Marek Lommatzsch

Abundant Production of Brain-Derived Neurotrophic Factor by Adult Visceral Epithelia: Implications for Paracrine and Target-Derived Neurotrophic Functions

Brain-derived neurotrophic factor (BDNF) plays a crucial role for the survival of visceral sensory neurons during development. However, the physiological sources and the function of BDNF in the adult viscera are poorly described. We have investigated the cellular sources and the potential role of BDNF in adult murine viscera. We found markedly different amounts of BDNF protein in different organs. Surprisingly, BDNF levels in the urinary bladder, lung, and colon were higher than those found in the brain or skin. In situ hybridization experiments revealed that BDNF mRNA was made by visceral epithelial cells, several types of smooth muscle, and neurons of the myenteric plexus. Epithelia that expressed BDNF lacked both the high- and low-affinity receptors for BDNF, trkB and p75(NTR). In contrast, both receptors were present on neurons of the peripheral nervous system. Studies with BDNF-/-mice demonstrated that epithelial and smooth muscle cells developed normally in the absence of BDNF. These data provide evidence that visceral epithelia are a major source, but not a target, of BDNF in the adult viscera. The abundance of BDNF protein in certain internal organs suggests that this neurotrophin may regulate the function of adult visceral sensory and motor neurons.

Extracellular Adenosine Triphosphate and Chronic Obstructive Pulmonary Disease

RATIONALE Extracellular ATP promotes inflammation, but its role in chronic obstructive pulmonary disease (COPD) is unknown. OBJECTIVES To analyze the expression of ATP and its functional consequences in never-smokers, asymptomatic smokers, and patients with COPD. METHODS ATP was quantified in bronchoalveolar lavage fluid (BALF) of never-smokers, asymptomatic smokers, and patients with COPD of different severity. The expression of specific ATP (purinergic) receptors was measured in airway macrophages and blood neutrophils from control subjects and patients with COPD. The release of mediators by macrophages and neutrophils and neutrophil chemotaxis was assessed after ATP stimulation. MEASUREMENTS AND MAIN RESULTS Chronic smokers had elevated ATP concentrations in BALF compared with never-smokers. Acute smoke exposure led to a further increase in endobronchial ATP concentrations. Highest ATP concentrations in BALF were present in smokers and ex-smokers with COPD. In patients with COPD, BALF ATP concentrations correlated negatively with lung function and positively with BALF neutrophil counts. ATP induced a stronger chemotaxis and a stronger elastase release in blood neutrophils from patients with COPD, as compared with control subjects. In addition, airway macrophages from patients with COPD responded with an increased secretion of proinflammatory and tissue-degrading mediators after ATP stimulation. These findings were accompanied by an up-regulation of specific purinergic receptors in blood neutrophils and airway macrophages of patients with COPD. CONCLUSIONS COPD is characterized by a strong and persistent up-regulation of extracellular ATP in the airways. Extracellular ATP appears to contribute to the pathogenesis of COPD by promoting inflammation and tissue degradation.

Tumor necrosis factor-α and interleukin-6 regulate secretion of brain-derived neurotrophic factor in human monocytes

Activated macrophages have been shown to produce brain-derived neurotrophic factor (BDNF) in diseases such as multiple sclerosis (MS) or allergic bronchial asthma (BA). However, there is little data on BDNF regulation in these cells. We demonstrate that unstimulated human peripheral blood monocytes, but not lymphocytes, constitutively secrete BDNF. IL-6 and TNF-alpha specifically enhanced BDNF secretion in monocytes, whereas typical Th1- and Th2-cytokines did not show any effect. None of the cytokines induced BDNF secretion in T- or B-cells. Thus, our data provide evidence that IL-6 and TNF-alpha represent a specific link between monocyte infiltration and neuronal changes in inflammatory diseases.

P2X7 receptor signaling in the pathogenesis of smoke-induced lung inflammation and emphysema.

Extracellular ATP is up-regulated in the airways of patients with chronic obstructive pulmonary disease, and may contribute to the pathogenesis of the disease. However, the precise mechanisms are poorly understood. Our objective was to investigate the functional role of the ATP receptor P2X(7) in the pathogenesis of cigarette smoke (CS)-induced lung inflammation and emphysema in vivo. Expression of the P2X(7) receptor (P2X(7)R) was measured in lung tissue und immune cells of mice with CS-induced lung inflammation. In a series of experiments using P2X(7) antagonists and genetically engineered mice, the functional role of the P2X(7)R in CS-induced lung inflammation was explored. CS-induced inflammation was associated with an up-regulation of the P2X(7)R on blood and airway neutrophils, alveolar macrophages, and in whole lung tissue. Selective intrapulmonary inhibition of the P2X(7)R reduced CS-induced lung inflammation and prevented the development of emphysema. Accordingly, P2X(7)R knockout mice showed a reduced pulmonary inflammation after acute CS exposure. Experiments with P2X(7)R chimera animals revealed that immune cell P2X(7)R expression plays an important role in CS-induced lung inflammation and emphysema. Extracellular ATP contributes to the development of CS-induced lung inflammation and emphysema via activation of the P2X(7)R. Inhibition of this receptor may be a new therapeutic target for the treatment of chronic obstructive pulmonary disease.

A new role for neurotrophins: involvement of brain-derived neurotrophic factor and neurotrophin-4 in hair cycle control

Neurotrophins exert many biological effects not directly targeted at neurons, including modulation of keratinocyte proliferation and apo‐ptosis in vitro. Here we exploit the cyclic growth and regression activity of the murine hair follicle to explore potential nonneuronal functions of neurotrophins in the skin, and analyze the follicular expression and hair growth‐modulatory function of BDNF, NT‐4, and their high‐affinity receptor, TrkB. The cutaneous expression of BDNF and NT‐4 mRNA was strikingly hair cycle dependent and peaked during the spontaneous, apoptosis‐driven hair follicle regression (catagen). During catagen, BDNF mRNA and immunoreactivity, as well as NT‐4‐immunoreactivity, were expressed in the regressing hair follicle compartments, whereas TrkB mRNA and immunoreactivity were seen in dermal papilla fibroblasts, epithelial strand, and hair germ. BDNF or NT‐4 knockout mice showed significant catagen retardation, whereas BDNF‐overexpressing mice displayed acceleration of catagen and significant shortening of hair length. Finally, BDNF and NT‐4 accelerated catagen development in murine skin organ culture. Together, our data suggest that BDNF and NT‐4 play a previously unrecognized role in skin physiology as agents of hair growth control. Thus, TrkB agonists and antagonists deserve exploration as novel hair growth‐modulatory drugs for the management of common hair growth disorders.—Botch‐karev, V. A., Botchkareva, N. V., Welker, P., Metz, M., Lewin, G. R., Subramaniam, A., Bulfone‐Paus, S., Hagen, E., Braun, A., Lommatzsch, M., Renz, H., Paus, R. A new role for neurotrophins: involvement of brain‐derived neurotrophic factor and neurotro‐phin‐4 in hair cycle control. FASEB J. 13, 395–410 (1999)

Purinergic Receptor Inhibition Prevents the Development of Smoke-Induced Lung Injury and Emphysema

Extracellular ATP acts as a “danger signal” and can induce inflammation by binding to purinergic receptors. Chronic obstructive pulmonary disease is one of the most common inflammatory diseases associated with cigarette smoke inhalation, but the underlying mechanisms are incompletely understood. In this study, we show that endogenous pulmonary ATP levels are increased in a mouse model of smoke-induced acute lung inflammation and emphysema. ATP neutralization or nonspecific P2R-blockade markedly reduced smoke-induced lung inflammation and emphysema. We detected an upregulation the purinergic receptors subtypes on neutrophils (e.g., P2Y2R), macrophages, and lung tissue from animals with smoke-induced lung inflammation. By using P2Y2R deficient (−/−) animals, we show that ATP induces the recruitment of blood neutrophils to the lungs via P2Y2R. Moreover, P2Y2R deficient animals had a reduced pulmonary inflammation following acute smoke-exposure. A series of experiments with P2Y2R−/− and wild type chimera animals revealed that P2Y2R expression on hematopoietic cell plays the pivotal role in the observed effect. We demonstrate, for the first time, that endogenous ATP contributes to smoke-induced lung inflammation and then development of emphysema via activation of the purinergic receptor subtypes, such as P2Y2R.

Function-Associated Surface Molecules on Airway Dendritic Cells in Cigarette Smokers

Airway dendritic cells (DCs) control pulmonary immune responses to inhaled particles. However, the profile of function-associated surface molecules on airway DCs in smokers is unknown. In this study, function-associated surface molecules were analyzed using four-color flow cytometry on myeloid DCs (mDCs) in bronchoalveolar lavage fluid (BALF) of cigarette smokers and never-smokers. Furthermore, the lung function was assessed directly before bronchoscopy in all participants. There was a 7-fold increase in total cell numbers in BALF of smokers, as compared with never-smokers. The percentage of mDCs among BALF cells and the expression of the maturation marker CD83 on mDCs did not differ between smokers and never-smokers. However, there was a strong increase in the expression of Langerin and CD1a (markers of Langerhans cells) on mDCs of smokers. Furthermore, mDCs of smokers were characterized by an increased expression of antigen presentation markers such as CD80 and CD86. By contrast, mDCs of smokers displayed a decreased expression of the lymph node homing receptor CCR7, as compared with mDCs of never-smokers. Decreased expression of CCR7 on mDCs, but not any of the other surface molecules studied, was specifically associated with airway obstruction and pulmonary hyperinflation in smokers. In conclusion, our data suggest that smoking affects the expression profile of function-associated surface molecules on airway mDCs. We provide the first evidence that a reduced CCR7 expression on airway mDCs is associated with airflow limitation in smokers.

Neurotrophins: A Link between Airway Inflammation and Airway Smooth Muscle Contractility in Asthma?

Background: Bronchial asthma (BA) is characterized by a unique type of airway inflammation, epithelial cell damage and increased airway smooth muscle (ASM) contractility. The regulatory network between the immunological events and the neuronal control of ASM contractility remains to be defined. Methods: Utilizing a well–characterized mouse model of airway inflammation and BA, we analyzed the production and function of neurotrophins in allergic asthma. To confirm these data in humans, segmental allergen provocation was performed in mild asthmatics. Results: Allergen–induced airway inflammation was associated with increased local production of the neurotrophins nerve growth factor (NGF) and brain–derived neurotrophic factor (BDNF) in mice as well as in humans. In bronchoalveolar lavage fluid (BALF), NGF levels were increased 4– to 5–fold in men and mice 1 day after allergen provocation. The increase in BDNF was about 2–fold in both models. Treatment of mice with anti–NGF prevented development of airway hyperresponsiveness (AHR). In the human study group, NGF levels in BALF after allergen provocation were correlated significantly with baseline FEV1 levels. Conclusion: These data strongly suggest that neurotrophins serve as a link between airway inflammation and neuronal control of ASM constriction in BA.

A role for brain-derived neurotrophic factor in B cell development

In the present study, we demonstrated a significant reduction of B lymphocytes in the blood, spleen and bone marrow of BDNF deficient mice. The observed developmental block in bone marrow B cell development was linked specifically to the Pre-BII stage. B lymphocytes express the BDNF receptors p75NTR and TrkB(gp95), while no BDNF expression was found. However, a strong BDNF expression was demonstrated in bone marrow stromal cells. An increase of intracellular free calcium [Ca2+]i in B lymphocytes after BDNF application confirms a direct responsiveness of B lymphocytes to BDNF. In conclusion, these results suggest a role of BDNF for normal B lymphocyte development through paracrine effects in the bone marrow.

BDNF overexpression induces differential increases among subsets of sympathetic innervation in murine back skin

Besides their recognized dependence on nerve growth factor (NGF) during development, the dependence of mature sympathetic ganglion neurons on other neurotrophins is still unclear. Here, we have investigated the sympathetic innervation of back skin in mice overexpressing brain‐derived neurotrophic factor (BDNF) under the alpha‐myosin heavy‐chain promoter, as well as in BDNF knockout (–/–) mice. Compared with wild‐type controls, the dorsal skin of BDNF overexpressing mice displayed a significantly enhanced number of adrenergic, tyrosine hydroxylase‐immunoreactive (IR) nerve fibres, while cholinergic or peptidergic sensory nerve fibres appeared unaltered. The adrenergic hyperinnervation in dorsal skin of BDNF overexpressing mice was most pronounced in the arrector pili muscle of hair follicles, while no increase of tyrosine hydroxylase‐or neuropeptide Y‐IR fibres associated with subcutaneous blood vessels was found. Instead, back skin of BDNF knockout (–/–) mice contained significantly fewer tyrosine hydroxylase‐IR dermal nerve fibres than wild‐type animals. This suggests that BDNF plays an important role in the control of different subsets of adrenergic innervation in murine back skin, and indicates that paravertebral sympathetic ganglia display a previously unrecognized differential BDNF‐dependence in vivo.