Systemic coagulopathy promotes host lethality in a new Drosophila tumor model.

Malignant tumors trigger a complex network of inflammatory and wound repair responses, prompting Dvorak's characterization of tumors as "wounds that never heal."1 Some of these responses lead to profound defects in blood clotting, such as disseminated intravascular coagulopathy (DIC), which correlate with poor prognoses.2,3,4 Here, we demonstrate that a new tumor model in Drosophila provokes phenotypes that resemble coagulopathies observed in patients. Fly ovarian tumors overproduce multiple secreted components of the clotting cascade and trigger hypercoagulation of fly blood (hemolymph). Hypercoagulation occurs shortly after tumor induction and is transient; it is followed by a hypocoagulative state that is defective in wound healing. Cellular clotting regulators accumulate on the tumor over time and are depleted from the body, suggesting that hypocoagulation is caused by exhaustion of host clotting components. We show that rescuing coagulopathy by depleting a tumor-produced clotting factor improves survival of tumor-bearing flies, despite the fact that flies have an open (non-vascular) circulatory system. As clinical studies suggest that lethality in patients with high serum levels of clotting components can be independent of thrombotic events,5,6 our work establishes a platform for identifying alternative mechanisms by which tumor-driven coagulopathy triggers early mortality. Moreover, it opens up exploration of other conserved mechanisms of host responses to chronic wounds.

Restoration of Immune Privilege in Human Dermal Papillae Controlling Epithelial-Mesenchymal Interactions in Hair Formation.

BACKGROUND: Hair follicles are among a handful of organs that exhibit immune privilege. Dysfunction of the hair follicle immune system underlies the development of inflammatory diseases, such as alopecia areata. METHODS: Quantitative reverse transcription PCR and immunostaining was used to confirm the expression of major histocompatibility complex class I in human dermal papilla cells. Through transcriptomic analyses of human keratinocyte stem cells, major histocompatibility complex class I was identified as differentially expressed genes. Organ culture and patch assay were performed to assess the ability of WNT3a conditioned media to rescue immune privilege. Lastly, CD8+ T cells were detected near the hair bulb in alopecia areata patients through immunohistochemistry. RESULTS: Inflammatory factors such as tumor necrosis factor alpha and interferon gamma were verified to induce the expression of major histocompatibility complex class I proteins in dermal papilla cells. Additionally, loss of immune privilege of hair follicles was rescued following treatment with conditioned media from outer root sheath cells. Transcriptomic analyses found 58 up-regulated genes and 183 down-regulated genes related in MHC class I+ cells. Using newborn hair patch assay, we demonstrated that WNT3a conditioned media with epidermal growth factor can restore hair growth. In alopecia areata patients, CD8+ T cells were increased during the transition from mid-anagen to late catagen. CONCLUSION: Identification of mechanisms governing epithelial and mesenchymal interactions of the hair follicle facilitates an improved understanding of the regulation of hair follicle immune privilege.

Tumour-host interactions through the lens of Drosophila.

There is a large gap between the deep understanding of mechanisms driving tumour growth and the reasons why patients ultimately die of cancer. It is now appreciated that interactions between the tumour and surrounding non-tumour (sometimes referred to as host) cells play critical roles in mortality as well as tumour progression, but much remains unknown about the underlying molecular mechanisms, especially those that act beyond the tumour microenvironment. Drosophila has a track record of high-impact discoveries about cell-autonomous growth regulation, and is well suited to now probe mysteries of tumour - host interactions. Here, we review current knowledge about how fly tumours interact with microenvironmental stroma, circulating innate immune cells and distant organs to influence disease progression. We also discuss reciprocal regulation between tumours and host physiology, with a particular focus on paraneoplasias. The fly's simplicity along with the ability to study lethality directly provide an opportunity to shed new light on how cancer actually kills.

Wound Regeneration Deficit in Rats Correlates with Low Morphogenetic Potential and Distinct Transcriptome Profile of Epidermis.

Large excisional wounds in mice prominently regenerate new hair follicles (HFs) and fat, yet humans are deficient for this regenerative behavior. Currently, wound-induced regeneration remains a clinically desirable, but only partially understood phenomenon. We show that large excisional wounds in rats across seven strains fail to regenerate new HFs. We compared wound transcriptomes between mice and rats at the time of scab detachment, which coincides with the onset of HF regeneration in mice. In both species, wound dermis and epidermis share core dermal and epidermal transcriptional programs, respectively, yet prominent interspecies differences exist. Compared with mice, rat epidermis expresses distinct transcriptional and epigenetic factors, markers of epidermal repair, hyperplasia, and inflammation, and lower levels of WNT signaling effectors and regulators. When recombined on the surface of excisional wounds with vibrissa dermal papillae, partial-thickness skin grafts containing distal pelage HF segments, but not interfollicular epidermis, readily regenerated new vibrissa-like HFs. Together, our findings establish rats as a nonregenerating rodent model for excisional wound healing and suggest that low epidermal competence and associated transcriptional profile may contribute to its regenerative deficiency. Future comparison between rat and mouse may lend further insight into the mechanism of wounding-induced regeneration and causes for its deficit.

Regeneration of fat cells from myofibroblasts during wound healing.

Although regeneration through the reprogramming of one cell lineage to another occurs in fish and amphibians, it has not been observed in mammals. We discovered in the mouse that during wound healing, adipocytes regenerate from myofibroblasts, a cell type thought to be differentiated and nonadipogenic. Myofibroblast reprogramming required neogenic hair follicles, which triggered bone morphogenetic protein (BMP) signaling and then activation of adipocyte transcription factors expressed during development. Overexpression of the BMP antagonist Noggin in hair follicles or deletion of the BMP receptor in myofibroblasts prevented adipocyte formation. Adipocytes formed from human keloid fibroblasts either when treated with BMP or when placed with human hair follicles in vitro. Thus, we identify the myofibroblast as a plastic cell type that may be manipulated to treat scars in humans.

A Guide to Studying Human Hair Follicle Cycling In Vivo.

Hair follicles (HFs) undergo lifelong cyclical transformations, progressing through stages of rapid growth (anagen), regression (catagen), and relative "quiescence" (telogen). Given that HF cycling abnormalities underlie many human hair growth disorders, the accurate classification of individual cycle stages within skin biopsies is clinically important and essential for hair research. For preclinical human hair research purposes, human scalp skin can be xenografted onto immunocompromised mice to study human HF cycling and manipulate long-lasting anagen in vivo. Although available for mice, a comprehensive guide on how to recognize different human hair cycle stages in vivo is lacking. In this article, we present such a guide, which uses objective, well-defined, and reproducible criteria, and integrates simple morphological indicators with advanced, (immuno)-histochemical markers. This guide also characterizes human HF cycling in xenografts and highlights the utility of this model for in vivo hair research. Detailed schematic drawings and representative micrographs provide examples of how best to identify human HF stages, even in suboptimally sectioned tissue, and practical recommendations are given for designing human-on-mouse hair cycle experiments. Thus, this guide seeks to offer a benchmark for human hair cycle stage classification, for both hair research experts and newcomers to the field.

Principles and mechanisms of regeneration in the mouse model for wound-induced hair follicle neogenesis.

Wound induced hair follicle neogenesis (WIHN) describes a regenerative phenomenon in adult mammalian skin, wherein fully functional hair follicles regenerate de novo in the center of large excisional wounds. Originally described in rats, rabbits, sheep, and humans in 1940-60, the WIHN phenomenon was reinvestigated in mice only recently. The process of de novo hair regeneration largely duplicates the morphological and signaling features of normal embryonic hair development. Similar to hair development, WIHN critically depends on the activation of canonical WNT signaling. However, unlike hair development, WNT activation in WIHN is dependent on Fgf9 signaling generated by the immune system's gamma delta (γδ) T cells. The cellular bases of WIHN remain to be fully characterized, however, the available evidence leaves open the possibility for a blastema-like mechanism, wherein epidermal and/or dermal wound cells undergo epigenetic reprogramming toward a more plastic, embryonic-like state. De novo hair follicles do not regenerate from preexisting hair-fated bulge stem cells. This suggests that hair neogenesis is not driven by preexisting lineage-restricted progenitors, as is the case for amputation-induced mouse digit tip regeneration, but rather may require a blastema-like mechanism. The WIHN model is characterized by several intriguing features, which await further explanation. These include: (i) minimum wound size requirement for activating neogenesis, (ii) restriction of hair neogenesis to the wound's center, (iii) imperfect patterning outcomes, both in terms of neogenic hair positioning within the wound and in terms of their orientation. Future inquires into the WIHN process, made possible by a wide array of the available skin-specific genetic tools, will undoubtedly expand our understanding of the regeneration mechanisms in adult mammals.

Light-emitting hair follicles: studying skin regeneration with in vivo imaging.

Cutting-edge imaging technologies and new luminescent and fluorescent genetic tools now make it possible to study hair regeneration in vivo in real time at the microscopic single-cell level and at the macroscopic level of hair follicle populations. These technologies also allow for noninvasive assessment of the skin's clinically relevant homeostatic parameters, such as oxidative stress levels and pH.