Single-nucleotide-specific siRNA targeting in a dominant-negative skin model

RNA interference offers a novel approach for developing therapeutics for dominant-negative genetic disorders. The ability to inhibit expression of the mutant allele without affecting wild-type gene expression could be a powerful new treatment option. Targeting the single-nucleotide keratin 6a (K6a) N171K mutation responsible for the rare monogenic skin disorder pachyonychia congenita (PC), we demonstrate that small interfering RNAs (siRNAs) can potently and selectively block expression of mutant K6a. To test whether lead siRNAs could discriminate mutant mRNA in the presence of both wild-type and mutant forms, a dominant-negative PC cell culture model was developed. As predicted for a dominant-negative disease, simultaneous expression of both wild-type and mutant K6a resulted in defective keratin filament formation. Addition of mutant-specific siRNAs allowed normal filament formation, suggesting selective inhibition of mutant K6a. The effectiveness of our siRNA in skin was tested by co-delivering a firefly luciferase/mutant K6a bicistronic reporter construct and mutant-specific siRNAs to mouse footpads. Potent inhibition of the fluorescent reporter was demonstrated using the Xenogen IVIS200 in vivo imaging system. Additionally, wild type-specific siRNAs knocked down the expression of pre-existing endogenous K6a in human keratinocytes. These results suggest that efficient delivery of these "designer siRNAs" may allow effective treatment of numerous genetic disorders including PC.     

Generic and personalized RNAi-based therapeutics for a dominant-negative epidermal fragility disorder

Epidermolytic palmoplantar keratoderma (EPPK) is one of >30 autosomal-dominant human keratinizing disorders that could benefit from RNA interference (RNAi)-based therapy. EPPK is caused by mutations in the keratin 9 (KRT9) gene, which is exclusively expressed in thick palm and sole skin where there is considerable keratin redundancy. This, along with the fact that EPPK is predominantly caused by a few hotspot mutations, makes it an ideal proof-of-principle model skin disease to develop gene-specific, as well as mutation-specific, short interfering RNA (siRNA) therapies. We have developed a broad preclinical RNAi-based therapeutic package for EPPK containing generic KRT9 siRNAs and allele-specific siRNAs for four prevalent mutations. Inhibitors were systematically identified in vitro using a luciferase reporter gene assay and validated using an innovative dual-Flag/Strep-TagII quantitative immunoblot assay. siKRT9-1 and siKRT9-3 were the most potent generic K9 inhibitors, eliciting >85% simultaneous knockdown of wild-type and mutant K9 protein synthesis at picomolar concentrations. The allele-specific inhibitors displayed similar potencies and, importantly, exhibited strong specificities for their target dominant-negative alleles with little or no effect on wild-type K9. The most promising allele-specific siRNA, siR163Q-13, was tested in a mouse model and was confirmed to preferentially inhibit mutant allele expression in vivo.     

Use of self-delivery siRNAs to inhibit gene expression in an organotypic pachyonychia congenita model

Although RNA interference offers therapeutic potential for treating skin disorders, delivery hurdles have hampered clinical translation. We have recently demonstrated that high pressure, resulting from intradermal injection of large liquid volumes, facilitated nucleic acid uptake by keratinocytes in mouse skin. Furthermore, similar intradermal injections of small interfering RNA (siRNA; TD101) into pachyonychia congenita (PC) patient foot lesions resulted in improvement. Unfortunately, the intense pain associated with hypodermic needle administration to PC lesions precludes this as a viable delivery option for this disorder. To investigate siRNA uptake by keratinocytes, an organotypic epidermal model, in which pre-existing endogenous gene or reporter gene expression can be readily monitored, was used to evaluate the effectiveness of "self-delivery" siRNA (i.e., siRNA chemically modified to enhance cellular uptake). In this model system, self-delivery siRNA treatment resulted in reduction of pre-existing fluorescent reporter gene expression under conditions in which unmodified controls had little or no effect. Additionally, treatment of PC epidermal equivalents with self-delivery "TD101" siRNA resulted in marked reduction of mutant keratin 6a mRNA with little or no effect on wild-type expression. These results indicate that chemical modification of siRNA may overcome certain limitations to transdermal delivery (specifically keratinocyte uptake) and may have clinical utility for inhibition of gene expression in the skin.     

Development of therapeutic siRNAs for pachyonychia congenita

Pachyonychia congenita (PC) is an autosomal-dominant keratin disorder where the most painful, debilitating aspect is plantar keratoderma. PC is caused by mutations in one of four keratin genes; however, most patients carry K6a mutations. Knockout mouse studies suggest that ablation of one of the several K6 genes can be tolerated owing to compensatory expression of the others. Here, we have developed potent RNA interference against K6a as a paradigm for treating a localized dominant skin disorder. Four small interfering RNAs (siRNAs) were designed against unique sequences in the K6a 3'-untranslated region. We demonstrated near-complete ablation of endogenous K6a protein expression in two keratinocyte cell lines, HaCaT and NEB-1, by transient transfection of each of the four K6a siRNAs. The siRNAs were effective at very low, picomolar concentrations. One potent lead K6a inhibitor, which was highly specific for K6a, was tested in a mouse model where reporter gene constructs were injected intradermally into mouse paw and luciferase activity was used as an in vivo readout. Imaging in live mice using the Xenogen IVIS system demonstrated that the K6a-specific siRNA strongly inhibited bicistronic K6a-luciferase gene expression in vivo. These data suggest that siRNAs can specifically and very potently target mutated genes in the skin and support development of these inhibitors as potential therapeutics.     

Therapeutic siRNAs for dominant genetic skin disorders including pachyonychia congenita

The field of science and medicine has experienced a flood of data and technology associated with the human genome project. Over 10,000 human diseases have been genetically defined, but little progress has been made with respect to the clinical application of this knowledge. A notable exception to this exists for pachyonychia congenita (PC), a rare, dominant-negative keratin disorder. The establishment of a non-profit organization, PC Project, has led to an unprecedented coalescence of patients, scientists, and physicians with a unified vision of developing novel therapeutics for PC. Utilizing the technological by-products of the human genome project, such as RNA interference (RNAi) and quantitative RT-PCR (qRT-PCR), physicians and scientists have collaborated to create a candidate siRNA therapeutic that selectively inhibits a mutant allele of KRT6A, the most commonly affected PC keratin. In vitro investigation of this siRNA demonstrates potent inhibition of the mutant allele and reversal of the cellular aggregation phenotype. In parallel, an allele-specific quantitative real-time RT-PCR assay has been developed and validated on patient callus samples in preparation for clinical trials. If clinical efficacy is ultimately demonstrated, this "first-in-skin" siRNA may herald a paradigm shift in the treatment of dominant-negative genetic disorders.     

Small-interfering RNA targeted at antiapoptotic mRNA increases keratinocyte sensitivity to apoptosis

Background Gene silencing RNA interference technology concentrates on downregulation of gene expression using specific double‐stranded RNA molecules (small‐interfering RNA, siRNA), which induce the degradation of complementary mRNA. SiRNA therapeutics is currently being tested in several clinical trials. Skin disorders are an attractive target for siRNA‐based technology because effective agents can be delivered by topical application. In several inflammatory skin disorders, the barrier function of the skin is markedly impaired and this may increase the delivery efficiency. Psoriasis is a very common skin disorder. The characteristics of this disorder are abnormal keratinocyte proliferation and inflammation. Keratinocytes from psoriatic epidermis express much higher levels of the antiapoptotic protein, Bcl‐xL, compared with normal keratinocytes. Insulin‐like growth factor 1 receptor (IGF‐1R) plays a major role in cell growth, differentiation and apoptosis in many cell types, including keratinocytes and IGF‐1R activation plays an important role in the pathogenesis of psoriasis. Keratinocytes from patients with psoriasis are more susceptible to IGF‐1‐stimulated proliferation compared with normal keratinocytes. IGF‐1R is expressed by proliferating basal and suprabasal keratinocytes and is more abundant in psoriatic lesions. Objectives To prove the validity of IGF‐1R and Bcl‐xL as useful targets for siRNA‐based therapeutics and to deliver siRNA selectively and efficiently to primary human keratinocytes; this is a primary essential step in the development of siRNA. Methods Primary normal human keratinocytes were transfected with various siRNA molecules, and transfection efficiency was monitored by fluorescent labelling. Cell growth and apoptosis induction were evaluated in the transfected cells. Results We were able to deliver efficiently siRNA targeting Bcl‐xL or IGF‐1R to primary human keratinocyte cultures. We also showed that siRNAs targeting Bcl‐xL and IGF‐1R induce growth inhibition, apoptosis and increased sensitivity to ultraviolet B in keratinocytes. Conclusions The present findings demonstrate that Bcl‐xL and IGF‐1R are valid, important targets for siRNA‐based technology directed at the suppression of keratinocyte hyperproliferation.     

Development of a 3D pigmented skin model to evaluate RNAi-induced depigmentation

Because current skin whitening agents often have insufficient efficacy and side effects, we aim to develop effective and safe therapeutics using RNA interference (RNAi). We established a pigmented human-reconstructed skin model as a first step in the development of novel siRNA-based depigmenting agents. Histological characterization revealed that our model had a similar morphology as normal human skin, expressed keratinocyte differentiation as well as basement membrane markers, and showed a high degree of pigmentation. The utility of the model to study RNAi-induced depigmentation was validated by incorporation of melanocytes transfected with siRNA against tyrosinase, a key enzyme in skin pigmentation. This resulted in a strong reduction in pigmentation and inhibition of melanin transfer proving that siRNA-mediated gene silencing in melanocytes worked successfully in our model. Therefore, this self-made 3D skin model will be a useful and easy tool to validate the whitening potential of candidate genes with a presumed function in melanin synthesis or transfer.     

Development of allele-specific therapeutic siRNA for keratin 5 mutations in epidermolysis bullosa simplex

Epidermolysis bullosa simplex (EBS) is an incurable, inherited skin-blistering disorder predominantly caused by dominant-negative mutations in the genes encoding keratins K5 or K14. RNA interference, particularly in the form of small interfering RNA (siRNA), offers a potential therapy route for EBS and related keratin disorders by selectively silencing the mutant allele. Here, using a systemic screening system based on a luciferase reporter gene assay, we have developed mutant-specific siRNAs for two independent EBS-causing missense mutations in the K5 gene (p.Ser181Pro and p.Asn193Lys). The specificity of the allele-specific inhibitors identified in the screen was subsequently confirmed at the protein level, where the lead inhibitors were shown to strongly knock down the expression of mutant proteins with negligible effect on wild-type K5 expression. In a cell-based model system, the lead inhibitors were able to significantly reverse the cytoskeletal aggregation phenotype. Overall, this approach shows promise for the treatment of EBS and paves the way for future clinical trials.     

小干预RNA对人乳头瘤病毒6bE6基因的沉默作用

目的 探讨小干预RNA(siRNA)对稳定表达人乳头瘤病毒(HPV)6bE6基因的细胞株中靶基因的干预作用。方法 建立并筛选稳定表达靶基因HPV6bE6的阳性细胞株,分别设计同源于HPV6bE6基因的不同序列的4对siRNA,采用实时定量PCR技术检测siRNA转染前后细胞内靶mRNA的表达情况。结果 转染细胞中HPV6bE6基因表达最低有90%以上被抑制,低浓度siRNA水平(1nmol/L~150nmol/L)即能有效抑制靶基因表达,靶mRNA的沉默于转染siRNA后24h达到最强,且至少可维持4d。结论 siRNA-HPV6bE6可以高效、特异地沉默HPV6bE6基因,可能为治疗HPV6b型感染提供实验室依据。     

Melanocyte receptors: clinical implications and therapeutic relevance

The activation or the inhibition of melanocyte-specific receptors offers novel means of augmenting normal melanocyte function, skin color, and photoprotection, or treating melanocytic disorders, namely at this time, metastatic melanoma. Melanocyte-specific receptors include melanocortin-1 (MCR1) and melatonin receptors. Other receptors that play an important role in melanoma progression are G-protein couple receptors such as Frizzled 5 and receptor tyrosine kinases such as c-Kit and hepatocyte growth factor (HGF) receptor. These receptors activate two crucial cell-signaling pathways, RAS/RAF/MEK/ERK and PI3K/AKT, integral to melanoma cell survival, and can serve as targets for therapy of disseminated melanoma. Activation of death receptors is another pathway that can be exploited with targeted therapeutics to control advanced melanoma. This article reviews the current understanding of melanocyte receptors, their agonists and inhibitors, and their potential to treat the melanocytic pathology.     

A simple,noninvasive and efficient method for transdermal delivery of siRNA

Effective delivery of therapeutic agents is the most challenging hurdle in the use of RNA interference for research and in the clinic. Here, we assessed whether a short synthetic peptide, ACSSSPSKHCG (TD-1), could be transported through rat footpad (follicle-free) skin and efficiently deliver small interfering RNA (siRNA) to knock down a target gene. Fluorescence microscopy revealed that topical co-administration of FITC-labeled TD-1 and FAM-labeled siRNA distributed uniformly from the epidermis to the subcutaneous tissue of rat footpad skin. Transmission electron microscopy revealed the absence of cell–cell junctions and enlarged spaces between epithelial cells in the TD-1-treated footpad skin. TD-1 delivery of anti-GAPDH siRNA significantly reduced the level of GAPDH in 72 h. TD-1 can create a transient opening in non-follicle rat skin for delivery of siRNA and reveal a novel mechanism of transdermal delivery of TD-1 and siRNA into the epidermis for gene knockdown. The system might have potential for siRNA delivery in skin for drug therapy.     

RNA干扰对系统性硬化病皮肤成纤维细胞结缔组织生长因子表达的影响

目的 研究RNA干扰对系统性硬化病(SS)皮肤成纤维细胞结缔组织生长因子(CTGF)mRNA和蛋白表达水平的影响.方法 设计4个针对CTGF的特异性小干扰RNA(siRNA)及一个非特异性siRNA.体外转录获得siRNA,将siRNA用6-羧基荧光素(FAM)标记后瞬时转染至原代培养的SS患者皮肤成纤维细胞;转染48h后,以RT-PCR及蛋白印迹法分别检测CTGF mRNA及蛋白量的变化.结果 转染了4个特异性siRNA的成纤维细胞中CTGF mRNA水平均有不同程度下调(P<0.001),抑制效果由强至弱为,siRNA742>siRNA828>siRNA578>siRNA948.蛋白印迹则显示有3个siRNA能使CTGF蛋白表达水平不同程度下调(P<0.001),其中siRNA742的抑制效应最强.结论 RNA干扰能显著抑制SS成纤维细胞CTGF的表达.     

iRNA抑制人黑素瘤M14细胞生存素的表达

目的 通过构建生存素(survivin)的小干扰RNA(siRNA)表达质粒,研究其对人黑素瘤M14细胞生存素表达的抑制作用,为后续研究奠定基础.方法 设计有小发夹结构的生存素siRNA对应模板DNA序列,克隆至pRNAT-H1.1/neo质粒,构建重组质粒pRNAT-H1.1/neo-survivin,转染人黑素瘤M14细胞,采用逆转录-聚合酶链反应(RT-PCR)、蛋白质印迹检测生存素表达.结果 酶切及测序结果 证实重组质粒pRNAT-H1.1/neo-survivin构建成功.将重组质粒及空载体(阴性对照)转染M14细胞48 h后,siRNA处理组M14细胞生存素表达较空白对照组显著下降,表达抑制率在mRNA和蛋白水平分别为62.3%±1.5%和53.6%±0.9%.结论 生存素siRNA表达质粒pRNAT-H1.1/neo-survivin可抑制人黑素瘤M14细胞生存素的表达.     

The phenotypic and molecular genetic features of pachyonychia congenita

Pachyonychia congenita (PC) is an autosomal dominant genodermatosis caused by heterozygous mutations in any one of the genes encoding the differentiation-specific keratins K6a, K6b, K16, or K17. The main clinical features of the condition include painful and highly debilitating plantar keratoderma, hypertrophic nail dystrophy, oral leukokeratosis, and a variety of epidermal cysts. Although the condition has previously been subdivided into PC-1 and PC-2 subtypes, the phenotypic characterization of 1,000 mutation-verified PC patients enrolled in the International PC Research Registry, coordinated by the patient advocacy group PC Project, shows that there is considerable overlap between these subtypes. Thus, a new genotypic nomenclature is proposed, in which PC-6a represents a patient carrying a mutation in the K6a gene, etc. Although a rare disorder, PC represents a good model for therapy development, and international efforts are ongoing to develop and deliver siRNA, gene, correction, small molecule, and other strategies to treat this painful, disabling skin condition. The special relationship between PC Project and the PC research community has greatly accelerated the development pathway from gene identification to clinical trials in only a few years and represents a paradigm of hope for other orphan diseases.     

Inhibition of keratin 17 expression with antisense and RNAi strategies: exploring novel therapy for psoriasis

Psoriasis is now considered to be a chronic, immune-mediated and inflammatory skin disease. As the precise cause of psoriasis remains unknown, its treatment is challenging for dermatologists. Keratin 17 (K17), an intermediate filament protein, is highly expressed in psoriatic lesions, while not normally expressed in healthy epidermis. Studies have suggested that K17 plays a role in the pathogenesis of psoriasis. However, no study has been performed to determine the potential application of K17 down-regulation as a treatment option for psoriatic lesions. We hypothesized that anti-K17 interference may suppress the development and progression of psoriasis and potentially serve as a novel strategy for the treatment of psoriasis. Therefore, we down-regulated and silenced K17 gene expression in keratinocytes (KCs) using antisense and RNA interference (RNAi) techniques. We found that K17-specific antisense oligonucleotides (ASODN) or siRNAs inhibited proliferation and induced apoptosis in KCs as well as down-regulated K17 expression at both mRNA and protein levels. For our in vivo study, we constructed the SCID-hu xenogeneic transplantation psoriasis mouse model by grafting psoriatic lesions onto SCID mice and topically applied K17-specific ASODN and liposome-encapsulated siRNA to the grafts. We observed morphological and histological improvement in the treated psoriatic grafts. As a result, K17 mRNA and protein expression was significantly decreased in the grafts of the mouse model. Taken together, we conclude that anti-K17 therapy is an effective treatment option for psoriasis, and the K17 molecule, as a new target, may hold tremendous potential for the treatment of psoriasis in the future.     

In vivo imaging of human and mouse skin with a handheld dual-axis confocal fluorescence microscope

Advancing molecular therapies for the treatment of skin diseases will require the development of new tools that can reveal spatiotemporal changes in the microanatomy of the skin and associate these changes with the presence of the therapeutic agent. For this purpose, we evaluated a handheld dual-axis confocal (DAC) microscope that is capable of in vivo fluorescence imaging of skin, using both mouse models and human skin. Individual keratinocytes in the epidermis were observed in three-dimensional image stacks after topical administration of near-infrared (NIR) dyes as contrast agents. This suggested that the DAC microscope may have utility in assessing the clinical effects of a small interfering RNA (siRNA)-based therapeutic (TD101) that targets the causative mutation in pachyonychia congenita (PC) patients. The data indicated that (1) formulated indocyanine green (ICG) readily penetrated hyperkeratotic PC skin and normal callused regions compared with nonaffected areas, and (2) TD101-treated PC skin revealed changes in tissue morphology, consistent with reversion to nonaffected skin compared with vehicle-treated skin. In addition, siRNA was conjugated to NIR dye and shown to penetrate through the stratum corneum barrier when topically applied to mouse skin. These results suggest that in vivo confocal microscopy may provide an informative clinical end point to evaluate the efficacy of experimental molecular therapeutics.     

Keratin 17 as a therapeutic target for the treatment of psoriasis

Keratin 17 (K17) is the only ectopically expressed keratin in psoriatic lesional epidermis. This review focuses mainly on reports that have addressed the mechanism of K17 up-regulation and its biological role in psoriasis. In addition to IFN-γ, IL-17A and IL-22, which are derived from Th17 and Th22 cells, could up-regulate K17 mRNA and protein levels in keratinocytes in a dose-dependent manner. Moreover, these effects are partially blocked with STAT1- and STAT3-specific inhibitors, as well as small interfering RNA (siRNA) targeting STAT1 and STAT3. On the other hand, the HLA DRB1*04 and/or *07 positive patients show significant T cell responses to two peptides from K17 protein selected on the basis of predicted HLA DRB1*04 and/or *07 bindings. One peptide contains the ALEEAN sequence, while the other peptide has an amino acid sequence that has not been previously reported. Analysis of these processes led us to propose the existence of a K17/T cells/cytokine autoimmune loop, in which ectopically expressed K17 impacts on the maintenance of psoriasis by activating autoreactive T cells. Furthermore, it has been found that altered peptide ligands, which are produced through single alanine residue substitutions at a critical TCR contact position, abolish the T cell proliferation and IFN-γ production induced by K17 pathogenic peptides. K17-specific antisense ODNs and RNAi suppress K17 mRNA and protein expression in psoriatic skin in vivo, which coincides with marked clinical and histological improvement. These findings highlight K17 as an attractive target for novel therapies aimed at curtailing psoriasis driven by chronic inflammation.     

The anti‐apoptotic protein G1P3 is overexpressed in psoriasis and regulated by the non‐coding RNA,PRINS

Please cite this paper as: The anti‐apoptotic protein G1P3 is overexpressed in psoriasis and regulated by the non‐coding RNA, PRINS. Experimental Dermatology 2010; 19: 269–278. Abstract: Psoriasis Susceptibility‐Related RNA Gene Induced by Stress (PRINS) is a non‐coding RNA overexpressed in lesional and non‐lesional psoriatic epidermis and induced by stress. Its function in healthy and psoriatic skin is still not known. Here, we report that PRINS regulates G1P3, a gene with anti‐apoptotic effects in keratinocytes. siRNA‐mediated inhibition of PRINS gene resulted in altered cell morphology and gene expression alterations, as demonstrated in a microarray experiment. One of the genes regulated by PRINS ncRNA was G1P3, an interferon‐inducible gene with anti‐apoptotic effects in cancer cells. Interestingly, we found that G1P3 was 400‐fold upregulated in hyperproliferative lesional and ninefold upregulated in non‐lesional psoriatic epidermis compared to healthy epidermis. In vitro, G1P3 protein levels were highest in proliferating keratinocytes and siRNA‐mediated downregulation of G1P3 resulted in increased cell apoptosis. These data indicate that G1P3 inhibits spontaneous keratinocyte apoptosis and hence its high expression in psoriatic skin may contribute to the development of psoriatic lesions. We hypothesize that the deregulation of the PRINS ncRNA may contribute to psoriasis and results in decreased sensitivity to spontaneous keratinocyte apoptosis via the regulation of G1P3.     

Epidermal growth factor-induced matrix metalloproteinase-1 expression is negatively regulated by p38 MAPK in human skin fibroblasts

Background

Many extracellular stimuli, including epidermal growth factor (EGF), are known to induce MMP-1 expression. Recently, several reports have shown that ERK activity plays an important role in EGF-induced MMP-1 expression. However, EGF is also known to activate many signaling pathways in addition to the ERK pathway, but the roles of these pathways during the induction of MMP-1 by EGF are unclear.

Objective

We investigated the role of JNK, p38 MAPK, and PI3K/Akt pathways in EGF-induced MMP-1 expression in human skin fibroblasts. Then, we further explored the inhibitory effect of p38 MAPK pathway on EGF-induced MMP-1 expression and studied the molecular mechanisms involved in the processes.

Methods

Human skin fibroblasts were pretreated with various chemical inhibitors or small interfering RNA (siRNA) at the indicated concentrations and then treated with EGF, TNF-alpha, or IL-1beta for the indicated times. Protein and mRNA levels of various target molecules were assessed by Western blotting and quantitative real-time PCR, respectively.

Results

We found that EGF-induced MMP-1 expression was positively regulated by JNK as well as ERK but negatively regulated by p38 MAPK in human skin fibroblasts. On the other hand, the PI3K/Akt pathway did not significantly affect MMP-1 induction by EGF. Then we found that the inhibition of p38 MAPK pathway specifically increased the MMP-1 expression stimulated by EGF but not by TNF-alpha or IL-1beta, indicating that the effect of p38 MAPK on MMP-1 expression may be stimulus-type specific in human skin fibroblasts. In addition, the inhibitory effect of p38 MAPK on EGF-induced MMP-1 expression was shown to be mainly mediated by p38-alpha MAPK. Our further studies showed that the inhibition of p38 MAPK but not PI3K specifically increased EGF-induced ERK and JNK activations, and that the augmentation of EGF-induced MMP-1 expression by p38 MAPK inhibition was significantly attenuated by inhibiting the activities of ERK and/or JNK.

Conclusions

Our results indicate that EGF-induced MMP-1 expression is differentially regulated by the JNK, p38 MAPK, and PI3K/Akt pathways, and suggest that p38 MAPK negatively regulates EGF-induced MMP-1 expression by suppressing the activations of ERK and JNK.