Beyond the NFAT Horizon: From Cyclosporine A-Induced Adverse Skin Effects to Novel Therapeutics

The immunophilin ligand, cyclosporine A (CsA), which inhibits nuclear factor of activated T cells (NFAT) activity, is a cornerstone of immunosuppressive therapy. Yet, the molecular basis of its prominent, nonimmunosuppression-related adverse skin effects, namely drug-induced excessive hair growth (hypertrichosis), is insufficiently understood. Here, we argue that analysis of these adverse effects can uncover clinically important, previously unknown mechanisms of CsA and identify new molecular targets and lead compounds for therapeutic intervention. We exemplify this through our recent discovery that CsA suppresses the potent Wnt inhibitor, secreted frizzled related protein (SFRP)1, in human hair follicles, thereby promoting hair growth and causing hypertrichosis. On this basis, we advocate a new focus on deciphering the molecular basis of the adverse effects of CsA in suitable human model systems as a lead to developing novel therapeutics. Cyclosporine A (CsA) is a potent immunosuppressant that is required to prevent transplant rejection.CsA treatment leads to a wide range of adverse effects such as hypertrichosis. This adverse effect has served as a blueprint to identify novel strategies to enhance human hair growth.The molecular basis of CsA is thought to occur via canonical nuclear factor of activated T cells (NFAT) inhibition in murine models. However, recent mechanistic work in human tissue reveals nonimmunosuppressive NFAT-independent mechanisms through enhancing Wnt activity.Therefore, it is time to look beyond the NFAT horizon and explore the molecular basis of the complex adverse effects of CsA as a research strategy for identifying novel and well-tolerated therapeutics

Neuroendocrine Controls of Keratin Expression in Human Skin

The human skin serves as a source for a large number of neurohormones and neuropeptides, which affect skin biology on multiple different levels. Intriguingly, this includes the control of keratin expression by neurohormones such as thyrotropin-releasing hormone, thyrotropin, opioids, prolactin, and cannabinoid receptor 1-ligands. While this neuroendocrine regulation of human keratin biology in situ is likely to be involved in the maintenance of skin and hair follicle homeostasis and may participate in skin pathology, this regulation remains to be appreciated and explored by mainstream keratin research. Here, we review recent progress in this frontier of neuroendocrine and keratin skin research, define the many open questions in the field, and elaborate how neurohormones may be harnessed to treat selected genodermatoses and other skin disorders accompanied by abnormal keratin expression

Human hair follicles operate an internal Cori cycle and modulate their growth via glycogen phosphorylase

AbstractHair follicles (HFs) are unique, multi-compartment, mini-organs that cycle through phases of active hair growth and pigmentation (anagen), apoptosis-driven regression (catagen) and relative quiescence (telogen). Anagen HFs have high demands for energy and biosynthesis precursors mainly fulfilled by aerobic glycolysis. Histochemistry reports the outer root sheath (ORS) contains high levels of glycogen. To investigate a functional role for glycogen in the HF we quantified glycogen by Periodic-Acid Schiff (PAS) histomorphometry and colorimetric quantitative assay showing ORS of anagen VI HFs contained high levels of glycogen that decreased in catagen. qPCR and immunofluorescence microscopy showed the ORS expressed all enzymes for glycogen synthesis and metabolism. Using human ORS keratinocytes (ORS-KC) and ex vivo human HF organ culture we showed active glycogen metabolism by nutrient starvation and use of a specific glycogen phosphorylase (PYGL) inhibitor. Glycogen in ORS-KC was significantly increased by incubation with lactate demonstrating a functional Cori cycle. Inhibition of PYGL significantly stimulated the ex vivo growth of HFs and delayed onset of catagen. This study defines translationally relevant and therapeutically targetable new features of HF metabolism showing that human scalp HFs operate an internal Cori cycle, synthesize glycogen in the presence of lactate and modulate their growth via PYGL activity

Thyroxine differentially modulates the peripheral clock: lessons from the human hair follicle

The human hair follicle (HF) exhibits peripheral clock activity, with knock-down of clock genes (BMAL1 and PER1) prolonging active hair growth (anagen) and increasing pigmentation. Similarly, thyroid hormones prolong anagen and stimulate pigmentation in cultured human HFs. In addition they are recognized as key regulators of the central clock that controls circadian rhythmicity. Therefore, we asked whether thyroxine (T4) also influences peripheral clock activity in the human HF. Over 24 hours we found a significant reduction in protein levels of BMAL1 and PER1, with their transcript levels also decreasing significantly. Furthermore, while all clock genes maintained their rhythmicity in both the control and T4 treated HFs, there was a significant reduction in the amplitude of BMAL1 and PER1 in T4 (100 nM) treated HFs. Accompanying this, cell-cycle progression marker Cyclin D1 was also assessed appearing to show an induced circadian rhythmicity by T4 however, this was not significant. Contrary to short term cultures, after 6 days, transcript and/or protein levels of all core clock genes (BMAL1, PER1, clock, CRY1, CRY2) were up-regulated in T4 treated HFs. BMAL1 and PER1 mRNA was also up-regulated in the HF bulge, the location of HF epithelial stem cells. Together this provides the first direct evidence that T4 modulates the expression of the peripheral molecular clock. Thus, patients with thyroid dysfunction may also show a disordered peripheral clock, which raises the possibility that short term, pulsatile treatment with T4 might permit one to modulate circadian activity in peripheral tissues as a target to treat clock-related disease

Topical Estrogen Accelerates Hair Regrowth in Mice After Chemotherapy-Induced Alopecia by Favoring the Dystrophic Catagen Response Pathway to Damage

Estrogen receptor ligands are important modulators of skin physiology and are involved in the control of normal hair follicle cycling. Here, we have studied the effects of topically applied 17-β-estradiol on pathologic hair follicle cycling as seen during chemotherapy-induced alopecia, one of the major unresolved problems of clinical oncology. For this study we employed a well-established murine model that mimics chemotherapy-induced alopecia in humans. For precisely quantifying the area of hair loss and hair regrowth in this model in vivo, we developed a simple planimetric assay (dotmatrix planimetry). We show that topical 17-β-estradiol significantly alters the cycling response of murine follicles to cyclophosphamide, whereas the estrogen antagonist ICI 182.780 exerted no such effects. Initially, topical 17-β-estradiol enhanced chemotherapy-induced alopecia significantly by forcing the follicles into the dystrophic catagen response pathway to hair follicle damage, whereas follicles treated by ICI 182.780 or vehicle shifted into the dystrophic anagen response pathway. Consequently, the regrowth of normally pigmented hair shafts after chemotherapy-induced alopecia was significantly accelerated in the 17-β-estradiol treated group. Our data encourage one to explore topical estrogens as a potential stimulant for hair re-growth after chemotherapy-induced alopecia

The gut-skin axis in health and disease: A paradigm with therapeutic implications.

As crucial interface organs gut and skin have much in common. Therefore it is unsurprising that several gut pathologies have skin co-morbidities. Nevertheless, the reason for this remains ill explored, and neither mainstream gastroenterology nor dermatology research have systematically investigated the ‘gut-skin axis'. Here, in reviewing the field, we propose several mechanistic levels on which gut and skin may interact under physiological and pathological circumstances. We focus on the gut microbiota, with its huge metabolic capacity, and the role of dietary components as potential principle actors along the gut-skin axis. We suggest that metabolites from either the diet or the microbiota are skin accessible. After defining open key questions around the nature of these metabolites, how they are sensed, and which cutaneous changes they can induce, we propose that understanding of these pathways will lead to novel therapeutic strategies based on targeting one organ to improve the health of the other

The Fate of Hair Follicle Melanocytes During the Hair Growth Cycle

The fate of the follicular pigmentary unit during the hair growth cycle has long been one of the great enigmas of both hair follicle and pigment cell biology. Although melanocytes are distributed in several different compartments of the anagen hair follicle, melanogenically active cells are located only in the hair bulb, where they are directly involved in hair shaft pigmentation. These pigment cells are readily detectable only when they become melanogenically active during anagen III of the hair growth cycle. Thus, their status during hair follicle regression (catagen), when melanogenesis is switched off, until they re-appear again as pigment-producing cells in the anagen III hair follicle, has remained poorly defined. Historically, it has been proposed that hair bulb melanocytes adopt a self-perpetuating, catagen-resistant strategy of de-differentiation during hair follicle regression and re-differentiation upon entry into a new anagen phase; however, this explanation remains problematic in the absence of evidence for de-differentiation/re-differentiation plasticity in most nonmalignant cell systems

Neural Mechanisms of Hair Growth Control

Clinical and experimental observations have long suggested that skin nerves have “trophic” functions in hair follicle development, growth and/or cycling, even though the molecular and cellular basis of the underlying neuroepithelial interactions has remained obscure. Here, we critically review currently available evidence arguing in favor of or against the existence of neural mechanisms of hair growth control, and outline why the murine hair cycle provides an excellent experimental system for characterizing and manipulating piloneural interactions. Summarizing relevant, recent data from the C57BL/6 mouse model, it is pointed out that the sensory and autonomic innervation of normal pelage hair follicles, the substance P skin content, and cutaneous mast cell-nerve contacts show striking changes during synchronized hair follicle cycling. Furthermore, the murine hair follicle appears to be both a source and a target of neurotrophins, whereas neuropharmacologic manipulations alter murine hair follicle cycling in vivo. For example, anagen is induced by substance P or adrenocorticotropin (ACTH), and by the experimentally triggered release of neuropeptides from sensory nerves and of neurotransmitters from adrenergic nerves. Taken together, this argues in favor of neuroepithelial interactions as regulatory elements in hair growth control and suggests that the study of piloneural interactions promises important insights into general principles of neuroepithelial communication, namely during epithelial morphogenesis and remodeling. We delineate a hypothetical working model of piloneural interactions and propose that targeted manipulations deserve systematic exploration as a novel strategy for managing hair growth disorders. Journal of Investigative Dermatology Symposium Proceedings 2:61–68, 199

Inhibition of vascular endothelial growth factor‐A downregulates angiogenesis in psoriasis: A pilot study

BackgroundVascular Endothelial Growth Factor (VEGF)-A-mediated angiogenesis participates in the pathogenesis of psoriasis, thus inviting the hypothesis that anti-VEGF-A therapy could be beneficial in psoriasis. While anti-angiogenic agents are used in oncology and ophthalmology, these therapeutic strategies remain unexplored for the management of psoriasis.ObjectiveOur objective was to investigate ex vivo how VEGF-A blockade impacts blood vessels, epidermis and immune cells in organ-cultured plaque and non-lesional skin from patients with psoriasis.MethodsSkin biopsies from patients with psoriasis (n = 6; plaque and non-lesional skin) and healthy controls (n = 6) were incubated with anti-VEGF-A monoclonal antibody (bevacizumab, Avastin®) or a human IgG1 isotype control for 72-h in serum-free organ culture. CD31/LYVE-1, Ki-67, and mast cell tryptase expression were assessed by quantitative immunohistomorphometry. VEGF-A levels in plasma, PBMCs and skin culture supernatants were measured.ResultsInhibition of VEGF-A blocked all free VEGF-A ex vivo, reduced blood vessel area and the number of blood vessel endothelial cells in plaques of psoriasis (*p < 0.05). The treatment effect correlated significantly with levels of VEGF-A in organ culture supernatants (r = 0.94; *p < 0.05) from plaque skin and with plasma levels of VEGF-A from patients with psoriasis (r = 0.943; *p = 0.017).ConclusionsThese ex vivo data are the first studies to objectively investigate the potential of VEGF-A inhibition as a novel adjuvant treatment strategy for psoriasis. Taken together, our data encourage further investigation by clinical trial to explore whether downregulating pathological angiogenesis has clinical utility, especially in patients with severe psoriasis or those with elevated levels of VEGF-A in plasma and/or skin