The role of NT-3 signaling in Merkel cell development

Gibberellic acid application on biomass, oxidative stress response, and photosynthesis in spinach (Spinacia oleracea L.) seedlings under copper stress

The mechanism of Cu tolerance in plants and its control measures are of considerable significance for the remediation of Cu-contaminated soils. Gibberellic acid (GA₃) is involved in plant growth and development and in the response to heavy metal stress. In the present study, changes in the biomass, oxidative stress response responses, and photosynthesis of spinach seedlings were examined under Cu stress with exogenous GA₃ applied at concentrations of 0, 3, 5, 10, 20, 40, 60, or 80 mg L^-1. Under Cu stress, the plant Cu concentration and oxidative damage were greater, photosynthetic parameters and biomass declined, and antioxidant enzyme activities and the proline concentration increased. However, spinach growth did not terminate, indicating that spinach seedlings had strong Cu tolerance. When low concentrations of GA₃ (3-5 mg L^-1) were added to Cu-stressed spinach seedlings, the damage caused by Cu stress to spinach seedlings was reduced, and the Cu tolerance of spinach seedlings was enhanced, which mainly manifested as reduced oxidation damage, an increased proline concentration, elevated antioxidant enzyme activities, decreased Cu concentration in leaves, and increased Cu concentration in roots, increased photosynthetic parameters, and an increased in the total biomass. In contrast, additions of GA₃ at concentrations higher than 40 mg L^-1 intensified oxidative damage and decreased the activities of antioxidant enzymes, photosynthetic parameters, and biomass. Additionally, the Cu concentration increased in leaves and decreased Cu concentration in roots, indicating that high concentrations of GA₃ aggravated stress damage and severely influenced physiological functions in spinach seedlings. In summary, the application of 3-5 mg L^-1 GA₃ to spinach seedlings in Cu-contaminated soil can be used to reduce Cu toxicity to plants and increase Cu tolerance.

Histogenesis of Merkel Cell Carcinoma: A Comprehensive Review

Merkel cell carcinoma (MCC) is a primary neuroendocrine carcinoma of the skin. This neoplasia features aggressive behavior, resulting in a 5-year overall survival rate of 40%. In 2008, Feng et al. identified Merkel cell polyomavirus (MCPyV) integration into the host genome as the main event leading to MCC oncogenesis. However, despite identification of this crucial viral oncogenic trigger, the nature of the cell in which MCC oncogenesis occurs is actually unknown. In fact, several hypotheses have been proposed. Despite the large similarity in phenotype features between MCC tumor cells and physiological Merkel cells (MCs), a specialized subpopulation of the epidermis acting as mechanoreceptor of the skin, several points argue against the hypothesis that MCC derives directly from MCs. Alternatively, MCPyV integration could occur in another cell type and induce acquisition of an MC-like phenotype. Accordingly, an epithelial as well as a fibroblastic or B-cell origin of MCC has been proposed mainly based on phenotype similarities shared by MCC and these potential ancestries. The aim of this present review is to provide a comprehensive review of the current knowledge of the histogenesis of MCC.

Mechanosensory and ATP Release Deficits following Keratin14-Cre-Mediated TRPA1 Deletion Despite Absence of TRPA1 in Murine Keratinocytes

Keratinocytes are the first cells that come into direct contact with external tactile stimuli; however, their role in touch transduction in vivo is not clear. The ion channel Transient Receptor Potential Ankyrin 1 (TRPA1) is essential for some mechanically-gated currents in sensory neurons, amplifies mechanical responses after inflammation, and has been reported to be expressed in human and mouse skin. Other reports have not detected Trpa1 mRNA transcripts in human or mouse epidermis. Therefore, we set out to determine whether selective deletion of Trpa1 from keratinocytes would impact mechanosensation. We generated K14Cre-Trpa1fl/fl mice lacking TRPA1 in K14-expressing cells, including keratinocytes. Surprisingly, Trpa1 transcripts were very poorly detected in epidermis of these mice or in controls, and detection was minimal enough to preclude observation of Trpa1 mRNA knockdown in the K14Cre-Trpa1fl/fl mice. Unexpectedly, these K14Cre-Trpa1fl/fl mice nonetheless exhibited a pronounced deficit in mechanosensitivity at the behavioral and primary afferent levels, and decreased mechanically-evoked ATP release from skin. Overall, while these data suggest that the intended targeted deletion of Trpa1 from keratin 14-expressing cells of the epidermis induces functional deficits in mechanotransduction and ATP release, these deficits are in fact likely due to factors other than reduction of Trpa1 expression in adult mouse keratinocytes because they express very little, if any, Trpa1.

Integrative physiology of depression and antidepressant drug action: implications for serotonergic mechanisms of action and novel therapeutic strategies for treatment of depression

Major depressive disorder (MDD) is predicted to be the second leading cause of disability worldwide by the year 2020. Currently available treatments for MDD are suboptimal. Only 50% of MDD patients recover in less than 12 weeks with adequate treatment, and up to 20% of patients will fail to adequately respond to all currently available interventions. Moreover, current treatments come at the cost of significant central nervous system (CNS) side effects, further highlighting the need for more effective treatments with fewer side effects. A greater mechanistic understanding of MDD and the actions of antidepressant drugs would provide opportunities for development of novel therapeutic approaches to treatment. With this aim in mind, we explore the novel, but empirically supported, hypothesis that an evolutionarily ancient thermoafferent pathway, signaling via the spinoparabrachial pathway from serotonergic sensory cells in the skin and other epithelial linings to serotonergic neurons and depression-related circuits in the brain, is dysfunctional in MDD and that antidepressant therapies, including antidepressant drugs and exercise, act by restoring its function.

Development and neuronal dependence of cutaneous sensory nerve formations: Lessons from neurotrophins

Null mutations of genes from the NGF family of NTs and their receptors (NTRs) lead to loss/reduction of specific neurons in sensory ganglia; conversely, cutaneous overexpression of NTs results in skin hyperinnervation and increase or no changes in the number of sensory neurons innervating the skin. These neuronal changes are paralleled with loss of specific types of sensory nerve formations in the skin. Therefore, mice carrying mutations in NT or NTR genes represent an ideal model to identify the neuronal dependence of each type of cutaneous sensory nerve ending from a concrete subtype of sensory neuron, since the development, maintenance, and structural integrity of sensory nerve formations depend upon sensory neurons. Results obtained from these mouse strains suggest that TrkA positive neurons are connected to intraepithelial nerve fibers and other sensory nerve formations depending from C and Adelta nerve fibers; the neurons expressing TrkB and responding to BDNF and NT-4 innervate Meissner corpuscles, a subpopulation of Merkell cells, some mechanoreceptors of the piloneural complex, and the Ruffini's corpuscles; finally, a subpopulation of neurons, which are responsive to NT-3, support postnatal survival of some intraepithelial nerve fibers and Merkel cells in addition to the muscle mechanoreceptors. On the other hand, changes in NTs and NTRs affect the structure of non-nervous structures of the skin and are at the basis of several cutaneous pathologies. This review is an update about the role of NTs and NTRs in the maintenance of normal cutaneous innervation and maintenance of skin integrity.

Effects of tacrolimus ointment on the expression of substance P, nerve growth factor, and neurotrophin-3 in atopic dermatitis

BACKGROUND

There is increasing evidence that neuropeptides may be involved in the pathogenesis of atopic dermatitis (AD). Objectives To investigate the effects of tacrolimus on the neuropeptides substance P (SP), nerve growth factor (NGF), and neurotrophin-3 (NT-3) in the skin, and SP and NGF in the serum, of patients with AD.

METHODS

Lesional skin specimens were obtained from eight AD patients and eight normal controls. For 8 weeks, AD patients applied 0.03% tacrolimus ointment to all affected areas twice daily. Blood samples and skin biopsies were then repeated. The participants' serum SP and NGF levels, as well as the SP, NGF, and NT-3 immunoreactive cell counts, were evaluated in the epidermal, dermal, and perivascular areas of lesional skin before and after treatment.

RESULTS

The immunoreactive cell counts of SP, NGF, and NT-3 in skin were higher in AD patients than in normal controls. Most cell counts decreased significantly after treatment; however, the change in serum SP and NGF was not statistically significant.

CONCLUSIONS

We demonstrated semiquantitative differences in neuropeptides in the skin of AD patients. In addition, topical tacrolimus reduced the levels of neuropeptides in the tissues of AD patients.

The Meissner and Pacinian sensory corpuscles revisited new data from the last decade

This article reviews the biochemical, physiological, and experimental data cumulated during the last decade on the Meissner and Pacinian corpuscles. It includes information about (i) the localization of molecules recently detected in sensory corpuscles; (ii) the unsolved problem of the accessory fibers in sensory corpuscles and the occurrence of myelin within them; (iii) the development of sensory corpuscles, especially their neuronal and growth factor dependency; (iv) the composition and functional significance of the extracellular matrix as an essential part of the mechanisms involved in the genesis of the stimuli generated in sensory corpuscles; (v) the molecular basis of mechanotransduction; (vi) a miscellaneous section containing sparse new data on the protein composition of sensory corpuscles, as well as in the proteins involved in live-death cell decisions; (vii) the changes in sensory corpuscles as a consequence of aging, the central, or peripheral nervous system injury; and finally, (viii) the special interest of Meissner corpuscles and Pacinian corpuscles for pathologists for the diagnosis of some peripheral neuropathies and neurodegenerative diseases.

Immunophenotyping of the human bulge region: the quest to define useful in situ markers for human epithelial hair follicle stem cells and their niche

Since the discovery of epithelial hair follicle stem cells (eHFSCs) in the bulge of human hair follicles (HFs) an important quest has started: to define useful markers. In the current study, we contribute to this by critically evaluating corresponding published immunoreactivity (IR) patterns, and by attempting to identify markers for the in situ identification of human eHFSCs and their niche. For this, human scalp skin cryosections of at least five different individuals were examined, employing standard immunohistology as well as increased sensitivity methods. Defined reference areas were compared by quantitative immunohistochemistry for the relative intensity of their specific IR. According to our experience, the most useful positive markers for human bulge cells turned out to be cytokeratin 15, cytokeratin 19 and CD200, but were not exclusive, while beta1 integrin and Lhx2 IR were not upregulated by human bulge keratinocytes. Absent IR for CD34, connexin43 and nestin on human bulge cells may be exploited as negative markers. alpha6 integrin, fibronectin, nidogen, fibrillin-1 and latent transforming growth factor (TGF)-beta-binding protein-1 were expressed throughout the connective tissue sheath of human HFs. On the other hand, tenascin-C was upregulated in the bulge and may thus constitute a component of the bulge stem cell niche of human HFs. These immunophenotyping results shed further light on the in situ expression patterns of claimed follicular 'stem cell markers' and suggest that not a single marker alone but only the use of a limited corresponding panel of positive and negative markers may offer a reasonable and pragmatic compromise for identifying human bulge stem cells in situ.

Merkel cells

Merkel cells are post-mitotic cells scattered throughout the epidermis of vertebrates. They are particularly interesting because of the close connections that they develop with sensory nerve endings and the number of peptides they can secrete. These features suggest that they may make an important contribution to skin homeostasis and cutaneous nerve development. However, these cells remain mysterious because they are difficult to study. They have not been successfully cultured and cannot be isolated, severely hampering molecular biology and functional analysis. Merkel cells probably originate in the neural crest of avians and mammalians, and their "spontaneous" appearance in the epidermis may be caused by a neuron-independent epidermal differentiation process. Their functions are still unclear: they take part in mechanoreception or at least interact with neurons, but little is known about their interactions with other epidermal cells. This review provides a new look at these least-known cells of the skin. The numerous peptides they synthesize and release may allow them to communicate with many cells other than neurons, and it is plausible that Merkel cells play a key role in skin physiology and physiopathology.

Hair follicle stem cells: walking the maze

The discovery of epithelial stem cells (eSCs) in the bulge region of the outer root sheath of hair follicles in mice and man has encouraged research into utilizing the hair follicle as a therapeutic source of stem cells (SCs) for regenerative medicine, and has called attention to the hair follicle as a highly instructive model system for SC biology. Under physiological circumstances, bulge eSCs serve as cell pool for the cyclic regeneration of the anagen hair bulb, while they can also regenerate the sebaceous gland and the epidermis after injury. More recently, melanocyte SCs, nestin+, mesenchymal and additional, as yet ill-defined "stem cell" populations, have also been identified in or immediately adjacent to the hair follicle epithelium, including in the specialized hair follicle mesenchyme (connective tissue sheath), which is crucial to wound healing. Thus the hair follicle and its adjacent tissue environment contain unipotent, multipotent, and possibly even pluripotent SC populations of different developmental origin. It provides an ideal model system for the study of central issues in SC biology such as plasticity and SC niches, and for the identification of reliable, specific SC markers, which distinguish them from their immediate progeny (e.g. transient amplifying cells). The current review attempts to provide some guidance in this growing maze of hair follicle-associated SCs and their progeny, critically reviews potential or claimed hair follicle SC markers, highlights related differences between murine and human hair follicles, and defines major unanswered questions in this rapidly advancing field.

Current considerations about Merkel cells

Since the discovery of Merkel cells by Friedrich S. Merkel in 1875, knowledge of their structure has increased with the progression of new technologies such as electron and laser microscopy, and immunohistochemical techniques. For most vertebrates, Merkel cells are located in the basal layer of the epidermis and characterized by dense-core granules that contain a variety of neuropeptides, plasma membrane spines and cytoskeletal filaments consisting of cytokeratins and desmosomes. The presence of the two latter structures would suggest that Merkel cells originate from the epidermis rather than from the neural crest, even though such a hypothesis is not unanimously accepted. The function of the Merkel cell is also very controversial. For a long time, it has been accepted that Merkel cells with associated nerve terminals act as mechanoreceptors although the transduction mechanism has not yet been elucidated. Merkel cells that do not make contact with nerve terminals have an endocrine function. The present review aims to shed new and comparative light on this field with an attempt to investigate the stimuli that Merkel cells are able to perceive.

Mice lacking the p75 receptor fail to acquire a normal complement of taste buds and geniculate ganglion neurons by adulthood

Brain-derived neurotrophic factor and neurotrophin-4 are required for normal taste bud development. Although these neurotrophins normally function via the tyrosine kinase receptor, trkB, they also bind to the pan-neurotrophin receptor, p75. The goal of the present study was to determine whether the p75 receptor is required for the development or maintenance of a full complement of adult taste buds. Mice with p75 null mutations lose 34% of their circumvallate taste buds, 36% of their fungiform papillae, and 26% of their fungiform taste buds by adulthood. The reduction of taste buds in the adult circumvallate papilla was similar to that observed previously at postnatal day 7 (Fan et al. Brain Res Dev Brain Res 2004;150:23-39). Taken together, these findings indicate that the p75 receptor is critical for the development of a full complement of taste buds, but is not required for maintenance of circumvallate taste buds in adulthood. Immunolabeling for p75 was not observed in taste buds, indicating that p75 signaling influences taste bud number indirectly. Geniculate ganglion neurons, which provides innervation to fungiform taste buds, express the p75 receptor. Mice with p75 null mutations also have fewer neurons in the geniculate ganglion. Together, these results suggest that the p75 receptor is important for the survival of geniculate neurons and geniculate neuron survival is required for the development of a full complement of taste buds by adulthood.