Matthias Goebeler

Macrophages and angiogenesis.

Macrophages are supposed to play a key role in inflammatory and tumor angiogenesis. Their importance derives from (1) their ubiquitous presence in normal and especially inflamed tissues, (2) their potential to become activated in response to appropriate stimuli, and (3) their repertoire of secretory products. By release of proteases, growth factors (bFGF, GM‐CSF, TGF‐α, IGF‐I, PDGF, VEGF/VPF, TGF‐β), and other monokines (IL‐1, IL‐6, IL‐8, TNF‐α, substance P, prostaglandins, interferons, thrombospondin 1), activated macrophages have the capability to influence each phase of the angiogenic process, such as alterations of the local extracellular matrix, induction of endothelial cells to migrate or proliferate, and inhibition of vascular growth with formation of differentiated capillaries. This review describes macrophage physiology and the influence of macrophage secretory products on the different phases of angiogenesis in vitro and in vivo. J. Lcukoc. Biol. 55: 410–422; 1994.

Chemokines in cutaneous wound healing

Healing of wounds is one of the most complex biological events afterbirth as a result of the interplay of different tissue structures and alarge number of resident and infiltrating cell types. The latter aremainly constituted by leukocyte subsets (neutrophils, macrophages, mastcells, and lymphocytes), which sequentially infiltrate the wound siteand serve as immunological effector cells but also as sources ofinflammatory and growth‐promoting cytokines. Recent data demonstratethat recruitment of leukocyte subtypes is tightly regulated bychemokines. Moreover, the presence of chemokine receptors on residentcells (e.g., keratinocytes, endothelial cells) indicates thatchemokines also contribute to the regulation of epithelialization,tissue remodeling, and angiogenesis. Thus, chemokines are in anexclusive position to integrate inflammatory events and reparativeprocesses and are important modulators of human‐skin wound healing.This review will focus preferentially on the role of chemokines duringskin wound healing and intends to provide an update on the multiplefunctions of individual chemokines during the phases of woundrepair.

TNF-mediated inflammatory skin disease in mice with epidermis-specific deletion of IKK2

The IκB kinase (IKK), consisting of the IKK1 and IKK2 catalytic subunits and the NEMO (also known as IKKγ) regulatory subunit, phosphorylates IκB proteins, targeting them for degradation and thus inducing activation of NF-κB (reviewed in refs 1, 2). IKK2 and NEMO are necessary for NF-κB activation through pro-inflammatory signals. IKK1 seems to be dispensable for this function but controls epidermal differentiation independently of NF-κB. Previous studies suggested that NF-κB has a function in the growth regulation of epidermal keratinocytes. Mice lacking RelB or IκBα, as well as both mice and humans with heterozygous NEMO mutations, develop skin lesions. However, the function of NF-κB in the epidermis remains unclear. Here we used Cre/loxP-mediated gene targeting to investigate the function of IKK2 specifically in epidermal keratinocytes. IKK2 deficiency inhibits NF-κB activation, but does not lead to cell-autonomous hyperproliferation or impaired differentiation of keratinocytes. Mice with epidermis-specific deletion of IKK2 develop a severe inflammatory skin disease, which is caused by a tumour necrosis factor-mediated, αβ T-cell-independent inflammatory response that develops in the skin shortly after birth. Our results suggest that the critical function of IKK2-mediated NF-κB activity in epidermal keratinocytes is to regulate mechanisms that maintain the immune homeostasis of the skin.

Crucial role for human Toll-like receptor 4 in the development of contact allergy to nickel

Allergies to nickel (Ni2+) are the most frequent cause of contact hypersensitivity (CHS) in industrialized countries. The efficient development of CHS requires both a T lymphocyte-specific signal and a proinflammatory signal. Here we show that Ni2+ triggered an inflammatory response by directly activating human Toll-like receptor 4 (TLR4). Ni2+-induced TLR4 activation was species-specific, as mouse TLR4 could not generate this response. Studies with mutant TLR4 proteins revealed that the non-conserved histidines 456 and 458 of human TLR4 are required for activation by Ni2+ but not by the natural ligand lipopolysaccharide. Accordingly, transgenic expression of human TLR4 in TLR4-deficient mice allowed efficient sensitization to Ni2+ and elicitation of CHS. Our data implicate site-specific human TLR4 inhibition as a potential strategy for therapeutic intervention in CHS that would not affect vital immune responses.

Chemokines IL-8, GROα, MCP-1, IP-10, and Mig Are Sequentially and Differentially Expressed During Phase-Specific Infiltration of Leukocyte Subsets in Human Wound Healing

Healing of cutaneous wounds requires a complex integrated network of repair mechanisms, including the action of newly recruited leukocytes. Using a skin repair model in adult humans, we investigated the role chemokines play in sequential infiltration of leukocyte subsets during wound healing. At day 1 after injury, the C-X-C chemokines IL-8 and growth-related oncogene alpha are maximally expressed in the superficial wound bed and are spatially and temporally associated with neutrophil infiltration. IL-8 and growth-related oncogene alpha profiles also correlate with keratinocyte migration and subsequently subside after wound closure at day 4. Macrophage infiltration reaches the highest levels at day 2 and is paralleled by monocyte chemoattractant protein-1 mRNA expression in both the basal layer of the proliferative epidermis at the wound margins and mononuclear cells in the wound area. Other monocyte-attracting chemokines such as monocyte chemoattractant protein-3, macrophage inflammatory protein-1alpha and -1beta, RANTES, and 1309 are undetectable. At day 4, perivascular focal lymphocyte accumulation correlates with strong focal expression of the C-X-C chemokines Mig and IP-10. Our results suggest that a dynamic set of chemokines contributes to the spatially and temporally different infiltration of leukocyte subsets and thus integrates the inflammatory and reparative processes during wound repair.

MACROPHAGE-DERIVED ANGIOGENESIS FACTORS.

A majority of angiogenic factors has been shown to be produced by macrophages. This review will give a concise description of their biochemical nature, their isolation from macrophages and their angiogenic activity. Among the factors with mitogenic effects on endothelial cells are basic fibroblast growth factor (bFGF), transforming growth factor-alpha (TGF-alpha) and very probably insulin-like growth factor-1 (IGF-1). Other secretory products such as angiotropin and human angiogenic factor (HAF) are nonmitogenic but promote angiogenesis by inducing migration of endothelial cells. Prostaglandins, platelet-derived growth factor (PDGF), granulocyte-macrophage- and granulocyte-colony stimulating factor (GM-CSF, G-CSF), interleukin 6 (IL-6) and angiotensin converting enzyme (ACE) have also been shown to be angiogenic, but their mode of action is still to be clearly defined. As the extracellular matrix appears to be involved in the control of angiogenesis, macrophage-derived factors that can alter this structure via degradation or via the clotting system will also be discussed. Tumor necrosis factor alpha (TNF-alpha), interleukin 1 (IL-1) and transforming growth factor-beta (TGF-beta) have complex actions on endothelial cells, and can partially inhibit angiogenesis. Among the factors which solely inhibit neovascularization are the interferons. As it is not known whether all of these factors play a role in angiogenesis in vivo attempts to detect them in situ during the course of neovascularization will be described. Finally macrophages will be discussed as cells that may not be mandatory for each phase of the angiogenic process but whose angiogenic capabilities are comprehensive and unsurpassed by any other cell.

The Stress Inducer Arsenite Activates Mitogen-activated Protein Kinases Extracellular Signal-regulated Kinases 1 and 2 via a MAPK Kinase 6/p38-dependent Pathway

Cell response to a wide variety of extracellular signals is mediated by either mitogenic activation of the Raf/MEK/ERK kinase cascade or stress-induced activation of the mitogen-activated protein kinase (MAPK) family members c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) or p38. We have examined communications between these stress- and mitogen-induced signaling pathways. We show here that the stress cascade activator arsenite activates extracellular signal-regulated kinase (ERK) in addition to p38 albeit with different kinetics. Whereas p38 is an early response kinase, ERK activation occurs with delayed time kinetics at 2–4 h. We observed activation of ERK upon arsenite treatment in many different cell lines. ERK activation is strongly enhanced by overexpression of p38 and mitogen-activated protein kinase kinase 6 (MKK6) but is blocked by dominant negative kinase versions of p38 and MKK6 or the specific p38 inhibitor SB203580. Arsenite-induced ERK activation is mediated by Ras, Raf, and MEK but appears to be independent of de novoprotein synthesis. These data provide the first evidence for a p38 dependent activation of the mitogenic kinase cascade in stress-stimulated cells.

Differential and Sequential Expression of Multiple Chemokines during Elicitation of Allergic Contact Hypersensitivity

Regulation of chemokine-mediated leukocyte migration within inflammatory tissues is a complex event that cannot be mimicked and analyzed in vitro. We therefore investigated the role of macrophage- and T-lymphocyte-specific chemoattractants involved in the positioning of immune effector cells during the elicitation phase of contact hypersensitivity, a prototype of a T-lymphocyte-mediated immune reaction. Serial sections of skin biopsies obtained from sensitized individuals at distinct time intervals after epicutaneous application of allergens were hybridized with anti-sense probes of a large panel of chemokines or immunohistologically labeled with leukocyte-specific antibodies. Multifocal expression of monocyte chemoattractant protein-1 (MCP-1) was already detected after 6 hours in basal keratinocytes clearly preceding the infiltration of monocytes and T cells. Increasing basal expression of MCP-1 and, in addition, of regulated upon activation, normal T-cell expressed and secreted (RANTES) after 12 hours was accompanied by dermal expression of MCP-1, macrophage-derived chemoattractant (MDC), and RANTES and paralleled by infiltration of mononuclear cells into dermis and epidermis. Expression of the T-lymphocyte-specific chemokines IP-10 and MIG in epidermis and dermis and of MDC, pulmonary and activation-regulated chemokine (PARC), and thymus and activation-regulated chemokine (TARC) exclusively in the dermis started after 12 hours reaching maximum levels at 72 hours and was associated with infiltration of T cells into the epidermal compartment. Our data provide evidence that migrating effector cells encounter multiple chemoattractant signals in a complex spatial and temporal pattern. In particular, keratinocytes contribute to the vigorous immigration by sequential expression of MCP-1, RANTES, and interferon-inducible protein-10 (IP-10) monokine induced by gamma interferon (MIG), indicating that chemokine-mediated nonimmunological mechanisms precede and corroborate antigen-specific mechanisms during elicitation of contact hypersensitivity.

Rituximab in autoimmune bullous diseases: mixed responses and adverse effects

Background  Intolerably high doses of systemic corticosteroids and additional immunosuppressants may be required to control disease activity in autoimmune bullous skin diseases. New therapeutic options are needed for such patients.

Proteasome Inhibition Results in TRAIL Sensitization of Primary Keratinocytes by Removing the Resistance-Mediating Block of Effector Caspase Maturation

ABSTRACT Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) exerts potent cytotoxic activity against transformed keratinocytes, whereas primary keratinocytes are relatively resistant. In several cell types, inhibition of the proteasome sensitizes for TRAIL-induced apoptosis by interference with NF-κB activation. Here we describe a novel intracellular mechanism of TRAIL resistance in primary cells and how this resistance is removed by proteasome inhibitors independent of NF-κB in primary human keratinocytes. This sensitization was not mediated at the receptor-proximal level of TRAIL DISC formation or caspase 8 activation but further downstream. Activation of caspase 3 was critical, as it only occurred when mitochondrial apoptotic pathways were activated, as reflected by Smac/DIABLO, HtrA2, and cytochrome c release. Smac/DIABLO and HtrA2 are needed to release the X-linked inhibitor-of-apoptosis protein (XIAP)-mediated block of full caspase 3 maturation. XIAP can effectively block caspase 3 maturation and, intriguingly, is highly expressed in primary but not in transformed keratinocytes. Ectopic XIAP expression in transformed keratinocytes resulted in increased resistance to TRAIL. Our data suggest that breaking of this resistance via proteasome inhibitors, which are potential anticancer drugs, may sensitize certain primary cells to TRAIL-induced apoptosis and could thereby complicate the clinical applicability of a combination of TRAIL receptor agonists with proteasome inhibitors.