Replenishment of type VII collagen and re-epithelialization of chronically ulcerated skin after intradermal administration of allogeneic mesenchymal stromal cells in two patients with recessive dystrophic epidermolysis bullosa

In animal models it has been shown that mesenchymal stromal cells (MSC) contribute to skin regeneration and accelerate wound healing. We evaluated whether allogeneic MSC administration resulted in an improvement in the skin of two patients with recessive dystrophic epidermolysis bullosa (RDEB; OMIM 226600). Patients had absent type VII collagen immunohistofluorescence and since birth had suffered severe blistering and wounds that heal with scarring. Vehicle or 0.5 × 10⁶ MSC were infused intradermally in intact and chronic ulcerated sites. One week after intervention, in MSC-treated skin type VII collagen was detected along the basement membrane zone and the dermal–epidermal junction was continuous. Re-epithelialization of chronic ulcerated skin was observed only near MSC administration sites. In both patients the observed clinical benefit lasted for 4 months. Thus intradermal administration of allogeneic MSC associates with type VII collagen replenishment at the dermal–epidermal junction, prevents blistering and improves wound healing in unconditioned patients with RDEB.     

Lysyl Hydroxylase 3 Localizes to Epidermal Basement Membrane and Is Reduced in Patients with Recessive Dystrophic Epidermolysis Bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is caused by mutations in COL7A1 resulting in reduced or absent type VII collagen, aberrant anchoring fibril formation and subsequent dermal-epidermal fragility. Here, we identify a significant decrease in PLOD3 expression and its encoded protein, the collagen modifying enzyme lysyl hydroxylase 3 (LH3), in RDEB. We show abundant LH3 localising to the basement membrane in normal skin which is severely depleted in RDEB patient skin. We demonstrate expression is in-part regulated by endogenous type VII collagen and that, in agreement with previous studies, even small reductions in LH3 expression lead to significantly less secreted LH3 protein. Exogenous type VII collagen did not alter LH3 expression in cultured RDEB keratinocytes and we show that RDEB patients receiving bone marrow transplantation who demonstrate significant increase in type VII collagen do not show increased levels of LH3 at the basement membrane. Our data report a direct link between LH3 and endogenous type VII collagen expression concluding that reduction of LH3 at the basement membrane in patients with RDEB will likely have significant implications for disease progression and therapeutic intervention.     

Generation of 3D Skin Equivalents Fully Reconstituted from Human Induced Pluripotent Stem Cells (iPSCs)

Recent generation of patient-specific induced pluripotent stem cells (PS-iPSCs) provides significant advantages for cell- and gene-based therapy. Establishment of iPSC-based therapy for skin diseases requires efficient methodology for differentiating iPSCs into both keratinocytes and fibroblasts, the major cellular components of the skin, as well as the reconstruction of skin structures using these iPSC-derived skin components. We previously reported generation of keratinocytes from human iPSCs for use in the treatment of recessive dystrophic epidermolysis bullosa (RDEB) caused by mutations in the COL7A1 gene. Here, we developed a protocol for differentiating iPSCs into dermal fibroblasts, which also produce type VII collagen and therefore also have the potential to treat RDEB. Moreover, we generated in vitro 3D skin equivalents composed exclusively human iPSC-derived keratinocytes and fibroblasts for disease models and regenerative therapies for skin diseases, first demonstrating that iPSCs can provide the basis for modeling a human organ derived entirely from two different types of iPSC-derived cells.     

BMP12 and BMP13 gene transfer induce ligamentogenic differentiation in mesenchymal progenitor and anterior cruciate ligament cells

Background aimsTo date there are only very few data available on the ligamentogenic differentiation capacity of mesenchymal stromal/progenitor cells (MSC) and anterior cruciate ligament (ACL) fibroblasts.MethodsWe describe the in vitro potential of MSC and ACL cells to undergo ligamentogenic differentiation upon transduction with adenoviral vectors encoding the human cDNA for bone morphogenetic protein (BMP) 12 and BMP13, also known as growth and differentiation factors (GDF) 6 and 7, respectively.ResultsTransgene expression for at least 14 days was confirmed by Western blot analyzes. After 21 days of cell culture within collagen type I hydrogels, histochemical (hematoxylin/eosin (H&E), Azan and van Gieson), immunohistochemical and polymerase chain reaction (PCR) analyzes of the genetically modified constructs of both cell types revealed elongated, viable fibroblast-like cells embedded in a ligament-like matrix rich in collagens, vimentin, fibronectin, decorin, elastin, scleraxis, tenascin, and tenomodulin.ConclusionsIt appears that both MSC and ACL fibroblasts are capable of ligamentogenic differentiation with these factors. This information may aid in the development of biologic approaches to repair and restore ACL after injury.     

Prenatal diagnosis for recessive dystrophic epidermolysis bullosa in 10 families by mutation and haplotype analysis in the type VII collagen gene (COL7A1).

BACKGROUND: Epidermolysis bullosa (EB) is a group of heritable diseases that manifest as blistering and erosions of the skin and mucous membranes. In the dystrophic forms of EB (DEB), the diagnostic hallmark is abnormalities in the anchoring fibrils, attachment structures beneath the cutaneous basement membrane zone. The major component of anchoring fibrils is type VII collagen, and DEB has been linked to the type VII collagen gene (COL7A1) at 3p21, with no evidence for locus heterogeneity. Due to life-threatening complications and significant long-term morbidity associated with the severe, mutilating form of recessive dystrophic EB (RDEB), there has been a demand for prenatal diagnosis from families with affected offspring. MATERIALS AND METHODS: Intragenic polymorphisms in COL7A1 and flanking microsatellite markers on chromosome 3p21, as well as detection of pathogenetic mutations in families, were used to perform PCR-based prenatal diagnosis from DNA obtained by chorionic villus sampling at 10-15 weeks or amniocentesis at 12-15 weeks gestation in 10 families at risk for recurrence of RDEB. RESULTS: In nine cases, the fetus was predicted to be normal or a clinically unaffected carrier of a mutation in one allele. These predictions have been validated in nine cases by the birth of a healthy child. In one case, an affected fetus was predicted, and the diagnosis was confirmed by fetal skin biopsy. CONCLUSIONS: DNA-based prenatal diagnosis of RDEB offers an early, expedient method of testing which will largely replace the previously available invasive fetal skin biopsy at 18-20 weeks gestation.     

Bone mesenchymal stromal cell-derived small extracellular vesicles inhibit inflammation and ameliorate sepsis via delivery of microRNA-21a-5p

Background aimsSepsis is a potentially life-threatening disease that results from a severe systemic inflammatory response due to infection. Mesenchymal stromal cell-derived small extracellular vesicles (MSC sEVs) are able to transfer bioactive molecules and have been demonstrated to play an important role in the pathophysiological process of sepsis. Herein the authors aimed to investigate the potential role and downstream molecular mechanism of MSC sEVs in sepsis.MethodsMSC sEVs were acquired by ultracentrifugation and then injected into a cecal ligation and puncture mouse model. The efficacy of MSC sEVs in both in vitro and in vivo models of sepsis was evaluated.ResultsMSC sEV therapy improved survival, reduced sepsis-induced inflammation, attenuated pulmonary capillary permeability and improved liver and kidney function in septic mice. In addition, the authors found that microRNA-21a-5p (miR-21a-5p) was highly enriched in MSC sEVs, could be transferred to recipient cells, inhibited inflammation and increased survival in septic mice. Furthermore, the authors demonstrated that MSC sEV miR-21a-5p suppressed inflammation by targeting toll-like receptor 4 and programmed cell death 4. The therapeutic efficacy of MSC sEVs was partially abrogated by transfection with miR-21a-5p inhibitors.ConclusionsCollectively, the authors’ data suggest that miR-21a-5p-bearing MSC sEVs may be a prospective and effective sepsis therapeutic strategy.     

Basic fibroblast growth factor: a missing link between collagen VII, increased collagenase, and squamous cell carcinoma in recessive dystrophic epidermolysis bullosa.

BACKGROUND: Patients with recessive dystrophic epidermolysis bullosa (RDEB) have deficiencies of collagen type VII and have elevated levels of fibroblast collagenase, and a greatly increased risk of cutaneous squamous cell carcinoma. Patients with other genetic blistering disorders do not have elevated collagenase or an increased risk of squamous cell carcinoma, despite chronic wounding. The connection between collagen type VII deficiency, increased collagenase, and squamous cell carcinoma is not understood. MATERIALS AND METHODS: Urine from 81 patients with RDEB (39 patients), junctional epidermolysis bullosa (JEB; 12 patients), and epidermolysis bullosa simplex (EBS; 30 patients), as well as unaffected family members of RDEB patients (33 patients), was tested for the presence of basic fibroblast growth factor (bFGF) using a sensitive radioimmunoassay. These patients included many who were enrolled in the Epidermolysis Bullosa Registry and others who were referred by their physicians. RESULTS: Fifty-one percent of patients with RDEB had elevated levels (> 5000 pg/g) of urinary bFGF. In contrast, none of the patients with JEB had elevated levels of bFGF. Twenty-one percent of clinically unaffected family members had elevated levels of bFGF, and 13% of patients with EBS had elevated levels of bFGF. The frequency of elevated bFGF values among all groups was statistically significant (p = 0.002), and the levels of bFGF in RDEB patients were significantly elevated compared with those of other groups (p < 0.05). CONCLUSIONS: We have found that patients with RDEB have elevated levels of bFGF, which may contribute to increased fibroblast collagenase and the development of squamous cell carcinoma. These results suggest a novel treatment for RDEB, namely, angiogenesis inhibitors, which may antagonize the effects of bFGF in this disorder. There are currently no other means of treatment for this disorder, which has a high morbidity and mortality rate.     

Injection of mesenchymal stromal cells into a mechanically stimulated in vitro model of cardiac fibrosis has paracrine effects on resident fibroblasts

Background aimsMyocardial infarction results in the formation of scar tissue populated by myofibroblasts, a phenotype characterized by increased contractility and matrix deposition. Mesenchymal stromal cells (MSC) delivered to the myocardium can attenuate scar growth and restore cardiac function, though the mechanism is unclear.MethodsThis study describes a simple yet robust three-dimensional (3D) in vitro co-culture model to examine the paracrine effects of implanted MSC on resident myofibroblasts in a controlled biochemical and mechanical environment. The fibrosis model consisted of fibroblasts embedded in a 3D collagen gel cultured under defined oxygen tensions and exposed to either cyclic strain or interstitial fluid flow. MSC were injected into this model, and the effect on fibroblast phenotype was evaluated 48 h after cell injection.ResultsAnalysis of gene and protein expression of the fibroblasts indicated that injection of MSC attenuated the myofibroblast transition in response to reduced oxygen and mechanical stress. Assessment of vascular endothelial growth factor and insulin-like growth factor-1 levels demonstrated that their release by fibroblasts was markedly upregulated in hypoxic conditions but attenuated by strain or fluid flow. In fibroblast-MSC co-cultures, vascular endothelial growth factor levels were increased by hypoxia but not affected by mechanical stimuli, whereas insulin-like growth factor-1 levels were generally low and not affected by experimental conditions.ConclusionsThis study demonstrates how a 3D in vitro model of the cardiac scar can be used to examine paracrine effects of MSC on the phenotype of resident fibroblasts and therefore illuminates the role of injected progenitor cells on the progression of cardiac fibrosis.     

Analysis of chemotactic molecules in bone marrow-derived mesenchymal stem cells and the skin: Ccl27-Ccr10 axis as a basis for targeting to cutaneous tissues

Background aimsAdult stem cells produce a plethora of extracellular matrix molecules and have a high potential as cell-based therapeutics for connective tissue disorders of the skin. However, the primary challenge of the stem cell-based approach is associated with the inefficient homing of systemically infused stem cells to the skin.MethodsWe examined chemotactic mechanisms that govern directional migration of mesenchymal stem cells (MSCs) into the skin by conducting a comprehensive expression analysis of chemotactic molecules in MSCs and defined cutaneous tissues from normal and hereditary epidermolysis bullosa (EB)-affected skin.ResultsAnalysis of chemokine receptors in short-term and long-term MSC cultures showed tissue culture-dependent expression of several receptors. Assessment of epidermis-derived and dermis-derived chemokines showed that most chemotactic signals that originate from the skin preferentially recruit different sets of leukocytes rather than MSCs. Analysis of the chemotactic molecules derived from EB-affected non-blistered skin showed only minor changes in expression of selected chemokines and receptors. Nevertheless, the data allowed us to define the Ccl27-Ccr10 chemotactic axis as the most potent for the recruitment of MSCs to the skin. Our in vivo analysis demonstrated that uniform expression of Ccr10 on MSCs and alteration of Ccl27 level in the skin enhance extravasation of stem cells from circulation and facilitate their migration within cutaneous tissue.ConclusionsCollectively, our study provides a comprehensive analysis of chemotactic signals in normal and EB-affected skin and proof-of-concept data demonstrating that alteration of the chemotactic pathways can enhance skin homing of the therapeutic stem cells.     

Dominant-negative Effects of COL7A1 Mutations Can be Rescued by Controlled Overexpression of Normal Collagen VII

Dominant-negative interference by glycine substitution mutations in the COL7A1 gene causes dominant dystrophic epidermolysis bullosa (DDEB), a skin fragility disorder with mechanically induced blistering. Although qualitative and quantitative alterations of the COL7A1 gene product, collagen VII, underlie DDEB, the lack of direct correlation between mutations and the clinical phenotype has rendered DDEB less amenable to therapeutic targeting. To delineate the molecular mechanisms of DDEB, we used recombinant expression of wild-type (WT) and mutant collagen VII, which contained a naturally occurring COL7A1 mutation, G1776R, G2006D, or G2015E, for characterization of the triple helical molecules. The mutants were co-expressed with WT in equal amounts and could form heterotrimeric hybrid triple helices, as demonstrated by affinity purification and mass spectrometry. The thermal stability of the mutant molecules was strongly decreased, as evident in their sensitivity to trypsin digestion. The helix-to-coil transition, T_m, of the mutant molecules was 31–34 °C, and of WT collagen VII 41 °C. Co-expression of WT with G1776R- or G2006D-collagen VII resulted in partial intracellular retention of the collagen, and mutant collagen VII had reduced ability to support cell adhesion. Intriguingly, controlled overexpression of WT collagen VII gradually improved the thermal stability of the collective of collagen VII molecules. Co-expression in a ratio of 90% WT:10% mutant increased the T_m to 41 °C for G1776R-collagen VII and to 39 °C for G2006D- and G2015E-collagen VII. Therefore, increasing the expression of WT collagen VII in the skin of patients with DDEB can be considered a valid therapeutic approach.Mutations in the collagen VII gene, COL7A1, cause dystrophic epidermolysis bullosa (DEB),³ a heritable skin fragility disorder characterized by mechanically induced blistering of the skin and mucosa, and excessive scarring (1). DEB is classified into clinical subtypes with dominant or recessive inheritance (2), and so far more than 400 different COL7A1 mutations are known, which underlie a broad spectrum of clinical presentations.Collagen VII is the major molecular constituent of anchoring fibrils in the skin. These centro-symmetrically banded fibrils extend from the epidermal basement membrane into the underlying dermal stroma and connect the epidermis to the dermis. Collagen VII is synthesized as three identical pro-α1(VII) polypeptide chains, which are hydroxylated and glycosylated in a coordinated manner and then fold into triple-helical procollagen VII in the endoplasmic reticulum (ER). The procollagen, which contains a central collagenous triple-helix flanked by two non-collagenous domains, NC-1 and NC-2, is secreted into the extracellular space, where the C-terminal NC-2 propeptide is proteolytically removed by bone morphogenetic protein-1 (3). Subsequently, mature collagen VII undergoes a multistep fibril polymerization process to form the anchoring fibrils (4).The pathology in DDEB has been thought to result from negative interference of mutant pro-α1(VII) chains that are incorporated into the triple-helical monomers and affect folding and registration of normal polypeptides. Typically, substitution of a glycine within the collagenous domain by a larger amino acid residue causes imperfections and delays in triple-helix folding and increased post-translational modifications (5). These can have different consequences: 1) newly synthesized mutant pro-α(VII) chains or procollagen VII molecules do not pass the ER quality control and are retained in the ER or designated for ubiquitin-proteasome degradation (6), resulting in reduced amounts of collagen VII in the skin; 2) assembly into loosely folded collagen VII monomers, which are secreted, incorporated into anchoring fibrils, and perturb the fibril architecture and render them sensitive to tissue proteases; 3) a combination of the above. All variants lead to paucity of anchoring fibrils at the dermal-epidermal junction, impaired resistance of the skin to shearing forces, and to skin blistering as a clinical symptom.Accessibility makes the skin an ideal organ for testing of molecular therapies. Development of causal treatments for DEB is urged by the severe impact of permanent skin fragility on the life of affected individuals. Therapeutic considerations for DDEB have included an array of approaches including oligonucleotides and oligoribonucleotides (7, 8). Intriguingly, findings in a mouse model for epidermolysis bullosa simplex (EBS), a skin fragility disorder associated with dominant keratin mutations, delivered first evidence that increasing the ratio of wild-type (WT) to mutated polypeptides may improve the phenotype (9). Furthermore, our recent investigation of the collagen VII hypomorphic mouse suggested that relatively small biological changes, e.g. moderately raised levels of collagen VII, can have substantial clinical effects (10). These observations encouraged us to test the possibility that controlled overexpression of normal collagen VII may have therapeutic potential for DDEB.Here we used protein biochemical, mass spectrometry and cell biological in vitro analysis to show that mutant α1(VII) chains can fold with WT α1(VII) chains into hybrid triple helices and exert dominant-negative interference on the protein function. The resulting destabilization and partial intracellular accumulation of the mutant molecules can be diminished by controlled overexpression of WT collagen VII.     

mPGES-1 null mice are resistant to bleomycin-induced skin fibrosis

Introduction

Microsomal prostaglandin E2 synthase-1 (mPGES-1) is an inducible enzyme that acts downstream of cyclooxygenase (COX) to specifically catalyze the conversion of prostaglandin (PG) H₂ to PGE₂. mPGES-1 plays a key role in inflammation, pain and arthritis; however, the role of mPGES-1 in fibrogenesis is largely unknown. Herein, we examine the role of mPGES-1 in a mouse model of skin scleroderma using mice deficient in mPGES-1.

Methods

Wild type (WT) and mPGES-1 null mice were subjected to the bleomycin model of cutaneous skin scleroderma. mPGES-1 expressions in scleroderma fibroblasts and in fibroblasts derived from bleomycin-exposed mice were assessed by Western blot analysis. Degree of fibrosis, dermal thickness, inflammation, collagen content and the number of α-smooth muscle actin (α-SMA)-positive cells were determined by histological analyses. The quantity of the collagen-specific amino acid hydroxyproline was also measured.

Results

Compared to normal skin fibroblasts, mPGES-1 protein expression was elevated in systemic sclerosis (SSc) fibroblasts and in bleomycin-exposed mice. Compared to WT mice, mPGES-1-null mice were resistant to bleomycin-induced inflammation, cutaneous thickening, collagen production and myofibroblast formation.

Conclusions

mPGES-1 expression is required for bleomycin-induced skin fibrogenesis. Inhibition of mPGES-1 may be a viable method to alleviate the development of cutaneous sclerosis and is a potential therapeutic target to control the onset of fibrogenesis.     

Comparative analysis of multilineage properties of mesenchymal stromal cells derived from fetal sources shows an advantage of mesenchymal stromal cells isolated from cord blood in chondrogenic differentiation potential

Background aimsCord blood (CB) and amniotic fluid (AF) could represent new and attractive mesenchymal stromal cell (MSC) sources, but their potential therapeutic applications are still limited by lack of standardized protocols for isolation and differentiation. In particular, chondrogenic differentiation has never been deeply investigated.MethodsMSCs were obtained from CB and AF samples collected during cesarean sections at term and compared for their biological and differentiation properties, with particular interest in cartilage differentiation, in which quantitative real-time polymerase chain reaction and immunohistochemical analyses were performed to evaluate the expression of type 2 collagen, type 10 collagen, SRY-box9 and aggrecan.ResultsWe were able to isolate MSCs from 12 of 30 (40%) and 5 of 20 (25%) CB and AF units, respectively. Fluorescence in situ hybridization analysis indicated the fetal origin of isolated MSC strains. Both populations expressed mesenchymal but not endothelial and hematopoietic markers, even though we observed a lower expression of human leukocyte antigen (HLA) I in CB-MSCs. No differences in proliferation rate and cell cycle analysis could be detected. After osteogenic induction, both populations showed matrix mineralization and typical marker expression. Under chondrogenic conditions, pellets derived from CB-MSCs, in contrast with AF-MSCs pellets, were significantly larger, showed cartilage-like morphology and resulted positive for chondrocyte-associated markers, such as type 2 collagen, type 10 collagen, SRY-box9 and aggrecan.ConclusionsOur results show that CB-MSCs and AF-MSCs collected at term differ from each other in their biological and differentiation properties. In particular, only CB-MSCs showed a clear chondrogenic potential and thus could represent an ideal candidate for cartilage-tissue engineering.     

Auto-transplanted mesenchymal stromal cell fate in periodontal tissue of beagle dogs

Background aimsMesenchymal stromal cells (MSC) possess multilineage differentiation potential and characteristics of self-renewal. It has been reported that MSC can acquire characteristics of cells in the periodontal ligament (PDL) in vitro. Moreover, the transplantation of MSC has been shown to be a promising strategy for treating periodontal defects. However, little is known about the fate of MSC in periodontal tissue in vivo. The aim of this study was to trace the paths of MSC after transplantation into periodontal tissues in vivo.MethodsMSC labeled with bromodeoxyuridine (BrdU) were transplanted into periodontal defects of beagle dogs. Six weeks after surgery, the animals were killed and decalcified specimens were prepared. Migration and differentiation of MSC were detected by single/double immunohistochemistry and a combination of immunohistochemistry and in situ hybridization.ResultsBrdU-labeled MSC were observed distributing into periodontal tissue that included alveolar bone, PDL, cementum and blood vessels and expressing surface markers typical of osteoblasts and fibroblasts.ConclusionsCumulatively, our data suggest that MSC migrate throughout periodontal tissue and differentiate into osteoblasts and fibroblasts after transplantation into periodontal defects at 6 weeks in vivo, and have the potential to regenerate periodontal tissue.     

Mesenchymal stromal cell‐derived factors promote the colonization of collagen 3D scaffolds with human skin cells

The development of stem cell technology in combination with advances in biomaterials has opened new ways of producing engineered tissue substitutes. In this study, we investigated whether the therapeutic potential of an acellular porous scaffold made of type I collagen can be improved by the addition of a powerful trophic agent in the form of mesenchymal stromal cells conditioned medium (MSC‐CM) in order to be used as an acellular scaffold for skin wound healing treatment. Our experiments showed that MSC‐CM sustained the adherence of keratinocytes and fibroblasts as well as the proliferation of keratinocytes. Moreover, MSC‐CM had chemoattractant properties for keratinocytes and endothelial cells, attributable to the content of trophic and pro‐angiogenic factors. Also, for the dermal fibroblasts cultured on collagen scaffold in the presence of MSC‐CM versus serum control, the ratio between collagen III and I mRNAs increased by 2‐fold. Furthermore, the gene expression for α‐smooth muscle actin, tissue inhibitor of metalloproteinase‐1 and 2 and matrix metalloproteinase‐14 was significantly increased by approximately 2‐fold. In conclusion, factors existing in MSC‐CM improve the colonization of collagen 3D scaffolds, by sustaining the adherence and proliferation of keratinocytes and by inducing a pro‐healing phenotype in fibroblasts.     

Metalloproteinase 1 downregulation in neurofibromatosis 1: Therapeutic potential of antimalarial hydroxychloroquine and chloroquine

Neurofibromatosis type 1 is an autosomal dominant genetic disorder caused by mutation in the neurofibromin 1 (NF1) gene. Its hallmarks are cutaneous findings including neurofibromas, benign peripheral nerve sheath tumors. We analyzed the collagen and matrix metalloproteinase 1 (MMP1) expression in Neurofibromatosis 1 cutaneous neurofibroma and found excessive expression of collagen and reduced expression of MMP1. To identify new therapeutic drugs for neurofibroma, we analyzed phosphorylation of components of the Ras pathway, which underlies NF1 regulation, and applied treatments to block this pathway (PD184352, U0126, and rapamycin) and lysosomal processes (chloroquine (CQ), hydroxychloroquine (HCQ), and bafilomycin A (BafA)) in cultured Neurofibromatosis 1 fibroblasts. We found that downregulation of the MMP1 protein was a key abnormal feature in the neurofibromatosis 1 fibroblasts and that the decreased MMP1 was restored by the lysosomal blockers CQ and HCQ, but not by the blockers of the Ras pathway. Moreover, the MMP1-upregulating activity of those lysosomal blockers was dependent on aryl hydrocarbon receptor (AHR) activation and ERK phosphorylation. Our findings suggest that lysosomal blockers are potential candidates for the treatment of Neurofibromatosis 1 neurofibroma.Subject terms: Drug development, Mechanisms of disease