ATP-Dependent Dynamic Protein Aggregation Regulates Bacterial Dormancy Depth Critical for Antibiotic Tolerance.

Cell dormancy is a widespread mechanism used by bacteria to evade environmental threats, including antibiotics. Here we monitored bacterial antibiotic tolerance and regrowth at the single-cell level and found that each individual survival cell shows different "dormancy depth," which in return regulates the lag time for cell resuscitation after removal of antibiotic. We further established that protein aggresome-a collection of endogenous protein aggregates-is an important indicator of bacterial dormancy depth, whose formation is promoted by decreased cellular ATP level. For cells to leave the dormant state and resuscitate, clearance of protein aggresome and recovery of proteostasis are required. We revealed that the ability to recruit functional DnaK-ClpB machineries, which facilitate protein disaggregation in an ATP-dependent manner, determines the lag time for bacterial regrowth. Better understanding of the key factors regulating bacterial regrowth after surviving antibiotic attack could lead to new therapeutic strategies for combating bacterial antibiotic tolerance.

The metabolic slowdown caused by the deletion of pspA accelerates protein aggregation during stationary phase facilitating antibiotic persistence.

Entering a dormant state is a prevailing mechanism used by bacterial cells to transiently evade antibiotic attacks and become persisters. The dynamic progression of bacterial dormancy depths driven by protein aggregation has been found to be critical for antibiotic persistence in recent years. However, our current understanding of the endogenous genes that affects dormancy depth remains limited. Here, we discovered a novel role of phage shock protein A (pspA) gene in modulating bacterial dormancy depth. Deletion of pspA of Escherichia coli resulted in increased bacterial dormancy depths and prolonged lag times for resuscitation during the stationary phase. ∆pspA exhibited a higher persister ratio compared to the wild type when challenged with various antibiotics. Microscopic images revealed that ∆pspA showed accelerated formation of protein aggresomes, which were collections of endogenous protein aggregates. Time-lapse imaging established the positive correlation between protein aggregation and antibiotic persistence of ∆pspA at the single-cell level. To investigate the molecular mechanism underlying accelerated protein aggregation, we performed transcriptome profiling and found the increased abundance of chaperons and a general metabolic slowdown in the absence of pspA. Consistent with the transcriptomic results, the ∆pspA strain showed a decreased cellular ATP level, which could be rescued by glucose supplementation. Then, we verified that replenishment of cellular ATP levels by adding glucose could inhibit protein aggregation and reduce persister formation in ∆pspA. This study highlights the novel role of pspA in maintaining proteostasis, regulating dormancy depth, and affecting antibiotic persistence during stationary phase.

Enhanced Efflux Activity Facilitates Drug Tolerance in Dormant Bacterial Cells.

Natural variations in gene expression provide a mechanism for multiple phenotypes to arise in an isogenic bacterial population. In particular, a sub-group termed persisters show high tolerance to antibiotics. Previously, their formation has been attributed to cell dormancy. Here we demonstrate that bacterial persisters, under ß-lactam antibiotic treatment, show less cytoplasmic drug accumulation as a result of enhanced efflux activity. Consistently, a number of multi-drug efflux genes, particularly the central component TolC, show higher expression in persisters. Time-lapse imaging and mutagenesis studies further establish a positive correlation between tolC expression and bacterial persistence. The key role of efflux systems, among multiple biological pathways involved in persister formation, indicates that persisters implement a positive defense against antibiotics prior to a passive defense via dormancy. Finally, efflux inhibitors and antibiotics together effectively attenuate persister formation, suggesting a combination strategy to target drug tolerance.

Whole genome analysis of echinocandin non-susceptible Candida Glabrata clinical isolates: a multi-center study in China.

BACKGROUND: Candida glabrata is an important cause of invasive candidiasis. Echinocandins are the first-line treatment of invasive candidiasis caused by C. glabrata. The epidemiological echinocandin sensitivity requires long-term surveillance and the understanding about whole genome characteristics of echinocandin non-susceptible isolates was limited. RESULTS: The present study investigated the echinocandin susceptibility of 1650 C. glabrata clinical isolates in China from August 2014 to July 2019. The in vitro activity of micafungin was significantly better than those of caspofungin and anidulafungin (P < 0.001), assessed by MIC50/90 values. Whole genome sequencing was conducted on non-susceptible isolates and geography-matched susceptible isolates. Thirteen isolates (0.79%) were resistant to at least one echinocandin. Six isolates (0.36%) were solely intermediate to caspofungin. Common evolutionary analysis of echinocandin-resistant and echinocandin-intermediate isolates revealed genes related with reduced caspofungin sensitivity, including previously identified sphinganine hydroxylase encoding gene SUR2. Genome-wide association study identified SNPs at subtelometric regions that were associated with echinocandin non-susceptibility. In-host evolution of echinocandin resistance of serial isolates revealed an enrichment for non-synonymous mutations in adhesins genes and loss of subtelometric regions containing adhesin genes. CONCLUSIONS: The echinocandins are highly active against C. glabrata in China with a resistant rate of 0.79%. Echinocandin non-susceptible isolates carried common evolved genes which are related with reduced caspofungin sensitivity. In-host evolution of C. glabrata accompanied intensive changing of adhesins profile.

TSMiner: a novel framework for generating time-specific gene regulatory networks from time-series expression profiles.

Time-series gene expression profiles are the primary source of information on complicated biological processes; however, capturing dynamic regulatory events from such data is challenging. Herein, we present a novel analytic tool, time-series miner (TSMiner), that can construct time-specific regulatory networks from time-series expression profiles using two groups of genes: (i) genes encoding transcription factors (TFs) that are activated or repressed at a specific time and (ii) genes associated with biological pathways showing significant mutual interactions with these TFs. Compared with existing methods, TSMiner demonstrated superior sensitivity and accuracy. Additionally, the application of TSMiner to a time-course RNA-seq dataset associated with mouse liver regeneration (LR) identified 389 transcriptional activators and 49 transcriptional repressors that were either activated or repressed across the LR process. TSMiner also predicted 109 and 47 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways significantly interacting with the transcriptional activators and repressors, respectively. These findings revealed the temporal dynamics of multiple critical LR-related biological processes, including cell proliferation, metabolism and the immune response. The series of evaluations and experiments demonstrated that TSMiner provides highly reliable predictions and increases the understanding of rapidly accumulating time-series omics data.

Enhanced Antibacterial Ability of Electrospun PCL Scaffolds Incorporating ZnO Nanowires.

The infection of implanted biomaterial scaffolds presents a major challenge. Existing therapeutic solutions, such as antibiotic treatment and silver nanoparticle-containing scaffolds are becoming increasingly impractical because of the growth of antibiotic resistance and the toxicity of silver nanoparticles. We present here a novel concept to overcome these limitations, an electrospun polycaprolactone (PCL) scaffold functionalised with zinc oxide nanowires (ZnO NWs). This study assessed the antibacterial capabilities and biocompatibility of PCL/ZnO scaffolds. The fabricated scaffolds were characterised by SEM and EDX, which showed that the ZnO NWs were successfully incorporated and distributed in the electrospun PCL scaffolds. The antibacterial properties were investigated by co-culturing PCL/ZnO scaffolds with Staphylococcus aureus. Bacterial colonisation was reduced to 51.3% compared to a PCL-only scaffold. The biocompatibility of the PCL/ZnO scaffolds was assessed by culturing them with HaCaT cells. The PCL scaffolds exhibited no changes in cell metabolic activity with the addition of the ZnO nanowires. The antibacterial and biocompatibility properties make PCL/ZnO a good choice for implanted scaffolds, and this work lays a foundation for ZnO NWs-infused PCL scaffolds in the potential clinical application of tissue engineering.

The Nax (SCN7A) channel: an atypical regulator of tissue homeostasis and disease.

Within an articulately characterized family of ion channels, the voltage-gated sodium channels, exists a black sheep, SCN7A (Nax). Nax, in contrast to members of its molecular family, has lost its voltage-gated character and instead rapidly evolved a new function as a concentration-dependent sensor of extracellular sodium ions and subsequent signal transducer. As it deviates fundamentally in function from the rest of its family, and since the bulk of the impressive body of literature elucidating the pathology and biochemistry of voltage-gated sodium channels has been performed in nervous tissue, reports of Nax expression and function have been sparse. Here, we investigate available reports surrounding expression and potential roles for Nax activity outside of nervous tissue. With these studies as justification, we propose that Nax likely acts as an early sensor that detects loss of tissue homeostasis through the pathological accumulation of extracellular sodium and/or through endothelin signaling. Sensation of homeostatic aberration via Nax then proceeds to induce pathological tissue phenotypes via promotion of pro-inflammatory and pro-fibrotic responses, induced through direct regulation of gene expression or through the generation of secondary signaling molecules, such as lactate, that can operate in an autocrine or paracrine fashion. We hope that our synthesis of much of the literature investigating this understudied protein will inspire more research into Nax not simply as a biochemical oddity, but also as a potential pathophysiological regulator and therapeutic target.

Application of decellularized human reticular allograft dermal matrix promotes rapid re-epithelialization in a diabetic murine excisional wound model.

BACKGROUND AIMS: The treatment and care of human wounds represent an enormous burden on the medical system and patients alike. Chronic or delayed healing wounds are characterized by the inability to form proper granulation tissue, followed by deficiencies in keratinocyte migration and wound re-epithelialization, leading to increased likelihood of infection and poor wound outcomes. Human reticular acellular dermal matrix (HR-ADM) is one type of tissue graft developed to enhance closure of delayed healing wounds that has demonstrated clinical utility through accelerating closure of lower extremity diabetic ulcers, but the mechanisms underlying this clinical success are not well understood. METHODS: The authors utilized a diabetic murine splinted excisional wound model to investigate the effects of HR-ADM application on wound closure. RESULTS: The authors demonstrate that application of HR-ADM served as a dermal scaffold and promoted rapid re-epithelialization and keratinocyte proliferation, resulting in accelerated wound closure while minimizing granulation tissue formation. HR-ADM-applied wounds also demonstrated evidence of cellular infiltration, neovascularization and collagen remodeling by the host organism. CONCLUSIONS: These data suggest that HR-ADM supports epidermal closure in delayed healing wounds and remodeling of the matrix into host tissue, lending further support to the clinical success of HR-ADM described in clinical reports.

Knockout of sodium channel Nax delays re-epithelializathion of splinted murine excisional wounds.

Mammalian wound healing is a carefully orchestrated process in which many cellular and molecular effectors respond in concert to perturbed tissue homeostasis in order to close the wound and re-establish the skin barrier. The roles of many of these molecular effectors, however, are not entirely understood. Our lab previously demonstrated that the atypical sodium channel Nax (encoded by Scn7a) responds to wound-induced epidermal dehydration, resulting in molecular cascades that drive pro-inflammatory signaling. Acute inhibition of Nax was sufficient to attenuate dermatopathological symptoms in models of hypertrophic scar and dermatitis. To date, however, the role of Nax in excisional wound healing has not been demonstrated. Here we report development of a knockout mouse that lacks expression of functional Nax , and we demonstrate that lack of functional Nax results in deficient wound healing in a murine splinted excisional wound healing model. This deficiency in wound healing was reflected in impaired re-epithelialization and decreased keratinocyte proliferation, a finding which was further supported by decreased proliferation upon Nax knockdown in HaCaT cells in vitro. Defective wound healing was observed alongside increased expression of inflammatory genes in the wound epidermis of Nax -/- mice, suggesting that mice lacking functional Nax retain the ability to undergo skin inflammation. Our observations here motivate further investigation into the roles of Nax in wound healing and other skin processes.

A General Workflow for Characterization of Nernstian Dyes and Their Effects on Bacterial Physiology.

The electrical membrane potential (Vm) is one of the components of the electrochemical potential of protons across the biological membrane (proton motive force), which powers many vital cellular processes. Because Vm also plays a role in signal transduction, measuring it is of great interest. Over the years, a variety of techniques have been developed for the purpose. In bacteria, given their small size, Nernstian membrane voltage probes are arguably the favorite strategy, and their cytoplasmic accumulation depends on Vm according to the Nernst equation. However, a careful calibration of Nernstian probes that takes into account the tradeoffs between the ease with which the signal from the dye is observed and the dyes' interactions with cellular physiology is rarely performed. Here, we use a mathematical model to understand such tradeoffs and apply the results to assess the applicability of the Thioflavin T dye as a Vm sensor in Escherichia coli. We identify the conditions in which the dye turns from a Vm probe into an actuator and, based on the model and experimental results, propose a general workflow for the characterization of Nernstian dye candidates.

Prevalence of nontuberculous mycobacteria in a tertiary hospital in Beijing, China, January 2013 to December 2018.

BACKGROUND: To investigate the species distribution of non-tuberculous mycobacteria (NTM) among tuberculosis (TB) specimens collected from January 2013 to December 2018 at Peking Union Medical Hospital (Beijing), China. NTM species identification was carried out by DNA microarray chip. RESULTS: Mycobacterial species were detected in 1514 specimens from 1508 patients, among which NTM accounted for 37.3% (565/1514), increasing from a proportion of 15.6% in 2013 to 46.1% in 2018 (P < 0.001). Among the 565 NTM positive specimens, the majority (55.2%) were from female patients. Furthermore, patients aged 45-65 years accounted for 49.6% of the total patients tested. Among 223 NTM positive specimens characterized further, the majority (86.2%) were from respiratory tract, whilst 3.6 and 3.1% were from lymph nodes and pus, respectively. Mycobacterium intracellulare (31.8%) and Mycobacterium chelonae / Mycobacterium abscessus (21.5%) were the most frequently detected species, followed by M. avium (13.5%), M. gordonae (11.7%), M. kansasii (7.6%), and others. CONCLUSION: The proportion of NTM among mycobacterial species detected in a tertiary hospital in Beijing, China, increased rapidly from year 2013 to 2018. Middle-aged patients are more likely to be infected with NTM, especially females. Mycobacterium intracellulare and Mycobacterium chelonae/ Mycobacterium abscessus were the most frequently detected NTM pathogens. Accurate and timely identification of NTM is important for diagnosis and treatment.

Effect of ulipristal acetate and mifepristone at emergency contraception dose on the embryo-endometrial attachment using an in vitro human trophoblastic spheroid and endometrial cell co-culture model.

STUDY QUESTION: Do both ulipristal acetate (UPA) and mifepristone inhibit embryo-endometrial attachment at concentrations corresponding to the emergency contraception (EC) dose? SUMMARY ANSWER: Both UPA and mifepristone at concentrations corresponding to the EC dose do not have an inhibitory effect on embryo implantation, although mifepristone at a higher concentration appeared to have such an effect. WHAT IS KNOWN ALREADY: Levonorgestrel is commonly used for EC, but it only acts through inhibition of ovulation. UPA and mifepristone have higher efficacy as EC compared to levonorgestrel; while there is some suggestion that mifepristone may interfere with implantation, whether UPA has post-ovulatory action in inhibiting implantation is yet to be confirmed. STUDY DESIGN, SIZE, DURATION: An in vitro experimental study using trophoblastic spheroids made from JAr cell line as the embryo surrogate, and the Ishikawa cell line and primary human endometrial cells cultured to monolayer as the endometrial surrogate. The primary endometrial cells were collected from nine volunteer women in the mid-luteal phase with consent. PARTICIPANTS/MATERIALS, SETTING, METHODS: The study was conducted in a university gynaecology unit. The JAr and Ishikawa cell lines (or primary endometrial cells) were treated with graded concentrations of UPA (0, 0.04, 0.4 and 4 µM) or mifepristone (0, 0.1, 1 and 10 µM) for 24 h. Embryo-endometrial attachment was studied using an in vitro JAr spheroid-endometrial co-culture model. Expressions of progesterone receptor, ß-catenin and glycogen synthase kinase 3 ß (GSK-3ß) were studied with real-time RT-PCR and Western blotting, respectively. MAIN RESULTS AND THE ROLE OF CHANCE: In the Ishikawa experiments, there was no significant difference in the JAr spheroid attachment rate after treatment with UPA at 0 (93.0%), 0.04 (93.6%), 0.4 (93.4%) and 4 (91.4%) µM concentrations (P > 0.05); the attachment rate was reduced after treatment with mifepristone only at 10 µM (79.8%, P < 0.0001) but not at 0.1 (92.1%) or 1.0 (95.2%) µM concentrations. In the primary endometrial cell experiments, again no significant difference was observed in the JAr spheroid attachment rate after treatment with UPA 4 µM (42.6%) compared to control (46.5%, P > 0.05). Both UPA and mifepristone could significantly up-regulate progesterone receptor expression. There was no significant alteration in expression of ß-catenin and GSK-3ß after treatment with UPA 4 µM or mifepristone 10 µM (P > 0.05). LIMITATIONS, REASONS FOR CAUTION: The co-culture model is only a surrogate which may not fully represent the complicated process of embryo implantation in vivo, although there is no existing perfect model for studying implantation in vitro which fully resembles the latter. WIDER IMPLICATIONS OF THE FINDINGS: The lack of inhibitory effect on embryo implantation by UPA and possibly mifepristone at concentrations corresponding to the EC dose is an important information for contraceptive counseling. STUDY FUNDING/COMPETING INTEREST(S): We had free supply of the UPA compound used in this study from Laboratoire HRA Pharma. This work was supported by a Seed Fund from the Centre of Reproduction, Development and Growth, Faculty of Medicine, The University of Hong Kong, Hong Kong.

Bayesian inferences for beta semiparametric-mixed models to analyze longitudinal neuroimaging data.

Diffusion tensor imaging (DTI) is a quantitative magnetic resonance imaging technique that measures the three-dimensional diffusion of water molecules within tissue through the application of multiple diffusion gradients. This technique is rapidly increasing in popularity for studying white matter properties and structural connectivity in the living human brain. One of the major outcomes derived from the DTI process is known as fractional anisotropy, a continuous measure restricted on the interval (0,1). Motivated from a longitudinal DTI study of multiple sclerosis, we use a beta semiparametric-mixed regression model for the neuroimaging data. This work extends the generalized additive model methodology with beta distribution family and random effects. We describe two estimation methods with penalized splines, which are formalized under a Bayesian inferential perspective. The first one is carried out by Markov chain Monte Carlo (MCMC) simulations while the second one uses a relatively new technique called integrated nested Laplace approximation (INLA). Simulations and the neuroimaging data analysis show that the estimates obtained from both approaches are stable and similar, while the INLA method provides an efficient alternative to the computationally expensive MCMC method.

Autophagy suppression in DNA damaged cells occurs through a newly identified p53-proteasome-LC3 axis.

Macroautophagy is thought to have a critical role in shaping and refining cellular proteostasis in eukaryotic cells recovering from DNA damage. Here, we report a mechanism by which autophagy is suppressed in cells exposed to bacterial toxin-, chemical-, or radiation-mediated sources of genotoxicity. Autophagy suppression is directly linked to cellular responses to DNA damage, and specifically the stabilization of the tumor suppressor p53, which is both required and sufficient for regulating the ubiquitination and proteasome-dependent reduction in cellular pools of microtubule-associated protein 1 light chain 3 (LC3A/B), a key precursor of autophagosome biogenesis and maturation, in both epithelial cells and an ex vivo organoid model. Our data indicate that suppression of autophagy, through a newly identified p53-proteasome-LC3 axis, is a conserved cellular response to multiple sources of genotoxicity. Such a mechanism could potentially be important for realigning proteostasis in cells undergoing DNA damage repair.

Pan-drug resistance and hypervirulence in a human fungal pathogen are enabled by mutagenesis induced by mammalian body temperature.

The continuing emergence of invasive fungal pathogens poses an increasing threat to public health. Here, through the China Hospital Invasive Fungal Surveillance Net programme, we identified two independent cases of human infection with a previously undescribed invasive fungal pathogen, Rhodosporidiobolus fluvialis, from a genus in which many species are highly resistant to fluconazole and caspofungin. We demonstrate that R. fluvialis can undergo yeast-to-pseudohyphal transition and that pseudohyphal growth enhances its virulence, revealed by the development of a mouse model. Furthermore, we show that mouse infection or mammalian body temperature induces its mutagenesis, allowing the emergence of hypervirulent mutants favouring pseudohyphal growth. Temperature-induced mutagenesis can also elicit the development of pan-resistance to three of the most commonly used first-line antifungals (fluconazole, caspofungin and amphotericin B) in different Rhodosporidiobolus species. Furthermore, polymyxin B was found to exhibit potent activity against the pan-resistant Rhodosporidiobolus mutants. Collectively, by identifying and characterizing a fungal pathogen in the drug-resistant genus Rhodosporidiobolus, we provide evidence that temperature-dependent mutagenesis can enable the development of pan-drug resistance and hypervirulence in fungi, and support the idea that global warming can promote the evolution of new fungal pathogens.

Identification of functional gene modules by integrating multi-omics data and known molecular interactions.

Multi-omics data integration has emerged as a promising approach to identify patient subgroups. However, in terms of grouping genes (or gene products) into co-expression modules, data integration methods suffer from two main drawbacks. First, most existing methods only consider genes or samples measured in all different datasets. Second, known molecular interactions (e.g., transcriptional regulatory interactions, protein-protein interactions and biological pathways) cannot be utilized to assist in module detection. Herein, we present a novel data integration framework, Correlation-based Local Approximation of Membership (CLAM), which provides two methodological innovations to address these limitations: 1) constructing a trans-omics neighborhood matrix by integrating multi-omics datasets and known molecular interactions, and 2) using a local approximation procedure to define gene modules from the matrix. Applying Correlation-based Local Approximation of Membership to human colorectal cancer (CRC) and mouse B-cell differentiation multi-omics data obtained from The Cancer Genome Atlas (TCGA), Clinical Proteomics Tumor Analysis Consortium (CPTAC), Gene Expression Omnibus (GEO) and ProteomeXchange database, we demonstrated its superior ability to recover biologically relevant modules and gene ontology (GO) terms. Further investigation of the colorectal cancer modules revealed numerous transcription factors and KEGG pathways that played crucial roles in colorectal cancer progression. Module-based survival analysis constructed four survival-related networks in which pairwise gene correlations were significantly correlated with colorectal cancer patient survival. Overall, the series of evaluations demonstrated the great potential of Correlation-based Local Approximation of Membership for identifying modular biomarkers for complex diseases. We implemented Correlation-based Local Approximation of Membership as a user-friendly application available at https://github.com/free1234hm/CLAM.

G-quadruplex from precursor miR-1587 modulated its maturation and function.

A certain proportion of pre-miRNAs, which contained potential G-quadruplex forming sequences, was found to act as a mediator to Dicer-mediated cleavage, and that the regulation of miRNA production and function may be achieved through the G-quadruplex structure. In this study, human precursor miR-1587 sequence was transfected after the incubation with different solution conditions (K+, TMPyP4, etc.). Firstly, the formation of G-quadruplex from precursor miR-1587 sequences was confirmed by CD and UV melting. The expression of miR-1587 level was then evaluated by Q-RT-PCR, and the results showed that the formation of G-quadruplex inhibited the miR-1587 maturation process, resulting in a reduced miR-1587 expression. Meanwhile the destabilization of G-quadruplex led to an increased miR-1587 expression by contrast. Then, the weakened inhibition of miR-1587 towards its target genes, such as TAGLN or NCOR1, was presented confirming by Q-RT-PCR and western blot. Molecular mechanism by dual-luciferase assays showed that the modulations of miR-1587 expression and function were due to the G-quadruplex structure transformation, but not the simple change of solution conditions. This study highlighted the importance of maintaining specific structures during miRNA biosynthesis and provided a way to alter the function of G-rich precursor miRNAs by modulating molecular conformation using ionic solutions or ligands.

Simvastatin cream alleviates dermal fibrosis in a rabbit ear hypertrophic scar model.

BACKGROUND: Hypertrophic scars (HTS) result from injury to the skin and represent a clinical burden with limited treatment options. Previously, we demonstrated that statin drugs could attenuate HTS formation, but convenient topical delivery and retention of these drugs at the wound site remains a challenge. AIMS: Here, we aimed to develop a topical cream formulation that can deliver statin drugs simply and conveniently to reduce scar hypertrophy. METHODS: We formulated creams containing 10% pravastatin, 2% simvastatin, and 10% simvastatin. We tested these creams for their ability to reduce scar hypertrophy and attenuate dermal fibrosis in a clinically relevant HTS wound model performed in rabbit ear skin. We also monitored trans-epidermal water loss (TEWL) over the course of wound healing in order to understand the effects of statin treatment on epidermal barrier recovery. RESULTS: Of the three creams formulated, only application of 10% simvastatin cream significantly attenuated hypertrophy of resultant scars compared with vehicle cream application. Application of 10% simvastatin cream resulted in a decrease in macrophage and myofibroblast density at post-operative day 28 (POD28) harvest. Application of 10% simvastatin cream resulted in visible symptoms of dryness and increased TEWL at POD28, but subsequent withdrawal of statin cream treatment resulted in rapid alleviation of dryness and decrease in TEWL back to normal levels. CONCLUSIONS: Our data demonstrate that topical administration of 10% simvastatin cream antagonizes dermal fibrosis and reduces hypertrophy in an HTS model, and withdrawal of the cream enables recovery of epidermal barrier and resolution of skin dryness.

Comparison of Thermal Burn-Induced and Excisional-Induced Scarring in Animal Models: A Review of the Literature.

Significance: Scar formation is a natural result of mammalian wound healing. In humans and other mammals, however, deep dermal wounds and thermal injuries often result in formation of hypertrophic scars, leading to substantial morbidity and lending great importance to development of therapeutic modalities for burn scars. Clinical Issues: Thus, preclinical burn wound models that adequately simulate processes underlying human burn-induced wound healing, particularly those processes leading to chronic inflammation and development of hypertrophic scars, are critical to developing further treatment paradigms for clinical use. Approach: In this study, we review literature describing various burn models, focusing on their characteristics and the functional readouts that lead to generation of useful data. We also briefly discuss recent work using human ex vivo skin culture as an alternative to animal models, as well as our own development of rabbit ear wound models for burn scars, and assess the pros and cons of these models compared to other models. Future Direction: Understanding of the strengths and weaknesses of preclinical burn wound models will enable choice of the most appropriate wound model to answer particular clinically relevant questions, furthering research aimed at treating burn scars.