Hair growth control by innate immunocytes: Perifollicular macrophages revisited

The role of innate immunocytes such as mast cells, γδ T cells, NK cells and macrophages (MACs) in hair growth control under physiological and pathological conditions has recently begun to be re-explored. Here, we revisit the role of resident perifollicular macrophages (pfMACs) located in the hair follicle (HF) mesenchyme (CTS). Substantial, stringently timed fluctuations in the number and localization of pfMACs were first observed long ago during murine HF morphogenesis and cycling. This already suggested some involvement of these innate immunocytes, with a recognized role in tissue remodelling and in hair growth control. The relatively recent demonstration of a Wnt signalling-driven crosstalk between these immunocytes and HF epithelial stem cells in telogen HFs, which promotes anagen induction, has reinvigorated interest in the role that pfMAC plays in hair biology. Besides the apoptosis-associated secretion of stem cell-activating Wnts and the differential secretion of HF-targeting growth factors such as FGF-5 and FGF5s from pfMACs, we also explore how MAC polarization, and thus function, may be influenced by the local metabolic and immune environment. Moreover, we examine how pfMACs may contribute to hair cycle-associated angiogenesis, vascular remodelling, HF immune privilege and immunopathology. On this basis, we discuss why targeting pfMACs may be relevant in the management of hair growth disorders. Finally, we argue that studying pfMACs offers an excellent, clinically relevant model system for characterizing and experimentally manipulating MAC interactions with an easily accessible mammalian, continuously remodelled (mini-)organ under both physiological and pathological conditions.

Identifying novel strategies for treating human hair loss disorders: Cyclosporine A suppresses the Wnt inhibitor, SFRP1, in the dermal papilla of human scalp hair follicles

Hair growth disorders often carry a major psychological burden. Therefore, more effective human hair growth–modulatory agents urgently need to be developed. Here, we used the hypertrichosis-inducing immunosuppressant, Cyclosporine A (CsA), as a lead compound to identify new hair growth–promoting molecular targets. Through microarray analysis we identified the Wnt inhibitor, secreted frizzled related protein 1 (SFRP1), as being down-regulated in the dermal papilla (DP) of CsA-treated human scalp hair follicles (HFs) ex vivo. Therefore, we further investigated the function of SFRP1 using a pharmacological approach and found that SFRP1 regulates intrafollicular canonical Wnt/β-catenin activity through inhibition of Wnt ligands in the human hair bulb. Conversely, inhibiting SFRP1 activity through the SFRP1 antagonist, WAY-316606, enhanced hair shaft production, hair shaft keratin expression, and inhibited spontaneous HF regression (catagen) ex vivo. Collectively, these data (a) identify Wnt signalling as a novel, non–immune-inhibitory CsA target; (b) introduce SFRP1 as a physiologically important regulator of canonical β-catenin activity in a human (mini-)organ; and (c) demonstrate WAY-316606 to be a promising new promoter of human hair growth. Since inhibiting SFRP1 only facilitates Wnt signalling through ligands that are already present, this ‘ligand-limited’ therapeutic strategy for promoting human hair growth may circumvent potential oncological risks associated with chronic Wnt over-activation.

Hair loss is a common disorder and can lead to psychological distress. Cyclosporine A, a fungal metabolite commonly used as an immunosuppressant, can potently induce hair growth in humans. However, it cannot be effectively used to restore hair growth because of its toxic profile. In this study, we used Cyclosporine A as a lead compound to identify novel therapeutic targets that can aid the development of new hair growth–promoting agents. Through microarray analysis, we found that the level of the secreted Wnt inhibitor, SFRP1, was significantly reduced by Cyclosporine A. This inspired us to design a new pharmacological approach that uses WAY-316606, a reportedly well-tolerated and specific antagonist of SFRP1, to prolong the growth phase of the hair cycle. We show that WAY-316606 enhances human hair growth ex vivo, suggesting that it is a more targeted hair growth promoter with the potential to treat human hair loss disorders.

Autophagy is essential for maintaining the growth of a human (mini-)organ: Evidence from scalp hair follicle organ culture

Autophagy plays a crucial role in health and disease, regulating central cellular processes such as adaptive stress responses, differentiation, tissue development, and homeostasis. However, the role of autophagy in human physiology is poorly understood, highlighting a need for a model human organ system to assess the efficacy and safety of strategies to therapeutically modulate autophagy. As a complete, cyclically remodelled (mini-)organ, the organ culture of human scalp hair follicles (HFs), which, after massive growth (anagen), spontaneously enter into an apoptosis-driven organ involution (catagen) process, may provide such a model. Here, we reveal that in anagen, hair matrix keratinocytes (MKs) of organ-cultured HFs exhibit an active autophagic flux, as documented by evaluation of endogenous lipidated Light Chain 3B (LC3B) and sequestosome 1 (SQSTM1/p62) proteins and the ultrastructural visualization of autophagosomes at all stages of the autophagy process. This autophagic flux is altered during catagen, and genetic inhibition of autophagy promotes catagen development. Conversely, an anti-hair loss product markedly enhances intrafollicular autophagy, leading to anagen prolongation. Collectively, our data reveal a novel role of autophagy in human hair growth. Moreover, we show that organ-cultured scalp HFs are an excellent preclinical research model for exploring the role of autophagy in human tissue physiology and for evaluating the efficacy and tissue toxicity of candidate autophagy-modulatory agents in a living human (mini-)organ.

Delayed Hair Follicle Morphogenesis and Hair Follicle Dystrophy in a Lipoatrophy Mouse Model of Pparg Total Deletion

PPARγ regulates multiple aspects of skin physiology, including sebocyte differentiation, keratinocyte proliferation, epithelial stem cell survival, adipocyte biology, and inflammatory skin responses. However, the effects of its global deletion, namely of nonredundant key functions of PPARγ signaling in mammalian skin, are yet unknown because of embryonic lethality. Here, we describe the skin and hair phenotype of a whole-body PPARγ-null mouse (Pparg^Δ/Δ), obtained by preserving PPARγ expression in the placenta. Pparg^Δ/Δ mice exhibited total lipoatrophy and complete absence of sebaceous glands. Right after birth, hair follicle (HF) morphogenesis was transiently delayed, along with reduced expression of HF differentiation markers and of transcriptional regulators necessary for HF development. Later, adult Pparg^Δ/Δ mice developed scarring alopecia and severe perifollicular inflammation. Skin analyses in other models of lipodystrophy, AZIP^tg/+ and Adipoq-Cre^tg/+Pparg^fl/fl mice, coupled with skin graft experiments, showed that the early defects observed in hair morphogenesis were caused by the absence of adipose tissue. In contrast, the late alteration of HF cycle and appearance of inflammation were observed only in Pparg^Δ/Δ mice and likely were due to the lack sebaceous glands. Our findings underscore the increasing appreciation for the importance of adipose tissue-mediated signals in HF development and function.

Is the eccrine gland an integral, functionally important component of the human scalp pilosebaceous unit?

The pilosebaceous unit (PSU) and the eccrine sweat gland (ESG) are classically described as completely independent skin appendages. However, careful inspection of scalp follicular units reveals that the secretory segment of the ESG spatially approximates the hair follicle in a position below the sebaceous gland and the insertion of the arrector pili muscle. Therefore, we propose here that, contrary to conventional wisdom, the PSU and the ESG should not be viewed in isolation, and may form instead, along with the arrector pili muscle and the apocrine gland (where present),one functional unit. For this, we suggest the more inclusive term of 'Hair Cluster' (HC). If confirmed, e.g. by 3D imaging techniques, the novel concept of a functional HC, whose individual components may communicate via secreted molecules and may share selected progenitor cell populations for HC repair/regeneration, has major physiological and pathological implications, which are briefly discussed.

The peripheral clock regulates human pigmentation

Although the regulation of pigmentation is well characterized, it remains unclear whether cell-autonomous controls regulate the cyclic on-off switching of pigmentation in the hair follicle (HF). As human HFs and epidermal melanocytes express clock genes and proteins, and given that core clock genes (PER1, BMAL1) modulate human HF cycling, we investigated whether peripheral clock activity influences human HF pigmentation. We found that silencing BMAL1 or PER1 in human HFs increased HF melanin content. Furthermore, tyrosinase expression and activity, as well as TYRP1 and TYRP2 mRNA levels, gp100 protein expression, melanocyte dendricity, and the number gp100+ HF melanocytes, were all significantly increased in BMAL1 and/or PER1-silenced HFs. BMAL1 or PER1 silencing also increased epidermal melanin content, gp100 protein expression, and tyrosinase activity in human skin. These effects reflect direct modulation of melanocytes, as BMAL1 and/or PER1 silencing in isolated melanocytes increased tyrosinase activity and TYRP1/2 expression. Mechanistically, BMAL1 knockdown reduces PER1 transcription, and PER1 silencing induces phosphorylation of the master regulator of melanogenesis, microphthalmia-associated transcription factor, thus stimulating human melanogenesis and melanocyte activity in situ and in vitro. Therefore, the molecular clock operates as a cell-autonomous modulator of human pigmentation and may be targeted for future therapeutic strategies.

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.

A meeting of two chronobiological systems: circadian proteins Period1 and BMAL1 modulate the human hair cycle clock

The hair follicle (HF) is a continuously remodeled mini organ that cycles between growth (anagen), regression (catagen), and relative quiescence (telogen). As the anagen-to-catagen transformation of microdissected human scalp HFs can be observed in organ culture, it permits the study of the unknown controls of autonomous, rhythmic tissue remodeling of the HF, which intersects developmental, chronobiological, and growth-regulatory mechanisms. The hypothesis that the peripheral clock system is involved in hair cycle control, i.e., the anagen-to-catagen transformation, was tested. Here we show that in the absence of central clock influences, isolated, organ-cultured human HFs show circadian changes in the gene and protein expression of core clock genes (CLOCK, BMAL1, and Period1) and clock-controlled genes (c-Myc, NR1D1, and CDKN1A), with Period1 expression being hair cycle dependent. Knockdown of either BMAL1 or Period1 in human anagen HFs significantly prolonged anagen. This provides evidence that peripheral core clock genes modulate human HF cycling and are an integral component of the human hair cycle clock. Specifically, our study identifies BMAL1 and Period1 as potential therapeutic targets for modulating human hair growth.

MR imaging of suspected acute spinal instability

Twenty-two patients with suspected acute vertebral instability were imaged within 48 h of injury using a 0.5 Tesla magnet. In all patients plain radiographs, T1 weighted gradient echo (GE) and STIR sequences were performed. Two radiologists blindly evaluated the magnetic resonance imaging (MRI) scans defining injuries with bony or soft tissue disruption of both columns as unstable. Indirect signs of instability such as soft tissue haemorrhage were recorded and correlated where possible with operative findings. Sixteen patients were radiologically unstable on MRI, five more than on plain films alone. Instability was confirmed operatively in 10 patients. The six other patients with unstable injuries were treated conservatively. Two of these patients had evidence of increased deformity before fracture union. The radiologically stable patients were treated as such and at 6-month review showed no evidence of progressive instability. The presence of soft tissue haemorrhage in the interspinous gap was not associated with ligament rupture unless actual discontinuity was demonstrated at that level. We conclude that using MRI acutely, most unstable spinal injuries can be rapidly and accurately evaluated without the need for further imaging.

MRI of idiopathic orbital inflammatory syndrome using fat saturation and Gd-DTPA

Idiopathic orbital inflammatory syndrome encompasses a group of inflammatory conditions for which no systemic or local cause can be found, and is commonly referred to as orbital pseudotumour. On conventional MRI sequences subtle areas of inflammation or enhancing tissue can easily be masked by the high signal intensity of orbital fat and involvement of the fat itself may not be appreciated. We describe the MRI features of three patients with idiopathic orbital inflammation using frequency-selective fat saturation and Gd-DTPA.

Corticosteroid prophylaxis for patients with increased risk of adverse reactions to intravascular contrast agents: a survey of current practice in the UK

There is no definite experimental evidence that prophylactic corticosteroids reduce the frequency or severity of adverse effects from low-osmolar contrast agents in patients at increased risk of reaction. There is no consensus in terms of how prophylaxis should be conducted. We have studied current radiologists' practice in the UK by sending postal questionnaires to 212 radiologists randomly selected from a list of current consultants who are Fellows of the Royal College of Radiologists. One hundred and seventy (80.2%) of the 212 questionnaires were completed. The majority of radiologists routinely use non-ionic low osmolar contrast media for intravenous administration, only 30 (17.6%) routinely using conventional ionic agents and six (3.5%) ionic low osmolar agents. All 170 use low osmolar contrast media for those patients perceived to be at increased risk of adverse reactions. Seventy-six radiologists (44.7%) never use steroid cover. There is no consistent practice amongst the 94 consultants (55.3%) who do use steroid cover. The indications for prophylaxis vary, as do the corticosteroid used and the dose regime employed. The total dose used varied from the equivalent of 7.5 mg to 400 mg of prednisolone, and the duration of prophylaxis varied from a single dose to a 4 day course. One hundred and forty-two radiologists (83.5%) would welcome nationally agreed guidelines for the use of steroid cover. The great variation in the use of steroid cover in the UK reflects the lack of clear evidence of its benefit in combination with low osmolar contrast media.

Hereditary anemias in Hawaii. 1987

The differential diagnosis of microcytic anemias in Hawaii presents special problems because of the hereditary anemias prevalent in its large Asian subpopulations. Both the alpha- and beta-thalassemias are important because of morbidity and mortality. Heterozygous carriers for either type mimic iron deficiency, which may lead to inappropriate work-up or treatment. The thalassemias and hemoglobin (Hb) variants are all benign in heterozygotes, but if a couple are both heterozygous for the same or for incompatible variants, their children have 25% risk of inheriting a serious anemia. These can be prevented by detecting the heterozygotes, and by offering genetic counseling and fetal testing to couples at risk of having severely affected children. Early detection is also possible by the screening of newborns. Fetal diagnosis, or early detection and treatment, can greatly reduce the consequences of these anemias. Screening and prevention will cost far less than the cost of care for affected patients.

Primary structure of the human renin gene

The gene encoding human renin has been isolated on two overlapping clones from a bacteriophage lambda library of human DNA. The entire gene spans about 12,000 bp and contains 10 exons separated by 9 intervening sequences. The gene structure is similar to that of human pepsinogen in terms of overall size, homology in the coding regions, position of introns, and sizes of the exons, suggesting that the two genes are evolutionarily related. However, a novel exon coding for only three amino acids was detected that is not present in the pepsinogen gene and whose amino acids are also not found in mouse renin. Although the nucleotide sequence of the 5'-flanking DNA differs from that of the pepsinogen gene, in both cases this region contains a structure of almost perfect dyad symmetry which immediately precedes the TATA box and may have functional importance. Furthermore, sequences resembling the putative consensus sequence for glucocorticoid regulation of gene expression are located approximately 200 and 300 bp upstream from the gene. The overall structural anatomy suggests that the human renin gene evolved by mechanisms that include a duplication of exon segments, particularly those containing the codons for the catalytically important aspartate residues, together with the insertion of other exon and flanking DNA structures. An analysis of human chromosomal DNA demonstrates that there is only one gene with high homology to human renin.