Engineering dense tumor constructs via cellular contraction of extracellular matrix hydrogels.

Physical characteristics of solid tumors such as dense internal microarchitectures and pathological stiffness influence cancer progression and treatment. While it is routine to engineer culture substrates and scaffolds with elastic moduli that approximate tumors, these models often fail to capture characteristic internal microarchitectures such as densely compacted concentric ECM fibers at the stromal interface. Contractile mesenchymal cells can solve this engineering challenge by deforming, contracting, and compacting extracellular matrix (ECM) hydrogels to decrease tissue volume and increase tissue density. Here we demonstrate that allowing human fibroblasts of varying origins to freely contract collagen type I-containing hydrogels co-seeded with carcinoma cell spheroids produces a tissue engineered construct with structural features that mimic dense solid tumors in vivo. Morphometry and mechanical testing were conducted in tandem with biochemical analysis of proliferation and viability to confirm that dense carcinoma constructs engineered using this approach capture relevant physical characteristics of solid carcinomas in a tractable format that preserves viability and is amenable to extended culture. The reported method is adaptable to the use of multiple mesenchymal cell types and the inclusion of fibrin in the ECM combined with seeding of endothelial cells to produce prevascularized constructs. The physical dense carcinoma constructs engineered using this approach may provide more clinically relevant venues for studying cancer pathophysiology and the challenges associated with the delivery of macromolecular drugs and cellular immunotherapies to solid tumors.

Protein kinase C-delta inhibition is organ-protective, enhances pathogen clearance, and improves survival in sepsis.

Sepsis is a leading cause of morbidity and mortality in intensive care units. Previously, we identified Protein Kinase C-delta (PKCδ) as an important regulator of the inflammatory response in sepsis. An important issue in development of anti-inflammatory therapeutics is the risk of immunosuppression and inability to effectively clear pathogens. In this study, we investigated whether PKCδ inhibition prevented organ dysfunction and improved survival without compromising pathogen clearance. Sprague Dawley rats underwent sham surgery or cecal ligation and puncture (CLP) to induce sepsis. Post-surgery, PBS or a PKCδ inhibitor (200µg/kg) was administered intra-tracheally (IT). At 24 hours post-CLP, there was evidence of lung and kidney dysfunction. PKCδ inhibition decreased leukocyte influx in these organs, decreased endothelial permeability, improved gas exchange, and reduced blood urea nitrogen/creatinine ratios indicating organ protection. PKCδ inhibition significantly decreased bacterial levels in the peritoneal cavity, spleen and blood but did not exhibit direct bactericidal properties. Peritoneal chemokine levels, neutrophil numbers, or macrophage phenotypes were not altered by PKCδ inhibition. Peritoneal macrophages isolated from PKCδ inhibitor-treated septic rats demonstrated increased bacterial phagocytosis. Importantly, PKCδ inhibition increased survival. Thus, PKCδ inhibition improved survival and improved survival was associated with increased phagocytic activity, enhanced pathogen clearance, and decreased organ injury.

Revascularization of decellularized lung scaffolds: principles and progress.

There is a clear unmet clinical need for novel biotechnology-based therapeutic approaches to lung repair and/or replacement, such as tissue engineering of whole bioengineered lungs. Recent studies have demonstrated the feasibility of decellularizing the whole organ by removal of all its cellular components, thus leaving behind the extracellular matrix as a complex three-dimensional (3D) biomimetic scaffold. Implantation of decellularized lung scaffolds (DLS), which were recellularized with patient-specific lung (progenitor) cells, is deemed the ultimate alternative to lung transplantation. Preclinical studies demonstrated that, upon implantation in rodent models, bioengineered lungs that were recellularized with airway and vascular cells were capable of gas exchange for up to 14 days. However, the long-term applicability of this concept is thwarted in part by the failure of current approaches to reconstruct a physiologically functional, quiescent endothelium lining the entire vascular tree of reseeded lung scaffolds, as inferred from the occurrence of hemorrhage into the airway compartment and thrombosis in the vasculature in vivo. In this review, we explore the idea that successful whole lung bioengineering will critically depend on 1) preserving and/or reestablishing the integrity of the subendothelial basement membrane, especially of the ultrathin respiratory membrane separating airways and capillaries, during and following decellularization and 2) restoring vascular physiological functionality including the barrier function and quiescence of the endothelial lining following reseeding of the vascular compartment. We posit that physiological reconstitution of the pulmonary vascular tree in its entirety will significantly promote the clinical translation of the next generation of bioengineered whole lungs.

Biodistribution and Efficacy of Targeted Pulmonary Delivery of a Protein Kinase C-δ Inhibitory Peptide: Impact on Indirect Lung Injury.

Sepsis and sepsis-induced lung injury remain a leading cause of death in intensive care units. We identified protein kinase C-δ (PKCδ) as a critical regulator of the acute inflammatory response and demonstrated that PKCδ inhibition was lung-protective in a rodent sepsis model, suggesting that targeting PKCδ is a potential strategy for preserving pulmonary function in the setting of indirect lung injury. In this study, whole-body organ biodistribution and pulmonary cellular distribution of a transactivator of transcription (TAT)-conjugated PKCδ inhibitory peptide (PKCδ-TAT) was determined following intratracheal (IT) delivery in control and septic [cecal ligation and puncture (CLP)] rats to ascertain the impact of disease pathology on biodistribution and efficacy. There was negligible lung uptake of radiolabeled peptide upon intravenous delivery [<1% initial dose (ID)], whereas IT administration resulted in lung retention of >65% ID with minimal uptake in liver or kidney (<2% ID). IT delivery of a fluorescent-tagged (tetramethylrhodamine-PKCδ-TAT) peptide demonstrated uniform spatial distribution and cellular uptake throughout the peripheral lung. IT delivery of PKCδ-TAT at the time of CLP surgery significantly reduced PKCδ activation (tyrosine phosphorylation, nuclear translocation and cleavage) and acute lung inflammation, resulting in improved lung function and gas exchange. Importantly, peptide efficacy was similar when delivered at 4 hours post-CLP, demonstrating therapeutic relevance. Conversely, spatial lung distribution and efficacy were significantly impaired at 8 hours post-CLP, which corresponded to marked histopathological progression of lung injury. These studies establish a functional connection between peptide spatial distribution, inflammatory histopathology in the lung, and efficacy of this anti-inflammatory peptide.

Pulmonary endothelial protein kinase C-delta (PKCδ) regulates neutrophil migration in acute lung inflammation.

Excessive neutrophil migration across the pulmonary endothelium into the lung and release of oxidants and proteases are key elements in pathogenesis of acute lung injury. Previously, we identified protein kinase C-delta (PKCδ) as an important regulator of proinflammatory signaling in human neutrophils and demonstrated that intratracheal instillation of a TAT-conjugated PKCδ inhibitory peptide (PKCδ-TAT) is lung protective in a rat model of sepsis-induced indirect pulmonary injury (cecal ligation and puncture). In the present study, intratracheal instillation of this PKCδ inhibitor resulted in peptide distribution throughout the lung parenchyma and pulmonary endothelium and decreased neutrophil influx, with concomitant attenuation of sepsis-induced endothelial ICAM-1 and VCAM-1 expression in this model. To further delineate the role of PKCδ in regulating neutrophil migration, we used an in vitro transmigration model with human pulmonary microvascular endothelial cells (PMVECs). Consistent with in vivo findings, inhibition of PMVEC PKCδ decreased IL-1ß-mediated neutrophil transmigration. PKCδ regulation was stimulus-dependent; PKCδ was required for transmigration mediated by IL-1ß and fMLP (integrin-dependent), but not IL-8 (integrin-independent). PKCδ was essential for IL-1ß-mediated neutrophil adherence and NF-κB-dependent expression of ICAM-1 and VCAM-1. In PMVECs, IL-1ß-mediated production of ROS and activation of redox-sensitive NF-κB were PKCδ dependent, suggesting an upstream signaling role. Thus, PKCδ has an important role in regulating neutrophil-endothelial cell interactions and recruitment to the inflamed lung.

Xenohormetic Phytochemicals Inhibit Neovascularization in Microphysiological Models of Vasculogenesis and Tumor Angiogenesis.

Xenohormesis proposes that phytochemicals produced to combat stressors in the host plant exert biochemical effects in animal cells lacking cognate receptors. Xenohormetic phytochemicals such as flavonoids and phytoalexins modulate a range of human cell signaling mechanisms but functional correlations with human pathophysiology are lacking. Here, potent inhibitory effects of grapefruit-derived Naringenin (Nar) and soybean-derived Glyceollins (Gly) in human microphysiological models of bulk tissue vasculogenesis and tumor angiogenesis are reported. Despite this interference of vascular morphogenesis, Nar and Gly are not cytotoxic to endothelial cells and do not prevent cell cycle entry. The anti-vasculogenic effects of Glyceollin are significantly more potent in sex-matched female (XX) models. Nar and Gly do not decrease viability or expression of proangiogenic genes in triple negative breast cancer (TNBC) cell spheroids, suggesting that inhibition of sprouting angiogenesis by Nar and Gly in a MPS model of the (TNBC) microenvironment are mediated via direct effects in endothelial cells. The study supports further research of Naringenin and Glyceollin as health-promoting agents with special attention to mechanisms of action in vascular endothelial cells and the role of biological sex, which can improve the understanding of dietary nutrition and the pharmacology of phytochemical preparations.

Sex-specific actions of estradiol and testosterone on human fibroblast and endothelial cell proliferation, bioenergetics, and vasculogenesis.

Progress toward the development of sex-specific tissue engineered systems has been hampered by the lack of research efforts to define the effects of sex-specific hormone concentrations on relevant human cell types. Here, we investigated the effects of defined concentrations of estradiol (E2) and dihydrotestosterone (DHT) on primary human dermal and lung fibroblasts (HDF and HLF), and human umbilical vein endothelial cells (HUVEC) from female (XX) and male (XY) donors in both 2D expansion cultures and 3D stromal vascular tissues. Sex-matched E2 and DHT stimulation in 2D expansion cultures significantly increased the proliferation index, mitochondrial membrane potential, and the expression of genes associated with bioenergetics (Na+/K+ ATPase, somatic cytochrome C) and beneficial stress responses (chaperonin) in all cell types tested. Notably, cross sex hormone stimulation, i.e., DHT treatment of XX cells in the absence of E2 and E2 stimulation of XY cells in the absence of DHT, decreased bioenergetic capacity and inhibited cell proliferation. We used a microengineered 3D vasculogenesis assay to assess hormone effects on tissue scale morphogenesis. E2 increased metrics of vascular network complexity compared to vehicle in XX tissues. Conversely, and in line with results from 2D expansion cultures, E2 potently inhibited vasculogenesis compared to vehicle in XY tissues. DHT did not significantly alter vasculogenesis in XX or XY tissues but increased the number of non-participating endothelial cells in both sexes. This study establishes a scientific rationale and adaptable methods for using sex hormone stimulation to develop sex-specific culture systems.

Expression of Novel Kinase MAP3K19 in Various Cancers and Survival Correlations.

Mitogen Activated Protein (MAP) kinases are a category of serine/threonine kinases that have been demonstrated to regulate intracellular events including stress responses, developmental processes, and cancer progression Although many MAP kinases have been extensively studied in various disease processes, MAP3K19 is an understudied kinase whose activities have been linked to lung disease and fibroblast development. In this manuscript, we use bioinformatics databases starBase, GEPIA, and KMPlotter, to establish baseline expressions of MAP3K19 in different tissue types and its correlation with patient survival in different cancers.

Surface-directed engineering of tissue anisotropy in microphysiological models of musculoskeletal tissue.

Here, we present an approach to model and adapt the mechanical regulation of morphogenesis that uses contractile cells as sculptors of engineered tissue anisotropy in vitro. Our method uses heterobifunctional cross-linkers to create mechanical boundary constraints that guide surface-directed sculpting of cell-laden extracellular matrix hydrogel constructs. Using this approach, we engineered linearly aligned tissues with structural and mechanical anisotropy. A multiscale in silico model of the sculpting process was developed to reveal that cell contractility increases as a function of principal stress polarization in anisotropic tissues. We also show that the anisotropic biophysical microenvironment of linearly aligned tissues potentiates soluble factor-mediated tenogenic and myogenic differentiation of mesenchymal stem cells. The application of our method is demonstrated by (i) skeletal muscle arrays to screen therapeutic modulators of acute oxidative injury and (ii) a 3D microphysiological model of lung cancer cachexia to study inflammatory and oxidative muscle injury induced by tumor-derived signals.

Role of Protein Kinase C-delta in regulating platelet activation and platelet-leukocyte interaction during sepsis.

Sepsis is characterized by an intense systemic inflammatory response activating a cascade of proinflammatory events resulting in leukocyte dysregulation and host tissue damage. The lung is particularly susceptible to systemic inflammation, leading to acute lung injury. Key to inflammation-induced lung damage is the excessive migration of neutrophils across the vascular endothelium. The mechanisms which regulate neutrophil activation and migration in sepsis are not well defined but there is growing evidence that platelets are actively involved and play a key role in microvascular permeability and neutrophil-mediated organ damage. We previously identified PKC-delta (PKCδ) as a critical regulator of the inflammatory response in sepsis and demonstrated PKCδ inhibition was lung protective. However, the role of PKCδ in sepsis-induced platelet activation and platelet-leukocyte interactions is not known. In this study, rats underwent sham surgery or cecal ligation and puncture (CLP) to induce sepsis. Following surgeries, a PKCδ inhibitor (200µg/kg) or vehicle (PBS) was administered intra-tracheally. At 24 hours post-surgeries, lung tissue, BAL fluid, and blood samples were collected. While sepsis caused thrombocytopenia, the remaining circulating platelets were activated as demonstrated by increased p-selectin expression, elevated plasma PF4, and enhanced platelet-leukocyte aggregate formation compared to Sham animals. Platelet activation was associated with increased platelet PKCδ activity. Inhibition of PKCδ attenuated sepsis-induced platelet activation, secretion and aggregate formation. Sepsis-induced thrombocytopenia was also significantly reduced and circulating platelet numbers were similar to sham animals. In the lung, sepsis induced significant influx of platelets and neutrophils and the development of lung injury. Administration of the PKCδ inhibitor decreased platelet and neutrophil influx, and was lung protective. Thus, PKCδ inhibition modulated platelet activity both locally and systemically, decreased neutrophil influx into the lung, and was lung protective. We demonstrate for the first time that PKCδ plays an important role in platelet activation and platelet-neutrophil interaction during sepsis.

Heterogeneous breast tumoroids: An in vitro assay for investigating cellular heterogeneity and drug delivery.

Breast tumors are typically heterogeneous and contain diverse subpopulations of tumor cells with differing phenotypic properties. Planar cultures of cancer cell lines are not viable models of investigation of cell-cell and cell-matrix interactions during tumor development. This article presents an in vitro coculture-based 3-dimensional heterogeneous breast tumor model that can be used in drug resistance and drug delivery investigations. Breast cancer cell lines of different phenotypes (MDAMB231, MCF7, and ZR751) were cocultured in a rotating wall vessel bioreactor to form a large number of heterogeneous tumoroids in a single cell culture experiment. Cells in the rotating vessels were labeled with Cell Tracker fluorescent probes to allow for time course fluorescence microscopy to monitor cell aggregation. Histological sections of tumoroids were stained with hematoxylin and eosin, progesterone receptor, E-cadherin (E-cad), and proliferation marker ki67. In vitro tumoroids developed in this study recapture important features of the temporal-spatial organization of solid tumors, including the presence of necrotic areas at the center and higher levels of cell division at the tumor periphery. E-cad-positive MCF7 cells form larger tumoroids than E-cad-negative MDAMB231 cells. In heterogeneous tumors, the irregular surface roughness was mainly due to the presence of MDAMB231 cells, whereas MCF7 cells formed smooth surfaces. Moreover, when heterogeneous tumoroids were placed onto collagen gels, highly invasive MDAMB231 cell-rich surface regions produced extensions into the matrix, whereas poorly invasive MCF7 cells did not. The fact that one can form a large number of 1-mm tumoroids in 1 coculture attests to the potential use of this system at high-throughput investigations of cancer drug development and drug delivery into the tumor.

Native extracellular matrix-derived semipermeable, optically transparent, and inexpensive membrane inserts for microfluidic cell culture.

Semipermeable cell culture membranes are commonly used in multilayered microfluidic devices to mimic the basement membrane in vivo and to create compartmentalized microenvironments for physiological cell growth and differentiation. However, existing membranes are predominantly made up of synthetic polymers, providing limited capacity to replicate cellular interactions with native extracellular matrices that play a crucial role in the induction of physiological phenotypes. Here we describe a new type of cell culture membranes engineered from native extracellular matrix (ECM) materials that are thin, semipermeable, optically transparent, and amenable to integration into microfluidic cell culture devices. Facile and cost-effective fabrication of these membranes was achieved by controlled sequential steps of vitrification that transformed three-dimensional (3D) ECM hydrogels into structurally stable thin films. By modulating the composition of the ECM, our technique provided a means to tune key membrane properties such as optical transparency, stiffness, and porosity. For microfluidic cell culture, we constructed a multilayered microdevice consisting of two parallel chambers separated by a thin membrane insert derived from different types of ECM. This study showed that our ECM membranes supported attachment and growth of various types of cells (epithelial, endothelial, and mesenchymal cells) under perfusion culture conditions. Our data also revealed the promotive effects of the membranes on adhesion-associated intracellular signaling that mediates cell-ECM interactions. Moreover, we demonstrated the use of these membranes for constructing compartmentalized microfluidic cell culture systems to induce physiological tissue differentiation or to replicate interfaces between different tissue types. Our approach provides a robust platform to produce and engineer biologically active cell culture substrates that serve as promising alternatives to conventional synthetic membrane inserts. This strategy may contribute to the development of physiologically relevant in vitro cell culture models for a wide range of applications.

Porogen-based solid freeform fabrication of polycaprolactone-calcium phosphate scaffolds for tissue engineering.

Drop on demand printing (DDP) is a solid freeform fabrication (SFF) technique capable of generating microscale physical features required for tissue engineering scaffolds. Here, we report results toward the development of a reproducible manufacturing process for tissue engineering scaffolds based on injectable porogens fabricated by DDP. Thermoplastic porogens were designed using Pro/Engineer and fabricated with a commercially available DDP machine. Scaffolds composed of either pure polycaprolactone (PCL) or homogeneous composites of PCL and calcium phosphate (CaP, 10% or 20% w/w) were subsequently fabricated by injection molding of molten polymer-ceramic composites, followed by porogen dissolution with ethanol. Scaffold pore sizes, as small as 200 microm, were attainable using the indirect (porogen-based) method. Scaffold structure and porosity were analyzed by scanning electron microscopy (SEM) and microcomputed tomography, respectively. We characterized the compressive strength of 90:10 and 80:20 PCL-CaP composite materials (19.5+/-1.4 and 24.8+/-1.3 Mpa, respectively) according to ASTM standards, as well as pure PCL scaffolds (2.77+/-0.26 MPa) fabricated using our process. Human embryonic palatal mesenchymal (HEPM) cells attached and proliferated on all scaffolds, as evidenced by fluorescent nuclear staining with Hoechst 33258 and the Alamar Blue assay, with increased proliferation observed on 80:20 PCL-CaP scaffolds. SEM revealed multilayer assembly of HEPM cells on 80:20 PCL-CaP composite, but not pure PCL, scaffolds. In summary, we have developed an SFF-based injection molding process for the fabrication of PCL and PCL-CaP scaffolds that display in vitro cytocompatibility and suitable mechanical properties for hard tissue repair.

Engineering three-dimensional pulmonary tissue constructs.

In this paper, we report on engineering 3-D pulmonary tissue constructs in vitro. Primary isolates of murine embryonic day 18 fetal pulmonary cells (FPC) were comprised of a mixed population of epithelial, mesenchymal, and endothelial cells as assessed by immunohistochemistry and RT-PCR of 2-D cultures. The alveolar type II (AE2) cell phenotype in 2-D and 3-D cultures was confirmed by detection of SpC gene expression and presence of the gene product prosurfactant protein C. Three-dimensional constructs of FPC were generated utilizing Matrigel hydrogel and synthetic polymer scaffolds of poly-lactic-co-glycolic acid (PLGA) and poly-L-lactic-acid (PLLA) fabricated into porous foams and nanofibrous matrices, respectively. Three-dimensional Matrigel constructs contained alveolar forming units (AFU) comprised of cells displaying AE2 cellular ultrastructure while expressing the SpC gene and gene product. The addition of tissue-specific growth factors induced formation of branching, sacculated epithelial structures reminiscent of the distal lung architecture. Importantly, 3-D culture was necessary for inducing expression of the morphogenesis-associated distal epithelial gene fibroblast growth factor receptor 2 (FGFr2). PLGA foams and PLLA nanofiber scaffolds facilitated ingrowth of FPC, as evidenced by histology. However, these matrices did not support the survival of distal lung epithelial cells, despite the presence of tissue-specific growth factors. Our results may provide the first step on the long road toward engineering distal pulmonary tissue for augmenting and/or replacing dysfunctional native lung in diseases, such as neonatal pulmonary hypoplasia.

Co-electrospun poly(lactide-co-glycolide), gelatin, and elastin blends for tissue engineering scaffolds.

In this study, we describe composite scaffolds composed of synthetic and natural materials with physicochemical properties suitable for tissue engineering applications. Fibrous scaffolds were co-electrospun from a blend of a synthetic biodegradable polymer (poly(lactic-co-glycolic acid), PLGA, 10% solution) and two natural proteins, gelatin (denatured collagen, 8% solution) and alpha-elastin (20% solution) at ratios of 3:1:2 and 2:2:2 (v/v/v). The resulting PLGA-gelatin-elastin (PGE) fibers were homogeneous in appearance with an average diameter of 380 +/- 80 nm, which was considerably smaller than fibers made under identical conditions from the starting materials (PLGA, 780 +/- 200 nm; gelatin, 447 +/- 123 nm; elastin, 1060 +/- 170 nm). Upon hydration, PGE fibers swelled to an average fiber diameter of 963 +/- 132 nm, but did not disintegrate. Importantly, PGE scaffolds were stable in an aqueous environment without crosslinking and were more elastic than those made of pure elastin fibers. To investigate the cytocompatibility of PGE, we cultured H9c2 rat cardiac myoblasts and rat bone marrow stromal cells (BMSCs) on fibrous PGE scaffolds. We found that myoblasts grew equally as well or slightly better on the scaffolds than on tissue-culture plastic. Microscopic evaluation confirmed that myoblasts reached confluence on the scaffold surfaces while simultaneously growing into the scaffolds. Histological characterization of the PGE constructs indicated that BMSCs penetrated into the center of scaffolds and began proliferating shortly after seeding. Our results suggest that fibrous scaffolds made of PGE and similar biomimetic blends of natural and synthetic polymers may be useful for engineering soft tissues, such as heart, lung, and blood vessels.

Enhanced Re-Endothelialization of Decellularized Rat Lungs.

Decellularized lung tissue has been recognized as a potential platform to engineer whole lung organs suitable for transplantation or for modeling a variety of lung diseases. However, many technical hurdles remain before this potential may be fully realized. Inability to efficiently re-endothelialize the pulmonary vasculature with a functional endothelium appears to be the primary cause of failure of recellularized lung scaffolds in early transplant studies. Here, we present an optimized approach for enhanced re-endothelialization of decellularized rodent lung scaffolds with rat lung microvascular endothelial cells (ECs). This was achieved by adjusting the posture of the lung to a supine position during cell seeding through the pulmonary artery. The supine position allowed for significantly more homogeneous seeding and better cell retention in the apex regions of all lobes than the traditional upright position, especially in the right upper and left lobes. Additionally, the supine position allowed for greater cell retention within large diameter vessels (proximal 100-5000 µm) than the upright position, with little to no difference in the small diameter distal vessels. EC adhesion in the proximal regions of the pulmonary vasculature in the decellularized lung was dependent on the binding of EC integrins, specifically α1ß1, α2ß1, and α5ß1 integrins to, respectively, collagen type-I, type-IV, and fibronectin in the residual extracellular matrix. Following in vitro maturation of the seeded constructs under perfusion culture, the seeded ECs spread along the vascular wall, leading to a partial reestablishment of endothelial barrier function as inferred from a custom-designed leakage assay. Our results suggest that attention to cellular distribution within the whole organ is of paramount importance for restoring proper vascular function.

Electrospun protein fibers as matrices for tissue engineering.

Electrospinning has recently emerged as a leading technique for generating biomimetic scaffolds made of synthetic and natural polymers for tissue engineering applications. In this study, we compared collagen, gelatin (denatured collagen), solubilized alpha-elastin, and, as a first, recombinant human tropoelastin as biopolymeric materials for fabricating tissue engineered scaffolds by electrospinning. In extending previous studies, we optimized the shape and size (diameter or width) of the ensuing electrospun fibers by varying important parameters of the electrospinning process, such as solute concentration and delivery rate of the polymers. Our results indicate that the average diameter of gelatin and collagen fibers could be scaled down to 200-500 nm without any beads, while the alpha-elastin and tropoelastin fibers were several microns in width. Importantly, and contrary to any hitherto reported structures of electrospun polymers, fibers composed of alpha-elastin, especially tropoelastin, exhibited "quasi-elastic" wave-like patterns at increased solution delivery rates. The periodicity of these wave-like tropoelastin fibers was partly affected by the delivery rate. Atomic force microscopy was utilized to profile the topography of individual electrospun fibers and microtensile testing was performed to measure their mechanical properties. Cell culture studies confirmed that the electrospun engineered protein scaffolds support attachment and growth of human embryonic palatal mesenchymal (HEPM) cells.

Osseointegrative properties of electrospun hydroxyapatite-containing nanofibrous chitosan scaffolds.

Our long-term goal is to develop smart biomaterials that can facilitate regeneration of critical-size craniofacial lesions. In this study, we tested the hypothesis that biomimetic scaffolds electrospun from chitosan (CTS) will promote tissue repair and regeneration in a critical size calvarial defect. To test this hypothesis, we first compared in vitro ability of electrospun CTS scaffolds crosslinked with genipin (CTS-GP) to those of mineralized CTS-GP scaffolds containing hydroxyapatite (CTS-HA-GP), by assessing proliferation/metabolic activity and alkaline phosphatase (ALP) levels of murine mesenchymal stem cells (mMSCs). The cells' metabolic activity exhibited a biphasic behavior, indicative of initial proliferation followed by subsequent differentiation for all scaffolds. ALP activity of mMSCs, a surrogate measure of osteogenic differentiation, increased over time in culture. After 3 weeks in maintenance medium, ALP activity of mMSCs seeded onto CTS-HA-GP scaffolds was approximately two times higher than that of cells cultured on CTS-GP scaffolds. The mineralized CTS-HA-GP scaffolds were also osseointegrative in vivo, as inferred from the enhanced bone regeneration in a murine model of critical size calvarial defects. Tissue regeneration was evaluated over a 3 month period by microCT and histology (Hematoxylin and Eosin and Masson's Trichrome). Treatment of the lesions with CTS-HA-GP scaffolds induced a 38% increase in the area of de novo generated mineralized tissue area after 3 months, whereas CTS-GP scaffolds only led to a 10% increase. Preseeding with mMSCs significantly enhanced the regenerative capacity of CTS-GP scaffolds (by ∼3-fold), to 35% increase in mineralized tissue area after 3 months. CTS-HA-GP scaffolds preseeded with mMSCs yielded 45% new mineralized tissue formation in the defects. We conclude that the presence of HA in the CTS-GP scaffolds significantly enhances their osseointegrative capacity and that mineralized chitosan-based scaffolds crosslinked with genipin may represent a unique biomaterial with possible clinical relevance for the repair of critical calvarial bone defects.

Engineering de novo assembly of fetal pulmonary organoids.

Induction of morphogenesis by competent lung progenitor cells in a 3D environment is a central goal of pulmonary tissue engineering, yet little is known about the microenvironmental signals required to induce de novo assembly of alveolar-like tissue in vitro. In extending our previous reports of alveolar-like tissue formation by fetal pulmonary cells stimulated by exogenous fibroblast growth factors (FGFs), we identified some of the key endogenous mediators of FGF-driven morphogenesis (organoid assembly), for example, epithelial sacculation, endothelial network assembly, and epithelial-endothelial interfacing. Sequestration of endogenously secreted vascular endothelial growth factor-A (VEGF-A) potently inhibited endothelial network formation, with little or no effect on epithelial morphogenesis. Inhibition of endogenous sonic hedgehog (SHH) partially attenuated FGF-driven endothelial network formation, while the addition of exogenous SHH in the absence of FGFs was able to induce epithelial and endothelial morphogenesis, although with distinct morphological characteristics. Notably, SHH-induced endothelial networks exhibited fewer branch points, reduced sprouting behavior, and a periendothelial extracellular matrix (ECM) virtually devoid of tenascin-C (TN-C). By contrast, focal deposition of endogenous TN-C was observed in the ECM-surrounding endothelial networks of FGF-induced organoids, especially around sprouting tips. In the FGF-induced organoids, TN-C was also observed in the clefts of sacculated epithelium and at the epithelial-endothelial interface. In support of a critical role in the formation of alveolar-like tissue in vitro, TN-C blocking inhibited endothelial network formation and epithelial sacculation. Upon engraftment of in-vitro-generated pulmonary organoids beneath the renal capsule of syngeneic mice, robust neovascularization occurred in 5 days with a large contribution of patent vessels from engrafted organoids, providing proof of principle for exploring intrapulmonary engraftment of prevascularized hydrogel constructs. Expression of proSpC, VEGF-A, and TN-C following 1 week in vivo mirrored the patterns observed in vitro. Taken together, these findings advance our understanding of endogenous growth factor and ECM signals important for de novo formation of pulmonary tissue structures in vitro and demonstrate the potential of an organoid-based approach to lung tissue augmentation.

Protein kinase C and acute respiratory distress syndrome.

The acute respiratory distress syndrome (ARDS) is a major public health problem and a leading source of morbidity in intensive care units. Lung tissue in patients with ARDS is characterized by inflammation, with exuberant neutrophil infiltration, activation, and degranulation that is thought to initiate tissue injury through the release of proteases and oxygen radicals. Treatment of ARDS is supportive primarily because the underlying pathophysiology is poorly understood. This gap in knowledge must be addressed to identify urgently needed therapies. Recent research efforts in anti-inflammatory drug development have focused on identifying common control points in multiple signaling pathways. The protein kinase C (PKC) serine-threonine kinases are master regulators of proinflammatory signaling hubs, making them attractive therapeutic targets. Pharmacological inhibition of broad-spectrum PKC activity and, more importantly, of specific PKC isoforms (as well as deletion of PKCs in mice) exerts protective effects in various experimental models of lung injury. Furthermore, PKC isoforms have been implicated in inflammatory processes that may be involved in the pathophysiologic changes that result in ARDS, including activation of innate immune and endothelial cells, neutrophil trafficking to the lung, regulation of alveolar epithelial barrier functions, and control of neutrophil proinflammatory and prosurvival signaling. This review focuses on the mechanistic involvement of PKC isoforms in the pathogenesis of ARDS and highlights the potential of developing new therapeutic paradigms based on the selective inhibition (or activation) of specific PKC isoforms.