Endocannabinoids regulate growth and survival of human eccrine sweat gland-derived epithelial cells

Cannabinoids for the treatment of autoimmune and inflammatory skin diseases: A systematic review

In recent years, the medical use of cannabinoids has attracted growing attention worldwide. In particular, anti-inflammatory properties of cannabinoids led to their emergence as potential therapeutic options for autoimmune and inflammatory disorders. Recent studies have also shown that cannabinoid receptors are widely expressed and have endogenous ligands in the skin, suggesting that the skin has its own endocannabinoid system. The aim of this review is to discuss the potential therapeutic effects of cannabinoids in autoimmune and inflammatory skin diseases. Following an overview of cannabinoids and the endocannabinoid system, we describe the cellular and molecular mechanisms of cannabinoids in skin health and disease. We then review the clinical studies of cannabinoids in autoimmune and inflammatory skin diseases including systemic sclerosis (SSc), dermatomyositis (DM), psoriasis (Pso) and atopic dermatitis (AD). A primary literature search was conducted in July 2023, using PubMed and Web of Science. A total of 15 articles were included after excluding reviews, non-human studies and in vitro studies from 389 non-duplicated articles. Available evidence suggests that cannabinoids may be beneficial for SSc, DM, Pso and AD. However, further studies, ideally randomized controlled trials, are needed to further evaluate the use of cannabinoids in autoimmune and inflammatory skin diseases.

The Skin and Natural Cannabinoids-Topical and Transdermal Applications

The chemical constituents of the Cannabis plant known as cannabinoids have been extensively researched for their potential therapeutic benefits. The use of cannabinoids applied to the skin as a potential method for both skin-related benefits and systemic administration has attracted increasing interest in recent years. This review aims to present an overview of the most recent scientific research on cannabinoids used topically, including their potential advantages for treating a number of skin conditions like psoriasis, atopic dermatitis, and acne. Additionally, with a focus on the pharmacokinetics and security of this route of administration, we investigate the potential of the transdermal delivery of cannabinoids as a method of systemic administration. The review also discusses the restrictions and difficulties related to the application of cannabinoids on the skin, emphasizing the potential of topical cannabinoids as a promising route for both localized and systemic administration. More studies are required to fully comprehend the efficacy and safety of cannabinoids in various settings.

Cannabinoid Compounds as a Pharmacotherapeutic Option for the Treatment of Non-Cancer Skin Diseases

The endocannabinoid system has been shown to be involved in various skin functions, such as melanogenesis and the maintenance of redox balance in skin cells exposed to UV radiation, as well as barrier functions, sebaceous gland activity, wound healing and the skin's immune response. In addition to the potential use of cannabinoids in the treatment and prevention of skin cancer, cannabinoid compounds and derivatives are of interest as potential systemic and topical applications for the treatment of various inflammatory, fibrotic and pruritic skin conditions. In this context, cannabinoid compounds have been successfully tested as a therapeutic option for the treatment of androgenetic alopecia, atopic and seborrhoeic dermatitis, dermatomyositis, asteatotic and atopic eczema, uraemic pruritis, scalp psoriasis, systemic sclerosis and venous leg ulcers. This review provides an insight into the current literature on cannabinoid compounds as potential medicines for the treatment of skin diseases.

Effects of Rare Phytocannabinoids on the Endocannabinoid System of Human Keratinocytes

The decriminalization and legalization of cannabis has paved the way for investigations into the potential of the use of phytocannabinoids (pCBs) as natural therapeutics for the treatment of human diseases. This growing interest has recently focused on rare (less abundant) pCBs that are non-psychotropic compounds, such as cannabigerol (CBG), cannabichromene (CBC), Δ⁹-tetrahydrocannabivarin (THCV) and cannabigerolic acid (CBGA). Notably, pCBs can act via the endocannabinoid system (ECS), which is involved in the regulation of key pathophysiological processes, and also in the skin. In this study, we used human keratinocytes (HaCaT cells) as an in vitro model that expresses all major ECS elements in order to systematically investigate the effects of CBG, CBC, THCV and CBGA. To this end, we analyzed the gene and protein expression of ECS components (receptors: CB₁, CB₂, GPR55, TRPV1 and PPARα/γ/δ; enzymes: NAPE-PLD, FAAH, DAGLα/β and MAGL) using qRT-PCR and Western blotting, along with assessments of their functionality using radioligand binding and activity assays. In addition, we quantified the content of endocannabinoid(-like) compounds (AEA, 2-AG, PEA, etc.) using UHPLC-MS/MS. Our results demonstrated that rare pCBs modulate the gene and protein expression of distinct ECS elements differently, as well as the content of endocannabinoid(-like) compounds. Notably, they all increased CB_1/2 binding, TRPV1 channel stimulation and FAAH and MAGL catalytic activity. These unprecedented observations should be considered when exploring the therapeutic potential of cannabis extracts for the treatment of human skin diseases.

Cannabis and the skin

The public and health care providers are increasingly curious about the potential medical benefits of Cannabis. In vitro and in vivo studies of Cannabis have suggested it has favorable effects on regulating pain, pruritus, and inflammation, making it a potentially attractive therapeutic agent for many dermatologic conditions. The body of literature reporting on the role of cannabinoids in dermatology is in its infancy but growing. We review the current research, possible cutaneous adverse effects, and future directions for cannabinoids and their use in skin cancer, acne, psoriasis, pruritus, dermatitis, scleroderma, dermatomyositis, cutaneous lupus erythematous, epidermolysis bullosa, pain, and wound healing.

Therapeutic Potential of Cannabidiol (CBD) for Skin Health and Disorders

Though there is limited research confirming the purported topical benefits of cannabinoids, it is certain that cutaneous biology is modulated by the human endocannabinoid system (ECS). Receptors from the ECS have been identified in the skin and systemic abuse of synthetic cannabinoids, and their analogs, have also been associated with the manifestation of dermatological disorders, indicating the effects of the ECS on cutaneous biology. In particular, cannabidiol (CBD), a non-psychoactive compound from the cannabis plant, has garnered significant attention in recent years for its anecdotal therapeutic potential for various pathologies, including skin and cosmetic disorders. Though a body of preclinical evidence suggests topical application of CBD may be efficacious for some skin disorders, such as eczema, psoriasis, pruritis, and inflammatory conditions, confirmed clinical efficacy and elucidation of underlying molecular mechanisms have yet to be fully identified. This article provides an update on the advances in CBD research to date and the potential areas of future exploration.

Beyond the physico-chemical barrier: Glycerol and xylitol markedly yet differentially alter gene expression profiles and modify signalling pathways in human epidermal keratinocytes

Polyols (e.g. glycerol, xylitol) are implicated as moisturizers of the skin and other epithelial tissues. However, we lack information about their exact cellular mechanisms and their effects on the gene expression profiles. Therefore, in this study, we aimed at investigating the effects of glycerol and xylitol on human epidermal keratinocytes. The polyols (identical osmolarities; xylitol: 0.0045%-0.45%; glycerol: 0.0027%-0.27%) did not alter cellular viability or intracellular calcium concentration. However, they exerted differential effects on the expression of certain genes and signalling pathways. Indeed, both polyols up-regulated the expression of filaggrin, loricrin, involucrin and occludin; yet, xylitol exerted somewhat more profound effects. Moreover, while both polyols stimulated the MAPK pathway, only xylitol induced the activation-dependent translocation of protein kinase Cδ, a key promoter of epidermal differentiation. Finally, in various keratinocyte inflammation models, both polyols (albeit with different efficacies) exerted anti-inflammatory effects. Taken together, these data strongly suggest that glycerol and xylitol differentially modulate expressions of multiple genes and activities of signalling pathways in epidermal keratinocytes. Thus, our findings invite clinical trials to explore the applicability and the impact of a combined glycerol-xylitol therapy in the management of various skin conditions.

Cannabinoid Signaling in the Skin: Therapeutic Potential of the "C(ut)annabinoid" System

The endocannabinoid system (ECS) has lately been proven to be an important, multifaceted homeostatic regulator, which influences a wide-variety of physiological processes all over the body. Its members, the endocannabinoids (eCBs; e.g., anandamide), the eCB-responsive receptors (e.g., CB₁, CB₂), as well as the complex enzyme and transporter apparatus involved in the metabolism of the ligands were shown to be expressed in several tissues, including the skin. Although the best studied functions over the ECS are related to the central nervous system and to immune processes, experimental efforts over the last two decades have unambiguously confirmed that cutaneous cannabinoid ("c[ut]annabinoid") signaling is deeply involved in the maintenance of skin homeostasis, barrier formation and regeneration, and its dysregulation was implicated to contribute to several highly prevalent diseases and disorders, e.g., atopic dermatitis, psoriasis, scleroderma, acne, hair growth and pigmentation disorders, keratin diseases, various tumors, and itch. The current review aims to give an overview of the available skin-relevant endo- and phytocannabinoid literature with a special emphasis on the putative translational potential, and to highlight promising future research directions as well as existing challenges.

Noninvasive profiling of sweat-derived lipid mediators for cutaneous research

BACKGROUND AND OBJECTIVE

Recent increases in the use of noninvasive matrices for biomedical analysis has led to interest in the evaluation of sweat for both clinical and research applications. However, despite being one of the two main cutaneous secretions, until very recently, only one study actually analyzed sweat in the context of cutaneous disease. This review attempts to make the case for increased use of sweat in cutaneous research, and discusses lipid mediators as potential analytical targets in sweat.

METHODS

Sweat composition and its relationship with the skin and systemic circulation are discussed, as are practical considerations for sweat sampling and analysis. Previous analyses of lipid mediators in skin biopsies are provided to show that lipid mediators can regulate cutaneous processes and disease pathways. Summaries of recent studies involving the analysis of sweat lipid mediators are provided to demonstrate the utility of sweat lipid mediator testing to support future cutaneous research studies.

RESULTS

Sweat has the potential to reflect both local and systemic biochemical changes in response to disease or intervention, and two recent studies of sweat lipid mediators confirm this ability. Additionally, sweat lipid mediators appear to be temporally stable with individual variability comparable to other matrices, suggesting that these analytes could be useful biomarkers.

CONCLUSIONS

Sweat metabolites may be capable of reporting changes in cutaneous biochemical pathways, thereby providing insight into the immunomodulatory biochemistry of the skin. Lipid mediator analysis of sweat appears to be a non invasive approach that could enhance existing cutaneous research and diagnostic methodologies.

Oral ibuprofen differentially affects plasma and sweat lipid mediator profiles in healthy adult males

Sweat contains a variety of lipid mediators, but whether they originate from the plasma filtrate or from the cutaneous sweat glandular tissues themselves is unknown. To explore this knowledge gap, we collected plasma and sweat from healthy men (n = 9) immediately before and 0.5, 2 and 4 h after oral administration of 400 mg ibuprofen. Of the over 100 lipid mediators assayed by liquid chromatography-tandem mass spectrometry, ∼45 were detected in both plasma and sweat, and 36 were common to both matrices. However, baseline concentrations in each matrix were not correlated and metabolite relative abundances between matrices differed. Oral ibuprofen administration altered sweat lipid mediators, reducing prostaglandin E2, linoleoylethanolamide, and oleoylethanolamide, while increasing 11-hydroxyeicosatetraenoic acid, and causing transient changes in 9-nitrooleate, N-arachidonylglycine and 20-hydroxyeicosatetraenoic acid. Meanwhile, plasma N-acylethanolamide concentrations increased with ibuprofen administration. These results suggest that sweat and plasma differentially reflect biochemical changes due to oral ibuprofen administration, and that plasma is unlikely to be the predominant source of the sweat lipid mediator profile.

Endocannabinoid Tone Regulates Human Sebocyte Biology

We have previously shown that endocannabinoids (eCBs) (e.g., anandamide) are involved in the maintenance of homeostatic sebaceous lipid production in human sebaceous glands and that eCB treatment dramatically increases sebaceous lipid production. Here, we aimed to investigate the expression of the major eCB synthesizing and degrading enzymes and to study the effects of eCB uptake inhibitors on human SZ95 sebocytes, thus exploring the role of the putative eCB membrane transporter, which has been hypothesized to facilitate the cellular uptake and subsequent degradation of eCBs. We found that the major eCB synthesizing (N-acyl phosphatidylethanolamine-specific phospholipase D, and diacylglycerol lipase-α and -β) and degrading (fatty acid amide hydrolase, monoacylglycerol lipase) enzymes are expressed in SZ95 sebocytes and also in sebaceous glands (except for diacylglycerol lipase-α, the staining of which was dubious in histological preparations). eCB uptake-inhibition with VDM11 induced a moderate increase in sebaceous lipid production and also elevated the levels of various eCBs and related acylethanolamides. Finally, we found that VDM11 was able to interfere with the proinflammatory action of the TLR4 activator lipopolysaccharide. Collectively, our data suggest that inhibition of eCB uptake exerts anti-inflammatory actions and elevates both sebaceous lipid production and eCB levels; thus, these inhibitors might be beneficial in cutaneous inflammatory conditions accompanied by dry skin.

Serum is an indispensable factor in the maintenance of the biological characteristics of sweat gland cells

The tolerance of sweat gland cells for in vitro amplification and subcultivation is low as they are somatic cells. The present study aimed to formulate an optimal medium for the culture of human eccrine sweat gland cells (HESGCs) and to establish a method for induction of HESGCs proliferation, whilst maintaining the characteristics of sweat gland cells. HESGCs cultured in sweat gland (SG):keratinocyte growth medium-2 (KGM-2) (1:1) medium had a higher proliferation rate and a stable morphology compared with cells cultured in SG and KGM-2 medium only. Reverse transcription-quantitative polymerase chain reaction indicated that cells cultured in the SG:KGM-2 (1:1) medium exhibited higher expression levels of α-smooth muscle actin, keratin (K)77, carcinoembryonic antigen, K8, K18, ectodysplasin A receptor, c-Myc, Kruppel-like factor 4 and octamer-binding transcription factor 4 compared with cells cultured in SG only or KGM-2 only medium. Three-dimensional culture analysis revealed that HESGCs cultured in SG:KGM-2 1:1 medium differentiated into sweat gland-like structures, whereas cells cultured in KGM-2 only medium underwent cornification. The present study also determined that the maintenance of the biological characteristics of HESGCs occurred due to the presence of fetal bovine serum (FBS). Cells cultured in medium without FBS differentiated into keratinocytes. Therefore, the SG:KGM-2 (1:1) medium may be a suitable culture medium for HESGCs. In conclusion, this mixed medium is a valuable compound and should be considered to be a potential supplemental medium for HESGCs.

Sweat lipid mediator profiling: a noninvasive approach for cutaneous research

Recent advances in analytical and sweat collection techniques provide new opportunities to identify noninvasive biomarkers for the study of skin inflammation and repair. This study aims to characterize the lipid mediator profile including oxygenated lipids, endocannabinoids, and ceramides/sphingoid bases in sweat and identify differences in these profiles between sweat collected from nonlesional sites on the unflared volar forearm of subjects with and without atopic dermatitis (AD). Adapting routine procedures developed for plasma analysis, over 100 lipid mediators were profiled using LC-MS/MS and 58 lipid mediators were detected in sweat. Lipid mediator concentrations were not affected by sampling or storage conditions. Increases in concentrations of C30-C40 [NS] and [NdS] ceramides, and C18:1 sphingosine, were observed in the sweat of study participants with AD despite no differences being observed in transepidermal water loss between study groups, and this effect was strongest in men (P < 0.05, one-way ANOVA with Tukey's post hoc HSD). No differences in oxylipins and endocannabinoids were observed between study groups. Sweat mediator profiling may therefore provide a noninvasive diagnostic for AD prior to the presentation of clinical signs.

TLN-58, an Additional hCAP18 Processing Form, Found in the Lesion Vesicle of Palmoplantar Pustulosis in the Skin

We previously reported that the early vesicle of the palmoplantar pustulosis (PPP) vesicle originated from eccrine sweat in the acrosyringium and that the PPP vesicle contains the antimicrobial peptide human cathelicidin-18/LL-37. The concentration of LL-37 was sufficient to induce the subsequent inflammation in lesions and human keratinocytes, and the PPP vesicles contained additional small fragments of human cathelicidin-18, of approximately 7 kDa, which have not been identified. The aim of the present study was to clarify the additional processed forms found in PPP vesicles and their physiological effects on normal keratinocytes and sweat gland cells. Lesional PPP vesicles were collected from PPP patients, and endogenous human cathelicidin-18/LL-37 was depleted using a LL-37 antibody affinity column. A designed recombinant human cathelicidin-18 peptide was prepared and incubated with the depleted PPP vesicle fluid to confirm the additional processed form. In-gel digestion analysis and protein sequencing confirmed the additional form as TLN-58. TLN-58 up-regulated IL-17C, IL-8, IL-23, IL-1α, and IL-1β mRNA and protein expression in normal human keratinocytes and also showed antibacterial activity against Staphylococcus aureus, Staphylococcus epidermidis, and group A Streptococcus species, similar to LL-37. This additional form could be involved in the continued inflammation in PPP lesions.

From Phytocannabinoids to Cannabinoid Receptors and Endocannabinoids: Pleiotropic Physiological and Pathological Roles Through Complex Pharmacology

Apart from having been used and misused for at least four millennia for, among others, recreational and medicinal purposes, the cannabis plant and its most peculiar chemical components, the plant cannabinoids (phytocannabinoids), have the merit to have led humanity to discover one of the most intriguing and pleiotropic endogenous signaling systems, the endocannabinoid system (ECS). This review article aims to describe and critically discuss, in the most comprehensive possible manner, the multifaceted aspects of 1) the pharmacology and potential impact on mammalian physiology of all major phytocannabinoids, and not only of the most famous one Δ9-tetrahydrocannabinol, and 2) the adaptive pro-homeostatic physiological, or maladaptive pathological, roles of the ECS in mammalian cells, tissues, and organs. In doing so, we have respected the chronological order of the milestones of the millennial route from medicinal/recreational cannabis to the ECS and beyond, as it is now clear that some of the early steps in this long path, which were originally neglected, are becoming important again. The emerging picture is rather complex, but still supports the belief that more important discoveries on human physiology, and new therapies, might come in the future from new knowledge in this field.

Endocannabinoid signaling at the periphery: 50 years after THC

In 1964, the psychoactive ingredient of Cannabis sativa, Δ(9)-tetrahydrocannabinol (THC), was isolated. Nearly 30 years later the endogenous counterparts of THC, collectively termed endocannabinoids (eCBs), were discovered: N-arachidonoylethanolamine (anandamide) (AEA) in 1992 and 2-arachidonoylglycerol (2-AG) in 1995. Since then, considerable research has shed light on the impact of eCBs on human health and disease, identifying an ensemble of proteins that bind, synthesize, and degrade them and that together form the eCB system (ECS). eCBs control basic biological processes including cell choice between survival and death and progenitor/stem cell proliferation and differentiation. Unsurprisingly, in the past two decades eCBs have been recognized as key mediators of several aspects of human pathophysiology and thus have emerged to be among the most widespread and versatile signaling molecules ever discovered. Here some of the pioneers of this research field review the state of the art of critical eCB functions in peripheral organs. Our community effort is aimed at establishing consensus views on the relevance of the peripheral ECS for human health and disease pathogenesis, as well as highlighting emerging challenges and therapeutic hopes.

Distribution of bioactive lipid mediators in human skin

The skin produces bioactive lipids that participate in physiological and pathological states, including homeostasis, induction, propagation, and resolution of inflammation. However, comprehension of the cutaneous lipid complement, and contribution to differing roles of the epidermal and dermal compartments, remains incomplete. We assessed the profiles of eicosanoids, endocannabinoids, N-acyl ethanolamides, and sphingolipids, in human dermis, epidermis, and suction blister fluid. We identified 18 prostanoids, 12 hydroxy-fatty acids, 9 endocannabinoids and N-acyl ethanolamides, and 21 non-hydroxylated ceramides and sphingoid bases, several demonstrating significantly different expression in the tissues assayed. The array of dermal and epidermal fatty acids was reflected in the lipid mediators produced, whereas similarities between lipid profiles in blister fluid and epidermis indicated a primarily epidermal origin of suction blister fluid. Supplementation with omega-3 fatty acids ex vivo showed that their action is mediated through perturbation of existing species and formation of other anti-inflammatory lipids. These findings demonstrate the diversity of lipid mediators involved in maintaining tissue homeostasis in resting skin and hint at their contribution to signaling, cross-support, and functions of different skin compartments. Profiling lipid mediators in biopsies and suction blister fluid can support studies investigating cutaneous inflammatory responses, dietary manipulation, and skin diseases lacking biomarkers and therapeutic targets.

Endocannabinoids and inflammatory response in periodontal ligament cells

Endocannabinoids are associated with multiple regulatory functions in several tissues. The main endocannabinoids, anandamide (AEA) and 2-arachidonylglycerol (2-AG), have been detected in the gingival crevicular fluid of periodontitis patients, but the association between periodontal disease or human periodontal ligament cells (hPdLCs) and endocannabinoids still remain unclear. The aim of the present study was to examine the effects of AEA and 2-AG on the proliferation/viability and cytokine/chemokine production of hPdLCs in the presence/absence of Porphyromonas gingivalis lipopolysaccharide (P. gingivalis LPS). The proliferation/viability of hPdLCs was measured using 3,4,5-dimethylthiazol-2-yl-2,5-diphenyl tetrazolium bromide (MTT)-assay. Interleukin-6 (IL-6), interleukin-8 (IL-8), and monocyte chemotactic protein-1 (MCP-1) levels were examined at gene expression and protein level by real-time PCR and ELISA, respectively. AEA and 2-AG did not reveal any significant effects on proliferation/viability of hPdLCs in the absence of P. gingivalis LPS. However, hPdLCs viability was significantly increased by 10–20 µM AEA in the presence of P. gingivalis LPS (1 µg/ml). In the absence of P. gingivalis LPS, AEA and 2-AG did not exhibit any significant effect on the expression of IL-8 and MCP-1 expression in hPdLCs, whereas IL-6 expression was slightly enhanced by 10 µM 2-AG and not affected by AEA. In P.gingivalis LPS stimulated hPdLCs, 10 µM AEA down-regulated gene-expression and protein production of IL-6, IL-8, and MCP-1. In contrast, 10 µM 2-AG had an opposite effect and induced a significant up-regulation of gene and protein expression of IL-6 and IL-8 (P<0.05) as well as gene-expression of MCP-1 in P. gingivalis LPS stimulated hPdLCs. Our data suggest that AEA appears to have an anti-inflammatory and immune suppressive effect on hPdLCs’ host response to P.gingivalis LPS, whereas 2-AG appears to promote detrimental inflammatory processes. In conclusion, AEA and 2-AG might play an important role in the modulation of periodontal inflammation.

Transient receptor potential vanilloid-2 mediates the effects of transient heat shock on endocytosis of human monocyte-derived dendritic cells

Our goal was to investigate the effect of heat shock on human monocyte-derived dendritic cells (DCs) and to dissect the role of thermosensitive transient receptor potential (TRP) channels in the process. We provide evidence that a short heat shock challenge (43 °C) decreased the endocytotic activity of the DCs and that this effect could be alleviated by the RNAi-mediated knockdown of TRPV2 but, importantly, not by the pharmacological (antagonists) or molecular (RNAi) suppression of TRPV1 and TRPV4 activities/levels. Likewise, the heat shock-induced robust membrane currents were selectively and markedly inhibited by TRPV2 "silencing" whereas modulation of TRPV1 and TRPV4 activities, again, had no effect. These intriguing data introduce TRPV2-coupled signaling as a key player in mediating the cellular actions of heat shock on DCs.

A novel control of human keratin expression: cannabinoid receptor 1-mediated signaling down-regulates the expression of keratins K6 and K16 in human keratinocytes in vitro and in situ

Cannabinoid receptors (CB) are expressed throughout human skin epithelium. CB1 activation inhibits human hair growth and decreases proliferation of epidermal keratinocytes. Since psoriasis is a chronic hyperproliferative, inflammatory skin disease, it is conceivable that the therapeutic modulation of CB signaling, which can inhibit both proliferation and inflammation, could win a place in future psoriasis management. Given that psoriasis is characterized by up-regulation of keratins K6 and K16, we have investigated whether CB1 stimulation modulates their expression in human epidermis. Treatment of organ-cultured human skin with the CB1-specific agonist, arachidonoyl-chloro-ethanolamide (ACEA), decreased K6 and K16 staining intensity in situ. At the gene and protein levels, ACEA also decreased K6 expression of cultured HaCaT keratinocytes, which show some similarities to psoriatic keratinocytes. These effects were partly antagonized by the CB1-specific antagonist, AM251. While CB1-mediated signaling also significantly inhibited human epidermal keratinocyte proliferation in situ, as shown by K6/Ki-67-double immunofluorescence, the inhibitory effect of ACEA on K6 expression in situ was independent of its anti-proliferative effect. Given recent appreciation of the role of K6 as a functionally important protein that regulates epithelial wound healing in mice, it is conceivable that the novel CB1-mediated regulation of keratin 6/16 revealed here also is relevant to wound healing. Taken together, our results suggest that cannabinoids and their receptors constitute a novel, clinically relevant control element of human K6 and K16 expression.