R. Rivkah Isseroff

Dynamics of Neutrophil Infiltration during Cutaneous Wound Healing and Infection Using Fluorescence Imaging

Neutrophil influx is an early inflammatory response that is essential for the clearance of bacteria and cellular debris during cutaneous wounding. A non-invasive real-time fluorescence imaging technique was developed to examine the kinetics of enhanced green fluorescence protein-polymorphonuclear leukocyte (EGFP-PMN) influx within a wound. We hypothesized that infection or systemic availability would directly regulate the dynamics of EGFP-PMN recruitment and the efficiency of wound closure. Neutrophil recruitment increased dramatically over the first 24 hours from 10(6) at 4 hours up to a maximum of 5 x 10(6) EGFP-PMNs at 18 hours. A high rate of EGFP-PMN turnover was evidenced by approximately 80% decrease in EGFP signal within 6 hours. In response to wound colonization by Staphylococcus aureus or injection of GM-CSF, systemic PMNs increased twofold above saline control. This correlated with an increase in EGFP-PMN recruitment up to approximately 10(7) within the wound. Despite this effect by these distinct inflammatory drivers, wound closure occurred at a rate similar to the saline-treated control group. In summary, a non-invasive fluorescence-based imaging approach combined with genetic labeling of neutrophils provides a dynamic inner view of inflammation and the kinetics of neutrophil infiltration into the wounded skin over extended durations.

A fibrin-based bioengineered ocular surface with human corneal epithelial stem cells

Purpose. The purpose of the investigation was to prepare a bioengineered ocular surface tissue replacement consisting of (presumed) human corneal epithelial stem cells in a cross-linked fibrin gel for potential transplant. Methods. Presumed human epithelial stem cells were harvested, isolated, and cultivated as previously described from adult donor corneas obtained from a tissue and organ bank. The cultured corneal epithelial stem cells were suspended in a fibronectin/fibrin gel cross-linked by factor XIII. Plasma components were derived from a fibrinogen-rich cryoprecipitate of human plasma. Suspended cells proliferated in the fibrin gel, giving rise to colonies that eventually coalesced to near confluence over the 15 days of cultivation. The gels were sectioned and immunostained for keratin 3 (AE5) and keratin 19. Results. The fibrin gel product with corneal stem cells was easily manageable and maneuverable. Addition of the protease inhibitor aprotinin to the incubation medium prevented gel degradation; once it was removed, gels disintegrated within 24 hours. All of the cells cultivated in the fibrin gel stained positively for keratin 3 (AE5), indicating differentiation along the corneal epithelium lineage. Cells located in the center of the colonies were keratin 19–positive, suggesting a more primitive cell type. Growth kinetics were documented. Conclusions. A bioengineered ocular surface with a combination of presumed corneal epithelial stem cells in a cross-linked fibrin gel represents a potential improvement in current attempts to create a transportable, pliable, and stable tissue replacement. Since both the cells and the plasma components of the fibrin gel are of human origin, this technique provides the potential for a totally autologous bioengineered replacement tissue.

Direct Binding of Integrin αvβ3 to FGF1 Plays a Role in FGF1 Signaling

Integrins play a role in fibroblast growth factor (FGF) signaling through cross-talk with FGF receptors (FGFRs), but the mechanism underlying the cross-talk is unknown. We discovered that FGF1 directly bound to soluble and cell-surface integrin αvβ3 (KD about 1 μm). Antagonists to αvβ3 (monoclonal antibody 7E3 and cyclic RGDfV) blocked this interaction. αvβ3 was the predominant, if not the only, integrin that bound to FGF1, because FGF1 bound only weakly to several β1 integrins tested. We presented evidence that the CYDMKTTC sequence (the specificity loop) within the ligand-binding site of β3 plays a role in FGF1 binding. We found that the integrin-binding site of FGF1 overlaps with the heparin-binding site but is distinct from the FGFR-binding site using docking simulation and mutagenesis. We identified an FGF1 mutant (R50E) that was defective in integrin binding but still bound to heparin and FGFR. R50E was defective in inducing DNA synthesis, cell proliferation, cell migration, and chemotaxis, suggesting that the direct integrin binding to FGF1 is critical for FGF signaling. Nevertheless, R50E induced phosphorylation of FGFR1 and FRS2α and activation of AKT and ERK1/2. These results suggest that the defect in R50E in FGF signaling is not in the initial activation of FGF signaling pathway components, but in the later steps in FGF signaling. We propose that R50E is a useful tool to identify the role of integrins in FGF signaling.

Stress-Mediated Increases in Systemic and Local Epinephrine Impair Skin Wound Healing: Potential New Indication for Beta Blockers

Background Stress, both acute and chronic, can impair cutaneous wound repair, which has previously been mechanistically ascribed to stress-induced elevations of cortisol. Here we aimed to examine an alternate explanation that the stress-induced hormone epinephrine directly impairs keratinocyte motility and wound re-epithelialization. Burn wounds are examined as a prototype of a high-stress, high-epinephrine, wound environment. Because keratinocytes express the β2-adrenergic receptor (β2AR), another study objective was to determine whether β2AR antagonists could block epinephrine effects on healing and improve wound repair. Methods and Findings Migratory rates of normal human keratinocytes exposed to physiologically relevant levels of epinephrine were measured. To determine the role of the receptor, keratinocytes derived from animals in which the β2AR had been genetically deleted were similarly examined. The rate of healing of burn wounds generated in excised human skin in high and low epinephrine environments was measured. We utilized an in vivo burn wound model in animals with implanted pumps to deliver β2AR active drugs to study how these alter healing in vivo. Immunocytochemistry and immunoblotting were used to examine the up-regulation of catecholamine synthetic enzymes in burned tissue, and immunoassay for epinephrine determined the levels of this catecholamine in affected tissue and in the circulation. When epinephrine levels in the culture medium are elevated to the range found in burn-stressed animals, the migratory rate of both cultured human and murine keratinocytes is impaired (reduced by 76%, 95% confidence interval [CI] 56%–95% in humans, p < 0.001, and by 36%, 95% CI 24%–49% in mice, p = 0.001), and wound re-epithelialization in explanted burned human skin is delayed (by 23%, 95% CI 10%–36%, p = 0.001), as compared to cells or tissues incubated in medium without added epinephrine. This impairment is reversed by β2AR antagonists, is absent in murine keratinocytes that are genetically depleted of the β2AR, and is reproduced by incubation of keratinocytes with other β2AR-specific agonists. Activation of the β2AR in cultured keratinocytes signals the down-regulation of the AKT pathway, accompanied by a stabilization of the actin cytoskeleton and an increase in focal adhesion formation, resulting in a nonmigratory phenotype. Burn wound injury in excised human skin also rapidly up-regulates the intra-epithelial expression of the epinephrine synthesizing enzyme phenylethanolamine-N-methyltransferase, and tissue levels of epinephrine rise dramatically (15-fold) in the burn wounded tissue (values of epinephrine expressed as pg/ug protein ± standard error of the mean: unburned control, 0.6 ± 0.36; immediately postburn, 9.6 ± 1.58; 2 h postburn, 3.1 ± 1.08; 24 h post-burn, 6.7 ± 0.94). Finally, using an animal burn wound model (20% body surface in mice), we found that systemic treatment with βAR antagonists results in a significant increase (44%, 95% CI 27%–61%, p < 0.00000001) in the rate of burn wound re-epithelialization. Conclusions This work demonstrates an alternate pathway by which stress can impair healing: by stress-induced elevation of epinephrine levels resulting in activation of the keratinocyte β2AR and the impairment of cell motility and wound re-epithelialization. Furthermore, since the burn wound locally generates epinephrine in response to wounding, epinephrine levels are locally, as well as systemically, elevated, and wound healing is impacted by these dual mechanisms. Treatment with beta adrenergic antagonists significantly improves the rate of burn wound re-epithelialization. This work suggests that specific β2AR antagonists may be apt, near-term translational therapeutic targets for enhancing burn wound healing, and may provide a novel, low-cost, safe approach to improving skin wound repair in the stressed individual.

Calcium channel blockers inhibit galvanotaxis in human keratinocytes.

Directed migration of keratinocytes is essential for wound healing. The migration of human keratinocytes in vitro is strongly influenced by the presence of a physiological electric field and these cells migrate towards the negative pole of such a field (galvanotaxis). We have previously shown that the depletion of extracellular calcium blocks the directional migration of cultured human keratinocytes in an electric field (Fang et al., 1998 ; J Invest Dermatol 111:751–756). Here we further investigate the role of calcium influx on the directionality and migration speed of keratinocytes during electric field exposure with the use of Ca2+ channel blockers. A constant, physiological electric field strength of 100 mV/mm was imposed on the cultured cells for 1 h. To determine the role of calcium influx during galvanotaxis we tested the effects of the voltage‐dependent cation channel blockers, verapamil and amiloride, as well as the inorganic Ca2+ channel blockers, Ni2+ and Gd3+ and the Ca2+ substitute, Sr2+, on the speed and directionality of keratinocyte migration during galvanotaxis. Neither amiloride (10 μM) nor verapamil (10 μM) had any effect on the galvanotaxis response. Therefore, calcium influx through amiloride‐sensitive channels is not required for galvanotaxis, and membrane depolarization via K+ channel activity is also not required. In contrast, Sr2+ (5 mM), Ni2+ (1–5 mM), and Gd3+ (100 μM) all significantly inhibit the directional migratory response to some degree. While Sr2+ strongly inhibits directed migration, the cells exhibit nearly normal migration speeds. These findings suggest that calcium influx through Ca2+ channels is required for directed migration of keratinocytes during galvanotaxis and that directional migration and migration speed are probably controlled by separate mechanisms. J. Cell. Physiol. 193: 1–9, 2002.

β2-Adrenergic receptor activation delays wound healing

Keratinocytes migrate directionally into the wound bed to initiate re‐epithelialization, necessary for wound closure and restoration of barrier function. They solely express the β2‐adrenergic receptor (β2‐AR) subtype of β‐ARs and can also synthesize β‐AR agonists generating a hormonal mediator network in the skin. Emerging studies from our laboratory demonstrate that β‐AR agonists decrease keratinocyte migration via a protein phosphatase (PP) 2A‐dependent mechanism. Here we have extended our investigations to observe the effects of β2‐AR activation on keratinocyte polarization, migration, and ERK phosphorylation at the wound edge, cytoskeletal organization, phospho‐ERK intracellular localization, proliferation, human skin wound re‐epithelialization, wound‐induced ERK phosphorylation, and murine skin wound healing. We demonstrate that in keratinocytes, β2‐AR activation is antimotogenic and anti‐mitogenic with both mechanisms being PP2A dependent. β2‐AR activation dramatically alters the organization of the actin cytoskeleton and prevents localization of phospho‐ERK to the lamellipodial edge and its colocalization with vinculin. Finally, we demonstrate a β2‐AR‐mediated delay in re‐epithelialization and decrease in wound‐induced epidermal ERK phosphorylation in human skin wounds and a delay in re‐epithelialization in murine tail‐clip wounds. Our work uncovers novel keratinocyte biology and a previously unrecognized role for the adrenergic hormonal mediator network in the wound repair process.— Pullar, C. E., Grahn, J. C., Liu, W., Isseroff, R. R. β2‐Adrenergic receptor activation delays wound healing. FASEB J. 20, 76 −86 (2006)

β-Adrenergic Receptor Antagonists Accelerate Skin Wound Healing EVIDENCE FOR A CATECHOLAMINE SYNTHESIS NETWORK IN THE EPIDERMIS

The skin is our primary defense against noxious environmental agents. Upon injury, keratinocytes migrate directionally into the wound bed to initiate re-epithelialization, essential for wound repair and restoration of barrier integrity. Keratinocytes express a high level of β2-adrenergic receptors (β2-ARs) that appear to play a role in cutaneous homeostasis as aberrations in either keratinocyte β2-AR function or density are associated with various skin diseases. Here we report the novel finding that β-AR antagonists promote wound re-epithelialization in a “chronic” human skin wound-healing model. β-AR antagonists increase ERK phosphorylation, the rate of keratinocyte migration, electric field-directed migration, and ultimately accelerate human skin wound re-epithelialization. We demonstrate that keratinocytes express two key enzymes required for catecholamine (β-AR agonist) synthesis, tyrosine hydroxylase and phenylethanolamine-N-methyl transferase, both localized within keratinocyte cytoplasmic vesicles. Finally, we confirm the synthesis of epinephrine by measuring the endogenously synthesized catecholamine in keratinocyte extracts. Previously, we have demonstrated that β-AR agonists delay wound re-epithelialization. Here we report that the mechanism for the β-AR antagonist-mediated augmentation of wound repair is due to β2-AR blockade, preventing the binding of endogenously synthesized epinephrine. Our work describes an endogenous β-AR mediator network in the skin that can temporally regulate skin wound repair. Further investigation of this network will improve our understanding of both the skin repair process and the multiple modes of action of one of the most frequently prescribed class of drugs, hopefully resulting in a new treatment for chronic wounds.

Ion channels are linked to differentiation in keratinocytes

SummaryIn vivo and in vitro, keratinocyte differentiation is linked with increased extracellular Ca2+. In order to correlate ion channels with cell differentiation and investigate keratinocyte membrane responses to Ca2+, keratinocyte single channel currents were studied using the patch-clamp technique. The most frequently observed channel was a 14 pS nonspecific cation channel. This channel was permeable to Ca2+ and activated by physiological concentrations of Ca2+. We also found a 35 pS Cl− channel whose open probability increased with depolarization. Finally, a 70 pS K+ channel was seen only in cell-attached or nystatin-permeabilized patches. We correlated channel types with staining for involucrin, an early marker of keratinocyte differentiation. While the nonspecific cation channel and Cl− channel were seen in both involucrin positive and involucrin negative cells, all channels in which the K+ channel activity was present were involucrin positive. Membrane currents through these channels may be one pathway by which signals for keratinocyte proliferation or differentiation are sent.

Immunolocalization of Low-Molecular-Weight Stress Protein HSP 27 in Normal Skin and Common Cutaneous Lesions

Stress proteins, which are found ubiquitously in mammalian cells, appear to be implicated in the regulation of cell growth and protection from environmental insult. Although we previously demonstrated the expression of low-molecular-weight stress protein, HSP 27, in cultured keratinocytes, HSP 27 has not yet been identified in human skin. Using standard immunohistochemistry on routinely processed paraffin sections, we examined specimens of common epidermal lesions and normal skin with a monoclonal antibody to HSP 27. Normal skin from the breast, foreskin, and lower extremity demonstrated strong cytoplasmic staining in the suprabasal epidermis. There was no change in the intensity of staining or cellular localization related to age, body location, or gender. Sections of actinic keratosis, superficial basal cell carcinoma, seborrheic keratosis, and psoriasis also exhibited strong cytoplasmic staining in the suprabasal layers of the epidermis. In contrast, cutaneous squamous cell carcinoma demonstrated only weak cytoplasmic staining throughout the infiltrating tumor. This is of particular interest, since other investigators have reported a loss of HSP 27 expression in oncogenically transformed cells that exhibit a tumorigenic phenotype. To our knowledge, this study provides the first demonstration of HSP 27 expression in human skin.

Galectin-3 Regulates Intracellular Trafficking of EGFR through Alix and Promotes Keratinocyte Migration

The epidermal growth factor receptor (EGFR)-mediated signaling pathways are important in a variety of cellular processes, including cell migration and wound re-epithelialization. Intracellular trafficking of EGFR is critical for maintaining EGFR surface expression. Galectin-3, a member of an animal lectin family, has been implicated in a number of physiological and pathological processes. Through studies of galectin-3-deficient mice and cells isolated from these mice, we demonstrated that absence of galectin-3 impairs keratinocyte migration and skin wound re-epithelialization. We have linked this pro-migratory function to a crucial role of cytosolic galectin-3 in controlling intracellular trafficking and cell surface expression of EGFR after EGF stimulation. Without galectin-3, the surface levels of EGFR are dramatically reduced and the receptor accumulates diffusely in the cytoplasm. This is associated with reduced rates of both endocytosis and recycling of the receptor. We have provided evidence that this novel function of galectin-3 may be mediated through interaction with its binding partner Alix, which is a protein component of the endosomal sorting complex required for transport (ESCRT) machinery. Our results suggest that galectin-3 is potentially a critical regulator of a number of important cellular responses through its intracellular control of trafficking of cell surface receptors.