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

What is the biological basis of pattern formation of skin lesions?

Pattern recognition is at the heart of clinical dermatology and dermatopathology. Yet, while every practitioner of the art of dermatological diagnosis recognizes the supreme value of diagnostic cues provided by defined patterns of 'efflorescences', few contemplate on the biological basis of pattern formation in and of skin lesions. Vice versa, developmental and theoretical biologists, who would be best prepared to study skin lesion patterns, are lamentably slow to discover this field as a uniquely instructive testing ground for probing theoretical concepts on pattern generation in the human system. As a result, we have at best scraped the surface of understanding the biological basis of pattern formation of skin lesions, and widely open questions dominate over definitive answer. As a symmetry-breaking force, pattern formation represents one of the most fundamental principles that nature enlists for system organization. Thus, the peculiar and often characteristic arrangements that skin lesions display provide a unique opportunity to reflect upon – and to experimentally dissect – the powerful organizing principles at the crossroads of developmental, skin and theoretical biology, genetics, and clinical dermatology that underlie these – increasingly less enigmatic – phenomena. The current 'Controversies' feature offers a range of different perspectives on how pattern formation of skin lesions can be approached. With this, we hope to encourage more systematic interdisciplinary research efforts geared at unraveling the many unsolved, yet utterly fascinating mysteries of dermatological pattern formation. In short: never a dull pattern

A practical guide for the study of human and murine sebaceous glands in situ

The skin of most mammals is characterised by the presence of sebaceous glands (SGs), whose predominant constituent cell population is sebocytes, that is, lipid-producing epithelial cells, which develop from the hair follicle. Besides holocrine sebum production (which contributes 90% of skin surface lipids), multiple additional SG functions have emerged. These range from antimicrobial peptide production and immunomodulation, via lipid and hormone synthesis/metabolism, to the provision of an epithelial progenitor cell reservoir. Therefore, in addition to its involvement in common skin diseases (e.g. acne vulgaris), the unfolding diversity of SG functions, both in skin health and disease, has raised interest in this integral component of the pilosebaceous unit. This practical guide provides an introduction to SG biology and to relevant SG histochemical and immunohistochemical techniques, with emphasis placed on in situ evaluation methods that can be easily employed. We propose a range of simple, established markers, which are particularly instructive when addressing specific SG research questions in the two most commonly investigated species in SG research, humans and mice. To facilitate the development of reproducible analysis techniques for the in situ evaluation of SGs, this methods review concludes by suggesting quantitative (immuno-)histomorphometric methods for standardised SG evaluation

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