Epidermolysis bullosa (EB) is a heterogeneous group of inherited skin disorders determined by mutations in genes encoding for structural components of the cutaneous basement membrane zone. Disease hallmarks are skin fragility and unremitting blistering. The most disabling EB (sub)types show defective wound healing, fibrosis and inflammation at lesional skin. These features expose patients to serious disease complications, including the development of cutaneous squamous cell carcinomas (SCCs). Almost all subjects affected with the severe recessive dystrophic EB (RDEB) subtype suffer from early and extremely aggressive SCCs (RDEB-SCC), which represent the first cause of death in these patients. The genetic determinants of RDEB-SCC do not exhaustively explain its unique behavior as compared to low-risk, ultraviolet-induced SCCs in the general population. On the other hand, a growing body of evidence points to the key role of tumor microenvironment in initiation, progression and spreading of RDEB-SCC, as well as of other, less-investigated, EB-related SCCs (EB-SCCs). Here, we discuss the recent advances in understanding the complex series of molecular events (i.e., fibrotic, inflammatory, and immune processes) contributing to SCC development in EB patients, cross-compare tumor features in the different EB subtypes and report the most promising therapeutic approaches to counteract or delay EB-SCCs.

Summary Background Recessive dystrophic epidermolysis bullosa (RDEB) is a skin fragility disorder caused by mutations in the COL7A1 gene encoding type VII collagen, a cutaneous basement membrane component essential for epidermal–dermal adhesion. Hallmarks of the disease are unremitting blistering and chronic wounds with severe inflammation and fibrosis. MicroRNAs (miRNAs) are post‐transcriptional regulators of gene expression also implicated in fibrotic processes. However, the role of miRNAs in RDEB fibrosis is almost unexplored. Objectives Our study aimed to identify miRNAs deregulated in primary RDEB skin fibroblasts (RDEBFs) and to characterize their function in RDEB fibrosis. Methods Real‐time quantitative polymerase chain reaction (qRT‐PCR) was used to screen RDEBFs for expression levels of a group of miRNAs deregulated in hypertrophic scars and keloids, pathological conditions with abnormal wound healing and fibrosis. Contractility, proliferation and migration rate were evaluated by different in vitro assays in RDEBFs transfected with a miR‐145‐5p inhibitor. Expression levels of fibrotic markers and miR‐145‐5p targets were measured using qRT‐PCR and western blot. Results The miR‐143/145 cluster was upregulated in RDEBFs compared with fibroblasts from healthy subjects. RDEBFs transfected with a miR‐145‐5p inhibitor showed attenuated fibrotic traits of contraction, proliferation and migration, accompanied by reduced expression of the contractile proteins α‐smooth muscle actin and transgelin. These effects were associated with upregulation of Krüppel‐like factor 4 transcriptional repressor and downregulation of Jagged1, a known inducer of fibrosis. Conclusions Our results highlight the profibrotic role of miR‐145‐5p and its regulatory networks in RDEB, shedding light on novel disease pathomechanisms and targets for future therapeutic approaches. What's already known about this topic? Recessive dystrophic epidermolysis bullosa (RDEB) is a highly disabling genetic skin disease caused by mutations in the collagen VII gene and characterized by unremitting blistering and defective wound healing, leading to inflammation and fibrosis. MicroRNAs (miRNAs) are post‐transcriptional regulators of gene expression in health and disease, and their deregulation has been implicated in fibrotic skin conditions. To date, only miR‐29 has been associated with injury‐driven fibrosis in RDEB. What does this study add? In patients with RDEB, miR‐145‐5p is overexpressed in RDEB skin fibroblasts (RDEBFs), where it plays a profibrotic role, as its inhibition reduces RDEBF fibrotic traits (contraction, proliferation and migration). miR‐145‐5p inhibition in RDEBFs determines the reduction of contractile markers α‐smooth muscle actin and transgelin through upregulation of Krüppel‐like factor 4, a transcriptional repressor of contractile proteins, and downregulation of Jagged1 (JAG1), an inducer of fibrosis. What is the translational message? Our findings expand the knowledge on miRNA‐driven pathomechanisms implicated in RDE...

Epidermolysis bullosa simplex (EBS) with cardiomyopathy (EBS-KLHL24) is an EBS subtype caused by dominantly inherited, gain-of-function mutations in the gene encoding for the ubiquitin-ligase KLHL24, which addresses specific proteins to proteasomal degradation. EBS-KLHL24 patients are born with extensive denuded skin areas and skin fragility. Whilst skin fragility rapidly ameliorates, atrophy and scarring develop over time, accompanied by life-threatening cardiomyopathy. To date, pathogenetic mechanisms underlying such a unique disease phenotype are not fully characterized. The basal keratin 14 (K14) has been indicated as a KLHL24 substrate in keratinocytes. However, EBS-KLHL24 pathobiology cannot be determined by the mutation-enhanced disruption of K14 alone, as K14 is similarly expressed in foetal and postnatal epidermis and its protein levels are preserved both in vivo and in vitro disease models. In this study, we focused on foetal keratins as additional KLHL24 substrates. We showed that K7, K8, K17 and K18 protein levels are markedly reduced via proteasome degradation in normal foetal keratinocytes transduced with the mutant KLHL24 protein (ΔN28-KLHL24) as compared to control cells expressing the wild-type form. In addition, heat stress led to keratin network defects and decreased resilience in ΔN28-KLHL24 cells. The KLHL24-mediated degradation of foetal keratins could contribute to congenital skin defects in EBS-KLHL24. Furthermore, we observed that primary keratinocytes from EBS-KLHL24 patients undergo accelerated clonal conversion with reduced colony forming efficiency (CFE) and early replicative senescence. Finally, our findings pointed out a reduced CFE in ΔN28-KLHL24-transduced foetal keratinocytes as compared to controls, suggesting that mutant KLHL24 contributes to patients’ keratinocyte clonogenicity impairment.

Summary Recessive dystrophic epidermolysis bullosa (RDEB) is a rare and highly disabling genetic disease. RDEB hallmarks are skin fragility, constant blistering, and defective wound healing leading to inflammation and fibrosis, which means tissue hardening. Fibrosis underlies major RDEB complications, including limb deformities and cancer, and preventing it is a strategy to improve the disease course. Despite the identification of several molecules that are deregulated in RDEB fibrosis, the disease mechanisms are not fully known. Our genetic code contains the information to produce RNA molecules, called messenger RNAs, which serve to build the proteins forming our body. However, a large family of RNA molecules, called microRNAs, are not transformed into proteins, but regulate the amount of proteins produced. The altered function of microRNAs contributes to the development of many diseases. This study, performed at Bambino Gesù Children's Hospital in Italy, aimed to identify and characterize the role of microRNAs that are altered in RDEB patients and contribute to their skin fibrosis. This laboratory study used a cell type, the fibroblast, which populates the skin and is a major player in fibrosis. The authors observed that some microRNAs are more abundant in fibroblasts obtained from RDEB patients as compared to cells from healthy individuals, and demonstrated that one of them, the miR‐145‐5p, fuels fibrosis. The researchers switched off the miR‐145‐5p in RDEB fibroblasts and then studied fibroblast ability to contract, proliferate, and move, all activities that are increased in fibrosis. Blocking miR‐145‐5p reduced the contractility, proliferation and migration of RDEB fibroblasts, and determined the reduction of various contractile and pro‐fibrotic (fibrosis causing) molecules. In conclusion, the authors have discovered a novel microRNA that contributes to the development of fibrosis in RDEB, and described its mode of action. These findings help us to understand more about the disease and possible targets for future treatment.

Summary 隐性营养不良性大疱性表皮松解症(RDEB)是一种罕见且致残性极高的遗传疾病。RDEB 的标志是皮肤脆弱、持续起疱以及伤口愈合不良,从而导致炎症和纤维化,这意味着组织变硬。纤维化是 RDEB 的主要并发症(包括肢体畸形和癌症)的潜在机制,而预防它是改善疾病进程的策略。尽管已鉴定出在 RDEB 纤维化过程中失控的几种分子,但其发病机理尚未完全明确。我们的遗传密码包含产生 RNA 分子(称为信使 RNA)的信息,这些 RNA 分子可用于构建形成人体的蛋白质。但是,一大类 RNA 分子(称为 microRNA)不会转化为蛋白质,而是调节所产生的蛋白质数量。microRNA 的功能改变导致许多疾病的发展。本研究在意大利 Bambino Gesù 儿童医院进行,旨在识别和鉴定 RDEB 患者中改变并导致其皮肤纤维化的 microRNA 的作用。这项实验室研究使用了一种细胞类型,即成纤维细胞,该细胞遍布皮肤,并且是纤维化的主要参与者。作者观察到,与健康个体的细胞相比,从 RDEB 患者获得的成纤维细胞中某些 microRNA 含量更高,并证明其中之一,miR‐145‐5p 促进了纤维化。研究人员关闭了 RDEB 成纤维细胞中的 miR‐145‐5p,然后研究了成纤维细胞收缩、增殖和移动的能力,这些都是纤维化过程中增加的活性。阻断 miR‐145‐5p 可减少 RDEB 成纤维细胞的收缩、增殖和迁移能力,并可确定各种收缩性和促纤维化(引起纤维化)分子的减少。总之,作者发现了一种可促使 RDEB 中纤维化的发展的新的 microRNA,并描述了其作用方式。这些结果有助于我们进一步了解该疾病以及未来治疗的可能目标。