Survival-Associated Cellular Response Maintained in Pancreatic Ductal Adenocarcinoma (PDAC) Switched Between Soft and Stiff 3D Microgel Culture.

Pancreatic ductal adenocarcinoma (PDAC) accounts for about 90% of all pancreatic cancer cases. Five-year survival rates have remained below 12% since the 1970s, in part due to the difficulty in detection prior to metastasis (migration and invasion into neighboring organs and glands). Mechanical memory is a concept that has emerged over the past decade that may provide a path toward understanding how invading PDAC cells "remember" the mechanical properties of their diseased ("stiff", elastic modulus, E ≈ 10 kPa) microenvironment even while invading a healthy ("soft", E ≈ 1 kPa) microenvironment. Here, we investigated the role of mechanical priming by culturing a dilute suspension of PDAC (FG) cells within a 3D, rheologically tunable microgel platform from hydrogels with tunable mechanical properties. We conducted a suite of acute (short-term) priming studies where we cultured PDAC cells in either a soft (E ≈ 1 kPa) or stiff (E ≈ 10 kPa) environment for 6 h, then removed and placed them into a new soft or stiff 3D environment for another 18 h. Following these steps, we conducted RNA-seq analyses to quantify gene expression. Initial priming in the 3D culture showed persistent gene expression for the duration of the study, regardless of the subsequent environments (stiff or soft). Stiff 3D culture was associated with the downregulation of tumor suppressors (LATS1, BCAR3, CDKN2C), as well as the upregulation of cancer-associated genes (RAC3). Immunofluorescence staining (BCAR3, RAC3) further supported the persistence of this cellular response, with BCAR3 upregulated in soft culture and RAC3 upregulated in stiff-primed culture. Stiff-primed genes were stratified against patient data found in The Cancer Genome Atlas (TCGA). Upregulated genes in stiff-primed 3D culture were associated with decreased survival in patient data, suggesting a link between patient survival and mechanical priming.

Extracellular Optogenetics at the Interface of Synthetic Biology and Materials Science.

We review fundamental mechanisms and applications of OptoGels: hydrogels with light-programmable properties endowed by photoswitchable proteins ("optoproteins") found in nature. Light, as the primary source of energy on earth, has driven evolution to develop highly-tuned functionalities, such as phototropism and circadian entrainment. These functions are mediated through a growing family of optoproteins that respond to the entire visible spectrum ranging from ultraviolet to infrared by changing their structure to transmit signals inside of cells. In a recent series of articles, engineers and biochemists have incorporated optoproteins into a variety of extracellular systems, endowing them with photocontrollability. While other routes exist for dynamically controlling material properties, light-sensitive proteins have several distinct advantages, including precise spatiotemporal control, reversibility, substrate selectivity, as well as biodegradability and biocompatibility. Available conjugation chemistries endow OptoGels with a combinatorially large design space determined by the set of optoproteins and polymer networks. These combinations result in a variety of tunable material properties. Despite their potential, relatively little of the OptoGel design space has been explored. Here, we aim to summarize innovations in this emerging field and highlight potential future applications of these next generation materials. OptoGels show great promise in applications ranging from mechanobiology, to 3D cell and organoid engineering, and programmable cell eluting materials.

Correction: Aqueous surface gels as low friction interfaces to mitigate implant-associated inflammation.

Correction for 'Aqueous surface gels as low friction interfaces to mitigate implant-associated inflammation' by Allison L. Chau et al., J. Mater. Chem. B, 2020, 8, 6782-6791, DOI: .

Poroelasticity of highly confined hydrogel films measured with a surface forces apparatus.

The influence of poroelasticity on the contact mechanics of thin polyacrylamide films was investigated with a surface forces apparatus (SFA). A model based on a thin film approximation described compression forces for hydrated gels; polymer scaling theory explained the effects of gel dehydration. The results demonstrate that fluid flow dictates the apparent stiffness of highly confined poroelastic films.

Aqueous surface gels as low friction interfaces to mitigate implant-associated inflammation.

Aqueous surface gels are fragile yet resilient biopolymer-based networks capable of sustaining extremely low friction coefficients despite tribologically-challenging environments. These superficial networks are ubiquitous in natural sliding interfaces and protect mechanosensitive cells from excessive contact pressures and frictional shear stresses from cell-fluid, cell-cell, or cell-solid interactions. Understanding these complex lubrication mechanisms may aid in the development of materials-based strategies for increasing biocompatibility in medical devices and implants. Equally as important is characterizing the interplay between soft and passive yet mobile implant materials and cellular reactions in response to direct contact and frictional shear stresses. Physically interrogating living biological systems without rupturing them in the process is nontrivial. To this end, custom biotribometers have been designed to precisely modulate contact pressures against living human telomerase-immortalized corneal epithelial (hTCEpi) cell layers using soft polyacrylamide membrane probes. Reverse-transcription quantitative polymerase chain-reaction (RT-qPCR) indicated that increased duration and, to a much greater extent, the magnitude of frictional shear stress lead to increased production of pro-inflammatory (IL-1ß, IL-6, MMP9) and pro-apoptotic (DDIT3, FAS) genes, which in clinical studies are linked to pathological pain. The hierarchical structure often found in biological systems has also been investigated through the fabrication of high-water content (polyacrylamide) hydrogels through free-radical polymerization inhibition. Nanoindentation experiments and friction coefficient measurements indicate that these "gradient surface gels" reduce contact pressures and frictional shear stresses at the surface of the material while still maintaining stiffness within the bulk. Reducing frictional shear stresses through informed materials and surface design may concomitantly increase lubricity and quiet the immune response, and thus provide bio-inspired routes to improve patient outcomes and quality of life.

MyD88 signaling promotes both mucosal homeostatic and fibrotic responses during Salmonella-induced colitis.

Salmonella enterica serovar Typhimurium is a clinically important gram-negative, enteric bacterial pathogen that activates several Toll-like receptors (TLRs). While TLR signaling through the adaptor protein MyD88 has been shown to promote inflammation and host defense against the systemic spread of S. Typhimurium, curiously, its role in the host response against S. Typhimurium within the mammalian gastrointestinal (GI) tract is less clear. We therefore used the recently described Salmonella-induced enterocolitis and fibrosis model: wild-type (WT) and MyD88-deficient (MyD88(-/-)) mice pretreated with streptomycin and then orally infected with the ΔaroA vaccine strain of S. Typhimurium. Tissues were analyzed for bacterial colonization, inflammation, and epithelial damage, while fibrosis was assessed by collagen quantification and Masson's trichrome staining. WT and MyD88(-/-) mice carried similar intestinal pathogen burdens to postinfection day 21. Infection of WT mice led to acute mucosal and submucosal inflammation and edema, as well as significant intestinal epithelial damage and proliferation, leading to widespread goblet cell depletion. Impressive collagen deposition in the WT intestine was also evident in the submucosa at postinfection days 7 and 21, with fibrotic regions rich in fibroblasts and collagen. While infected MyD88(-/-) mice showed levels of submucosal inflammation and edema similar to WT mice, they were impaired in the development of mucosal inflammation, along with infection-induced epithelial damage, proliferation, and goblet cell depletion. MyD88(-/-) mouse tissues also had fewer submucosal fibroblasts and 60% less collagen. We noted that cyclooxygenase (Cox)-2 expression was MyD88-dependent, with numerous Cox-2-positive cells identified in fibrotic regions of WT mice at postinfection day 7, but not in MyD88(-/-) mice. Treatment of WT mice with the Cox-2 inhibitor rofecoxib (20 mg/kg) significantly reduced fibroblast numbers and collagen levels without altering colitis severity. In conclusion, MyD88 and Cox-2 signaling play roles in intestinal fibrosis during Salmonella-induced enterocolitis.

Interleukin-11 reduces TLR4-induced colitis in TLR2-deficient mice and restores intestinal STAT3 signaling.

BACKGROUND & AIMS: The roles of intestinal Toll-like receptors (TLR) in the pathogenesis of colitis are not known. TLR2 and TLR4 appear to protect against dextran sodium sulfate-induced colitis by promoting mucosal integrity, but it is not clear whether this method of protection occurs in other models of colitis. We investigated the roles of TLR2 and TLR4 and the cell types that express these receptors during infectious colitis. METHODS: We generated chimeric mice with TLR2(-/-) or TLR4(-/-) bone marrow and infected them with the bacterial pathogen Citrobacter rodentium. We assessed their susceptibility to colitis and the mechanisms of TLR-mediated mucosal integrity. RESULTS: TLR2-expressing tissue resident cells prevented lethal colitis, whereas TLR4-dependent inflammatory responses of hematopoietic cells mediated intestinal damage. TLR2 expression protected against intestinal damage by maintaining epithelial barrier function and inducing expression of interleukin (IL)-11 from tissue resident cells in the muscularis mucosae, concurrent with epithelial activation of the transcription factor STAT3. Addition of exogenous IL-11 protected against the lethal colitis in TLR2-deficient mice via STAT3 activation in intestinal epithelial cells. CONCLUSIONS: TLR2-dependent cytoprotective responses from tissue resident cells maintain mucosal integrity against the ultimately lethal TLR4-dependent inflammatory responses of hematopoietic cells. Whereas TLR2 protects against various noxious agents, the role of TLR4 during colitis can be either protective or damaging, depending on the stimulus. Therefore, therapeutics that reduce innate immunity (TLR2 signaling in particular) may not be beneficial to patients with colitis; they could worsen symptoms. Therapies that stimulate cytoprotective responses, like IL-11, could have benefits for patients with colitis.

Analysis of binding sites on complement factor I that are required for its activity.

The central complement inhibitor factor I (FI) degrades activated complement factors C4b and C3b in the presence of cofactors such as C4b-binding protein, factor H, complement receptor 1, and membrane cofactor protein. FI is a serine protease composed of two chains. The light chain comprises the serine protease domain, whereas the heavy chain contains several domains; that is, the FI and membrane attack complex domain (FIMAC), CD5, low density lipoprotein receptor 1 (LDLr1) and LDLr2 domains. To understand better how FI acts as a complement inhibitor, we used homology-based models of FI domains to predict potential binding sites. Specific amino acids were then mutated to yield 16 well expressed mutants, which were then purified from media of eukaryotic cells for functional analyses. The Michaelis constant (K(m)) of all FI mutants toward a small substrate was not altered, whereas some mutants showed increased maximum initial velocity (V(max)). All the mutations in the FIMAC domain affected the ability of FI to degrade C4b and C3b irrespective of the cofactor used, whereas only some mutations in the CD5 and LDLr1/2 domains had a similar effect. These same mutants also showed impaired binding to C3met. In conclusion, the FIMAC domain appears to harbor the main binding sites important for the ability of FI to degrade C4b and C3b.

Bacterial infection-mediated mucosal signalling induces local renal ischaemia as a defence against sepsis.

Ascending urinary tract infections can cause extensive damage to kidney structure and function. We have used a number of advanced techniques including multiphoton microscopy to investigate the crucial early phases of uropathogenic Escherichia coli induced pyelonephritis within a living animal. Our results reveal a previously undescribed innate vascular response to mucosal infection, allowing isolation and eradication of the pathogen. The extremely rapid host response to mucosal infection was highlighted by the triggering of a cascade of events within 3-4 h. Epithelial signalling produced an increase in cellular O(2) consumption and affected microvascular flow by clotting, causing localized ischaemia. Subsequent ischaemic damage affected pathophysiology with actin re-arrangement and epithelial sloughing leading to paracellular bacterial movement. A denuded tubular basement membrane is shown to hinder immediate dissemination of bacteria, giving the host time to isolate the infection by clotting. Suppression of clotting by heparin treatment caused fatal urosepsis. Clinically these findings may be relevant in antibiotics delivery in pyelonephritis patients and to the use of anticoagulants in sepsis.

Progression of bacterial infections studied in real time--novel perspectives provided by multiphoton microscopy.

The holy grail of infection biology is to study a pathogen within its natural infectious environment, the living host. Advances in in vivo imaging techniques have begun to introduce the possibility to visualize, in real time, infection progression within a living model. In this review we detail the current advancements and knowledge in multiphoton microscopy and how it can be related to the field of microbial infections. This technology is a new and very valuable tool for in vivo imaging, and using this technique it is possible to begin to study various microbes within their natural infectious environment - the living host.

Real-time studies of the progression of bacterial infections and immediate tissue responses in live animals.

By combining intravital multiphoton microscopy and bacterial genetics we have developed a technique enabling real-time imaging of bacterial proliferation and tissue responses in a live animal. Spatial and temporal control of the infection process was achieved by microinjecting GFP(+)-expressing uropathogenic Escherichia coli (UPEC) into tubules of exteriorized kidneys in live rats. GFP(+) was introduced in the clinical UPEC strain CFT073 as a single-copy chromosomal gene fusion. Within hours, bacterial colonization was accompanied by marked ischaemic effects, perivascular leakage, loss of tubular integrity and localized recruitment of immune cells. The pathophysiology was altered in response to an isogenic bacterial strain lacking the exotoxin haemolysin, revealing the subtle and temporal roles of bacterial virulence factors in vivo. Microdissection and RNA extraction of the injected nephron allowed molecular analysis of prokaryotic and eukaryotic gene expression. The techniques described here can be applied to study the integrated cell communication evoked by a variety of bacterial pathogens, assisting in the design of strategies to combat bacterial infections.

Role of the lipopolysaccharide-CD14 complex for the activity of hemolysin from uropathogenic Escherichia coli.

Bacterial pathogens produce a variety of exotoxins, which often become associated with the bacterial outer membrane component lipopolysaccharide (LPS) during their secretion. LPS is a potent proinflammatory mediator; however, it is not known whether LPS contributes to cell signaling induced by those microbial components to which it is attached. This is partly due to the common view that LPS present in bacterial component preparations is an experimental artifact. The Escherichia coli exotoxin hemolysin (Hly) is a known inducer of proinflammatory signaling in epithelial cells, and the signal transduction pathway involves fluctuation of the intracellular-Ca(2+) concentration. Since LPS is known to interact with Hly, we investigated whether it is required as a cofactor for the activity of Hly. We found that the LPS/Hly complex exploits the CD14/LPS-binding protein recognition system to bring Hly to the cell membrane, where intracellular-Ca(2+) signaling is initiated via specific activation of the small GTPase RhoA. Hly-induced Ca(2+) signaling was found to occur independently of the LPS receptor TLR4, suggesting that the role of LPS/CD14 is to deliver Hly to the cell membrane. In contrast, the cytolytic effect triggered by exposure of cells to high Hly concentrations occurs independently of LPS/CD14. Collectively, our data reveal a novel molecular mechanism for toxin delivery in bacterial pathogenesis, where LPS-associated microbial compounds are targeted to the host cell membrane as a consequence of their association with LPS.