ORIGINAL ARTICLE Q-switched 1064 nm Nd-Yag nanosecond laser effects on skin barrier function and on molecular rejuvenation markers in keratinocyte-fibroblasts interaction Anna De Filippis 1 & Brunella Perfetto 1 & Luigi Pio Guerrera 2 & Giovanni Oliviero 2 & Adone Baroni 2 Received: 23 April 2018 /Accepted: 4 September 2018 # Springer-Verlag London Ltd., part of Springer Nature 2018 Abstract Skin represents an interface between internal and external environment; it protects human body by regulating the water loss and the maintenance of body temperature, defending against irritant and pathogen agents, and against physical, chemical, and UV damage. It provides to essential physiological functions, such as the important antioxidant defense capacity; its protective/defensive function is performed by a high number of proteins, and shows important functions in maintenance of skin barrier homeostasis. Keratinocytes and fibroblasts play a pivotal role to determine or prevent skin aging in response to intrinsic or extrinsic stimuli, modulating cytokines and several biochemical factors. Non-ablative technologies are playing an increasing role in the management of skin aging, inducing a dermal remodeling without a visible epidermal damage. The objective of this study was to evaluate the effect of Q- switched 1064 Nd-YAG laser (Medlite Conbio C6 Nd-YAG laser, Cynosure USA) in skin barrier function, analyzing the constit- uents which are strongly altered in aging skin. Particularly, we evaluated the expression of filaggrin, TGase, HSP70, and aquaporins, on HaCaT cells. The expression of proinflammatory cytokines has been investigated too. As a second step of the study, we analyzed the modulation of the rejuvenation molecular markers on human skin fibroblasts (HDFs) stimulated with keratinocytes conditioned medium (KCM). Our results demonstrated that Q-switched 1064 nm Nd:YAG laser acts on the skin barrier function, increasing the expression of aquaporins, filaggrin, TGase, and HSP70, modulating the proinflammatory cytokines. In fibroblasts stimulated with keratinocytes conditioned medium (KCM) and irradiated with Q-switched 1064 nm Nd:YAG laser, we can observe a reduction of MMP-1 and an increase in procollagen, collagen type I, and elastin. Our results highlight that Q-switched 1064 nm Nd:YAG laser treatment could represent an effective weapon to fight skin aging. Keywords Q-switched Nd:YAG laser . Keratinocytes . Photoaging . Collagen Introduction Skin aging is the effect of biological clock, influenced by genetic, intrinsic, and extrinsic factors that induce a reduction in the biological activity of cells, a slackening of regenerative processes, and a major sensitivity to environmental factors. Intrinsic factors are time dependent factors, influenced both by genetic background and by a decrease of sex hormone levels, represented by cumulative endogenous damage due to the accumulation of reactive oxygen species (ROS) gener- ated by oxidative cellular metabolism and affecting cellular constituents such as membranes, enzymes, and DNA. Environmental pollution, smoking, alcohol intake, poor nutri- tion, overeating, ionizing radiation, and particularly exposure to UV radiation are extrinsic factors [1]. The oxidative stress related to the inducing factors reduces production of antioxidants and the function of cytokines and signaling pathways leading to the production of matrix metal- loproteinases (MMPs) degrading dermal collagen and elastin [2]. In fact, skin aging is strongly associated with increased levels of matrix metalloproteinases, combined with impaired transforming growth factor (TGF)-β signaling, which may * Adone Baroni adone.baroni@unicampania.it 1 Department of Experimental Medicine, Section of Microbiology and Clinical Microbiology, University of Campania BLuigi Vanvitelli^, Naples, Italy 2 Department of Mental Health and Physics and Preventive Medicine, Unit of Dermatology, University of Campania BLuigi Vanvitelli^, Naples, Italy Lasers in Medical Science https://doi.org/10.1007/s10103-018-2635-1