Molecular cell biology is a field that investigates how cells develop, operate, communicate and control their activities. Cells communicate with body tissue, which is composed of cells. Tissue communicates with other tissues and organs throughout the body. Generally the transfer of information between cells, tissues and organs is through the interaction of proteins.
Techniques developed in the field of molecular biology are currently being used to screen cosmeceutical ingredients for skin and hair care applications. New findings are published on a daily basis, providing insight with respect to future innovations for skin and hair health and appearance. Several relevant developments are reviewed here.
Gene Expression and Epigenetics
Gene expression is the process by which information from a gene is used to direct the synthesis of a functional gene product—most frequently, a protein. Gene expression involves a large number of individual genes, and is a complex activity with many layers of control. It is a critical component of normal growth and development, and disruption or changes in gene expression are responsible for many diseases, as well as aging. UV radiation, chemical exposure, viruses, chronic inflammation and oxidative stress are all associated with skin conditions and aging. Recent publications also suggest that impaired cellular energy metabolism has an impact on the condition of skin.1, 2
Epigenetics is the study of heritable changes in gene expression or cellular appearance caused by mechanisms other than changes in the underlying DNA sequence. Another way to describe epigenetics is the branch of molecular biology related to mechanisms that affect gene activity continually occurring inside the cells of the body. Epigenetic events do not alter the DNA of the cell, rather they change the shape and chemical behavior of the molecules that form DNA. These changes alter the instructions coded in the DNA. Changes in gene expression may be temporary or they may be passed down to the next generation. Epigenetic effects can by stimulated by the environment, lifestyle choices or what are currently perceived as random events, which commonly occur when DNA is being formed—mutations, for example.
Hallmarks of Aging
A recent review of the hallmarks of aging3 noted nine common denominators that appeared most frequently in the scientific literature. These are: 1) genomic instability, i.e., damaged genes; 2) telomere attrition or exhaustion, whereby cells no longer proliferate; 3) epigenetic alterations, as described above; 4) loss of proteostasis, meaning impaired cell signaling caused by dysfunctional protein signaling; 5) deregulated nutrient sensing, examples of which are the insulin pathway or tumor suppressors; 6) mitochondrial oxidative metabolism, e.g., white/brown fat created and stored in the body, or mitochondrial dysfunction when DNA repair is hindered; 7) cellular senescence when cells are not replicating properly; 8) stem cell exhaustion, which is often observed in muscle tissue and epidermis—this is a state of reduced cell division and proliferation or reduced cell regeneration; and 9) altered intercellular communication, especially seen when cells are subject to increased inflammation and a weakened immune system. A tenth hallmark of aging would be low grade chronic inflammation, referred to as inflammaging.
The authors of the hallmark publication note that a major challenge is dissecting the interconnectedness of these denominators with their relative contributions to aging.3 The ultimate goal is to identify target products to improve human health during aging, and this is the promise of gene expression studies including epigenetics-related research.
Historically, the cosmetic chemist formulated a product and the marketing department created a story with limited scientific documentation to promote it. This paradigm has shifted to focus marketing on the proposed biological mechanism(s) underlying skin concerns the product is intended to address—such as acne, dry skin, inflammation and aging. Today, it is also expected that cosmetic ingredient suppliers provide a data package that includes a mechanism of activity with supporting laboratory test data, often in vitro.
For example, the ingredient vitamin B3, or niacinamide, could be marketed based on lab studies showing its ability, in co-cultures of melanocytes and keratinocytes, to improve skin hyperpigmentation by inhibiting the transfer of pigment-bearing melanosomes from melanocytes to keratinocytes.4 Also, certain soy products are reported to improve the evenness of skin tone by modulating the activity of a protease-activated receptor-2 (PAR-2) found in skin.5 Peptides function as cell signaling molecules and enzyme inhibitors, and these mechanisms have been identified using molecular biological techniques.6 And the current opinion, based on epigenetic studies, is that while the cell signaling role of antioxidants is important, this activity may have greater power unrelated to antioxidant activities.7, 8
Nrf2 Transcription Factor
A transcription factor is a protein that binds to specific DNA sequences to control the flow of genetic information, i.e., transcription, from DNA to messenger RNA. Transcription factors may work alone or with other proteins in a complex. The Nuclear Factor E2-Related Factor 2 (Nrf2) signaling pathway (see Figure 1) is one area of current interest. Nrf2 is a transcription factor that activates more than 200 genes crucial in the metabolism of drugs and toxins, signaling for protection against oxidative stress and inflammation. It is a stress-sensing genetic transcription factor that is thought to be a master regulator of cellular responses to oxidative damage. Nrf2 is one of a variety of proteins that controls which genes are turned on based on the specific needs of the cell.
Nrf2 plays a crucial role in stabilizing proteins and removing damaged ones from cells. Properly functioning proteins are essential for cellular communication, and Nrf2 was recently identified as a signaling mediator connected with the effects of caloric restriction through cross-talk with other metabolic signaling pathways. For example, it interacts with p53 and NF-ĸβ, and this combined interaction is thought to be a guardian of life span and to protect against age-related disease. It was also shown that signaling between Nrf2 and cellular metabolic pathways is associated with insulin signaling. In this way, it is hypothesized that Nrf2 signaling is a mediator of the effects of caloric restriction, including longevity.
Coffee, chocolate, turmeric, olive oil, broccoli, garlic, green tea and blueberries contain chemical components generically called phytochemicals, and many of these have been reported to induce the expression of enzymes influencing cellular antioxidant defense mechanisms. Multiple biological pathways are involved; most frequently, those for Nrf2/keap1, NF-kB, sirtuin-FOXO are reported.9
Nrf2 Pathways and Skin
In the majority of research papers published on the therapeutic activity and efficacy of synthetic and natural products, the test materials were ingested by or injected into test subjects or animal models. However, a select number of studies have been published evaluating the efficacy of products applied topically. Heng,10 for example, published data indicating that curcumin applied topically to damaged skin can modulate inflammation and reduce scar tissue formation. Heng et al.11 also observed topically applied curcumin improved psoriasis after three to eight weeks of treatment. Interestingly, Sonavane12 obtained equivalent results with topical and dietary curcumin for the treatment of skin cancer.
Nrf2 recently was also found to be important in wound healing and to skin exposed to UVB radiation. Higher levels of Nrf2 protein expression were found in the upper layer of skin than in the lower layer, and lower layer skin cells die at a higher rate than upper layers when exposed to UVB—probably for this reason.13 Another study found quercetin protected keratinocytes against UVA exposure in cell cultures via Nrf2.14 Table 1 lists the natural ingredients that have been shown to provide skin benefits via the Nrf2 pathway; Table 2 lists the different ways phytochemicals provide benefits for health.15
Skin Lipids and Possible Role of Nrf2
Skin is the largest organ of the body. The innermost layer is a subcutaneous fat layer. Next is the dermis containing fibroblasts that produce collagen and elastic fibers. Within the dermis are specialized organelles including sebaceous glands, sweat glands and hair follicles. Nerves and blood vessels are localized in the dermis as well. The epidermis is the outermost layer of skin, where highly active lipid synthesis occurs.
Studies in lipid metabolism have not previously been of major importance to skin care product development. However, it is becoming an area of greater interest as studies in molecular genetics increasingly show that barrier permeability abnormalities are the primary cause of atopic dermatitis and other skin diseases. Further, the sebaceous glands play a key role in acne, dry skin and other skin conditions. In short, there is renewed interest in lipid metabolism and elucidating its impact on skin.16 (For more on this topic, see the article by Dayan and Halperin.)
Nrf2 regulates lipid metabolism in the liver and adipose tissue, although the role of Nrf2 with respect to regulating adipose and other skin conditions is not clear at this time. Ceramide, cholesterol and phosphatidic acid are the basic structures of cell membrane lipids, and they can be modified by energizing cells with glucose, which facilitates metabolism. Ceramides are the major component of the stratum corneum and essential for a functioning permeability barrier; the role of Nrf2 in regulating lipid barrier function is an area of current investigation.17
Skin surface lipids are a mixture of sebum and keratinocyte membrane lipids.18 Major lipid components of sebum include squalene, wax esters and triglycerides. The squalene found in skin is different from squalene in other body parts. In humans, about 60% of dietary squalene is absorbed and transported in serum to tissue by very low density lipoproteins. The greatest accumulation in skin is from sebocyte concentrations. In the liver, it is metabolized to squalene epoxide and converted to lanosterol. In the sebaceous gland, two key oxygen-regulated enzymes are involved in squalene metabolism: squalene synthase and squalene oxidocyclase. This is biologically important, as peroxidable squalene is known to be a key mediator of skin reactions to environmental stressors.19 Previously, little research on epidermal lipids was available but more recently, the biological significance of sebum lipids to skin and hair has become the subject of research activity; specifically for acne, seborrheic dermatitis, pityriasis versicolor and androgenic alopecia.18
In relation, long-wavelength UV radiation (UVA-1, 340-400 nm) causes oxidative stress to skin cells, to which cells respond by producing detoxifying enzymes and antioxidants. The effects of UVA-1 exposure combined with oxidized lipid treatments on human dermal fibroblasts and keratinocytes have been studied. An increase in the accumulation of nuclear DNA binding of Nrf2 was observed. UV exposure to skin may result in the oxidation of lipids found in the membrane layer surrounding skin cells. The significance of the DNA binding of Nrf2 is that Nrf2 expression will be silenced, resulting in the absence of antioxidant defense mechanism activation. In the referenced paper,20 investigators view the lipids in skin as specific signaling mediators, whereas previously UV-generated lipid products were considered to be merely the end result of UV exposure.20
The quality of skin surface sebum lipids, including sebum oxidant levels, and the transport of these products to skin is an area requiring further research. The external lipid film represents a reliable in vivo biomarker that has the potential to indicate degrees of environmental stress, to evaluate drug delivery through the skin and chemical reactions on the skin, and to assess cross reactions of jewelry, textiles, cosmetics, drugs, industrial chemicals and other materials that come into contact with skin.18
The Fitzpatrick scale for skin types was developed about 40 years ago, is based on skin’s complexion and appearance, and provides subjective reporting of an individual’s reaction to UV exposure. Since that time, molecular biology has advanced considerably. Currently, the most common methods to collect data include genome sequencing, the study of single nucleotide polymorphisms, epigenomics and the evaluation of many different types of RNA expression in cells. As the cost and time to conduct such studies decreases, an increase in published research will provide new data and formulation opportunities for skin and hair care product development. The information generated from these studies is daunting, and there is much to be interpreted from it. Further, the analysis and interpretation remains an inexact science.21 However, one can envision the day, perhaps within the next 10 years, when personalized medicine and skin and hair care products will be common.
- TN Seyfries and LM Shelton, Cancer as a metabolic disease, Nutrition Metabol 7(7) 1-22 (2010)
- RK Singh, A Sudhakar and BL Lokeshwar, From normal cells to malignancy: Distinct role of pro-inflammatory factors and cellular redox mechanisms, J Cancer Sci Therapy 3(4) 70-75 (2011)
- C Lopez-Otin, MA Blasco, L Partridge, M Serrano and G Kromer, The hallmarks of aging, Cell 6 1194-1217 (2013)
- A Greatens et al, Effective inhibition of melanosome transfer to keratinocytes by lectins and niacinamide is reversible, Exp Dermatol 14 498-508 (2005)
- ER Sharlow et al, The protease-activated receptor-2 upregulates keratinocytes phagocytosis, J Cell Sci 113 3093-3101 (2000)
- L Zhang and TJ Falla, Cosmeceuticals and peptides, Clin Dermatol 27 485-494 (2009)
- T Finkel and NJ Holbrook, Oxidants, oxidative stress and the biology of aging, Nature 408(9) 239-7 (2000)
- S Oter, S Jin, L Cucullo and HJ Damien Dorman, Oxidants and antioxidants: Friends or foes? Oxid Antioxid Med Sci 1(1) 1-4 (2012)
- A Speciale, J Chirafisi, A Saija and F Cimino, Nutritional antioxidants and adaptive cell responses: An update, Curr Mol Med 11(9) 770-89 (2011)
- MC Heng, Curcumin targeted signaling pathways basis for anti-photoaging and anti-carcinogenic therapy, Int Soc Dermatol 49 608-622 (2010)
- MC Heng, MK Song, J Harker and MK Heng, Drug-induced suppression of phosphorylase kinase activity correlates with resolution of psoriasis as assessed by clinical, histological and immunohistochemical parameters, Br J Dermatol 143 937-49 (2000)
- K Sonavane et al, Topical curcumin-based cream is equivalent to dietary curcumin in a skin cancer model, J Skin Canc 1-9, Doi:10.1155/2012/147863 (2012)
- M Schafer et al, Nrf2 establishes a glutathione-mediated gradient of UVB cytoprotection in the epidermis, Genes and Devel 24 1045-1058 (2010)
- S Kimura, E Warabi, T Yanagawa, D Ma, K Itoh and Y Ishii, Essential role of Nrf2 in keratinocyte protection from UVA by quercetin, Biochem and Biophys Res Comm 378(1) 109-14 (2009)
- A Dinkova-Kostova, Phytochemicals as protectors against ultraviolet radiation: Versatility of effects and mechanisms, Planta Med 74 1548-1559 (2008)
- KR Feingold KR, The importance of lipids in cutaneous function, J Lipid Res 48 2529-30 (2007)
- Y Ishibashi, A Kohyama-Koganeya and Y Hirabayashi, New insights on glycosylated lipids: Metabolism and functions, Biochem et Biophysica Acta 1831 1475-1485 (2013)
- C De Luca and G Valacchi, Surface lipids as multifunctional mediators of skin responses to environmental stimuli, Mediator Inflamm 1-11 (2010)
- Y Yamamoto, Role of active oxygen species and antioxidants in photoaging, J Dermat Sci 27(1) s1-s4 (2001)
- F Gruber et al, NF-E2-related factor 2 regulates the stress response to UVA-1-oxidized phospoholipids in skin cells, FASEB J 24(1) 39-48 (2010)
- F Bonté, 11th annual LVMH recherché symposium: Skin rejuvenation, Eur J Dermatol 22(3) 432-6 (May/Jun 2012)