Male New Zealand Black/KN mice: a novel model for autoimmune-induced permanent alopecia?

Contribution of mouse models in our understanding of lupus

Laboratory animal models are beneficial when they recapitulate all or just some of the clinical and immunological manifestations of the disease. Various animals such as cats, rats, dogs, hamsters, guinea pigs, rabbits, horses, minks, pigs, and primates have been described lupus-like phenotype. However, a mouse has remained the preferable animal for scientific investigations as a result of their reduced lifespan, easy reproduction, markedly low costs, public acceptance, ease of genetic management, and the probability to stay under standardized conditions. It is highly challenging to establish a mouse model with all features of lupus because of the difficulty and the heterogeneity of the clinical features in systemic lupus erythematous (SLE). Additionally, due to the multiple differences between the mouse and human immune system, the direct translation usually fails. Each mouse model has specific characteristics and shares many subsets of aspects with the disease observed in humans, which gives researchers a tool to select their particular needs. Over 50 years, many mice models have been developed and used to dissect the pathogenesis of lupus, also to test novel drugs and therapies. In general, mice models that contribute considerably in SLE understanding can be divided into four groups: Spontaneous models, induced models, genetically modified models, along with humanizing mouse models that are the link between the mouse and human immune system. In this updated review, we will present what has been learned from different lupus mice models and how these models have contributed to a better understanding of lupus pathogenesis and treatment.

Cicatricial alopecia: What’s new in etiology?

Cicatricial alopecia is a rare, clinically diversified set of disorders causing permanent and irreversible hair loss, which often results in serious discomfort and patient’s mental problems.

Clinically, this form of irreversible hair loss is characterized by visible loss of hair follicle openings in the bald spots. Histologically, it consists in destroying a hair follicle and replacing it with fibrocartilage. Such disorders are perceived as primary if a hair follicle itself is the target of the disease process and secondary if hair follicles are damaged incidentally in the context of more general tissue damage (e.g. deep skin infections, thermal burns, trauma or ionizing radiation).

In this article we tried to summarize the knowledge on possible pathogenic mechanisms of cicatricial alopecia. The presented factors usually overlap and affect prognosis of particular patients. Their profound understanding may enable further research on the treatment methods of this challenging disease unit.

The pathogenesis of primary cicatricial alopecias

Cicatricial (scarring) alopecia results from irreversible damage to epithelial stem cells located in the bulge region of the hair follicle, generally as a result of inflammatory mechanisms (eg, in the context of autoimmune disease). In primary cicactricial alopecia (PCA), the hair follicle itself is the key target of autoaggressive immunity. This group of permanent hair loss disorders can be classified into distinct subgroups, characterized by the predominant peri-follicular inflammatory cell type. In none of these PCA forms do we know exactly why hair follicles begin to attract such an infiltrate. Thus, it is not surprising that halting or even reversing this inflammation in PCA is often extremely difficult. However, increasing evidence suggests that healthy hair follicle epithelial stem cells enjoy relative protection from inflammatory assault by being located in an immunologically "privileged" niche. Because this protection may collapse in PCA, one key challenge in PCA research is to identify the specific signaling pathways that endanger, or restore, the relative immunoprotection of these stem cells. After a summary of pathobiological principles that underlie the development and clinical phenotype of PCA, we close by defining key open questions that need to be answered if more effective treatment modalities for this therapeutically very frustrating, but biologically fascinating, group of diseases are to be developed.

[Pathogenesis of cutaneous lupus erythematosus from LE-prone mice]

Mouse models are similar but not identical to human diseases. However, they are important for research into the pathogenesis underlying autoimmune diseases because they allow us to evaluate similarities and differences between human diseases and mouse models. There are many inbred strains of systemic lupus erythematosus (SLE)-prone mice including New Zealand Black (NZB), F1 hybrids of NZB x New Zealand White (NZW) (B/W F1), MRL/Mp-lpr/lpr (MRL/lpr), and BXSB mice. The postulated etiology of these murine diseases includes many genetic and extrinsic factors such as retroviruses, an impaired balance of T cell interaction, ultraviolet irradiation, etc. For examples, genetic studies of MRL/lpr mice revealed that the appearance of macroscopic LE-like skin lesions needs the lpr mutation plus an additional factor in an autosomal dominant fashion. The candidate is ultraviolet (UV) B light, the susceptibility to which is regulated by the genetic background. Such abnormalities described in SLE now span the spectrum from innate immunity to acquired immunity. In this review, based on historical review, we focus on skin lesions from the well-studied MRL/lpr and B/W F1 mouse and discuss how SLE-prone mice can contribute to a better understanding of cutaneous LE pathogenesis.

Endocrine controls of primary adult human stem cell biology: thyroid hormones stimulate keratin 15 expression, apoptosis, and differentiation in human hair follicle epithelial stem cells in situ and in vitro

Here we demonstrate that physiological concentrations of the thyroid hormones T3 and T4 enhance the KERATIN 15 promoter activity and expression in epithelial stem cells of adult human scalp hair follicles in situ and in vitro. Additionally, T3 and T4 stimulate expression of the immuno-inhibitory surface molecule CD200. Subsequently, T3 and T4 induce apoptosis and differentiation and inhibit clonal growth of these progenitor cells in vitro. These data suggest that human hair follicle bulge-derived epithelial stem cells underlie profound, previously unknown hormonal regulation by thyroid hormones, and show that primary human keratin 15-GFP+ progenitor cells can be exploited to further elucidate fundamental endocrine controls of human epithelial stem cells.

Expression of hair follicle stem cells detected by cytokeratin 15 stain: implications for pathogenesis of the scarring process in cutaneous lupus erythematosus

BACKGROUND

Discoid lupus erythematosus (DLE) is a scarring disease. Although the scarring and deformity may affect any part of the body, such changes have been reported to be most obvious on the face and scalp. The pathogenesis behind this scarring process is not well understood. Once lesions have scarred, recurrent disease tends to occur at the edge of the scarred lesions but not within them.

OBJECTIVES

The fact that inflammation in DLE generally involves the bulge area of the follicles raises the possibility that damage to the stem cells of the bulge region may be one process leading to the permanent loss of follicles. The aim of this study was to investigate the role of the hair follicle stem cells which reside in the bulge region in the scarring process in cutaneous lupus erythematosus (CLE).

METHODS

We studied the reactivity of an antibody to the CD8 antigen (C8/144B), which recognizes cytokeratin (CK) 15 and preferentially immunostains hair follicle stem cells without staining the remaining hair follicle, on skin biopsies (scalp and body lesions) from patients with CLE (36 with discoid lesions and 10 with subacute lesions). Normal scalp and body biopsy specimens served as controls. The correlation between the extent of the cytotoxic inflammatory cell infiltrate (CD8+) and the presence of stem cells was investigated. Results were analysed semiquantitatively.

RESULTS

The expression of CK15 in hair follicle stem cells was variable in the DLE lesions; there was normal to moderate CK15 expression at the bulge region of hair follicles when surrounded by mild or moderate inflammatory infiltrate (CD8+), but in cases of severe inflammation, CK15 expression was weak or absent.

CONCLUSIONS

The bulge region appears to be involved in this disease as part of a broader involvement of the hair follicles; it is secondarily affected by the surrounding inflammatory cell infiltrate. Expression of C8/144B diminished and was then absent, indicating either damage to stem cells or differentiation to help in the repair process. Damage to follicular stem cells may help to explain the irreversible alopecia and the scarring process which characterize this disease.

Hair follicle stem cells in the pathogenesis of the scarring process in cutaneous lupus erythematosus

Lupus erythematosus (LE) is an autoimmune disease that can affect one or more internal organs (systemic LE [SLE]) as well as the skin (CLE). Common cutaneous subtypes of CLE are chronic CLE (CCLE) and subacute CLE (SCLE). CCLE is the only type of CLE which heals with scarring and this may affect any site in the body. The fact that inflammation in CCLE generally involves the bulge area of the follicles (where the stem cells reside) raises the possibility that damage to the stem cells may be one process leading to permanent loss of follicles. One of the most useful distinctive markers of the stem cells is cytokeratin 15 (CK15) and this has been used in some studies to demonstrate the involvement of the bulge region in the scarring process in primary cicatricial alopecia and DLE. The bulge region appears to be involved in the scarring process in CLE and other types of cicatricial alopecia as part of broader involvement of the hair follicles; it is secondarily affected by the surrounding inflammatory cell infiltrate. Expression of the stem cell marker CK15 diminished and was then absent indicating either damage to stem cells or differentiation to help in the repair process.

(Neuro-)endocrinology of epithelial hair follicle stem cells

The hair follicle is a repository of different types of somatic stem cells. However, even though the hair follicle is both a prominent target organ and a potent, non-classical site of production and/or metabolism of numerous polypetide- and steroid hormones, neuropeptides, neurotransmitters and neurotrophins, the (neuro-)endocrine controls of hair follicle epithelial stem cell (HFeSC) biology remain to be systematically explored. Focussing on HFeSCs, we attempt here to offer a "roadmap through terra incognita" by listing key open questions, by exploring endocrinologically relevant HFeSC gene profiling and mouse genomics data, and by sketching several clinically relevant pathways via which systemic and/or locally generated (neuro-)endocrine signals might impact on HFeSC. Exemplarily, we discuss, e.g. the potential roles of glucocorticoid and vitamin D receptors, the hairless gene product, thymic hormones, bone morphogenic proteins (BMPs) and their antagonists, and Skg-3 in HFeSC biology. Furthermore, we elaborate on the potential role of nerve growth factor (NGF) and substance P-dependent neurogenic inflammation in HFeSC damage, and explore how neuroendocrine signals may influence the balance between maintenance and destruction of hair follicle immune privilege, which protects these stem cells and their progeny. These considerations call for a concerted research effort to dissect the (neuro-)endocrinology of HFeSCs much more systematically than before.