spatially variant debiased profiling of cell and tissue mechanical properties

The role of the mechanical environment in defining tissue function, development and growth has been shown to be fundamental. Assessment of the changes in stiffness of tissue matrices at multiple scales has relied mostly on invasive and often specialist equipment such as AFM or mechanical testing devices poorly suited to the cell culture workflow.In this paper, we have developed a novel unbiased passive optical coherence elastography method, exploiting ambient vibrations in the sample that enables real-time noninvasive quantitative profiling of cells and tissues. We demonstrate a robust method that decouples optical scattering and mechanical properties by actively compensating for scattering associated noise bias and reducing variance. The efficiency for the method to retrieve ground truth is validated in silico and in vitro, and exemplified for key applications such as time course mechanical profiling of bone and cartilage spheroids, tissue engineering cancer models, tissue repair models and single cell. Our method is readily implementable with any commercial optical coherence tomography system without any hardware modifications, and thus offers a breakthrough in tissue mechanical assessment for novel on line assessment of spatial mechanical properties for organoids, soft tissues and tissue engineering.

bioengineering↗

bioRxiv2020

Significant functional differences despite morphological and molecular similarity in fully differentiated matched Conditionally Reprogrammed (CRC) and Feeder free dual SMAD inhibited expanded human nasal epithelial cells

BackgroundPatient-derived airway cells differentiated at Air Liquid Interface (ALI) are valuable models for Cystic fibrosis (CF) precision therapy. Advances in culture techniques have improved expansion capacity of airway basal cells, while retaining functional airway epithelium physiology. However, considerable variation in response to CFTR modulators is observed even when using similar ALI culture techniques. We aimed to address if variation in response reflects true biological differences between patients or technical differences as a consequence of different culture expansion methods. MethodsNasal epithelial brushings from 14 individuals (CF=9; non-CF=5) were collected, then equally divided and expanded under conditional reprogramming culture (CRC) and feeder-serum-free "dual-SMAD inhibition" (SMADi) methods. Expanded cells from each culture were differentiated with proprietary PneumaCult-ALI media. Morphology (Immunofluorescence), global proteomics (LC-MS/MS) and function (barrier integrity, cilia motility, and ion transport) were compared in CRCALI and SMADiALI under basal and CFTR corrector treated (VX-809) conditions. ResultsNo significant difference in the structural morphology or global proteomics profile were observed. Barrier integrity and cilia motility were significantly different, despite no difference in cell junction morphology or cilia abundance. Epithelial Sodium Channels and Calcium-activated Chloride Channel activity did not differ but CFTR mediated chloride currents were significantly reduced in SMADiALI compare to their CRCALI counterparts. ConclusionAlteration of cellular physiological function in vitro occurs were more prominent than structural and differentiation potential in airway ALI. Since culture conditions significantly influence CFTR activity, this could lead to false conclusions if data from different labs are compared against each other without specific reference ranges.

physiology↗

bioRxiv2019

Blood-spinal cord barrier leakage is not caused by neurodegeneration in amyotrophic lateral sclerosis

BackgroundAmyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease involving progressive degeneration of upper and lower motor neurons. Both lower motor neuron loss and the deposition of phosphorylated TDP-43 inclusions display regional patterning along the spinal cord. The blood-spinal cord barrier (BSCB) ordinarily restricts entry into the spinal cord parenchyma of blood components that are neurotoxic, but in ALS there is evidence for barrier breakdown. Here we sought to examine whether BSCB breakdown, motor neuron loss, and TDP-43 proteinopathy display the same regional patterning across and along the spinal cord.\n\nMethodsWe measured cerebrospinal fluid (CSF) hemoglobin in living ALS patients (n=87 controls, n=236 ALS) as a potential biomarker of BSCB and blood-brain barrier leakage. We then immunostained cervical, thoracic, and lumbar post mortem spinal cord tissue (n=5 controls, n=13 ALS) and employed semi-automated imaging and analysis to quantify and map lower motor neuron loss and phosphorylated TDP-43 inclusion load against hemoglobin leakage.\n\nResultsMotor neuron loss and TDP-43 proteinopathy were seen at all three levels of the ALS spinal cord, with most abundant TDP-43 deposition in the ventral grey (lamina IX) of the cervical and lumbar cord. In contrast, hemoglobin leakage was observed along the ALS spinal cord axis but was most severe in the dorsal grey and white matter in the thoracic spinal cord.\n\nConclusionsOur data show that leakage of the blood-spinal cord barrier occurs during life but at end-stage its distribution is independent from the major motor neuron pathology and is unlikely to be a major contributor to pathogenesis in ALS.

neuroscience↗

bioRxiv2017

Inducing Chondrogenesis In MSC/Chondrocyte Co-Cultures Using Exogenous TGF-β: A Mathematical Model

The differentiation of mesenchymal stem cells (MSCs) into chondrocytes (native cartilage cells), or chondrogenesis, is a key step in the tissue engineering of articular cartilage, where the motility and high proliferation rate of MSCs used as seed cells are exploited. Chondrogenesis is regulated by transforming growth factor-beta (TGF-{beta}), a short-lived cytokine whose effect is prolonged by storage in the extracellular matrix. Tissue engineering applications require the complete differentiation of an initial population of MSCs, and two common strategies used to achieve this in vitro are (1) co-culture the MSCs with chondrocytes, which constitutively produce TGF-{beta}; or (2) add exogenous TGF-{beta}. To investigate these strategies we develop an ordinary differential equation model of the interactions between TGF-{beta}, MSCs and chondrocyte. Here the dynamics of TGF-{beta} are much faster than those of the cell processes; this difference in time-scales is exploited to simplify subsequent model analysis. Using our model we demonstrate that under strategy 1 complete chondrogenesis will be induced if the initial proportion of chondrocytes exceeds a critical value. Similarly, under strategy 2 we find that there is a critical concentration of exogenous TGF-{beta} above which all MSCs will ultimately differentiate. Finally, we use the model to demonstrate the potential advantages of adopting a hybrid strategy where exogenous TGF-{beta} is added to a co-culture of MSCs and chondrocytes, as compared to using either strategy 1 or 2 in isolation.

bioengineering↗

bioRxiv2016

Cooperation not competition: bihemispheric tDCS and fMRI show role for ipsilateral hemisphere in motor learning

What is the role of ipsilateral motor and pre-motor areas in motor learning? One view supposes that ipsilateral activity suppresses contralateral motor cortex, and thus needs to be inhibited to improve motor learning. Alternatively, the ipsilateral motor cortex may play an active role in the control and learning of unilateral hand movements. We approached this question by applying double-blind bihemispheric transcranial direct current stimulation (tDCS) over both contralateral and ipsilateral motor cortex in a between-group design during four days of unimanual explicit sequence training. Independently of whether the anode was placed over contralateral or ipsilateral motor cortex, bihemispheric stimulation yielded substantial performance gains relative to unihemispheric or sham stimulation. This performance advantage appeared to be supported by plastic changes in both hemispheres: First, we found that behavioral advantages generalized strongly to the untrained hand, suggesting that tDCS strengthened effector-independent representations. Secondly, functional imaging during speed-matched execution of trained sequences conducted 48 h after training revealed sustained, polarity-independent increases in activity in both motor cortices relative to the sham group. These results suggest a cooperative rather than competitive interaction of the two motor cortices during skill learning and suggest that bihemispheric brain stimulation during unimanual skill learning may be beneficial, because it harnesses plasticity in the ipsilateral hemisphere.\n\nSignificance statementMany neurorehabilitation approaches are based on the idea that is beneficial to boost excitability in the contralateral hemisphere while attenuating that of the ipsilateral cortex to reduce interhemispheric inhibition. We observed that bihemispheric tDCS with the excitatory anode either over contralateral or ipsilateral motor cortex facilitated motor learning nearly twice as strongly as unihemispheric tDCS. These increases in motor learning were accompanied by increases in fMRI activation in both motor cortices that outlasted the stimulation period, as well as increased generalization to the untrained hand. Collectively, our findings suggest a cooperative--rather than competitive--role of the hemispheres and imply that it is most beneficial to harness plasticity in both hemispheres in neurorehabilitation of motor deficits.

neuroscience↗