Attila Gábor Szöllősi

Activation of transient receptor potential vanilloid-3 inhibits human hair growth.

In the current study, we aimed at identifying the functional role of transient receptor potential vanilloid-3 (TRPV3) ion channel in the regulation of human hair growth. Using human organ-cultured hair follicles (HFs) and cultures of human outer root sheath (ORS) keratinocytes, we provide the first evidence that activation of TRPV3 inhibits human hair growth. TRPV3 immunoreactivity was confined to epithelial compartments of the human HF, mainly to the ORS. In organ culture, TRPV3 activation by plant-derived (e.g., eugenol, 10-1,000 μM) or synthetic (e.g., 2-aminoethoxydiphenyl borate, 1-300 μM) agonists resulted in a dose-dependent inhibition of hair shaft elongation, suppression of proliferation, and induction of apoptosis and premature HF regression (catagen). Human ORS keratinocytes also expressed functional TRPV3, whose stimulation induced membrane currents, elevated intracellular calcium concentration, inhibited proliferation, and induced apoptosis. Of great importance, these effects on ORS keratinocytes were all mediated by TRPV3, as small interfering RNA-mediated silencing of TRPV3 effectively abrogated the cellular actions of the above agonists. These findings collectively support the concept that TRPV3 signaling is a significant player in human hair growth control. Therefore, TRPV3 and the related intracellular signaling mechanism might function as a promising target for pharmacological manipulations of clinically relevant hair growth disorders.

Transient receptor potential vanilloid-1 signaling inhibits differentiation and activation of human dendritic cells

The goal of the current study was to investigate the expression of transient receptor potential vanilloid‐1 (TRPV1) on human in vitro differentiated monocyte‐derived dendritic cells (DCs) and to dissect the corresponding role of TRPV1‐signaling in DC‐specific functions. TRPV1 expression was identified both at the protein and gene levels in human DCs. Moreover, the prototypic TRPV1 agonist capsaicin specifically (i.e. via TRPV1) and dose‐dependently inhibited cytokine‐induced DC differentiation, phagocytosis of bacteria, activation of DCs, and pro‐inflammatory cytokine secretion. These data introduce TRPV1‐coupled signaling as a novel player in human monocyte‐derived DC biology with anti‐inflammatory actions.

“Sebocytes’ makeup” - Novel mechanisms and concepts in the physiology of the human sebaceous glands

The pilosebaceous unit of the human skin consists of the hair follicle and the sebaceous gland. Within this “mini-organ”, the sebaceous gland has been neglected by the researchers of the field for several decades. Actually, it was labeled as a reminiscence of human development (“a living fossil with a past but no future”), and was thought to solely act as a producer of sebum, a lipid-enriched oily substance which protects our skin (and hence the body) against various insults. However, due to emerging research activities of the past two decades, it has now become evident that the sebaceous gland is not only a “passive” cutaneous “relic” to establish the physico-chemical barrier function of the skin against constant environmental challenges, but it rather functions as an “active” neuro-immuno-endocrine cutaneous organ. This review summarizes recent findings of sebaceous gland research by mainly focusing on newly discovered physiological functions, novel regulatory mechanisms, key events in the pathology of the gland, and future directions in both experimental and clinical dermatology.

TRP channels in the skin

Emerging evidence suggests that transient receptor potential (TRP) ion channels not only act as ‘polymodal cellular sensors’ on sensory neurons but are also functionally expressed by a multitude of non‐neuronal cell types. This is especially true in the skin, one of the largest organs of the body, where they appear to be critically involved in regulating various cutaneous functions both under physiological and pathophysiological conditions. In this review, we focus on introducing the roles of several cutaneous TRP channels in the regulation of the skin barrier, skin cell proliferation and differentiation, and immune functions. Moreover, we also describe the putative involvement of several TRP channels in the development of certain skin diseases and identify future TRP channel‐targeted therapeutic opportunities.

Transient receptor potential vanilloid-2 mediates the effects of transient heat shock on endocytosis of human monocyte-derived dendritic cells

Our goal was to investigate the effect of heat shock on human monocyte‐derived dendritic cells (DCs) and to dissect the role of thermosensitive transient receptor potential (TRP) channels in the process. We provide evidence that a short heat shock challenge (43 °C) decreased the endocytotic activity of the DCs and that this effect could be alleviated by the RNAi‐mediated knockdown of TRPV2 but, importantly, not by the pharmacological (antagonists) or molecular (RNAi) suppression of TRPV1 and TRPV4 activities/levels. Likewise, the heat shock‐induced robust membrane currents were selectively and markedly inhibited by TRPV2 “silencing” whereas modulation of TRPV1 and TRPV4 activities, again, had no effect. These intriguing data introduce TRPV2‐coupled signaling as a key player in mediating the cellular actions of heat shock on DCs.

The Channel Physiology of the Skin

During embryonic development, the skin, the largest organ of the human body, and nervous system are both derived from the neuroectoderm. Consequently, several key factors and mechanisms that influence and control central or peripheral nervous system activities are also present and hence involved in various regulatory mechanisms of the skin. Apparently, this is the case for the ion and non-ion selective channels as well. Therefore, in this review, we shall focus on delineating the regulatory roles of the channels in skin physiology and pathophysiology. First, we introduce key cutaneous functions and major characteristics of the channels in question. Then, we systematically detail the involvement of a multitude of channels in such skin processes (e.g. skin barrier formation, maintenance, and repair, immune mechanisms, exocrine secretion) which are mostly defined by cutaneous non-neuronal cell populations. Finally, we close by summarizing data suggesting that selected channels are also involved in skin diseases such as e.g. atopic dermatitis, psoriasis, non-melanoma cancers and malignant melanoma, genetic and autoimmune diseases, etc., as well as in skin ageing.

The strong in vivo anti-tumor effect of the UIC2 monoclonal antibody is the combined result of Pgp inhibition and antibody dependent cell-mediated cytotoxicity

P-glycoprotein (Pgp) extrudes a large variety of chemotherapeutic drugs from the cells, causing multidrug resistance (MDR). The UIC2 monoclonal antibody recognizes human Pgp and inhibits its drug transport activity. However, this inhibition is partial, since UIC2 binds only to 10–40% of cell surface Pgps, while the rest becomes accessible to this antibody only in the presence of certain substrates or modulators (e.g. cyclosporine A (CsA)). The combined addition of UIC2 and 10 times lower concentrations of CsA than what is necessary for Pgp inhibition when the modulator is applied alone, decreased the EC50 of doxorubicin (DOX) in KB-V1 (Pgp+) cells in vitro almost to the level of KB-3-1 (Pgp-) cells. At the same time, UIC2 alone did not affect the EC50 value of DOX significantly. In xenotransplanted severe combined immunodeficient (SCID) mice co-treated with DOX, UIC2 and CsA, the average weight of Pgp+ tumors was only ∼10% of the untreated control and in 52% of these animals we could not detect tumors at all, while DOX treatment alone did not decrease the weight of Pgp+ tumors. These data were confirmed by visualizing the tumors in vivo by positron emission tomography (PET) based on their increased 18FDG accumulation. Unexpectedly, UIC2+DOX treatment also decreased the size of tumors compared to the DOX only treated animals, as opposed to the results of our in vitro cytotoxicity assays, suggesting that immunological factors are also involved in the antitumor effect of in vivo UIC2 treatment. Since UIC2 binding itself did not affect the viability of Pgp expressing cells, but it triggered in vitro cell killing by peripheral blood mononuclear cells (PBMCs), it is concluded that the impressive in vivo anti-tumor effect of the DOX-UIC2-CsA treatment is the combined result of Pgp inhibition and antibody dependent cell-mediated cytotoxicity (ADCC).

Activation of TRPV3 Regulates Inflammatory Actions of Human Epidermal Keratinocytes

Transient receptor potential (TRP) ion channels were first characterized on neurons, where they are classically implicated in sensory functions; however, research in recent decades has shown that many of these channels are also expressed on nonneuronal cell types. Emerging findings have highlighted the role of TRP channels in the skin, where they have been shown to be important in numerous cutaneous functions. Of particular interest is TRPV3, which was first described on keratinocytes. Its functional importance was supported when its gain-of-function mutation was linked to Olmsted syndrome, which is characterized by palmoplantar keratoderma, periorifacial hyperkeratosis, diffuse hypotrichosis and alopecia, and itch. Despite these exciting results, we have no information about the role and functionality of TRPV3 on keratinocytes at the cellular level. In this study, we identified TRPV3 expression both on human skin and cultured epidermal keratinocytes. TRPV3 stimulation was found to function as a Ca2+-permeable ion channel that suppresses proliferation of epidermal keratinocytes and induces cell death. Stimulation of the channel also triggers a strong proinflammatory response via the NF-κB pathway. Collectively, our data show that TRPV3 is functionally expressed on human epidermal keratinocytes and that it plays a role in cutaneous inflammatory processes.

Protein kinase Cδ promotes proliferation and induces malignant transformation in skeletal muscle.

In this paper, we investigated the isoform‐specific roles of certain protein kinase C (PKC) isoforms in the regulation of skeletal muscle growth. Here, we provide the first intriguing functional evidence that nPKCδ (originally described as an inhibitor of proliferation in various cells types) is a key player in promoting both in vitro and in vivo skeletal muscle growth. Recombinant overexpression of a constitutively active nPKCδ in C2C12 myoblast increased proliferation and inhibited differentiation. Conversely, overexpression of kinase‐negative mutant of nPKCδ (DN‐nPKCδ) markedly inhibited cell growth. Moreover, overexpression of nPKCδ also stimulated in vivo tumour growth and induced malignant transformation in immunodeficient (SCID) mice whereas that of DN‐nPKCδ suppressed tumour formation. The role of nPKCδ in the formation of rhabdomyosarcoma was also investigated where recombinant overexpression of nPKCδ in human rhabdomyosarcoma RD cells also increased cell proliferation and enhanced tumour formation in mouse xenografts. The other isoforms investigated (PKCα, β, ε) exerted only minor (mostly growth‐inhibitory) effects in skeletal muscle cells. Collectively, our data introduce nPKCδ as a novel growth‐promoting molecule in skeletal muscles and invite further trials to exploit its therapeutic potential in the treatment of skeletal muscle malignancies.

Beyond the physico-chemical barrier: Glycerol and xylitol markedly yet differentially alter gene expression profiles and modify signalling pathways in human epidermal keratinocytes

Polyols (e.g. glycerol, xylitol) are implicated as moisturizers of the skin and other epithelial tissues. However, we lack information about their exact cellular mechanisms and their effects on the gene expression profiles. Therefore, in this study, we aimed at investigating the effects of glycerol and xylitol on human epidermal keratinocytes. The polyols (identical osmolarities; xylitol: 0.0045%‐0.45%; glycerol: 0.0027%‐0.27%) did not alter cellular viability or intracellular calcium concentration. However, they exerted differential effects on the expression of certain genes and signalling pathways. Indeed, both polyols up‐regulated the expression of filaggrin, loricrin, involucrin and occludin; yet, xylitol exerted somewhat more profound effects. Moreover, while both polyols stimulated the MAPK pathway, only xylitol induced the activation‐dependent translocation of protein kinase Cδ, a key promoter of epidermal differentiation. Finally, in various keratinocyte inflammation models, both polyols (albeit with different efficacies) exerted anti‐inflammatory effects. Taken together, these data strongly suggest that glycerol and xylitol differentially modulate expressions of multiple genes and activities of signalling pathways in epidermal keratinocytes. Thus, our findings invite clinical trials to explore the applicability and the impact of a combined glycerol‐xylitol therapy in the management of various skin conditions.