Age-dependent response of energy metabolism of human skin to UVA exposure: an in vivo study by 31P nuclear magnetic resonance spectroscopy

The Role of PGC-1α in Aging Skin Barrier Function

Skin provides a physical and immune barrier to protect the body from foreign substances, microbial invasion, and desiccation. Aging reduces the barrier function of skin and its rate of repair. Aged skin exhibits decreased mitochondrial function and prolonged low-level inflammation that can be seen in other organs with aging. Peroxisome proliferator-activated receptor (PPAR)-γ coactivator-1α (PGC-1α), an important transcriptional coactivator, plays a central role in modulating mitochondrial function and antioxidant production. Mitochondrial function and inflammation have been linked to epidermal function, but the mechanisms are unclear. The aim of this review is to discuss the mechanisms by which PGC-1α might exert a positive effect on aged skin barrier function. Initially, we provide an overview of the function of skin under physiological and aging conditions, focusing on the epidermis. We then discuss mitochondrial function, oxidative stress, cellular senescence, and inflamm-aging, the chronic low-level inflammation observed in aging individuals. Finally, we discuss the effects of PGC-1α on mitochondrial function, as well as the regulation and role of PGC-1α in the aging epidermis.

Nicotinamide preferentially protects glycolysis in dermal fibroblasts under oxidative stress conditions

BACKGROUND

Daily exposure of human skin to environmental insults such as solar radiation, pollution and smoke can lead to an elevation of oxidative stress, causing premature acceleration of skin ageing. Oxidative stress is known to disrupt cellular metabolism, which negatively impacts the skin's functionality at the cellular and tissue level.

OBJECTIVES

To examine the changes in cellular metabolism due to oxidative stress.

METHODS

Glycolysis and oxidative phosphorylation rates in human dermal fibroblasts were monitored in real time under controlled nonlethal oxidative stress conditions. Hydrogen peroxide was utilized as a surrogate stressor because numerous environmental stressors as well as intrinsic ageing trigger its production.

RESULTS

Hydrogen peroxide ranging between 0.5 and 3 mmol L(-1) caused a significant decrease in glycolytic and oxidative phosphorylation rates along with cellular ATP levels. Nicotinamide (NAM) was found to protect dose dependently as well as restore glycolytic rates concurrent with restoring ATP to control levels. NAM had an effective dose-response range between 0.1 and 1.0 mmol L(-1) , with maximal effects attained at 0.5 mmol L(-1) . Relative to oxidative phosphorylation, NAM was able to provide a diminished level of protection. FK866, a known NAM phosphoribosyltransferase inhibitor, was found to inhibit the protective effects of NAM significantly, suggesting part of the NAM mechanism of action involves nicotinamide adenine dinucleotide (NAD(+) ) synthesis.

CONCLUSIONS

These results support previous findings that NAM protects cellular metabolism from oxidative stress by preferentially affecting glycolysis. Additionally, part of its mechanism of action appears to include NAD(+) synthesis.

Prevention of oxidative damage that contributes to the loss of bioenergetic capacity in ageing skin

Skin ageing is a complex biological process related to a decline in physiological and biochemical performance. A decline in the mitochondrial energy production is a feature of ageing at the cellular level. This is partially attributed to excessive production of reactive oxygen species such as superoxide and hydrogen peroxide in aged individuals. We have investigated the effect of (glyc)oxidative stress on two biochemical targets relevant for the energy metabolism of the skin. First, we showed an age dependent decline in the activity of the hydrogen peroxide detoxifying antioxidant catalase in stratum corneum on a chronically sun-exposed site. Furthermore catalase was sensitive to peroxynitrite-induced in vitro inactivation. Catalase mimetics as well as peroxynitrite scavengers are proposed to maintain hydrogen peroxide detoxification pathways. The second target was creatine kinase, an enzyme that controls the creatine-creatine phosphate shuttle. Creatine kinase lost activity after in vitro glycation by methylglyoxal. This activity loss could be prevented by antiglycation actives. These data suggest that biomolecules involved in energy homeostasis become damaged by different sources of stress. Actives specifically selected for optimal protection against these stress situations will decrease skin vulnerability and prevent the premature loss of skin function.

Skin phosphocreatine

BACKGROUND/PURPOSE

The skin has the unique ability to survive ischemia associated with skin grafts, flaps and hair transplantation procedures. Spectroscopic data later confirmed by chromatography, immunohistochemistry and molecular biology techniques identified the presence of large quantities of phosphocreatine in human skin. Phosphocreatine molecules regenerate ATP cellular reserves during ischemia. This reaction is mediated by creatine phosphokinase enzymes that were also isolated and studied in normal and diseased skin.

METHODS

Literature search revealed important contributions by US, Swiss, German, French, Scandinavian and Japanese investigators in the development and understanding of this research field.

RESULTS

Serum creatine phosphokinase levels are elevated in burn victims and patients with toxic epidermal necrolysis. Phosphocreatine concentration and creatine phosphokinase activity are elevated in psoriatic skin and in non-melanoma malignancies in comparison with normal skin. Furthermore, skin phosphocreatine and creatine phosphokinase enzymes are localized almost exclusively within the epidermis and in hair follicles. Finally, phosphocreatine and creatine phosphokinase enzymes help to protect skin from UV damage.

CONCLUSIONS

Clearly, this research area is only starting to be appreciated by the scientific community. Topical and systemic phosphocreatine administration appears to reverse photodamage and improve wound healing. Spectroscopic monitoring of phosphocreatine and related phosphometabolites can be potentially used to monitor disease activity and respond to therapy in psoriasis, leg ulcers, skin malignancies and other skin conditions.