Skinly: A novel handheld IoT device for validating biophysical skin characteristics

BACKGROUND

Recent advancements in artificial intelligence have revolutionized dermatological diagnostics. These technologies, particularly machine learning (ML), including deep learning (DL), have shown accuracy equivalent or even superior to human experts in diagnosing skin conditions like melanoma. With the integration of ML, including DL, the development of at home skin analysis devices has become feasible. To this end, we introduced the Skinly system, a handheld device capable of evaluating various personal skin characteristics noninvasively.

MATERIALS AND METHODS

Equipped with a moisture sensor and a multi-light-source camera, Skinly can assess age-related skin parameters and specific skin properties. Utilizing state-of-the-art DL, Skinly processed vast amounts of images efficiently. The Skinly system's efficacy was validated both in the lab and at home, comparing its results to established "gold standard" methods.

RESULTS

Our findings revealed that the Skinly device can accurately measure age-associated parameters, that is, facial age, skin evenness, and wrinkles. Furthermore, Skinly produced data consistent with established devices for parameters like glossiness, skin tone, redness, and porphyrin levels. A separate study was conducted to evaluate the effects of two moisturizing formulations on skin hydration in laboratory studies with standard instrumentation and at home with Skinly.

CONCLUSION

Thanks to its capability for multi-parameter measurements, the Skinly device, combined with its smartphone application, holds the potential to replace more expensive, time-consuming diagnostic tools. Collectively, the Skinly device opens new avenues in dermatological research, offering a reliable, versatile tool for comprehensive skin analysis.

Development of an epigenetic clock to predict visual age progression of human skin

Aging is a complex process characterized by the gradual decline of physiological functions, leading to increased vulnerability to age-related diseases and reduced quality of life. Alterations in DNA methylation (DNAm) patterns have emerged as a fundamental characteristic of aged human skin, closely linked to the development of the well-known skin aging phenotype. These changes have been correlated with dysregulated gene expression and impaired tissue functionality. In particular, the skin, with its visible manifestations of aging, provides a unique model to study the aging process. Despite the importance of epigenetic age clocks in estimating biological age based on the correlation between methylation patterns and chronological age, a second-generation epigenetic age clock, which correlates DNAm patterns with a particular phenotype, specifically tailored to skin tissue is still lacking. In light of this gap, we aimed to develop a novel second-generation epigenetic age clock explicitly designed for skin tissue to facilitate a deeper understanding of the factors contributing to individual variations in age progression. To achieve this, we used methylation patterns from more than 370 female volunteers and developed the first skin-specific second-generation epigenetic age clock that accurately predicts the skin aging phenotype represented by wrinkle grade, visual facial age, and visual age progression, respectively. We then validated the performance of our clocks on independent datasets and demonstrated their broad applicability. In addition, we integrated gene expression and methylation data from independent studies to identify potential pathways contributing to skin age progression. Our results demonstrate that our epigenetic age clock, VisAgeX, specifically predicting visual age progression, not only captures known biological pathways associated with skin aging, but also adds novel pathways associated with skin aging.

Methylation profiling identifies two subclasses of squamous cell carcinoma related to distinct cells of origin

Cutaneous squamous cell carcinoma (cSCC) is the second most common skin cancer and usually progresses from a UV-induced precancerous lesion termed actinic keratosis (AK). Despite various efforts to characterize these lesions molecularly, the etiology of AK and its progression to cSCC remain partially understood. Here, we use Infinium MethylationEPIC BeadChips to interrogate the DNA methylation status in healthy, AK and cSCC epidermis samples. Importantly, we show that AK methylation patterns already display classical features of cancer methylomes and are highly similar to cSCC profiles. Further analysis identifies typical features of stem cell methylomes, such as reduced DNA methylation age, non-CpG methylation, and stem cell-related keratin and enhancer methylation patterns. Interestingly, this signature is detected only in half of the samples, while the other half shows patterns more closely related to healthy epidermis. These findings suggest the existence of two subclasses of AK and cSCC emerging from distinct keratinocyte differentiation stages.

An integrative metabolomics and transcriptomics study to identify metabolic alterations in aged skin of humans in vivo

Background

Aging human skin undergoes significant morphological and functional changes such as wrinkle formation, reduced wound healing capacity, and altered epidermal barrier function. Besides known age-related alterations like DNA-methylation changes, metabolic adaptations have been recently linked to impaired skin function in elder humans. Understanding of these metabolic adaptations in aged skin is of special interest to devise topical treatments that potentially reverse or alleviate age-dependent skin deterioration and the occurrence of skin disorders.

Results

We investigated the global metabolic adaptions in human skin during aging with a combined transcriptomic and metabolomic approach applied to epidermal tissue samples of young and old human volunteers. Our analysis confirmed known age-dependent metabolic alterations, e.g. reduction of coenzyme Q10 levels, and also revealed novel age effects that are seemingly important for skin maintenance. Integration of donor-matched transcriptome and metabolome data highlighted transcriptionally-driven alterations of metabolism during aging such as altered activity in upper glycolysis and glycerolipid biosynthesis or decreased protein and polyamine biosynthesis. Together, we identified several age-dependent metabolic alterations that might affect cellular signaling, epidermal barrier function, and skin structure and morphology.

Conclusions

Our study provides a global resource on the metabolic adaptations and its transcriptional regulation during aging of human skin. Thus, it represents a first step towards an understanding of the impact of metabolism on impaired skin function in aged humans and therefore will potentially lead to improved treatments of age related skin disorders.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3547-3) contains supplementary material, which is available to authorized users.

Acute Activation of Oxidative Pentose Phosphate Pathway as First-Line Response to Oxidative Stress in Human Skin Cells

Integrity of human skin is endangered by exposure to UV irradiation and chemical stressors, which can provoke a toxic production of reactive oxygen species (ROS) and oxidative damage. Since oxidation of proteins and metabolites occurs virtually instantaneously, immediate cellular countermeasures are pivotal to mitigate the negative implications of acute oxidative stress. We investigated the short-term metabolic response in human skin fibroblasts and keratinocytes to H2O2 and UV exposure. In time-resolved metabolomics experiments, we observed that within seconds after stress induction, glucose catabolism is routed to the oxidative pentose phosphate pathway (PPP) and nucleotide synthesis independent of previously postulated blocks in glycolysis (i.e., of GAPDH or PKM2). Through ultra-short (13)C labeling experiments, we provide evidence for multiple cycling of carbon backbones in the oxidative PPP, potentially maximizing NADPH reduction. The identified metabolic rerouting in oxidative and non-oxidative PPP has important physiological roles in stabilization of the redox balance and ROS clearance.

Quantification of cyclobutane pyrimidine dimers in human epidermal stem cells

The common procedures that are used to quantify cyclobutane pyrimidine dimers (CPD) comprise the extraction of cellular DNA followed by the detection of this nucleic acid modification by immunoblotting or electrophoretic methods. Consequently, these approaches provide an averaged damage intensity value of a whole population of cells and are not applicable to studies where a small subgroup such as somatic stem cells are intended to be investigated and the individual cellular damage is of interest. Here, we describe a strategy to isolate epidermal stem cells from minimum human epidermis samples and a subsequent immunocytochemical quantification of cellular CPDs. Besides the determination of the DNA damage status, this technique allows for the examination of cellular CPD intensity distributions.

The matricellular protein periostin contributes to proper collagen function and is downregulated during skin aging

BACKGROUND

Periostin is a secreted 90kDa matricellular protein, which is predominantly expressed in collagen-rich tissues. Collagen is the most abundant protein in mammals and has great tensile strength. Recent investigations have shown that periostin influences collagen fibrillogenesis and biomechanical properties of murine connective tissues.

OBJECTIVE

We investigated the function of periostin concerning collagen homeostasis during intrinsic and extrinsic skin aging. For this purpose, human skin samples of young and old donors as well as samples of photoaged and sun-protected skin areas were analyzed for periostin expression. Using in vitro models, we determined the cell types responsible for periostin expression and performed functional analyses with periostin knockdown cells.

METHODS

TaqMan Real-Time PCR, UV irradiation, knockdown experiments, immunostaining, electron microscopy, collagen degradation assay, collagen crosslink analysis.

RESULTS

Periostin expression is highest in the papillary dermis and downregulated during skin aging. Fibroblasts and non-follicular skin derived precursors were identified as main source for periostin expression in human skin. Periostin knockdown in fibroblasts has no effect on collagen expression, but results in an increased fibril diameter and aberrant collagen structure. This leads to an increased susceptibility of collagen toward proteases, whereas recombinant periostin protects collagen fibrils from degradation.

CONCLUSION

Our data show that periostin plays an important role for proper collagen assembly and homeostasis. During skin aging periostin expression decreases and contributes to the phenotype of aged skin.

MicroRNA profiling during human keratinocyte differentiation using a quantitative real-time PCR method

The terminal differentiation of epidermal keratinocytes requires transcriptional and posttranscriptional regulatory mechanisms. MicroRNAs (miRNAs) are small noncoding RNAs that play key roles during differentiation processes by regulating protein expression at the posttranscriptional level. Several studies have investigated miRNA expression in murine or human skin using northern blotting, microarrays, deep sequencing, or real-time PCR (Andl et al., Curr Biol 16:1041-1049, 2006; Hildebrand et al., J Invest Dermatol 131:20-29, 2011; Sonkoly et al., PLoS One 2:e610, 2007; Yi et al., Nat Genet 38:356-362, 2006; Yi et al., Proc Natl Acad Sci U S A 106:498-502, 2009). Conventional techniques such as northern blotting and microarrays often fail to detect miRNAs of low abundance, while the per-sample cost of deep sequencing approaches is still prohibitive in many cases. In contrast, stem loop primer-based real-time PCR methods for simultaneous detection of up to 380 miRNAs allow fast, specific, and reliable miRNA profiling. These methods are suitable for in vitro material, but also for samples which are of limited availability, such as epidermal stem cells isolated from human skin biopsies. Here, we describe a general real-time PCR method for miRNA profiling using isolated epidermal stem cells, transiently amplifying cells and terminally differentiated keratinocytes of human skin.

Dermal penetration of creatine from a face-care formulation containing creatine, guarana and glycerol is linked to effective antiwrinkle and antisagging efficacy in male subjects

BACKGROUND

  The dermal extracellular matrix provides stability and structure to the skin. With increasing age, however, its major component collagen is subject to degeneration, resulting in a gradual decline in skin elasticity and progression of wrinkle formation. Previous studies suggest that the reduction in cellular energy contributes to the diminished synthesis of cutaneous collagen during aging.

AIMS

  To investigate the potential of topically applied creatine to improve the clinical signs of skin aging by stimulating dermal collagen synthesis in vitro and in vivo.

PATIENTS/METHODS

  Penetration experiments were performed with a pig skin ex vivo model. Effects of creatine on dermal collagen gene expression and procollagen synthesis were studied in vitro using cultured fibroblast-populated collagen gels. In a single-center, controlled study, 43 male Caucasians applied a face-care formulation containing creatine, guarana extract, and glycerol to determine its influence on facial topometric features.

RESULTS

  Cultured human dermal fibroblasts supplemented with creatine displayed a stimulation of collagen synthesis relative to untreated control cells both on the gene expression and at the protein level. In skin penetration experiments, topically applied creatine rapidly reached the dermis. In addition, topical in vivo application of a creatine-containing formulation for 6 weeks significantly reduced the sagging cheek intensity in the jowl area as compared to baseline. This result was confirmed by clinical live scoring, which also demonstrated a significant reduction in crow's feet wrinkles and wrinkles under the eyes.

CONCLUSIONS

  In summary, creatine represents a beneficial active ingredient for topical use in the prevention and treatment of human skin aging.

Approach to quantify human dermal skin aging using multiphoton laser scanning microscopy

Extracellular skin structures in human skin are impaired during intrinsic and extrinsic aging. Assessment of these dermal changes is conducted by subjective clinical evaluation and histological and molecular analysis. We aimed to develop a new parameter for the noninvasive quantitative determination of dermal skin alterations utilizing the high-resolution three-dimensional multiphoton laser scanning microscopy (MPLSM) technique. To quantify structural differences between chronically sun-exposed and sun-protected human skin, the respective collagen-specific second harmonic generation and the elastin-specific autofluorescence signals were recorded in young and elderly volunteers using the MPLSM technique. After image processing, the elastin-to-collagen ratio (ELCOR) was calculated. Results show that the ELCOR parameter of volar forearm skin significantly increases with age. For elderly volunteers, the ELCOR value calculated for the chronically sun-exposed temple area is significantly augmented compared to the sun-protected upper arm area. Based on the MPLSM technology, we introduce the ELCOR parameter as a new means to quantify accurately age-associated alterations in the extracellular matrix.

Damage at the root of cell renewal--UV sensitivity of human epidermal stem cells

BACKGROUND

The epidermis harbors adult stem cells that reside in the basal layer and ensure the continuous maintenance of tissue homeostasis. Various studies imply that stem cells generally possess specific defense mechanisms against several forms of exogenous stress factors. As sun exposition is the most prevalent impact on human skin, this feature would be of particular importance in terms of sensitivity to UV-induced DNA damage.

OBJECTIVE

To investigate whether human epidermal stem cells are susceptible to UV-induced DNA damage and subsequent functional impairment.

METHODS

A method to isolate human epidermal stem cells from suction blister epidermis was established and validated. Volunteers were treated with solar-simulated irradiation on test areas of the forearm and stem cells were isolated from suction blister material of this region. DNA damage was analyzed by staining for cyclobutane thymidine dimers. The functional consequences of UV-induced damages were assessed by colony forming efficiency assays and gene expression analyses.

RESULTS

Compared to an unirradiated control, stem cells isolated from areas that were exposed to solar-simulated radiation showed significantly more DNA lesions. Although the number of stem cells was not reduced by this treatment, a functional impairment of stem cells could be shown by reduced colony forming efficiency and altered gene expression of stem cell markers.

CONCLUSIONS

Despite their essential role in skin maintenance, epidermal stem cells are sensitive to physiological doses of UV irradiation in vivo.

Impact of collagen crosslinking on the second harmonic generation signal and the fluorescence lifetime of collagen autofluorescence

BACKGROUND/PURPOSE

Collagen is the major structural protein of the skin and its crosslinks are essential for its mechanical stability. In photodamaged skin, a decrease of the mature collagen crosslink histidinohydroxylysino-norleucine was reported. In this study, we investigated the consequences and measurability of the reduced crosslinking.

METHODS

In order to determine the consequences of reduced collagen crosslinking, in vitro models of reduced collagen crosslinking were established. The collagen synthesis and structure was analyzed using the signals second harmonic generation (SHG) and the fluorescence lifetime of the collagen autofluorescence by a multiphoton laser scanning microscope.

RESULTS

Reduced collagen crosslinking results in a posttranscriptionally diminished collagen synthesis, a modified structure of the collagen fibers and fibrils and a higher intensity of the SHG signal. The SHG signal might be influenced by the interspaces of the collagen molecules within one collagen fibril. Because of these findings, it can be speculated that reduced collagen crosslinking changes the interspace of single collagen molecules within the collagen fibril, resulting in an enhanced SHG signal. Alternative explanations are discussed. Furthermore, the fluorescence lifetime was reduced in the in vitro models of reduced collagen crosslinking. In the crosslink sites of the collagen molecules, the main ratio of fluorescence is found. As the fluorescence lifetime is determined not only by the fluorescent molecule itself but also by its microenvironment, the change in the fluorescence lifetime might be explained by reduced crosslinking at the crosslink site.

CONCLUSION

A reduction of collagen crosslinking (as seen in photodamaged skin) results in an increase of the SHG signal and a decrease of the fluorescence lifetime in vitro. In vivo measurements of the two parameters might reveal the status of collagen crosslinking and therefore help to identify the status of dermal photodamage or pathogenesis using collagen crosslinking determination.

A comprehensive analysis of microRNA expression during human keratinocyte differentiation in vitro and in vivo

Here, we report a comprehensive investigation of changes in microRNA (miRNA) expression profiles on human keratinocyte (HK) differentiation in vitro and in vivo. We have monitored expression patterns of 377 miRNAs during calcium-induced differentiation of primary HKs, and have compared these patterns with miRNA expression profiles of epidermal stem cells, transient amplifying cells, and terminally differentiated HKs from human skin. Apart from the previously described miR-203, we found an additional nine miRNAs (miR-23b, miR-95, miR-210, miR-224, miR-26a, miR-200a, miR-27b, miR-328, and miR-376a) that are associated with HK differentiation in vitro and in vivo. In situ hybridization experiments confirmed miR-23b as a marker of HK differentiation in vivo. Additionally, gene ontology analysis and functional validation of predicted miRNA targets using 3'-untranslated region-luciferase assays suggest that multiple miRNAs that are upregulated on HK differentiation cooperate to regulate gene expression during skin development. Our results thus provide the basis for further analysis of miRNA functions during epidermal differentiation.

White Tea extract induces lipolytic activity and inhibits adipogenesis in human subcutaneous (pre)-adipocytes

BACKGROUND

The dramatic increase in obesity-related diseases emphasizes the need to elucidate the cellular and molecular mechanisms underlying fat metabolism. To investigate how natural substances influence lipolysis and adipogenesis, we determined the effects of White Tea extract on cultured human subcutaneous preadipocytes and adipocytes.

METHODS

For our in vitro studies we used a White Tea extract solution that contained polyphenols and methylxanthines. Utilizing cultured human preadipocytes we investigated White Tea extract solution-induced inhibition of triglyceride incorporation during adipogenesis and possible effects on cell viability. In vitro studies on human adipocytes were performed aiming to elucidate the efficacy of White Tea extract solution to stimulate lipolytic activity. To characterize White Tea extract solution-mediated effects on a molecular level, we analyzed gene expression of essential adipogenesis-related transcription factors by qRT-PCR and determined the expression of the transcription factor ADD1/SREBP-1c on the protein level utilizing immunofluorescence analysis.

RESULTS

Our data show that incubation of preadipocytes with White Tea extract solution significantly decreased triglyceride incorporation during adipogenesis in a dose-dependent manner (n = 10) without affecting cell viability (n = 10). These effects were, at least in part, mediated by EGCG (n = 10, 50 μM). In addition, White Tea extract solution also stimulated lipolytic activity in adipocytes (n = 7). Differentiating preadipocytes cultivated in the presence of 0.5% White Tea extract solution showed a decrease in PPARγ, ADD1/SREBP-1c, C/EBPα and C/EBPδ mRNA levels. Moreover, the expression of the transcription factor ADD1/SREBP-1c was not only decreased on the mRNA but also on the protein level.

CONCLUSION

White Tea extract is a natural source that effectively inhibits adipogenesis and stimulates lipolysis-activity. Therefore, it can be utilized to modulate different levels of the adipocyte life cycle.

Deregulation of versican and elastin binding protein in solar elastosis

Several changes in skin appearance including loss of elasticity and wrinkle formation are associated with alterations in the composition of the dermal extracellular matrix. They are induced by intrinsic aging or by environmental factors such as UV light referred to as photoaging. A general characteristic in the histology of photoaged skin is the accumulation of elastotic material suggesting impaired formation and/or massive breakdown of elastic fibres. In order to shed light on some of the underlying mechanisms we tracked two of the major players in elastic fibre formation in different skin conditions: EBP (elastin binding protein), a regulator of elastic fibre assembly and VER (versican), a component of functional elastic fibres as well as non-functional elastotic material. Using quantitative RT-PCR on skin biopsies we found that the expression levels of VER and EBP were unaltered during intrinsic skin aging. Upon acute UV stress however, VER and EBP showed different regulation patterns: VER mRNA increased after 6 h and was further up-regulated until 24 h. The EBP mRNA by contrast was reduced after 6 h but showed massive induction at 24 h after acute UV stress. In chronically sun-exposed skin, VER protein was accumulated similar to elastotic material in the extracellular space, whereas its mRNA level was consistently reduced compared to sun-protected skin. The EBP mRNA by contrast showed slightly increased expression levels in the sun-exposed area compared to its sun-protected counterpart. Based on these data we propose a model which may help to explain parts of the mechanisms leading to the formation of elastotic masses. We further hypothesize that the presence of elastotic material triggers some yet unknown feedback mechanism(s) resulting in altered expression patterns of VER and EBP in chronically sun-exposed skin.

The influence of folic acid depletion on the Nucleotide Excision Repair capacity of human dermal fibroblasts measured by a modified Host Cell Reactivation Assay

Animal and human studies have shown that low levels of folic acid are associated with an impaired DNA Repair Capacity (DRC) and an increased cancer risk. However, the molecular evidence that folic acid enhances the DRC of cultured human cells is still limited because of a paucity of in vitro studies. We investigated the effect of folic acid depletion in vitro on the DRC of human dermal fibroblasts derived from 17 donors of different ages. To assess the cellular Nucleotide Excision DRC, we used a modified Host Cell-Reactivation Assay (HCRA), adapted to the Fluorescence Activated Cell Sorting (FACS)-technology, which is highly sensitive in comparison to luminometer-technology and allows single cell based analysis. We used DsRed as a reporter (irradiated with UVC light) and pEGFP to control the performance of the transformations. Folic acid had a statistically significant effect on the DRC in all of the 17 donors, however, the levels varied considerably between individuals (2.0-19.6%). When the effect of folic acid substituted on the DRC was compared to donor age, we observed that there was less DNA repair in old donors compared to the younger donors, although this was only significant at lower levels.

Expression of decorin and collagens I and III in different layers of human skin in vivo: a laser capture microdissection study

Extracellular matrix (ECM) organization is a complex process that requires the coordinated efforts of many molecules. For the regulation of collagen fiber diameter, the proteoglycan decorin appears to be of major relevance. To investigate the role of decorin in the process of (photo-)aging in more detail, full-thickness punch biopsies were isolated from human buttock skin. Single exposure with two minimal erythemal doses of solar simulated irradiation caused down-regulation of decorin mRNA in young (n = 5) and old subjects (n = 5) after 24 h. Interestingly, decorin mRNA was elevated with age. To test the hypothesis that a decreased collagen-to-decorin-ratio impairs collagen structure we also investigated collagens I and III gene expression. Both were down-regulated with increasing age and after single UV-irradiation. As determined by laser capture microdissection-quantitative real time-Polymerase chain reaction (n = 11), decorin is mostly present in the reticular dermis while being absent from the papillary dermis. Minor expression was also observed in the epidermis. However, in contrast to full-thickness skin biopsies age-dependent changes in collagens I, III, and decorin expression could not be observed with this methodology indicating technical limitations. Together with our finding that collagens I and III mRNA are similarly expressed in the reticular and papillary dermis and are down-regulated by UV, our studies support the idea of a major role of decorin in ECM organization. Altered expression of decorin mRNA in the different dermal strata and a decrease in the collagen-to-decorin ratio inflicted by both age and ultraviolet irradiation possibly affect collagen bundle diameter and subsequently the mechanical properties of human skin.

Novel aspects of intrinsic and extrinsic aging of human skin: beneficial effects of soy extract

Biochemical and structural changes of the dermal connective tissue substantially contribute to the phenotype of aging skin. To study connective tissue metabolism with respect to ultraviolet (UV) exposure, we performed an in vitro (human dermal fibroblasts) and an in vivo complementary DNA array study in combination with protein analysis in young and old volunteers. Several genes of the collagen metabolism such as Collagen I, III and VI as well as heat shock protein 47 and matrix metalloproteinase-1 are expressed differentially, indicating UV-mediated effects on collagen expression, processing and degradation. In particular, Collagen I is time and age dependently reduced after a single UV exposure in human skin in vivo. Moreover, older subjects display a lower baseline level and a shorter UV-mediated increase in hyaluronan (HA) levels. To counteract these age-dependent changes, cultured fibroblasts were treated with a specific soy extract. This treatment resulted in increased collagen and HA synthesis. In a placebo-controlled in vivo study, topical application of an isoflavone-containing emulsion significantly enhanced the number of dermal papillae per area after 2 weeks. Because the flattening of the dermal-epidermal junction is the most reproducible structural change in aged skin, this soy extract appears to rejuvenate the structure of mature skin.

Elevated blood pressure in normotensive rats produced by ‘knockdown’ of the angiotensin type 2 receptor

Most of our knowledge of the function of the angiotensin type 2 receptor (AT(2)R) has been obtained from transgenic mouse models. The aim of the present study was to investigate the role of the AT(2)R in normotensive Sprague-Dawley (SD) rats by using antisense gene transfer technology to 'knockdown' this specific receptor subtype. A retroviral vector containing full-length AT(2)R antisense cDNA (AT(2)R-AS) was constructed and the effectiveness of the transduction of AT(2)R-AS was studied in vitro. In subsequent in vivo studies, 5-day-old normotensive SD rats received a single intracardiac bolus (25 microl) of AT(2)R-AS viral particles. When animals reached adulthood, direct blood pressure (BP), and both pressor and dipsogenic responses to angiotensin II were investigated. Long-lasting expression of the AT(2)R-AS transcript and a reduction in mRNA and binding of the AT(2)R was observed in vitro. Expression of AT(2)R-AS transcript was maintained for 90 days in heart, kidney, lung and brain, indicating a high degree of transgene transduction in vivo. As adults, systolic BP and the pressor responses to angiotensin were significantly elevated in AT(2)R-AS-treated rats. However, AT(2)R-AS-treated rats displayed significantly reduced dipsogenic responses to both angiotensin and water deprivation. Collectively, these data demonstrate that a single neonatal injection of the retroviral vector containing antisense to the AT(2) receptors in rats results in similar cardiovascular and dipsogenic responses as reported in AT(2)R knockout mice. The actions of the AT(2) receptors appear to be antagonistic to the cardiovascular actions of the AT(1) receptors, whereas AT(1) and AT(2) receptors appear to act synergistically in the regulation of water intake.

Tight control of matrix metalloproteinase-1 activity in human skin

Chronic ultraviolet irradiation leads to photoaging in human skin, which is associated with degradation of connective tissue. This is partly due to the fibroblast collagenase (matrix metalloproteinase 1 [MMP-1]). Using complementary DNA array technique we demonstrate that after UV irradiation, MMP-1, MMP-3 and the tissue inhibitor of matrix metalloproteinase 1 (TIMP-1) are time-dependently induced on the messenger RNA level in dermal fibroblasts in vitro and in vivo in human buttock skin. This increase in gene expression is paralleled by an increase of latent and active MMP-1 protein after low-dose UV-A exposure in vitro. In vivo the concentration of latent MMP-1 in suction blister fluids peaks 24 h after irradiation with 2 minimal erythema doses of solar simulated radiation. However, only a small proportion of MMP-1 in vitro (5.5 +/- 1.5%) and in vivo is active, whereas the majority of MMP-1 remains in its inactive proform. Interestingly, in suction blister fluid the concentration and duration of TIMP-1 expression exceeds that of MMP-1. Taken together, these data indicate that MMP-1 activity is tightly regulated transcriptionally and posttranscriptionally. Furthermore, the pronounced individual differences in all targets investigated provide a possible explanation for the different susceptibility of individuals to UV exposure and, thus, to the clinical features of photodamage.

Angiotensin AT2 receptor ligands: do they have potential as future treatments for neurological disease?

In addition to the systemic renin-angiotensin system (RAS), a local RAS has been identified. Recent research has focused on this latter system and has investigated the effects of locally generated angiotensin II, especially in the kidney, heart and CNS. In the mammalian brain, all components of the RAS are present including angiotensin AT(1) and AT(2) receptor subtypes. While the AT(1) receptor is responsible for the classical effects of angiotensin II, it has been found that the AT(2) receptor displays totally different signalling mechanisms and this has revealed hitherto unknown functions of angiotensin II. AT(2) receptors are expressed at low density in many healthy adult tissues, but are up-regulated in pathological circumstances, e.g. stroke or nerve lesion. Evidence has now emerged that the actions of angiotensin II that are exerted via the AT(2) receptor are directly opposed to those mediated by the AT(1 )receptor. For example, the AT(2) receptor has antiproliferative properties and therefore opposes the growth-promoting effect linked to AT(1) receptor stimulation. It has been reported that the AT(2) receptor regulates several functions of nerve cells, e.g. ionic fluxes, cell differentiation and axonal regeneration, but also modulates programmed cell death. It is possible that a more extensive knowledge of the AT(2) receptor could contribute to the understanding of the clinically beneficial effects of AT(1) receptor antagonists, as this treatment may unmask AT(2) receptor activity. This review presents selected aspects of advances in AT(2) receptor pharmacology, molecular biology and signal transduction with particular reference to possible novel therapeutic options for CNS diseases.

Novel role of macrophage migration inhibitory factor in angiotensin II regulation of neuromodulation in rat brain

Previously we determined that angiotensin II (Ang II) activates neuronal AT(1) receptors, located in the hypothalamus and the brainstem, to stimulate noradrenergic pathways. To link Ang II to the regulation of norepinephrine metabolism in neurons cultured from newborn rat hypothalamus and brainstem we have used cDNA arrays for high throughput gene expression profiling. Of several genes that were regulated, we focused on macrophage migration inhibitory factor (MIF), which has been associated with the modulation of norepinephrine metabolism. In the presence of the selective AT(2) receptor antagonist PD123,319 (10 microM), incubation of cultures with Ang II (100 nM; 1-24 h) elicited an increase in MIF gene expression. Western immunoblots further revealed that Ang II (100 nM; 1-24 h) increased neuronal MIF protein expression. This effect was inhibited by the AT(1) receptor antagonist losartan (10 microM), the PLC inhibitor U-73122 (10 or 25 microM), the PKC inhibitor chelerythrine (10 microM), and the Ca(2+) chelator 1,2-bis-[2-aminophenoxy]-ethane-N,N,N',N'-tetraacetic acid tetrakis acetoxymethyl ester (10 microM). Taken together with our observation that MIF is expressed in the terminal fields of noradrenergic neurons (hypothalamus) and that Ang II increases the expression of MIF in this region in vivo, our data may suggest a novel role of Ang II in norepinephrine metabolism.

Gene expression profiling of rat brain neurons reveals angiotensin II-induced regulation of calmodulin and synapsin I: possible role in neuromodulation

Angiotensin (Ang II) activates neuronal AT(1) receptors located in the hypothalamus and the brainstem and stimulates noradrenergic neurons that are involved in the control of blood pressure and fluid intake. In this study we used complementary DNA microarrays for high throughput gene expression profiling to reveal unique genes that are linked to the neuromodulatory actions of Ang II in neuronal cultures from newborn rat hypothalamus and brainstem. Of several genes that were regulated, we focused on calmodulin and synapsin I. Ang II (100 nM; 1-24 h) elicited respective increases and decreases in the levels of calmodulin and synapsin I messenger RNAs, effects mediated by AT(1) receptors. This was associated with similar changes in calmodulin and synapsin protein expression. The actions of Ang II on calmodulin expression involve an intracellular pathway that includes activation of phospholipase C, increased intracellular calcium, and stimulation of protein kinase C. Taken together with studies that link calmodulin and synapsin I to axonal transport and exocytotic processes, the data suggest that Ang II regulates these two proteins via a Ca(2+)-dependent pathway, and that this may contribute to longer term or slower neuromodulatory actions of this peptide.

Expression of angiotensin AT(1) and AT(2) receptors in adult rat cardiomyocytes after myocardial infarction. A single-cell reverse transcriptase-polymerase chain reaction study

The effector hormone of the renin-angiotensin system, angiotensin II, plays a major role in cardiovascular regulation. In rats, both angiotensin receptor subtypes, AT(1) and AT(2), are up-regulated after myocardial infarction but previous studies failed to identify the cell types which express the AT(2) receptor in the heart. To address this question we established a single-cell reverse transcriptase-polymerase chain reaction for AT(1) and AT(2) receptors to determine whether these receptor subtypes are expressed in adult rat cardiomyocytes before and 1 day after myocardial infarction. By laser-assisted cell picking, section profiles of single cells without genomic DNA contamination were isolated. After dividing samples into two identical aliquots, polymerase chain reaction amplification for AT(1) and AT(2) receptors was carried out and polymerase chain reaction products were subjected to gel electrophoresis. Compared to control (n = 4) and sham-operated animals (n = 4), the number of cardiomyocytes expressing the AT(1) receptor mRNA 1 day after myocardial infarction (n = 4) was not changed (42% and 33% versus 45%, respectively). On the other hand, AT(2) receptor mRNA was expressed in 8% and 13%, respectively, of cardiomyocytes gained from control (n = 4) and sham-operated animals (n = 4) and in 14% isolated after myocardial infarction (n = 4). These results demonstrate for the first time that the AT(2) receptor is expressed in adult cardiomyocytes in vivo. They further suggest that the previously observed up-regulation of cardiac AT(1) and AT(2) receptors after myocardial infarction involves cell types other than cardiomyocytes.

The angiotensin II type 2 receptor: an enigma with multiple variations

Since it was discovered ten years ago, the angiotensin II (ANG II) type 2 (AT(2)) receptor has been an enigma. This receptor binds ANG II with a high affinity but is not responsible for mediating any of the classical physiological actions of this peptide, all of which involve the ANG II type 1 (AT(1)) receptor. Furthermore, the AT(2) receptor exhibits dramatic differences in biochemical and functional properties and in patterns of expression compared with the AT(1) receptor. During the past decade, much information has been gathered about the AT(2) receptor, and the steadily increasing number of publications indicates a growing interest in this new and independent area of research. A number of studies suggest a role of AT(2) receptors in brain, renal, and cardiovascular functions and in the processes of apoptosis and tissue regeneration. Despite these advances, nothing stands out as the major singular function of these receptors. The study of AT(2) receptors has reached a crossroads, and innovative approaches must be considered so that unifying mechanisms as to the function of these unique receptors can be put forward. In this review we will discuss the advances that have been made in understanding the biology of the AT(2) receptor. Furthermore, we will consider how these discoveries, along with newer experimental approaches, may eventually lead to the elusive physiological and pathophysiological functions of these receptors.

Beyond blood pressure: new roles for angiotensin II

Since the discovery 100 years ago by Tigerstedt and Bergman of renin, an acid protease generating angiotensin peptide, numerous discoveries have advanced our understanding of the renin-angiotensin system (RAS). The recent cloning of angiotensin receptors and the availability of specific receptor ligands have allowed characterization of angiotensin-receptor-mediated actions, and an increasing number of studies using biochemical, pharmacological and molecular biological methods has focused on the many different physiological actions of the RAS in various tissues. Angiotensin II, the main effector peptide of the RAS, exerts most of its known actions in blood pressure control and body fluid homeostasis via the AT, receptor. AT, receptors not only play a role in growth control and cell differentiation but have been implicated in apoptosis and tissue regeneration. This review focuses on the extrarenal functions of angiotensin, especially in neuronal cells and the nervous system, and on recent advances in angiotensin receptor research.

AT2 receptor stimulation induces generation of ceramides in PC12W cells

The angiotensin AT2 receptor has been implicated in both regeneration and apoptosis. To further investigate the molecular mechanisms leading to AT2 receptor-induced programmed cell death in PC12W cells we studied the effects of angiotensin II (ANG II) on ceramide levels by HPTLC analysis. We could demonstrate that ANG II time- (1-10 h) and dose-dependently (10(-8)-5 X 10(-6) M) increased ceramide levels by maximally 175% but did not affect sphingomyelin degradation. The ANG 11 effects were mediated by AT2 receptors since they were completely abolished by co-incubation with the AT2 receptor antagonist, PD123177 (10(-5) M), but not by the AT1 receptor antagonist, losartan (10(-5) M). These data suggest a novel signal transduction pathway to the AT2 receptor leading to apoptosis in neuronal cells.

The angiotensin II type 2 (AT2) receptor promotes axonal regeneration in the optic nerve of adult rats

The renin-angiotensin system (RAS) has been traditionally linked to blood pressure and volume regulation mediated through the angiotensin II (ANG II) type 1 (AT1) receptor. Here we report that ANG II via its ANG II type 2 (AT2) receptor promotes the axonal elongation of postnatal rat retinal explants (postnatal day 11) and dorsal root ganglia neurons in vitro, and, moreover, axonal regeneration of retinal ganglion cells after optic nerve crush in vivo. In retinal explants, ANG II (10(-7)-10(-5) M) induced neurite elongation via its AT2 receptor, since the effects were mimicked by the AT2 receptor agonist CGP 42112 (10(-5) M) and were entirely abolished by costimulation with the AT2 receptor antagonist PD 123177 (10(-5) M), but not by the AT1 receptor antagonist losartan (10(-5) M). To investigate whether ANG II is able to promote axonal regeneration in vivo, we performed optic nerve crush experiments in the adult rats. After ANG II treatment (0.6 nmol), an increased number of growth-associated protein (GAP)-43-positive fibers was detected and the regenerating fibers regularly crossed the lesion site (1.6 mm). Cotreatment with the AT2 receptor antagonist PD 123177 (6 nmol), but not with the AT1 receptor antagonist losartan (6 nmol), completely abolished the ANG II-induced axonal regeneration, providing for the first time direct evidence for receptor-specific neurotrophic action of ANG II in the central nervous system of adult mammals and revealing a hitherto unknown function of the RAS.

Sciatic nerve transection evokes lasting up-regulation of angiotensin AT2 and AT1 receptor mRNA in adult rat dorsal root ganglia and sciatic nerves

The angiotensin AT2 receptor is involved in tissue repair and cellular stress responses in non-neuronal cells. We have previously observed that the AT2 receptor-induced neurite formation in PC12W cells is paralleled by a reduced neurofilament M expression as it occurs in nerve fiber regeneration. Here we show that transection and crush of sciatic nerve fibers of adult rats results in dramatic changes of AT2, AT1a and AT1b receptor mRNA in dorsal root ganglion neurons (DRGs) and in sciatic nerves 3, 14 and 28 days after axotomy and crush. The expression patterns were determined by reverse transcription polymerase chain reaction (RT-PCR) assay, and the specificity of amplification products was verified by Southern blot hybridization. Whereas axotomy evoked a transient increase of AT2 receptor mRNA by more than 1000% after 3 days in proximal and after 14 days in distal sciatic nerve stumps (510%), the maximum expression in DRGs was observed after 14 days (1100%). Sciatic nerve crush resulted in a time-dependent up-regulation of AT2 receptor mRNA in sciatic nerve segments coinciding with the successful regeneration of nerve fibers. In sciatic nerves, AT1a and AT1b receptor mRNA levels were increased within different time-courses and to different extents with a maximum expression of 570%. In contrast to AT1a receptor mRNAs, AT1b receptor mRNA levels were increased in DRGs by maximally 800%. These results suggest that AT2 and AT1 receptor-mediated pathways are involved in Schwann cell-mediated myelination and in neuroregenerative responses of DRGs.

Angiotensin II and NGF differentially influence microtubule proteins in PC12W cells: role of the AT2 receptor

Angiotensin AT2 receptors have been shown to play a role in cell differentiation characterized by neurite outgrowth in neuronal cells of different origin. To further investigate AT2 receptor-mediated events leading to neurite formation, we examined the effect of AT2 receptor stimulation on the microtubule components, beta-tubulin, MAP1B and MAP2, by Western blot analysis and immunofluorescence in quiescent and nerve growth factor (NGF)-differentiated PC12W cells. These proteins are involved in neurite extension and neuronal maturation. Whereas NGF (0.5, 10, and 50 ng/ml) up-regulated these proteins after 3 days of stimulation, angiotensin II (ANG II; 10(-7) M) induced a different pattern. In quiescent PC12W cells, AT2 receptor stimulation up-regulated polymerized beta-tubulin and MAP2 but down-regulated MAP1B protein levels. In PC12W cells, differentiated by NGF (0.5 ng/ml), ANG II elevated polymerized beta-tubulin and reduced MAP1B. All ANG II effects were abolished by the AT2 receptor antagonist PD123177 (10(-5) M) but not affected by the AT1 receptor antagonist losartan (10(-5) M). These results implicate a specific role of AT2 receptors in cell differentiation and nerve regeneration via regulation of the cytoskeleton.

The angiotensin AT2 receptor down-regulates neurofilament M in PC12W cells

The angiotensin (ANG II) AT2 receptor mediates antiproliferative effects and induces neurite outgrowth in PC12W cells. To further investigate the molecular events following AT2 receptor stimulation in these cells, we determined the expression pattern of the middle-sized neurofilament subunit (NF-M) using Western and Northern blot analysis and reverse-transcription polymerase chain reaction. On both, the protein and the mRNA level, ANG II via AT2 receptors not only counteracted nerve growth factor (NGF)-mediated NF-M up-regulation but also reduced NF-M levels in the absence of NGF by maximally 72%. The ANG II-induced effects were completely abolished by pretreatment with the AT2 receptor antagonist, PD123177. In view of previous findings of decreased NF levels in regenerating neurons and in neuronal cultures undergoing apoptosis, our observation suggests a new role of AT2 receptors in either of these processes.

Extrarenal aspects of angiotensin II function

The cloning of angiotensin II (Ang II) receptor genes and the availability of specific receptor ligands allows characterization of Ang II receptor-mediated actions. Most of the well-known Ang II effects such as vasoconstriction, drinking response and cell proliferation are mediated through the AT1 receptor. Little is known about the physiological effect of the AT2 receptor, though there are some reports describing the involvement of the AT2 receptor in blood pressure regulation. Recent data demonstrate that the AT2-mediated actions are inhibitory to AT1- and mitogen-induced growth effects, indicating a balancing mechanism for Ang II-controlled mechanisms. It has also been demonstrated that AT2 receptor inactivation induces endothelial cell proliferation in the presence of Ang II. Additionally, AT2 receptor activation enhances nerve growth factor-induced differentiation of PCI2W cells and a role in apoptotic changes has also been reported. Based on recent findings, this article focuses on the role of Ang II in growth and differentiation processes with respect to the AT2 receptor in these events.

Angiotensin receptors

INTRODUCTION

The octapeptide angiotensin II, the potent effector molecule of the renin-angiotensin system, has been implicated in the pathology of hypertension, in cardiovascular diseases like cardiac left ventricular hypertrophy and in structural alterations of the heart such as post-infarct remodelling.

ANGIOTENSIN RECEPTORS

The development of highly selective angiotensin II receptor ligands allowed the identification of angiotensin II receptor subtypes, designated AT1, AT2, AT3 and AT4. Most of the known effects of angiotensin II can be attributed to the AT1 receptor (e.g. vasoconstriction, aldosterone and vasopressin release and proliferative effects on vascular smooth muscle and other cells). The AT1 receptor is coupled to G-proteins and engages classical intracellular second messenger systems, for example activation of phospholipase C or inhibition of adenylate cyclase. In contrast, the function and the signal transduction pathways of the AT2 receptor, which exhibits only a 32-34% homology to the AT1 receptor, are so far not fully understood. Coupling of the AT2 receptor to phosphatases and inhibitory actions on AT1 receptor- and growth factor-mediated proliferation in endothelial and other cells as well as induction of neuronal outgrowth in PC12w cells have been demonstrated. Due to its wide distribution in fetal tissues including the central nervous system and its transient reappearance in the adult organism under pathological conditions (for instance after myocardial infarction) the AT2 receptor has been associated with cell differentiation and regeneration.

RECEPTOR ANTAGONISTS

The application of orally active AT1 receptor antagonists as antihypertensive drugs has, compared to angiotensin converting enzyme inhibitors, the potential advantage of a more specific renin-angiotensin system inhibition. It is conceivable that the AT2 receptor, left unopposed by AT1 receptor antagonists, contributes to some of the actions of these drugs.