Stabilizing mutations of KLHL24 ubiquitin ligase cause loss of keratin 14 and human skin fragility

Genome-Wide Mendelian Randomization Study Reveals Druggable Genes for Cerebral Small Vessel Disease

BACKGROUND

Cerebral small vessel disease (CSVD) is a group of neurological disorders that affect the small blood vessels within the brain, for which no effective treatments are currently available. We conducted a Mendelian randomization (MR) study to identify candidate therapeutic genes for CSVD.

METHODS

We retrieved genome-wide association study data from 6 recently conducted, extensive investigations focusing on CSVD magnetic resonance imaging markers and performed a 2-sample MR analysis to assess the potential causal effects of gene expression and protein level within druggable genes on CSVD in blood and brain tissues. Colocalization analyses and repeat studies were undertaken to verify the relationship. Additionally, mediation analysis was conducted to explore the potential mechanisms involving druggable genes and known risk factors for CSVD. Finally, phenome-wide MR analyses were applied to evaluate the potential adverse effects related to the identified druggable genes for CSVD treatment.

RESULTS

Overall, 5 druggable genes consistently showed associations with CSVD in MR analyses across both the discovery and validation cohorts. Notably, the ALDH2 and KLHL24 genes were identified as associated with CSVD in both blood and brain tissues, whereas the genes ADRB1, BTN3A2, and EFEMP1 were exclusively detected in brain tissue. Moreover, mediation analysis elucidated the proportion of the total effects mediated by CSVD risk factors through candidate druggable genes, which ranged from 5.5% to 18.5%, and offered potential explanations for the observed results. A comprehensive phenome-wide MR analysis further emphasized both the therapeutic benefits and potential side effects of targeting these candidate druggable genes.

CONCLUSIONS

This study provides genetic evidence supporting the potential therapeutic benefits of targeting druggable genes for treating CSVD, which will be useful for prioritizing CSVD drug development.

Skin Development and Disease: A Molecular Perspective

Skin, the largest organ in the human body, is a crucial protective barrier that plays essential roles in thermoregulation, sensation, and immune defence. This complex organ undergoes intricate processes of development. Skin development initiates during the embryonic stage, orchestrated by molecular cues that control epidermal specification, commitment, stratification, terminal differentiation, and appendage growth. Key signalling pathways are integral in coordinating the development of the epidermis, hair follicles, and sweat glands. The complex interplay among these pathways is vital for the appropriate formation and functionality of the skin. Disruptions in multiple molecular pathways can give rise to a spectrum of skin diseases, from congenital skin disorders to cancers. By delving into the molecular mechanisms implicated in developmental processes, as well as in the pathogenesis of diseases, this narrative review aims to present a comprehensive understanding of these aspects. Such knowledge paves the way for developing innovative targeted therapies and personalised treatment approaches for various skin conditions.

Syndromic epidermolysis bullosa simplex subtype due to mutations in the KLHL24 gene: series of case reports in Russian families

Objective

Epidermolysis bullosa simplex (EBS) is a common, well-characterized type of epidermolysis bullosa. However, some rare syndromic EBS phenotypes are not well described. The accumulation of clinical descriptions of patients with syndromic subtypes of EBS is important for understanding the natural history of the disease and assessing genotype-phenotype correlations.

Case summary

We present a series of case reports of the syndromic subtype of EBS associated with mutations in the KLHL24 gene in seven patients from four unrelated families. The clinical features of this rare phenotype in children and adult patients are described in detail. In two families, we revealed pathogenic variant c.1A > G (p.Met1?) in the KLHL24 gene. The third family had c.3G > A (p.Met1?) mutation, and the fourth family had a novel de novo variant c.23del (p.Arg8AsnfsTer2).

Conclusion

The description of the clinical manifestations of the disease in two generations of EBS families with different genetic variants allows the assessment and prediction of the natural course and severity of the disease in these families, the risk of complications, and the planning of the amount of medical care necessary.

Denticleless E3 ubiquitin protein ligase (DTL) maintains the proliferation and differentiation of epidermis and hair follicles during skin development

BACKGROUND

A precise balance between the proliferation and differentiation of epidermal progenitors is required to achieve the barrier function during the development of epidermis. During the entire process of skin development, the newly formed basal layer cells divide, differentiate, and migrate outward to the surface of the skin, which is tightly regulated by a series of events related to cell cycle progression. The CRL4DTL complex (Cullin 4 RING ligase, in association with the substrate receptor DTL) has long emerged as a master regulator in various cellular processes, which mediates the degradation of key cell cycle proteins. However, the roles of DTL in regulating epidermal morphogenesis during skin development remain unclear.

RESULTS

We showed that DTL deficiency in epidermal progenitor cells leads to defects in epidermal stratification and loss of hair follicles accompanied by reduced epidermal progenitor cells and disturbed cell cycle progression during skin development. Transcriptome analysis revealed that p53 pathway is activated in DTL-depleted epidermal progenitor cells. The apoptosis of epidermal cells showed in DTL deficiency mice is rescued by the absence of p53, but the proliferation and differentiation defects were p53-independent.

CONCLUSION

Our findings indicate that DTL plays a vital role in epidermal malformation during skin development.

The prognostic significance of ubiquitination-related genes in multiple myeloma by bioinformatics analysis

BACKGROUND

Immunoregulatory drugs regulate the ubiquitin-proteasome system, which is the main treatment for multiple myeloma (MM) at present. In this study, bioinformatics analysis was used to construct the risk model and evaluate the prognostic value of ubiquitination-related genes in MM.

METHODS AND RESULTS

The data on ubiquitination-related genes and MM samples were downloaded from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases. The consistent cluster analysis and ESTIMATE algorithm were used to create distinct clusters. The MM prognostic risk model was constructed through single-factor and multiple-factor analysis. The ROC curve was plotted to compare the survival difference between high- and low-risk groups. The nomogram was used to validate the predictive capability of the risk model. A total of 87 ubiquitination-related genes were obtained, with 47 genes showing high expression in the MM group. According to the consistent cluster analysis, 4 clusters were determined. The immune infiltration, survival, and prognosis differed significantly among the 4 clusters. The tumor purity was higher in clusters 1 and 3 than in clusters 2 and 4, while the immune score and stromal score were lower in clusters 1 and 3. The proportion of B cells memory, plasma cells, and T cells CD4 naïve was the lowest in cluster 4. The model genes KLHL24, HERC6, USP3, TNIP1, and CISH were highly expressed in the high-risk group. AICAr and BMS.754,807 exhibited higher drug sensitivity in the low-risk group, whereas Bleomycin showed higher drug sensitivity in the high-risk group. The nomogram of the risk model demonstrated good efficacy in predicting the survival of MM patients using TCGA and GEO datasets.

CONCLUSIONS

The risk model constructed by ubiquitination-related genes can be effectively used to predict the prognosis of MM patients. KLHL24, HERC6, USP3, TNIP1, and CISH genes in MM warrant further investigation as therapeutic targets and to combat drug resistance.

KBTBD4 Cancer Hotspot Mutations Drive Neomorphic Degradation of HDAC1/2 Corepressor Complexes

Cancer mutations can create neomorphic protein-protein interactions to drive aberrant function 1 . As a substrate receptor of the CULLIN3-RBX1 E3 ubiquitin ligase complex, KBTBD4 is recurrently mutated in medulloblastoma (MB) 2 , the most common embryonal brain tumor in children, and pineoblastoma 3 . These mutations impart gain-of-function to KBTBD4 to induce aberrant degradation of the transcriptional corepressor CoREST 4 . However, their mechanism of action remains unresolved. Here, we elucidate the mechanistic basis by which KBTBD4 mutations promote CoREST degradation through engaging HDAC1/2, the direct neomorphic target of the substrate receptor. Using deep mutational scanning, we systematically map the mutational landscape of the KBTBD4 cancer hotspot, revealing distinct preferences by which insertions and substitutions can promote gain-of-function and the critical residues involved in the hotspot interaction. Cryo-electron microscopy (cryo-EM) analysis of two distinct KBTBD4 cancer mutants bound to LSD1-HDAC1-CoREST reveals that a KBTBD4 homodimer asymmetrically engages HDAC1 with two KELCH-repeat propeller domains. The interface between HDAC1 and one of the KBTBD4 propellers is stabilized by the MB mutations, which directly insert a bulky side chain into the active site pocket of HDAC1. Our structural and mutational analyses inform how this hotspot E3-neo-substrate interface can be chemically modulated. First, our results unveil a converging shape complementarity-based mechanism between gain-of-function E3 mutations and a molecular glue degrader, UM171. Second, we demonstrate that HDAC1/2 inhibitors can block the mutant KBTBD4-HDAC1 interface, the aberrant degradation of CoREST, and the growth of KBTBD4-mutant MB models. Altogether, our work reveals the structural and mechanistic basis of cancer mutation-driven neomorphic protein-protein interactions and pharmacological strategies to modulate their action for therapeutic applications.

Evolution of genome diagnostics in epidermolysis bullosa: Unveiling the power of next-generation sequencing

BACKGROUND

Genome diagnostics is considered gold standard diagnostics for epidermolysis bullosa (EB), a phenotypically and genetically heterogeneous group of rare disorders characterized by blistering and wounding of mucocutaneous tissues. EB is caused by pathogenic variants in genes encoding proteins of the dermo-epidermal junction. Accurate genetic diagnosis of EB is crucial for prognostication, counselling and precision-medicine. Genome diagnostics for EB started in 1991 with the introduction of Sanger sequencing (SS), analysing one gene at a time. In 2013, SS was superseded by next-generation sequencing (NGS), that allow for high-throughput sequencing of multiple genes in parallel. Several studies have shown a beneficial role for NGS in EB diagnostics, but its true benefit has not been quantified.

OBJECTIVES

To determine the benefit of NGS in EB by systematically evaluating the performance of different genome diagnostics used over time based on robust data from the Dutch EB Registry.

METHODS

The diagnostic performances of SS and NGS were systematically evaluated in a retrospective observational study including all index cases with a clinical diagnosis of EB in whom genome diagnostics was performed between 01 January 1994 and 01 January 2022 (n = 308), registered at the Dutch EB Expertise Centre.

RESULTS

Over time, a genetic diagnosis was made in 289/308 (94%) EB cases. The diagnostic yield increased from 89% (SS) to 95% (NGS). Most importantly, NGS significantly reduced diagnostic turnaround time (39 days vs. 211 days, p < 0.001). The likelihood of detecting variants of uncertain significance and additional findings increased from 5% and 1% (SS) to 22% and 13% (NGS) respectively.

CONCLUSIONS

Our study quantifies the benefit of NGS-based methods and demonstrate they have had a major impact on EB diagnostics through an increased diagnostic yield and a dramatically decreased turnaround time (39 days). Although our diagnostic yield is high (95%), further improvement of genome diagnostics is urgently needed to provide a genetic diagnosis in all EB patients.

EBS in Children with De Novo Pathogenic Variants Disturbing Krt14

Epidermolysis bullosa simplex (EBS) is a dermatological condition marked by skin fragility and blister formation resulting from separation within the basal layer of the epidermis, which can be attributed to various genetic etiologies. This study presents three pathogenic de novo variants in young children, with clinical manifestations appearing as early as the neonatal period. The variants contribute to the EBS phenotype through two distinct mechanisms: direct keratin abnormalities due to pathogenic variants in the Krt14 gene, and indirect effects via pathogenic mutation in the KLHL24 gene, which interfere with the natural proteasome-mediated degradation pathway of KRT14. We report one severe case of EBS with mottled pigmentation arising from the Met119Thr pathogenic variant in KRT14, another case involving a pathogenic KLHL24 Met1Val variant, and a third case featuring the hot spot mutation Arg125His in KRT14, all manifesting within the first few weeks of life. This research underscores the complexity of genetic influences in EBS and highlights the importance of early genetic screening for accurate diagnosis and management.

Genome-wide association study identifies genetic variants underlying footrot in Portuguese Merino sheep

BACKGROUND

Ovine footrot caused by Dichelobacter nodosus (D. nodosus) is a contagious disease with serious economic and welfare impacts in sheep production systems worldwide. A better understanding of the host genetic architecture regarding footrot resistance/susceptibility is crucial to develop disease control strategies that efficiently reduce infection and its severity. A genome-wide association study was performed using a customized SNP array (47,779 SNPs in total) to identify genetic variants associated to footrot resistance/susceptibility in two Portuguese native breeds, i.e. Merino Branco and Merino Preto, and a population of crossbred animals. A cohort of 1375 sheep sampled across 17 flocks, located in the Alentejo region (southern Portugal), was included in the analyses.

RESULTS

Phenotypes were scored from 0 (healthy) to 5 (severe footrot) based on visual inspection of feet lesions, following the Modified Egerton System. Using a linear mixed model approach, three SNPs located on chromosome 24 reached genome-wide significance after a Bonferroni correction (p < 0.05). Additionally, six genome-wide suggestive SNPs were identified each on chromosomes 2, 4, 7, 8, 9 and 15. The annotation and KEGG pathway analyses showed that these SNPs are located within regions of candidate genes such as the nonsense mediated mRNA decay associated PI3K related kinase (SMG1) (chromosome 24) and the RALY RNA binding protein like (RALYL) (chromosome 9), both involved in immunity, and the heparan sulfate proteoglycan 2 (HSPG2) (chromosome 2) and the Thrombospodin 1 (THBS1) (chromosome 7) implicated in tissue repair and wound healing processes.

CONCLUSION

This is the first attempt to identify molecular markers associated with footrot in Portuguese Merino sheep. These findings provide relevant information on a likely genetic association underlying footrot resistance/susceptibility and the potential candidate genes affecting this trait. Genetic selection strategies assisted on the information obtained from this study could enhance Merino sheep-breeding programs, in combination with farm management strategies, for a more effective and sustainable long-term solution for footrot control.

Clinical and molecular features in a cohort of Middle Eastern patients with epidermolysis bullosa

BACKGROUND

Epidermolysis bullosa (EB) features skin and mucosal fragility due to pathogenic variants in genes encoding components of the cutaneous basement membrane. Based on the level of separation within the dermal-epidermal junction, EB is sub-classified into four major types including EB simplex (EBS), junctional EB (JEB), dystrophic EB (DEB), and Kindler EB (KEB) with 16 EB-associated genes reported to date.

METHODS

We ascertained a cohort of 151 EB patients of various Middle Eastern ethnic backgrounds.

RESULTS

The cohort was comprised of EBS (64%, 97/151), DEB (21%, 31/151), JEB (12%, 18/151), and KEB (3%, 5/151). KRT14 and KRT5 variants were most common among EBS patients with 43% (42/97) and 46% (45/97) of EBS patients carrying mutations in either of these two genes, respectively. Truncal involvement was more common in KRT14-associated EBS as compared to EBS due to KRT5 mutations (p < .05). Mutations in COL17A1 and laminin 332-encoding genes were identified in 55% (10/18) and 45% (8/18) of JEB patients. Scarring alopecia, caries, and EB nevi were most common among JEB patients carrying COL17A1 mutations as compared to laminin 332-associated JEB (p < .05). Abnormal nails were evident in most DEB and JEB patients while poikiloderma was exclusively observed in KEB (p < .001).

CONCLUSIONS

EB patients of Middle Eastern origin were found to feature specific phenotype-genotype correlations of relevance to the diagnosis and genetic counseling of patients in this region.

Excess KLHL24 Impairs Skin Wound Healing through the Degradation of Vimentin

Start codon variants in ubiquitin ligase KLHL24 lead to a gain-of-function mutant KLHL24-ΔN28, which mediates the excessive degradation of keratin 15, desmin, and keratin 14, resulting in alopecia, cardiopathy, and epidermolysis bullosa syndrome. Patients with alopecia, cardiopathy, and epidermolysis bullosa syndrome normally present atrophic scars after wounds heal, which is rare in KRT14-related epidermolysis bullosa. The mechanisms underlying the formation of atrophic scars in epidermolysis bullosa of patients with alopecia, cardiopathy, and epidermolysis bullosa syndrome remain unclear. This study showed that KLHL24-ΔN28 impaired skin wound healing by excessively degrading vimentin. Heterozygous Klhl24c.3G>T knock-in mice displayed delayed wound healing and decreased wound collagen deposition. We identified vimentin as an unreported substrate of KLHL24. KLHL24-ΔN28 mediated the excessive degradation of vimentin, which failed to maintain efficient fibroblast proliferation and activation during wound healing. Furthermore, by mediating vimentin degradation, KLHL24 can hinder myofibroblast activation, which attenuated bleomycin-induced skin fibrosis. These findings showed the function of KLHL24 in regulating tissue remodeling, atrophic scarring, and fibrosis.

The First Compound Heterozygous Mutations of DMP1 Causing Rare Autosomal Recessive Hypophosphatemic Rickets Type 1

CONTEXT

Hereditary hypophosphatemic rickets (HR) consists of a group of inherited hypophosphatemia due to mutations of different genes, which need genetic analysis to make a differential diagnosis. Among them, autosomal recessive hypophosphatemic rickets type 1 (ARHR1), caused by a homozygous mutation of dentin matrix protein 1 (DMP1), is extremely rare, with only 30 reported patients. To date, there has been no case with compound heterozygous DMP1 mutations.

OBJECTIVE

To report the first compound heterozygous mutations of DMP1 causing ARHR1 and confirm the effect of the mutation on DMP1 protein.

METHODS

We report the clinical features of a Chinese patient with HR. Whole-exome sequencing (WES) was performed on the proband. Then, Cytoscan HD array, Sanger sequencing, and genomic quantitative PCR (qPCR) were used to confirm the mutations. A cell experiment was conducted to explore the effect of the mutation.

RESULTS

The proband is a 4-year-old boy, who developed genu varum when he was able to walk at age 1 year and tooth loss after a mild hit at age 3.5 years. Physical examination, biochemical measurement, and imaging finding indicated HR. Family history was negative. WES performed on the proband revealed a novel start codon mutation (c.1A > T, p.Met1Leu) in DMP1 and a large deletion involving most of the small integrin-binding ligand N-linked glycoprotein (SIBLING) family gene, including DSPP, DMP1, IBSP, and MEPE. The novel paternally inherited start codon mutation, which resulted in decreased expression of DMP1 protein with smaller molecular weight and cleavage defect, was confirmed by Sanger sequencing. The maternally inherited deletion was validated by Cytoscan and qPCR, and the breakpoint was finally identified by long-range PCR and Sanger sequencing. Manifestation of dentin dysplasia (DD) or dentinogenesis imperfecta (DGI) caused by DSPP mutations was absent in the patient and his mother, confirming that haploinsufficiency could not lead to DD or DGI.

CONCLUSION

We report for the first time compound heterozygous DMP1 mutations consisting of a large deletion and a novel start codon mutation (c.1A > T, p.Met1Leu) in a Chinese patient with ARHR1.

Ubiquitin proteasome system in immune regulation and therapeutics

The ubiquitin proteasome system (UPS) is a proteolytic machinery for the degradation of protein substrates that are post-translationally conjugated with ubiquitin polymers through the enzymatic action of ubiquitin ligases, in a process termed ubiquitylation. Ubiquitylation of substrates precedes their proteolysis via proteasomes, a hierarchical feature of UPS. E3-ubiquitin ligases recruit protein substrates providing specificity for ubiquitylation. Innate and adaptive immune system networks are regulated by ubiquitylation and substrate degradation via E3-ligases/UPS. Deregulation of E3-ligases/UPS components in immune cells is involved in the development of lymphomas, neurodevelopmental abnormalities, and cancers. Targeting E3-ligases for therapeutic intervention provides opportunities to mitigate the unintended broad effects of 26S proteasome inhibition. Recently, bifunctional moieties such as PROTACs and molecular glues have been developed to re-purpose E3-ligases for targeted degradation of unwanted aberrant proteins, with a potential for clinical use. Here, we summarize the involvement of E3-ligases/UPS components in immune-related diseases with perspectives.

A translation re-initiation variant in KLHL24 also causes epidermolysis bullosa simplex and dilated cardiomyopathy via intermediate filament degradation

This study shows that gain-of-function variants in KLHL24 causing EBS and DCM, do not only originate in the start-codon and suggest that any nonsense-inducing variant affecting nucleotides c.4_84 will likely cause the same effect on protein level and a similar potential lethal phenotype.

Upregulation of KLHL17 promotes the proliferation and migration of non-small cell lung cancer by activating the Ras/MAPK signaling pathway

Analysis of the Gene Expression Profiling Interactive Analysis (GEPIA) database revealed that Kelch-like 17 (KLHL17) is overexpressed in non-small cell lung cancer (NSCLC) including adenocarcinoma (ADC) and squamous cell carcinoma (SCC). We therefore explored the role of KLHL17 in the development and progression of NSCLC. Immunohistochemistry and western blotting showed that KLHL17 expression was significantly higher in the tumor tissues from 173 patients with NSCLC, compared with the corresponding non-neoplastic tissue. In addition, upregulated KLHL17 expression was positively correlated with tumor size, lymph node metastasis and tumor node metastasis (TNM) stage, and affected the overall survival (OS) of patients with NSCLC. Consistent with clinical samples, in vitro studies demonstrated that KLHL17 expression was higher in various cell lines of NSCLC (A549, H1299, H460 and SK cells) as compared to normal human bronchial epithelial cells (HBE cells). Overexpression of KLHL17 in the cell lines of NSCLC with KLHL17-Flag plasmid promoted the proliferation and migration of tumor cells, which was associated with elevated activation of Rat sarcoma/Mitogen-activated protein kinases (Ras/MAPK) signaling and increased expression of cyclin D1, cyclin D-dependent kinases 4 (CDK4), matrix metalloproteinase 2 (MMP2) and Ras homolog gene family member A (RhoA). In contrast, knockdown of KLHL17 in the cell lines of NSCLC using KLHL17 small interfering RNA suppressed the proliferation and migration of tumor cells, in association with reduced activation of Ras/MAPK signaling and decreased expression of cyclin D1, CDK4, MMP2 and RhoA. Moreover, treatment of tumor cells with Ras inhibitor salirasib prevented KLHL17-induced Ras/MAPK activity as well as tumor proliferation and migration. These results suggest that upregulated KLHL17 in NSCLC promotes the proliferation and migration of tumor by activating Ras/MAPK signaling pathway. Therefore, KLHL17 may be a novel therapeutic target for the treatment of NSCLC.

Targeted NGS in Diagnostics of Genodermatosis Characterized by the Epidermolysis Bullosa Symptom Complex in 268 Russian Children

The pathogenic variants of genes encoding proteins, participating in the formation and functioning of epidermis and dermo-epidermal junctions, create a large variety of clinical phenotypes from: small localized to severe generalized dermatitis, as well as early, or even, prenatal death due to extensive epidermis loss. The diagnostic panel in this study was developed for the purposes of identifying these pathogenic genetic variants in 268 Russian children, who possessed the epidermolysis bullosa symptom complex in a selection of 247 families. This panel included the targeted areas of 33 genes, which are genetic variants that can lead to the development of the phenotype mentioned above. The usage of next generation sequencing allowed the revelation of 192 various altered alleles (of which 109 alleles were novel, i.e., had not been described previously). In addition, it allowed the definition of the genetic variants that are both typical for most of the examined children and for the separate ethnic groups inhabiting modern Russia. We found that the most characteristic mutations for the Dargin and Chechen ethnic groups are the c.3577del deletion in the COL7A1 gene and the c.2488G>A missense mutation in the COL17A1 gene, respectively. In addition, the study of haplotypes of microsatellite markers, which we managed to conduct in the Dargin population, confirmed the presence of the founder effect.

Towards a Better Understanding of Genotype-Phenotype Correlations and Therapeutic Targets for Cardiocutaneous Genes: The Importance of Functional Studies above Prediction

Genetic variants in gene-encoding proteins involved in cell−cell connecting structures, such as desmosomes and gap junctions, may cause a skin and/or cardiac phenotype, of which the combination is called cardiocutaneous syndrome. The cardiac phenotype is characterized by cardiomyopathy and/or arrhythmias, while the skin particularly displays phenotypes such as keratoderma, hair abnormalities and skin fragility. The reported variants associated with cardiocutaneous syndrome, in genes DSP, JUP, DSC2, KLHL24, GJA1, are classified by interpretation guidelines from the American College of Medical Genetics and Genomics. The genotype−phenotype correlation, however, remains poorly understood. By providing an overview of variants that are assessed for a functional protein pathology, we show that this number (n = 115) is low compared to the number of variants that are assessed by in silico algorithms (>5000). As expected, there is a mismatch between the prediction of variant pathogenicity and the prediction of the functional effect compared to the real functional evidence. Aiding to improve genotype−phenotype correlations, we separate variants into ‘protein reducing’ or ‘altered protein’ variants and provide general conclusions about the skin and heart phenotype involved. We conclude by stipulating that adequate prognoses can only be given, and targeted therapies can only be designed, upon full knowledge of the protein pathology through functional investigation.

KLHL24-Mediated Hair Follicle Stem Cells Structural Disruption Causes Alopecia

KLHL24 is an E3 ubiquitin ligase. Variants in the start codon of KLHL24 result in truncated KLHL24 protein lacking the initial 28 amino acids (KLHL24-ΔN28). KLHL24-ΔN28 is more stable than wild-type KLHL24 and causes excessive degradation of keratin 14, leading to epidermolysis bullosa. Patients with KLHL24-related epidermolysis bullosa usually develop alopecia, which is uncommon in patients with epidermolysis bullosa. The mechanisms by which KLHL24 variants cause alopecia is currently unclear. In this study, we show that KLHL24 regulates hair maintenance by mediating the stability of keratin 15. Using a Klhl24c.3G>T knock-in mouse model, we identify that KLHL24-ΔN28 disrupts the structure of hair follicle stem cells (HFSCs). Destructed HFSCs cannot anchor hairs and cause premature hair loss. Long-term destruction of HFSCs causes their exhaustion and hair follicle degeneration. Mechanically, KLHL24 mediates the ubiquitination and proteasomal degradation of keratin 15, an intermediate filament composing the HFSC cytoskeleton network. Keratin 15 is dramatically decreased in the skin of Klhl24c.3G>T mice and in patients with KLHL24-related epidermolysis bullosa. These findings show that KLHL24 plays a role in hair maintenance by regulating the cytoskeleton structure of HFSCs and highlight the importance of the ubiquitin‒proteasome system in the stability of HFSCs.

First case report of complete paternal isodisomy of chromosome 10 harbouring a novel variant in COL17A1 that causes junctional epidermolysis bullosa intermediate

Background

Uniparental disomy (UPD) is a condition in which both chromosomes are inherited from the same parent, except for imprinting disorders. Uniparental isodisomy (UPiD) may result in a homozygous variant contributing to an autosomal recessive disorder in the offspring of a heterozygous carrier. Junctional epidermolysis bullosa intermediate (JEB intermediate) is an autosomal recessive inherited disease that is associated with a series of gene variants, including those of COL17A1.

Case presentation

We report the first case of complete paternal UPiD of chromosome 10 harbouring a novel homozygous variant in COL17A1: c.1880(exon23)delG (p.G627Afs*56). This variant led to the clinical phenotype of junctional epidermolysis bullosa intermediate in a 5-year-old child. Trio-whole exome sequencing (Trio-WES) and in silico data analysis were used for variant identification, Sanger sequencing was performed for variant validation, and pathological examination was performed as the gold standard for phenotype confirmation.

Conclusions

We recommend the use of WES as a first-tier test for the diagnosis of epidermolysis bullosa, especially for paediatric patients. Moreover, UPD events should be detected and analysed routinely through WES data in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01285-x.

Defective protein degradation in genetic disorders

Understanding the molecular mechanisms that underlie different human pathologies is necessary to develop novel therapeutic strategies. An emerging mechanism of pathogenesis in many genetic disorders is the dysregulation of protein degradation, which leads to the accumulation of proteins that are responsible for the disease phenotype. Among the different cellular pathways that regulate active proteolysis, the Cullin RING E3 ligases represent an important group of sophisticated enzymatic complexes that mediate substrate ubiquitination through the interaction with specific adaptors. However, pathogenic variants in these adaptors affect the physiological ubiquitination of their substrates. This review discusses our current understanding of this emerging field.

AAV-Mediated Artificial miRNA Reduces Pathogenic Polyglucosan Bodies and Neuroinflammation in Adult Polyglucosan Body and Lafora Disease Mouse Models

Adult polyglucosan body disease (APBD) and Lafora disease (LD) are autosomal recessive glycogen storage neurological disorders. APBD is caused by mutations in the glycogen branching enzyme (GBE1) gene and is characterized by progressive upper and lower motor neuron dysfunction and premature death. LD is a fatal progressive myoclonus epilepsy caused by loss of function mutations in the EPM2A or EPM2B gene. These clinically distinct neurogenetic diseases share a common pathology. This consists of time-dependent formation, precipitation, and accumulation of an abnormal form of glycogen (polyglucosan) into gradually enlarging inclusions, polyglucosan bodies (PBs) in ever-increasing numbers of neurons and astrocytes. The growth and spread of PBs are followed by astrogliosis, microgliosis, and neurodegeneration. The key defect in polyglucosans is that their glucan branches are longer than those of normal glycogen, which prevents them from remaining in solution. Since the lengths of glycogen branches are determined by the enzyme glycogen synthase, we hypothesized that downregulating this enzyme could prevent or hinder the generation of the pathogenic PBs. Here, we pursued an adeno-associated virus vector (AAV) mediated RNA-interference (RNAi) strategy. This approach resulted in approximately 15% reduction of glycogen synthase mRNA and an approximately 40% reduction of PBs across the brain in the APBD and both LD mouse models. This was accompanied by improvements in early neuroinflammatory markers of disease. This work represents proof of principle toward developing a single lifetime dose therapy for two fatal neurological diseases: APBD and LD. The approach is likely applicable to other severe and common diseases of glycogen storage.

Functional investigation of two simultaneous or separately segregating DSP variants within a single family support the theory of a dose-dependent disease severity

Desmoplakin (DP) is an important component of desmosomes, essential in cell–cell connecting structures in stress‐bearing tissues. Over the years, many hundreds of pathogenic variants in DSP have been associated with different cutaneous and cardiac phenotypes or a combination, known as a cardiocutaneous syndrome. Of less than 5% of the reported DSP variants, the effect on the protein has been investigated. Here, we describe and have performed RNA, protein and tissue analysis in a large family where DSP^{c.273+5G>A/c.6687delA} segregated with palmoplantar keratoderma (PPK), woolly hair and lethal cardiomyopathy, while DSP^{WT/c.6687delA} segregated with PPK and milder cardiomyopathy. hiPSC‐derived cardiomyocytes and primary keratinocytes from carriers were obtained for analysis. Unlike the previously reported nonsense variants in the last exon of DSP that bypassed the nonsense‐mediated mRNA surveillance system leading to protein truncation, variant c.6687delA was shown to cause the loss of protein expression. Patients carrying both variants and having a considerably more severe phenotype were shown to have 70% DP protein reduction, while patients carrying only c.6687delA had 50% protein reduction and a milder phenotype. The analysis of RNA from patient cells did not show any splicing effect of the c.273+5G>A variant. However, a minigene splicing assay clearly showed alternative spliced transcripts originating from this variant. This study shows the importance of RNA and protein analyses to pinpoint the exact effect of DSP variants instead of solely relying on predictions. In addition, the particular pattern of inheritance, with simultaneous or separately segregating DSP variants within the same family, strongly supports the theory of a dose‐dependent disease severity.

Minor hypertrophic cardiomyopathy genes, major insights into the genetics of cardiomyopathies

Hypertrophic cardiomyopathy (HCM) was traditionally described as an autosomal dominant Mendelian disease but is now increasingly recognized as having a complex genetic aetiology. Although eight core genes encoding sarcomeric proteins account for >90% of the pathogenic variants in patients with HCM, variants in several additional genes (ACTN2, ALPK3, CSRP3, FHOD3, FLNC, JPH2, KLHL24, PLN and TRIM63), encoding non-sarcomeric proteins with diverse functions, have been shown to be disease-causing in a small number of patients. Genome-wide association studies (GWAS) have identified numerous loci in cardiomyopathy case-control studies and biobank investigations of left ventricular functional traits. Genes associated with Mendelian cardiomyopathy are enriched in the putative causal gene lists at these loci. Intriguingly, many loci are associated with both HCM and dilated cardiomyopathy but with opposite directions of effect on left ventricular traits, highlighting a genetic basis underlying the contrasting pathophysiological effects observed in each condition. This overlap extends to rare Mendelian variants with distinct variant classes in several genes associated with HCM and dilated cardiomyopathy. In this Review, we appraise the complex contribution of the non-sarcomeric, HCM-associated genes to cardiomyopathies across a range of variant classes (from common non-coding variants of individually low effect size to complete gene knockouts), which provides insights into the genetic basis of cardiomyopathies, causal genes at GWAS loci and the application of clinical genetic testing.

[A pedigree study of laryngo-onycho-cutaneous syndrome with a novel mutation on LAMA3 gene]

Objective:To detect genetic mutations in a case of laryngo-onycho-cutaneous syndrome, and to explore the possible molecular biological pathogenic causes. Methods:With informed consent, the family clinical data of the child with laryngo-onycho-cutaneous syndrome were collected, peripheral blood of the protester and his parents was collected and DNA was extracted, and gene detection was performed by high-throughput sequencing method. Sanger sequencing was used to verify and analyze the mutation sites of the probs and their families. Results:Genetic testing of the proband revealed homozygous mutation of LAMA3 gene c.171+1G>A site, which is splicing mutation. There was no report in the literature, which was a new mutation site. The parents of the proband had normal phenotype and heterozygous mutation at this locus was detected. Conclusion:Homozygous mutation of LAMA3 c.171+1G>A is the likely pathogenic of the proband, and this study expands the mutant spectrum of LAMA3. The clinical phenotype of laryngo-onycho-cutaneous syndrome is highly variable, and the multidisciplinary diagnosis and treatment can effectively avoid missed diagnosis and misdiagnosis.

Cardiomyopathies in Children and Systemic Disorders When Is It Useful to Look beyond the Heart?

Cardiomyopathy (CMP) is a rare disease in the pediatric population, with a high risk of morbidity and mortality. The genetic etiology of CMPs in children is extremely heterogenous. These two factors play a major role in the difficulties of establishing standard diagnostic and therapeutic protocols. Isolated CMP in children is a frequent finding, mainly caused by sarcomeric gene variants with a detection rate that can reach up to 50% of analyzed cohorts. Complex multisystemic forms of pediatric CMP are even more heterogenous. Few studies in literature take into consideration this topic as the main core since it represents a rarity (systemic CMP) within a rarity (pediatric population CMP). Identifying etiology in this cohort is essential for understanding prognosis, risk stratification, eligibility to heart transplantation and/or mechanical-assisted procedures, preventing multiorgan complications, and relatives' recurrence risk calculation. The previous points represent a cornerstone in patients' empowerment and personalized medical care approach. The aim of this work is to propose a new approach for an algorithm in the setting of the diagnostic framework of systemic pediatric CMP. On the other hand, during the literature review, we noticed a relatively common etiologic pattern in some forms of complex/multisystem CMP. In other words, certain syndromes such as Danon, Vici, Alström, Barth, and Myhre syndrome share a common pathway of directly or indirectly defective "autophagy" process, which appears to be a possible initiating/triggering factor for CMPs. This conjoint aspect could be important for possible prognostic/therapeutic implications in this category of patients. However, multicentric studies detailed functional and experimental models are needed prior to deriving conclusions.

Topical treatment of inherited epidermolysis bullosa

Inherited epidermolysis bullosa is a group of genetic skin disorders characterized by skin erosions, ulceration, skin and mucosal blistering requiring topical treatment. This review demonstrates major clinical manifestations of epidermolysis bullosa and its mechanisms of development. According to these features the main principles of topical treatment and drug therapy were developed, including physical protection from trauma, moisturizing, improvement of wound healing, prevention and management of infection, itch and pain management. Drug therapy is outlined with dosage forms, drug routes of administration, age restrictions indicated in the instruction for medical use for the medications that could be used in epidermolysis bullosa patients. The authors provide indications for clinical use of antiseptics, disinfectants, antibiotics, antimicrobial agents, emollient cream and drugs reducing itch and pain.

Development of Minicircle Vectors Encoding COL7A1 Gene with Human Promoters for Non-Viral Gene Therapy for Recessive Dystrophic Epidermolysis Bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a rare autosomal inherited skin disorder caused by mutations in the COL7A1 gene that encodes type VII collagen (C7). The development of an efficient gene replacement strategy for RDEB is mainly hindered by the lack of vectors able to encapsulate and transfect the large cDNA size of this gene. To address this problem, our group has opted to use polymeric-based non-viral delivery systems and minicircle DNA. With this approach, safety is improved by avoiding the usage of viruses, the absence of bacterial backbone, and the replacement of the control viral cytomegalovirus (CMV) promoter of the gene with human promoters. All the promoters showed impressive C7 expression in RDEB skin cells, with eukaryotic translation elongation factor 1 α (EF1α) promoter producing higher C7 expression levels than CMV following minicircle induction, and COL7A1 tissue-specific promoter (C7P) generating C7 levels similar to normal human epidermal keratinocytes. The improved system developed here has a high potential for use as a non-viral topical treatment to restore C7 in RDEB patients efficiently and safely, and to be adapted to other genetic conditions.

Case Report: De novo KLHL24 Gene Pathogenic Variants in Chinese Twin Boys With Epidermolysis Bullosa Simplex

Objectives: The aim of this study was to determine the molecular etiology and clinical manifestations of a pair of Chinese twins affected with epidermolysis bullosa simplex. Pediatricians should pay attention to the early genetic diagnosis of this disease. Methods: Histopathological examination of HE-stained skin, electron microscopy of biopsied normal skin, and whole-exome sequencing was performed to assess pathogenicity and conservation of detected mutations. Two years later, the cutaneous and extracutaneous manifestations of the twins were comprehensively evaluated. Results: A de novo pathogenic variant c.2T>C (p.M1T) in KLHL24 (NM_017,644) was identified in both twins. The characteristics of extensive skin defects on the extremities at birth and the tendency to lesson with increasing age were confirmed. No positive sensitive markers, such as B-type natriuretic peptide, cardiac troponin I, for cardiac dysfunction were detected. Conclusions: The de novo pathogenic variants c.2T>C (p.M1T) in KLHL24 (NM_017,644) contributes to the development of epidermolysis bullosa. Genetic diagnosis at birth or early infancy can better predict the disease prognosis and guide the treatment.

Keratins as an Inflammation Trigger Point in Epidermolysis Bullosa Simplex

Epidermolysis bullosa simplex (EBS) is a group of inherited keratinopathies that, in most cases, arise due to mutations in keratins and lead to intraepidermal ruptures. The cellular pathology of most EBS subtypes is associated with the fragility of the intermediate filament network, cytolysis of the basal layer of the epidermis, or attenuation of hemidesmosomal/desmosomal components. Mutations in keratins 5/14 or in other genes that encode associated proteins induce structural disarrangements of different strengths depending on their locations in the genes. Keratin aggregates display impaired dynamics of assembly and diminished solubility and appear to be the trigger for endoplasmic reticulum (ER) stress upon being phosphorylated by MAPKs. Global changes in cellular signaling mainly occur in cases of severe dominant EBS mutations. The spectrum of changes initiated by phosphorylation includes the inhibition of proteasome degradation, TNF-α signaling activation, deregulated proliferation, abnormal cell migration, and impaired adherence of keratinocytes. ER stress also leads to the release of proinflammatory danger-associated molecular pattern (DAMP) molecules, which enhance avalanche-like inflammation. Many instances of positive feedback in the course of cellular stress and the development of sterile inflammation led to systemic chronic inflammation in EBS. This highlights the role of keratin in the maintenance of epidermal and immune homeostasis.

Proteasome-mediated degradation of keratins 7, 8, 17 and 18 by mutant KLHL24 in a foetal keratinocyte model: Novel insight in congenital skin defects and fragility of epidermolysis bullosa simplex with cardiomyopathy

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.

LUBAC: a new player in polyglucosan body disease

Altered protein ubiquitination is associated with the pathobiology of numerous diseases; however, its involvement in glycogen metabolism and associated polyglucosan body (PB) disease has not been investigated in depth. In PB disease, excessively long and less branched glycogen chains (polyglucosan bodies, PBs) are formed, which precipitate in different tissues causing myopathy, cardiomyopathy and/or neurodegeneration. Linear ubiquitin chain assembly complex (LUBAC) is a multi-protein complex composed of two E3 ubiquitin ligases HOIL-1L and HOIP and an adaptor protein SHARPIN. Together they are responsible for M1-linked ubiquitination of substrates primarily related to immune signaling and cell death pathways. Consequently, severe immunodeficiency is a hallmark of many LUBAC deficient patients. Remarkably, all HOIL-1L deficient patients exhibit accumulation of PBs in different organs especially skeletal and cardiac muscle resulting in myopathy and cardiomyopathy with heart failure. This emphasizes LUBAC's important role in glycogen metabolism. To date, neither a glycogen metabolism-related LUBAC substrate nor the molecular mechanism are known. Hence, current reviews on LUBAC's involvement in glycogen metabolism are lacking. Here, we aim to fill this gap by describing LUBAC's involvement in PB disease. We present a comprehensive review of LUBAC structure, its role in M1-linked and other types of atypical ubiquitination, PB pathology in human patients and findings in new mouse models to study the disease. We conclude the review with recent drug developments and near-future gene-based therapeutic approaches to treat LUBAC related PB disease.

Genetic Studies of Natural Glycosphingolipid Ligands for NKT Cells

Glycosphingolipids (GSL) are natural ligands of NKT cells. Several laboratories have reported the in vitro activity of isoglobotriosylceramide (iGb3) in stimulating NKT cells. However, the knockout mice of iGb3 synthase showed no deficiency in development and function of NKT cells. There is a lack of knowledge on the genetics of redundant natural glycosphingolipid ligands. We have identified additional glycosphingolipid with stimulatory activity to NKT cells, including fucosyl lactosylceramide (H antigen). Here we describe the procedures to generate mice with deficiencies in Fut1, Fut2, and Sec1 genes to deplete H antigen through BAC engineering for the generation of ES cell-targeting construct, as well as the mice with deficiency of both blood group H-GSL ligand and isoglobotriosylceramide.

Identification of key molecules in recurrent miscarriage based on bioinformatics analysis

BACKGROUND

Recurrent miscarriage (RM) affects 1% to 5% of couples, and the mechanisms still stay unclear. In this study, we explored the underlying molecular mechanism and potential molecular biomarkers of RM as well as constructed a miRNA-mRNA regulation network.

METHODS

The microarray datasets GSE73025 and GSE22490, which represent mRNA and miRNA profiles, respectively, were downloaded from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) with p-value < 0.05 and fold-change > 2 were identified while the miRNAs with p-value < 0.05 and fold-change > 1.3 were considered as significant differentially expressed miRNAs (DEMs).

RESULTS

A total of 373 DEGs, including 218 up-regulated genes and 155 down-regulated genes, were identified, while 138 up-regulated and 68 down-regulated DEMs were screened out. After functional enrichment analysis, we found GO biological process (BP) terms significantly enriched in the Fc-gamma receptor signaling pathway involved in phagocytosis. Moreover, signaling pathway analyses indicated that the neurotrophin signaling pathway (hsa04722) was the top KEGG enrichment. 6 hub genes (FPR1, C5AR1, CCR1, ADCY7, CXCR2, NPY) were screened out to construct a complex regulation network in RM because they had the highest degree of affecting the network. Besides, we constructed miRNA-mRNA network between DEMs target genes and DEGs in RM, including hsa-miR-1297- KLHL24 and hsa-miR-548a-5p-KLHL24 pairs.

CONCLUSIONS

In conclusion, the novel differentially expressed molecules in the present study could provide a new sight to explore the pathogenesis of RM as well as potential biomarkers and therapeutic targets for RM diagnosis and treatment.

Gain-of-function mutation in ubiquitin-ligase KLHL24 causes desmin degradation and dilatation in hiPSC-derived engineered heart tissues

The start codon c.1A>G mutation in KLHL24, encoding ubiquitin-ligase KLHL24, results in the loss of 28 N-terminal amino acids (KLHL24-ΔN28) by skipping the initial start codon. In skin, KLHL24-ΔN28 leads to gain of function, excessively targeting intermediate filament keratin-14 for proteasomal degradation, ultimately causing epidermolysis bullosa simplex (EBS). The majority of these EBS-patients are also diagnosed with dilated cardiomyopathy (DCM), but the pathological mechanism in the heart is unknown. As desmin is the cardiac homologue of keratin-14, we hypothesized that KLHL24-ΔN28 leads to excessive degradation of desmin, resulting in DCM. Dynamically loaded engineered heart tissues (dyn-EHTs) were generated from human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes from two patients and three (non)familial controls. Ten-fold lower desmin protein levels were observed in patient-derived dyn-EHTs, in line with diminished desmin levels detected in patients' explanted heart. This was accompanied by tissue dilatation, impaired mitochondrial function, decreased force values and increased cardiomyocyte stress. HEK293 transfection studies confirmed KLHL24-mediated desmin degradation. KLHL24 RNA interference or direct desmin overexpression recovered desmin protein levels, restoring morphology and function in patient-derived dyn-EHTs. To conclude, presence of KLHL24-ΔN28 in cardiomyocytes leads to excessive degradation of desmin, affecting tissue morphology and function, that can be prevented by restoring desmin protein levels.

Lysophosphatidic Acid-Mediated GPR35 Signaling in CX3CR1+ Macrophages Regulates Intestinal Homeostasis

Single-nucleotide polymorphisms in the gene encoding G protein-coupled receptor 35 (GPR35) are associated with increased risk of inflammatory bowel disease. However, the mechanisms by which GPR35 modulates intestinal immune homeostasis remain undefined. Here, integrating zebrafish and mouse experimental models, we demonstrate that intestinal Gpr35 expression is microbiota dependent and enhanced upon inflammation. Moreover, murine GPR35⁺ colonic macrophages are characterized by enhanced production of pro-inflammatory cytokines. We identify lysophosphatidic acid (LPA) as a potential endogenous ligand produced during intestinal inflammation, acting through GPR35 to induce tumor necrosis factor (Tnf) expression in macrophages. Mice lacking Gpr35 in CX3CR1⁺ macrophages aggravate colitis when exposed to dextran sodium sulfate, which is associated with decreased transcript levels of the corticosterone-generating gene Cyp11b1 and macrophage-derived Tnf. Administration of TNF in these mice restores Cyp11b1 expression and intestinal corticosterone production and ameliorates DSS-induced colitis. Our findings indicate that LPA signals through GPR35 in CX3CR1⁺ macrophages to maintain TNF-mediated intestinal homeostasis.

Targeting Cul3-scaffold E3 ligase complex via KLHL substrate adaptors for cancer therapy

Targeted therapy has become increasingly important and indispensable in cancer therapy. Cullin3-RING ligases (CRL3) serve as essential executors for regulating protein homeostasis in cancer development, highlighting that CRL3 might be promising targets in various cancer treatment. However, how to design new targeted therapies by disrupting the function of CRL3 is poorly understood. Here, we focus on the substrate adaptors of CRL3, and carry out a systematical research on the function of Kelch-like (KLHL) family proteins. We have identified twenty-four KLHL proteins with function of tumor promotion and thirteen KLHL proteins with high clinical significance on cancer therapy. Furthermore, we have clarified the novel biological function of KLHL13 as a vital factor that contributes to malignant progression in lung cancer. Taken together, our findings reveal multiple potential therapeutical targets and provide evidence for targeting CRL3 via KLHL substrate adaptors for cancer therapy.

Advances in gene editing strategies for epidermolysis bullosa

Epidermolysis bullosa represents a monogenetic disease comprising a variety of heterogeneous mutations in at least 16 genes encoding structural proteins crucial for skin integrity. Due to well-defined mutations but still lacking causal treatment options for the disease, epidermolysis bullosa represents an ideal candidate for gene therapeutic interventions. Recent developments and improvements in the genome editing field have paved the way for the translation of various gene repair strategies into the clinic. With the ability to accurately predict and monitor targeting events within the human genome, the translation might soon be possible. Here, we describe current advancements in the genome editing field for epidermolysis bullosa, along with a discussion of aspects and strategies for precise and personalized gene editing-based medicine, in order to develop efficient and safe ex vivo as well as in vivo genome editing therapies for epidermolysis bullosa patients in the future.

Control of craniofacial and brain development by Cullin3-RING ubiquitin ligases: Lessons from human disease genetics

Metazoan development relies on intricate cell differentiation, communication, and migration pathways, which ensure proper formation of specialized cell types, tissues, and organs. These pathways are crucially controlled by ubiquitylation, a reversible post-translational modification that regulates the stability, activity, localization, or interaction landscape of substrate proteins. Specificity of ubiquitylation is ensured by E3 ligases, which bind substrates and co-operate with E1 and E2 enzymes to mediate ubiquitin transfer. Cullin3-RING ligases (CRL3s) are a large class of multi-subunit E3s that have emerged as important regulators of cell differentiation and development. In particular, recent evidence from human disease genetics, animal models, and mechanistic studies have established their involvement in the control of craniofacial and brain development. Here, we summarize regulatory principles of CRL3 assembly, substrate recruitment, and ubiquitylation that allow this class of E3s to fulfill their manifold functions in development. We further review our current mechanistic understanding of how specific CRL3 complexes orchestrate neuroectodermal differentiation and highlight diseases associated with their dysregulation. Based on evidence from human disease genetics, we propose that other unknown CRL3 complexes must help coordinate craniofacial and brain development and discuss how combining emerging strategies from the field of disease gene discovery with biochemical and human pluripotent stem cell approaches will likely facilitate their identification.

Clinical practice guidelines: Oral health care for children and adults living with epidermolysis bullosa

BACKGROUND

Inherited epidermolysis bullosa (EB) is a genetic disorder characterized by skin fragility and unique oral features.

AIMS

To provide (a) a complete review of the oral manifestations in those living with each type of inherited EB, (b) the current best practices for managing oral health care of people living with EB, (c) the current best practices on dental implant-based oral rehabilitation for patients with recessive dystrophic EB (RDEB), and (d) the current best practice for managing local anesthesia, principles of sedation, and general anesthesia for children and adults with EB undergoing dental treatment.

METHODS

Systematic literature search, panel discussion including clinical experts and patient representatives from different centers around the world, external review, and guideline piloting.

RESULTS

This article has been divided into five chapters: (i) general information on EB for the oral health care professional, (ii) systematic literature review on the oral manifestations of EB, (iii) oral health care and dental treatment for children and adults living with EB-clinical practice guidelines, (iv) dental implants in patients with RDEB-clinical practice guidelines, and (v) sedation and anesthesia for adults and children with EB undergoing dental treatment-clinical practice guidelines. Each chapter provides recommendations on the management of the different clinical procedures within dental practice, highlighting the importance of patient-clinician partnership, impact on quality of life, and the importance of follow-up appointments. Guidance on the use on nonadhesive wound care products and emollients to reduce friction during patient care is provided.

CONCLUSIONS

Oral soft and hard tissue manifestations of inherited EB have unique patterns of involvement associated with each subtype of the condition. Understanding each subtype individually will help the professionals plan long-term treatment approaches.

Epidermolysis bullosa

Epidermolysis bullosa (EB) is an inherited, heterogeneous group of rare genetic dermatoses characterized by mucocutaneous fragility and blister formation, inducible by often minimal trauma. A broad phenotypic spectrum has been described, with potentially severe extracutaneous manifestations, morbidity and mortality. Over 30 subtypes are recognized, grouped into four major categories, based predominantly on the plane of cleavage within the skin and reflecting the underlying molecular abnormality: EB simplex, junctional EB, dystrophic EB and Kindler EB. The study of EB has led to seminal advances in our understanding of cutaneous biology. To date, pathogenetic mutations in 16 distinct genes have been implicated in EB, encoding proteins influencing cellular integrity and adhesion. Precise diagnosis is reliant on correlating clinical, electron microscopic and immunohistological features with mutational analyses. In the absence of curative treatment, multidisciplinary care is targeted towards minimizing the risk of blister formation, wound care, symptom relief and specific complications, the most feared of which - and also the leading cause of mortality - is squamous cell carcinoma. Preclinical advances in cell-based, protein replacement and gene therapies are paving the way for clinical successes with gene correction, raising hopes amongst patients and clinicians worldwide.

Prenatal genetic diagnosis of cranioectodermal dysplasia in a Polish family with compound heterozygous variants in WDR35

The ciliary chondrodysplasias represent a group of clinically and genetically heterogeneous disorders that affect skeleton development. Cilia are organelles that project from the surface of many cell types and play an important role during prenatal and postnatal human development. Cranioectodermal dysplasia (Sensenbrenner syndrome, CED) is a ciliopathy primarily characterized by craniofacial, skeletal, and ectodermal abnormalities. To date six genes have been associated with CED: IFT122, WDR35, WDR19, IFT140, IFT43, and IFT52. Prenatal diagnosis of CED is challenging, and genetic testing can facilitate making a correct diagnosis. Here, we report on a family with two male siblings affected by CED: a 3.5 year-old patient and his 2 year-old brother. Molecular analysis of the proband at 1 year of age revealed compound heterozygous variants in WDR35: c.3G>A [p.(Met1-Ala30delinsMetfsTer4)] and c.2522A>T [p.(Asp841Val)]. Ultrasound examination during the second pregnancy revealed an increased nuchal translucency of 4.5 mm and a hypoplastic nasal bone at 12 weeks of gestation. Prenatal diagnostic testing was offered because of an increased risk for chromosomal abnormalities and recurrence risk for CED. Prenatal genetic analysis of a chorionic villus sample detected the WDR35 variants previously identified in the elder brother. This is the first report of a prenatal genetic diagnosis in CED.

Inherited epidermolysis bullosa: update on the clinical and genetic aspects

Inherited epidermolysis bullosa is a group of genetic diseases characterized by skin fragility and blistering on the skin and mucous membranes in response to minimal trauma. Epidermolysis bullosa is clinically and genetically very heterogeneous, being classified into four main types according to the layer of skin in which blistering occurs: epidermolysis bullosa simplex (intraepidermal), junctional epidermolysis bullosa (within the lamina lucida of the basement membrane), dystrophic epidermolysis bullosa (below the basement membrane), and Kindler epidermolysis bullosa (mixed skin cleavage pattern). Furthermore, epidermolysis bullosa is stratified into several subtypes, which consider the clinical characteristics, the distribution of the blisters, and the severity of cutaneous and extracutaneous signs. Pathogenic variants in at least 16 genes that encode proteins essential for the integrity and adhesion of skin layers have already been associated with different subtypes of epidermolysis bullosa. The marked heterogeneity of the disease, which includes phenotypes with a broad spectrum of severity and many causal genes, hinders its classification and diagnosis. For this reason, dermatologists and geneticists regularly review and update the classification criteria. This review aimed to update the state of the art on inherited epidermolysis bullosa, with a special focus on the associated clinical and genetic aspects, presenting data from the most recent reclassification consensus, published in 2020.

Genotype-phenotype correlations on epidermolysis bullosa with congenital absence of skin: A comprehensive review

Congenital absence of skin (CAS) is a clinical sign associated with the main types of epidermolysis bullosa (EB). Very few studies have investigated the genetic background that may influence the occurrence of this condition. Our objective was to investigate genotype-phenotype correlations on EB with CAS through a literature revision on the pathogenic variants previously reported. A total of 171 cases (49 EB simplex, EBS; 23 junctional EB, JEB; and 99 dystrophic EB, DEB), associated with 132 pathogenic variants in eight genes, were included in the genotype-phenotype analysis. In EBS, CAS showed to be a recurrent clinical sign in EBS with pyloric atresia (PA) and EBS associated with kelch-like protein 24; CAS was also described in patients with keratins 5/14 alterations, particularly involving severe phenotypes. In JEB, this is a common clinical sign in JEB with PA associated with premature termination codon variants and/or amino acid substitutions located in the extracellular domain of integrin α6β4 genes. In DEB with CAS, missense variants occurring close to non-collagenous interruptions of the triple-helix domain of collagen VII appear to influence this condition. This study is the largest review of patients with EB and CAS and expands the spectrum of known variants on this phenomenon.

Estrogen receptor-α expressing neurons in the ventrolateral VMH regulate glucose balance

Brain glucose-sensing neurons detect glucose fluctuations and prevent severe hypoglycemia, but mechanisms mediating functions of these glucose-sensing neurons are unclear. Here we report that estrogen receptor-α (ERα)-expressing neurons in the ventrolateral subdivision of the ventromedial hypothalamic nucleus (vlVMH) can sense glucose fluctuations, being glucose-inhibited neurons (GI-ERαvlVMH) or glucose-excited neurons (GE-ERαvlVMH). Hypoglycemia activates GI-ERαvlVMH neurons via the anoctamin 4 channel, and inhibits GE-ERαvlVMH neurons through opening the ATP-sensitive potassium channel. Further, we show that GI-ERαvlVMH neurons preferentially project to the medioposterior arcuate nucleus of the hypothalamus (mpARH) and GE-ERαvlVMH neurons preferentially project to the dorsal Raphe nuclei (DRN). Activation of ERαvlVMH to mpARH circuit and inhibition of ERαvlVMH to DRN circuit both increase blood glucose. Thus, our results indicate that ERαvlVMH neurons detect glucose fluctuations and prevent severe hypoglycemia in mice.