Wei-Li Di

Kallikrein 5 (KLK5) is a serine protease expressed in the outer skin layers, where it regulates the barrier function by cleaving desmosomal proteins. Elevated KLK5 causes excessive proteolysis, leading to corneocyte overdesquamation and barrier compromise. Increased KLK5 activity has been linked to atopic dermatitis (AD), a chronic inflammatory disease affecting up to 20% of children, highlighting the need for therapies that restore barrier integrity. While many serine protease inhibitors have been developed, most lack KLK5 selectivity. To address this, novel analogues of the sunflower trypsin inhibitor were designed and evaluated. Lead 7 emerged as a potent (IC50 = 14 ± 4 nM; Ki = 11 nM) selective KLK5 inhibitor. In keratinocytes from a Netherton syndrome patient, lead 7 significantly reduced the KLK5 activity and improved epithelial barrier integrity, as shown by transepithelial electrical resistance. These findings suggest lead 7 as a potential therapy for AD and other conditions with elevated KLK5 activity.

Keratinocyte stem cells (KSCs) can be cultured as ex vivo epidermal sheets and are attractive for cell and gene therapy. However, the growth and expansion of primary keratinocytes (including KSCs) in in vitro culture can be inefficient as KSCs undergo apoptotic cell death, known as anoikis when isolated from skin biopsies and dissociated from their extracellular environment. This further affects the survival and stemness of KSCs in in vitro culture and hinders clinical applications. Rho-associated kinase inhibitor (ROCKi) has been used to overcome this obstacle. However, it risks changing the characteristics of stem cells. In this study, we studied the effect of the Y-27632 ROCKi on cultured primary human keratinocytes. Following a short-term (6 days) ROCKi treatment, we assessed keratinocyte proliferation and differentiation potential and KSC stemness at the molecular-, cellular- and single-cell levels. A significant increase in colony-forming efficiency associated with increased expression of proliferation markers and mitochondrial mass was observed in treated cells vs. untreated cells. Similarly, treated cells showed a distinct transcriptional profile at the single-cell level, but these changes became indistinguishable after discontinuation of ROCKi treatment. Single-cell transcriptome analysis further confirmed that short-term ROCKi treatment did not affect stem cell characteristics. Finally, we showed that ROCKi rapidly activated Akt and upstream of ERK signalling pathways in primary human keratinocytes. In conclusion, rapid proliferation due to short-term ROCKi treatment was transient and reversible, and did not affect the KSC population or their characteristics. We thus present a safer approach for the use of ROCKi in ex vivo clinical applications.

Primary keratinocytes including keratinocyte stem cells (KSCs) can be cultured as epidermal sheets in vitro and are attractive for cell and gene therapies for genetic skin disorders. However, the initial slow growth of freshly isolated keratinocytes hinders clinical applications. Rho-associated kinase inhibitor (ROCKi) has been used to overcome this obstacle, but its influence on the characteristics of KSC and its safety for clinical application remains unknown. In this study, primary keratinocytes were treated with ROCKi Y-27632 for six days (short-term). Significant increases in colony formation and cell proliferation during the six-day ROCKi treatment were observed and confirmed by related protein markers and single-cell transcriptomic analysis. In addition, short-term ROCKi-treated cells maintained their differentiation ability as examined by 3D-organotypic culture. However, these changes could be reversed and became indistinguishable between treated and untreated cells once ROCKi treatment was withdrawn. Further, the short-term ROCKi treatment did not reduce the number of KSCs. In addition, AKT and ERK pathways were rapidly activated upon ROCKi treatment. In conclusion, short-term ROCKi treatment can transiently and reversibly accelerate initial primary keratinocyte expansion while preserving the holoclone-forming cell population (KSCs), providing a safe avenue for clinical applications.

Inflammatory linear verrucous epidermal naevus (ILVEN) is a rare congenital disease characterised by Blaschko-linear erythematous scaly skin. It | POSTER

Keratinocyte stem cells (KSCs) can be cultured in vitro and are thus attractive in epidermal sheet gene therapies for genodermatoses. However, th | POSTER

Somatic stem cells can be cultured in-vitro and are attractive for cell and gene therapies, but their slow growth in in-vitro culture affects survival and stemness and hinders clinical applications. Rho-associated kinase inhibitor (ROCKi) has been used to overcome these obstacles. However, it risks changing the characteristics of stem cells. We found that primary keratinocyte stem cells (KSCs) cultured with the ROCKi Y-27632 for six days exhibited rapid proliferation while maintaining the ability to differentiate. Importantly, after discontinuation of ROCKi treatment, KSC numbers and characteristics were indistinguishable from those in non-treated cultures. We further confirmed that ROCKi treatment resulted in the activation of AKT and ERK pathways, which could support cell survival and proliferation in keratinocytes. We thus concluded that accelerating keratinocyte expansion with short-term ROCKi treatment does not exhaust KSCs’ self-renewal and differentiation capacities, presenting a safe avenue for clinical applications.

Genetic skin diseases, also known as genodermatoses, are inherited disorders affecting skin and constitute a large and heterogeneous group of diseases. While genodermatoses are rare with the prevalence rate of less than 1 in 50,000 – 200,000, they frequently occur at birth or early in life and are generally chronic, severe, and could be life‐threatening. The quality of life of patients and their families are severely compromised by the negative psychosocial impact of disease, physical manifestations, and the lack or loss of autonomy. Currently, there are no curative treatments for these conditions. Ex vivo gene modification therapy that involves modification or correction of mutant genes in patients’ cells in vitro and then transplanted back to patients to restore functional gene expression has being developed for genodermatoses. In this review, the ex vivo gene modification therapy strategies for genodermatoses are reviewed, focusing on current advances in gene modification and correction in patients’ cells and delivery of genetically modified cells to patients with discussions on gene therapy trials which have been performed in this area.

RNA modifications play a fundamental role in cellular function. Pseudouridylation, the most abundant RNA modification, is catalyzed by the H/ACA small ribonucleoprotein (snoRNP) complex that shares four core proteins, dyskerin (DKC1), NOP10, NHP2, and GAR1. Mutations in DKC1 , NOP10 , or NHP2 cause dyskeratosis congenita (DC), a disorder characterized by telomere attrition. Here, we report a phenotype comprising nephrotic syndrome, cataracts, sensorineural deafness, enterocolitis, and early lethality in two pedigrees: males with DKC1 p.Glu206Lys and two children with homozygous NOP10 p.Thr16Met. Females with heterozygous DKC1 p.Glu206Lys developed cataracts and sensorineural deafness, but nephrotic syndrome in only one case of skewed X-inactivation. We found telomere attrition in both pedigrees, but no mucocutaneous abnormalities suggestive of DC. Both mutations fall at the dyskerin–NOP10 binding interface in a region distinct from those implicated in DC, impair the dyskerin–NOP10 interaction, and disrupt the catalytic pseudouridylation site. Accordingly, we found reduced pseudouridine levels in the ribosomal RNA (rRNA) of the patients. Zebrafish dkc1 mutants recapitulate the human phenotype and show reduced 18S pseudouridylation, ribosomal dysregulation, and a cell-cycle defect in the absence of telomere attrition. We therefore propose that this human disorder is the consequence of defective snoRNP pseudouridylation and ribosomal dysfunction.