Laura De Rosa

Transcriptional Repression of miR-34 Family Contributes to p63-Mediated Cell Cycle Progression in Epidermal Cells

p63, a p53 family member, is highly expressed in the basal proliferative compartment of the epidermis and its expression has been correlated with the growth ability and regenerative capacity of keratinocytes. In this study we report a mechanism through which p63 maintains cell cycle progression by directly repressing miR-34a and miR-34c. In the absence of p63, increased levels of miR-34a and miR-34c were observed in primary keratinocytes and in embryonic skin, with concomitant G1-phase arrest and inhibition of the cell cycle regulators cyclin D1 and cyclin-dependent kinase 4 (Cdk4). p63 directly bound to p53-consensus sites in both miR-34a and miR-34c regulatory regions and inhibited their activity. Concomitant downregulation of miR-34a and miR-34c substantially restored cell cycle progression and expression of cyclin D1 and Cdk4. Our data indicate that specific miR-34 family members have a significant role downstream of p63 in controlling epidermal cell proliferation.

Regeneration of the entire human epidermis using transgenic stem cells

Junctional epidermolysis bullosa (JEB) is a severe and often lethal genetic disease caused by mutations in genes encoding the basement membrane component laminin-332. Surviving patients with JEB develop chronic wounds to the skin and mucosa, which impair their quality of life and lead to skin cancer. Here we show that autologous transgenic keratinocyte cultures regenerated an entire, fully functional epidermis on a seven-year-old child suffering from a devastating, life-threatening form of JEB. The proviral integration pattern was maintained in vivo and epidermal renewal did not cause any clonal selection. Clonal tracing showed that the human epidermis is sustained not by equipotent progenitors, but by a limited number of long-lived stem cells, detected as holoclones, that can extensively self-renew in vitro and in vivo and produce progenitors that replenish terminally differentiated keratinocytes. This study provides a blueprint that can be applied to other stem cell-mediated combined ex vivo cell and gene therapies.

Mutant p63 causes defective expansion of ectodermal progenitor cells and impaired FGF signalling in AEC syndrome.

Ankyloblepharon‐ectodermal defects‐cleft lip/palate (AEC) syndrome, which is characterized by cleft palate and severe defects of the skin, is an autosomal dominant disorder caused by mutations in the gene encoding transcription factor p63. Here, we report the generation of a knock‐in mouse model for AEC syndrome (p63+/L514F) that recapitulates the human disorder. The AEC mutation exerts a selective dominant‐negative function on wild‐type p63 by affecting progenitor cell expansion during ectodermal development leading to a defective epidermal stem cell compartment. These phenotypes are associated with impairment of fibroblast growth factor (FGF) signalling resulting from reduced expression of Fgfr2 and Fgfr3, direct p63 target genes. In parallel, a defective stem cell compartment is observed in humans affected by AEC syndrome and in Fgfr2b−/− mice. Restoring Fgfr2b expression in p63+/L514F epithelial cells by treatment with FGF7 reactivates downstream mitogen‐activated protein kinase signalling and cell proliferation. These findings establish a functional link between FGF signalling and p63 in the expansion of epithelial progenitor cells and provide mechanistic insights into the pathogenesis of AEC syndrome.

Long-Term Stability and Safety of Transgenic Cultured Epidermal Stem Cells in Gene Therapy of Junctional Epidermolysis Bullosa

Summary We report a long-term follow-up (6.5 years) of a phase I/II clinical trial envisaging the use of autologous genetically modified cultured epidermal stem cells for gene therapy of junctional epidermolysis bullosa, a devastating genetic skin disease. The critical goals of the trial were to evaluate the safety and long-term persistence of genetically modified epidermis. A normal epidermal-dermal junction was restored and the regenerated transgenic epidermis was found to be fully functional and virtually indistinguishable from a normal control. The epidermis was sustained by a discrete number of long-lasting, self-renewing transgenic epidermal stem cells that maintained the memory of the donor site, whereas the vast majority of transduced transit-amplifying progenitors were lost within the first few months after grafting. These data pave the way for the safe use of epidermal stem cells in combined cell and gene therapy for genetic skin diseases.

p63 control of desmosome gene expression and adhesion is compromised in AEC syndrome

Ankyloblepharon, ectodermal defects, cleft lip/palate (AEC) syndrome is a rare autosomal dominant disorder caused by mutations in the p63 gene, essential for embryonic development of stratified epithelia. The most severe cutaneous manifestation of this disorder is the long-lasting skin fragility associated with severe skin erosions after birth. Using a knock-in mouse model for AEC syndrome, we found that skin fragility was associated with microscopic blistering between the basal and suprabasal compartments of the epidermis and reduced desmosomal contacts. Expression of desmosomal cadherins and desmoplakin was strongly reduced in AEC mutant keratinocytes and in newborn epidermis. A similar impairment in desmosome gene expression was observed in human keratinocytes isolated from AEC patients, in p63-depleted keratinocytes and in p63 null embryonic skin, indicating that p63 mutations causative of AEC syndrome have a dominant-negative effect on the wild-type p63 protein. Among the desmosomal components, desmocollin 3, desmoplakin and desmoglein 1 were the most significantly reduced by mutant p63 both at the RNA and protein levels. Chromatin immunoprecipitation experiments and transactivation assays revealed that p63 controls these genes at the transcriptional level. Consistent with reduced desmosome function, AEC mutant and p63-deficient keratinocytes had an impaired ability to withstand mechanical stress, which was alleviated by epidermal growth factor receptor inhibitors known to stabilize desmosomes. Our study reveals that p63 is a crucial regulator of a subset of desmosomal genes and that this function is impaired in AEC syndrome. Reduced mechanical strength resulting from p63 mutations can be alleviated pharmacologically by increasing desmosome adhesion with possible therapeutic implications.

TAp63 Is Important for Cardiac Differentiation of Embryonic Stem Cells and Heart Development

p63, a member of the p53 family, is essential for skin morphogenesis and epithelial stem cell maintenance. Here, we report an unexpected role of TAp63 in cardiogenesis. p63 null mice exhibit severe defects in embryonic cardiac development, including dilation of both ventricles, a defect in trabeculation and abnormal septation. This was accompanied by myofibrillar disarray, mitochondrial disorganization, and reduction in spontaneous calcium spikes. By the use of embryonic stem cells (ESCs), we show that TAp63 deficiency prevents expression of pivotal cardiac genes and production of cardiomyocytes. TAp63 is expressed by endodermal cells. Coculture of p63‐knockdown ESCs with wild‐type ESCs, supplementation with Activin A, or overexpression of GATA‐6 rescue cardiogenesis. Therefore, TAp63 acts in a non‐cell‐autonomous manner by modulating expression of endodermal factors. Our findings uncover a critical role for p63 in cardiogenesis that could be related to human heart disease. STEM CELLS 2011;29:1672–1683

p63 Suppresses Non-epidermal Lineage Markers in a Bone Morphogenetic Protein-dependent Manner via Repression of Smad7

p63, a p53 family member, plays an essential role in epidermal development by regulating its transcriptional program. Here we report a previously uncovered role of p63 in controlling bone morphogenetic protein (BMP) signaling, which is required for maintaining low expression levels of several non-epidermal genes. p63 represses transcription of the inhibitory Smad7 and activates Bmp7, thereby sustaining BMP signaling. In the absence of p63, compromised BMP signaling leads to inappropriate non-epidermal gene expression in postnatal mouse keratinocytes and in embryonic epidermis. Reactivation of BMP signaling by Smad7 knockdown and/or, to a lesser extent, by BMP treatment suppresses expression of non-epidermal genes in the absence of p63. Canonical BMP/Smad signaling is essential for control of non-epidermal genes as use of a specific inhibitor, or simultaneous knockdown of Smad1 and Smad5 counteract suppression of non-epidermal genes. Our data indicate that p63 prevents ectopic expression of non-epidermal genes by a mechanism involving Smad7 repression and, to a lesser extent, Bmp7 induction, with consequent enhancement of BMP/Smad signaling.

Closure of a Large Chronic Wound through Transplantation of Gene-Corrected Epidermal Stem Cells

Figure 1. Regeneration of a transgenic functional epidermis on the skin wound of the JEB patient. (a) The long-standing ulceration on the lower right leg of the patient 2 days before transplantation. (b) Western blot analysis of cell lysates (20 mg protein, 30 seconds exposure time) from (lane 1) normal control and patient keratinocyte cultures (lane 2) before and (lane 3) after gene correction, probed with a monoclonal antibody against laminin 332-b3. (lane 4) Western blot analysis of a higher amount of loaded protein (65 mg, 5 seconds exposure time) of uncorrected patient keratinocytes, and (lane 5) normal keratinocyte cultures using the same laminin-332-b3 antibody. The 75-kD band in lane 4 is consistent with the truncated laminin-332-b3 generated by the c.1903C>T; p.R635X mutation. (c) Transplantation of cultured transgenic epidermal sheets (asterisks) on the prepared wound bed. Grafts are overlaid with petrolatum gauze. (d) Initial epidermal regeneration at 14 days. (e) Complete epidermal regeneration at 3.5 months. (f) Stable epidermal regeneration at 16 months. Note crusting and erosions outside of the grafted area. JEB, junctional epidermolysis bullosa. TO THE EDITOR Generalized junctional epidermolysis bullosa (JEB) is caused by mutations in LAMA3, LAMB3, or LAMC2, which together encode laminin-332, a heterotrimeric protein consisting of a3, b3, and g2 chains (Fine et al., 2014). In nonlethal generalized intermediate JEB, laminin332 is highly reduced, and hemidesmosomes are rudimentary or completely absent, leading to blister formation within the lamina lucida of the basementmembrane uponminor trauma. The resulting chronic skin wounds invariably develop recurrent infections and scarring, which greatly impair patients’ quality of life (Fine et al., 2014; Laimer et al., 2010; Nakano et al., 2002). There is no cure for JEB; treatments are symptomatic and aimed at relieving the devastating clinical manifestations (Carulli et al., 2013). The only published evidence for the possibility of a permanent local treatment of JEB was provided by a phase I/II trial showing that autologous epidermal cultures containing geneticallymodified epidermal stem cells were able to restore a normal epidermis on a JEB patient (De Rosa et al., 2014; Mavilio et al., 2006). However, the transgenic epidermis was applied in areas still covered by a diseased but apparently functional epidermis, which was surgically removed before grafting (Mavilio et al., 2006). Although it is clear that the ideal clinical application of transgenic epidermis would aim at preventing the development of devastating chronic lesions,manypatients suffer from therapyresistant chronic ulcerations that are highly predisposed to cancer development and need timely closure (Goldberg

Cell biology: Dormant and restless skin stem cells

It has been unclear whether a uniform group of stem cells gives rise to most cells in the epidermis. A study reveals the presence of at least two stem-cell populations that have different proliferative abilities. See Article p.257

Tprg, a Gene Predominantly Expressed in Skin, Is a Direct Target of the Transcription Factor p63

p63 and p73 are highly homologous members of the p53 family that originated by gene duplication at the invertebrate-to-vertebrate transition. We characterize here a previously unreported gene, Transformation-related protein 63 regulated (Tprg), located upstream of the p63 gene in the vertebrate genome, with striking similarity to Transformation related protein 63 regulated like (Tprgl), an uncharacterized gene located upstream of p73, suggesting that p63/Tprg and p73/Tprgl are embedded in a paralogue region originated from a single duplication event. Tprg is predominantly expressed in the epithelial compartment of the skin, more abundantly in differentiated cells. Consistent with its relative higher expression in differentiated keratinocytes, finely tuned p63 expression levels are required for optimal Tprg expression in primary keratinocytes. p63 is essential for Tprg expression as shown in p63-knockdown keratinocytes; however, high levels of p63 result in Tprg downregulation. p63 directly binds in vivo to a canonical p63-binding site in an evolutionary conserved genomic region located in Tprg intron 4. This genomic region is sufficient to function as a p63-inducible enhancer in promoter studies. Thus, we demonstrate that the Tprg gene is predominantly expressed in skin, is physically associated with the p63 gene during evolution, and directly regulated by p63 through a long-distance enhancer located within the Tprg locus.