Vladimir A. Botchkarev

Noggin is a mesenchymally derived stimulator of hair-follicle induction

The induction of developmental structures derived from the ectoderm, such as the neural tube or tooth, occurs through neutralization of the inhibitory activity of members of the bone-morphogenetic protein (BMP) family by BMP antagonists. Here we show that, during hair-follicle development, the neural inducer and BMP-neutralizing protein Noggin is expressed in the follicular mesenchyme, that noggin-knockout mice show significant retardation of hair-follicle induction, and that Noggin neutralizes the inhibitory action of BMP-4 and stimulates hair-follicle induction in embryonic skin organ culture. As a crucial mesenchymal signal that stimulates hair-follicle induction, Noggin operates through antagonistic interactions with BMP-4, which result in upregulation of the transcription factor Lef-1 and the cell-adhesion molecule NCAM, as well as through BMP4-independent downregulation of the 75 kD neurotrophin receptor in the developing hair follicle.

Cathepsin L deficiency as molecular defect of furless: hyperproliferation of keratinocytes and pertubation of hair follicle cycling

Lysosomal cysteine proteinases of the papain family are involved in lysosomal bulk proteolysis, major histocompatibility complex class II mediated antigen presentation, prohormone processing, and extracellular matrix remodeling. Cathepsin L (CTSL) is a ubiquitously expressed major representative of the papain‐like family of cysteine proteinases. To investigate CTSL in vivo functions, the gene was inactivated by gene targeting in embryonic stem cells. CTSL‐deficient mice develop periodic hair loss and epidermal hyperplasia, acanthosis, and hyperkeratosis. The hair loss is due to alterations of hair follicle morphogenesis and cycling, dilatation of hair follicle canals, and disturbed club hair formation. Hyperproliferation of hair follicle epithelial cells and basal epidermal keratinocytes–both of ectodermal origin–are the primary characteristics underlying the mutant phenotype. Pathological inflammatory responses have been excluded as a putative cause of the skin and hair disorder. The phenotype of CTSL‐deficient mice is reminiscent of the spontaneous mouse mutant furless(fs). Analyses of the ctsl gene of fs mice revealed a G149R mutation inactivating the proteinase activity. CTSL is the first lysosomal proteinase shown to be essential for epidermal homeostasis and regular hair follicle morphogenesis and cycling.—Roth, W., Deussing, J., Botchkarev, V. A., Pauly‐Evers, M., Saftig, P., Hafner, A., Schmidt, P., Schmahl, W., Scherer, J., Anton‐Lamprecht, I., von Figura, K., Paus, R., Peters, C. Cathepsin L deficiency as molecular defect of furless: hyperproliferation of keratinocytes and pertubation of hair follicle cycling. FASEB J. 14, 2075–2086 (2000)

Role of nerve growth factor in a mouse model of allergic airway inflammation and asthma

The role of nerve growth factor (NGF), a potent mediator acting in the development and differentitation of both neuronal and immune cells, was examined in a mouse model of allergic asthma. NGF‐positive cells were detected in the inflammatory infiltrate of the lung and enhanced levels of NGF were detected in serum and broncho‐alveolar lavage fluids. Mononuclear cells in inflamed airway mucosa as well as broncho‐alveolar macrophages were identified as one source of NGF production. Splenic mononuclear cells from allergen‐sensitized mice produced NGF in response to allergen. They responded to exogenously added NGF with a dose‐dependent increase in IL‐4 and IL‐5 production and augmented IgE and IgG1 synthesis. In contrast, IFN‐γ and IgG2a levels remained unaffected. The effects were NGF specific, since they could be blocked by an anti‐NGF‐antibody. Nasal application of anti‐NGF to allergen‐sensitized mice significantly reduced IL‐4 and prevented development of airway hyperreactivity. These results show that allergic airway inflammation is accompanied by enhanced local NGF production that acts as an amplifier for Th2 effector functions and plays an important role in the development of airway hyperreactivity. Therefore it is suggested that NGF may serve as a link between the immune and nerve system.

Abundant Production of Brain-Derived Neurotrophic Factor by Adult Visceral Epithelia: Implications for Paracrine and Target-Derived Neurotrophic Functions

Brain-derived neurotrophic factor (BDNF) plays a crucial role for the survival of visceral sensory neurons during development. However, the physiological sources and the function of BDNF in the adult viscera are poorly described. We have investigated the cellular sources and the potential role of BDNF in adult murine viscera. We found markedly different amounts of BDNF protein in different organs. Surprisingly, BDNF levels in the urinary bladder, lung, and colon were higher than those found in the brain or skin. In situ hybridization experiments revealed that BDNF mRNA was made by visceral epithelial cells, several types of smooth muscle, and neurons of the myenteric plexus. Epithelia that expressed BDNF lacked both the high- and low-affinity receptors for BDNF, trkB and p75(NTR). In contrast, both receptors were present on neurons of the peripheral nervous system. Studies with BDNF-/-mice demonstrated that epithelial and smooth muscle cells developed normally in the absence of BDNF. These data provide evidence that visceral epithelia are a major source, but not a target, of BDNF in the adult viscera. The abundance of BDNF protein in certain internal organs suggests that this neurotrophin may regulate the function of adult visceral sensory and motor neurons.

Cutaneous Expression of CRH and CRH-R: Is There a “Skin Stress Response System?”

ABSTRACT: The classical neuroendocrine pathway for response to systemic stress is by hypothalamic release of corticotropin releasing hormone (CRH), subsequent activation of pituitary CRH receptors (CRH‐R), and production and release of proopiomelanocortin (POMC) derived peptides. It has been proposed that an equivalent to the hypothalamic‐pituitary‐adrenal axis functions in mammalian skin, in response to local stress (see Reference 1 ). To further define such system we used immunocytochemistry, RP‐HPLC separation, and RIA techniques, in rodent and human skin, and in cultured normal and malignant melanocytes and keratinocytes. Production of mRNA for CRH‐R1 was documented in mouse and human skin using RT‐PCR and Northern blot techniques; CRH binding sites and CRH‐R1 protein were also identified. Addition of CRH to immortalized human keratinocytes, and to rodent and human melanoma cells induced rapid, specific, and dose‐dependent increases in intracellular Ca2+. The latter were inhibited by the CRH antagonist α‐helical‐CRH(9–41) and by the depletion of extracellular calcium with EGTA. CRH production was enhanced by ultraviolet light radiation and forskolin (a stimulator for intracellular cAMP production), and inhibited by dexamethasone. Thus, evidence that skin cells, both produce CRH and express functional CRH‐R1, supports the existence of a local CRH/CRH‐R neuroendocrine pathway that may be activated within the context of a skin stress response system.

Hair cycle-dependent plasticity of skin and hair follicle innervation in normal murine skin

The innervation of normal, mature mammalian skin is widely thought to be constant. However, the extensive skin remodeling accompanying the transformation of hair follicles from resting stage through growth and regression back to resting (telogen‐anagen‐catagen‐telogen) may also be associated with alteration of skin innervation. We, therefore, have investigated the innervation of the back skin of adolescent C57BL/6 mice at various stages of the depilation‐induced hair cycle. By using antisera against neuronal (protein gene product 9.5 [PGP 9.5], neurofilament 150) and Schwann cell (S‐100, myelin basic protein) markers, as well as against neural cell adhesion molecule (NCAM) and growth‐associated protein‐43 (GAP‐43), we found a dramatic increase of single fibers within the dermis and subcutis during early anagen. This was paralleled by an increase in the number of anastomoses between the cutaneous nerve plexuses and by distinct changes in the nerve fiber supply of anagen vs. telogen hair follicles. The follicular isthmus, including the bulge, the seat of epithelial follicle stem cells, was found to be the most densely innervated skin area. Here, a defined subpopulation of nerve fibers increased in number during anagen and declined during catagen, accompanied by dynamic alterations in the expression of NCAM and GAP‐43. Thus, our study provides evidence for a surprising degree of plasticity of murine skin innervation. Because hair cycle‐associated tissue remodeling evidently is associated with tightly regulated sprouting and regression of nerve fibers, hair cycle‐dependent alterations in murine skin and hair follicle innervation offer an intriguing model for studying the controlled rearrangement of neuronal networks in peripheral tissues under physiological conditions. J. Comp. Neurol. 386:379‐395, 1997.

A simple immunofluorescence technique for simultaneous visualization of mast cells and nerve fibers reveals selectivity and hair cycle - dependent changes in mast cell - nerve fiber contacts in murine skin

Close contacts between mast cells (MC) and nerve fibers have previously been demonstrated in normal and inflamed skin by light and electron microscopy. A key step for any study in MC-nerve interactions in situ is to simultaneously visualize both communication partners, preferably with the option of double labelling the nerve fibers. For this purpose, we developed the following triple-staining technique. After paraformaldehyde-picric acid perfusion fixation, cryostat sections of back skin from C57BL/6 mice were incubated with a primary rat monoclonal antibody to substance P (SP), followed by incubation with a secondary goat-anti-rat TRITC-conjugated IgG. A rabbit antiserum to CGRP was then applied, followed by a secondary goat-anti-rabbit FITC-conjugated IgG. MCs were visualized by incubation with AMCA-labelled avidin, or (for a more convenient quantification of close MC-nerve fiber contacts) with a mixture of TRITC- and FITC-labelled avidins. Using this simple, novel covisualization method, we were able to show that MC-nerve associations in mouse skin are, contrary to previous suggestions, highly selective for nerve fiber types, and that these interactions are regulated in a hair cycle-dependent manner: in telogen and early anagen skin, MCs preferentially contacted CGRP-immunoreactive (IR) or SP/CGRP-IR double-labelled nerve fibers. Compared with telogen values, there was a significant increase in the number of close contacts between MCs and tyrosine hydroxylase-IR fibers during late anagen, and between MCs and peptide histidine-methionine-IR and choline acetyl transferase-IR fibers during catagen.

A role for p75 neurotrophin receptor in the control of apoptosis-driven hair follicle regression

To examine the mechanisms that underlie the neurotrophin‐induced, apoptosis‐driven hair follicle involution (catagen), the expression and function of p75 neurotrophin receptor (p75NTR), which is implicated in apoptosis control, were studied during spontaneous catagen development in murine skin. By RT‐PCR, high steady‐state p75NTR mRNA skin levels were found during the anagen– catagen transition of the hair follicle. By immunohistochemistry, p75NTR alone was strongly expressed in TUNEL+/Bcl2— keratinocytes of the regressing outer root sheath, but both p75NTR and TrkB and/or TrkC were expressed by the nonregressing TUNEL‐/Bcl2+ secondary hair germ keratinocytes. To determine whether p75NTR is functionally involved in catagen control, spontaneous catagen development was compared in vivo between p75NTR knockout (— /—) and wild‐type mice. There was significant catagen retardation in p75NTR knockout mice as compared to wild‐type controls (P<0.05). Instead, transgenic mice‐overexpressing NGF (promoter: K14) showed substantial acceleration of catagen (P<0.001). Although NGF, brain‐derived neurotrophic factor (BDNF), and neurotrophin 3 (NT‐3) accelerated catagen in the organ‐cultured skin of C57BL/6 mice, these neurotrophins failed to promote catagen development in the organ‐cultured p75NTR null skin. These findings suggest that p75NTR signaling is involved in the control of kerotinocyte apoptosis during catagen and that pharmacological manipulation of p75NTR signaling may prove useful for the treatment of hair disorders that display premature entry into catagen.—Botchkarev, V. A., Botchkareva, N. V., Albers, K. M., Chen, L.‐H., Welker, P., Paus, R. A role for p75 neurotrophin receptor in the control of apoptosisdriven hair follicle regression. FASEB J. 14, 1931–1942 (2000)

A New Role for Neurotrophin-3 : Involvement in the Regulation of Hair Follicle Regression (Catagen)

Nervous system and hair follicle epithelium share a common ectodermal origin, and some neurotrophins (NTs) can modulate keratinocyte proliferation and apoptosis. Therefore, it is reasonable to ask whether NTs are also involved in hair growth control. Here, we show that the expression of NT-3 and its high-affinity receptor, tyrosine kinase C, in the skin of C57BL/6 mice is strikingly hair cycle-dependent, with maximal transcript and protein expression seen during spontaneous hair follicle regression (catagen). During catagen, NT-3 and tyrosine kinase C are co-expressed by terminal deoxynucleotidyl transferase-mediated in situ nick end labeling-positive keratinocytes in the club hair and secondary germ. NT-3-overexpressing transgenic mice show precocious catagen development during the postnatal initiation of hair follicle cycling, whereas heterozygous NT-3 knockout (+/-) mice display a significant catagen retardation. Finally, NT-3 stimulates catagen development in organ culture of normal C57BL/6 mouse skin. These observations suggest that the hair follicle is both a source and target of NT-3 and that NT-3/tyrosine kinase C signaling is functionally important in the control of hair follicle regression. Therefore, tyrosine kinase C agonists and antagonists deserve systematic exploration for the management of hair growth disorders that are related to premature (alopecia/effluvium) or retarded catagen (hirsutism/hypertrichosis).

Developmental timing of hair follicle and dorsal skin innervation in mice

The innervation of hair follicles offers an intriguing, yet hardly studied model for the dissection of the stepwise innervation during cutaneous morphogenesis. We have used immunofluorescence and a panel of neuronal markers to characterize the developmental choreography of C57BL/6 mouse backskin innervation. The development of murine skin innervation occurs in successive waves. The first cutaneous nerve fibers appeared before any morphological evidence of hair follicle development at embryonic day 15 (E15). Stage 1 and 2 developing hair follicles were already associated with nerve fibers at E16. These fibers approached a location where later in development the follicular (neural) network A (FNA) is located on fully developed pelage hair follicles. Prior to birth (E18), some nerve fibers had penetrated the epidermis, and an additional set of perifollicular nerve fibers arranged itself around the isthmus and bulge region of stage 5 hair follicles, to develop into the follicular (neural) network B (FNB). By the day of birth (P1), the neuropeptides substance P and calcitonin gene‐related peptide became detectable in subcutaneous and dermal nerve fibers first. Newly formed hair follicles on E18 and P1 displayed the same innervation pattern seen in the first wave of hair follicle development. Just prior to epidermal penetration of hair shafts (P5), peptide histidine methionine‐IR nerve fibers became detectable and epidermal innervation peaked; such innervation decreased after penetration (P7– P17). Last, tyrosine hydroxylase‐IR and neuropeptide Y‐IR became readily detectable. This sequence of developing innervation consistently correlates with hair follicle development, indicating a close interdependence of neuronal and epithelial morphogenesis. J. Comp. Neurol. 448:28–52, 2002.