Relation Between Reactive Oxygen Species Production and Transient Receptor Potential Vanilloid1 Expression in Human Skin During Aging

Abstract

Skin sensitivity and impaired epidermal barrier function are associated with aging and are at least partly due to increased production of reactive oxygen species (ROS). Transient receptor potential vanilloid1 (TRPV1) is expressed in keratinocytes, fibroblasts, mast cells, and endothelial cells in skin. We investigated in skin biopsies of adult and elderly donors whether TRPV1 expression is involved in the skin aging process. We found that aging skin showed a strongly reduced epidermal thickness, strongly increased oxidative stress, protease expression, and mast cell degranulation and strongly increased TRPV1 expression both in epidermis and dermis. Based on our findings, the aging-related changes observed in the epidermis of the skin level are associated with increased ROS production, and hypothesized alterations in TRPV1 expression are mechanistically linked to this process.

Keywords: aging; cyclooxygenase-2; metalloproteinases; oxidative stress; skin; transient receptor potential vanilloid1 (TRPV1).

Figure 1.

Epidermal thickness measured in skin biopsies—The schematic representation (A) and the photograph (B) represent the incision site (indicated with a dashed black rectangle) where the skin biopsy was taken in all specimens: the right lateral ocular angle has been selected as the site of collection. The other macroscopically recognizable landmarks are indicated in the figure. Haematoxylin and eosin staining of adult specimen (C, D) and elderly specimen (E, F). Bars 20 μm (C, E) and 40 μm (D, F). The plot (G) shows the epidermal thickness distribution of all adult and elderly specimens. Abbreviations: E, epidermis; D, dermis. *p≤0.05 versus adult specimens.

Figure 2.

Evaluation of oxidative stress in skin biopsies—Skin reactive oxygen species (ROS) level evaluation in adult and elderly specimens (a). Representative skin photomicrographs of superoxide dismutase-1 (SOD-1) immunostaining of adult specimens (B, C) and of elderly specimens (D, E). SOD-1 negative control—elderly skin specimens (f). Bars 40 μm (B, D, F) and 80 μm (C, E). The plot (G) summarizes SOD-1 immunomorphometric measurement. Abbreviations: E, epidermis; D, dermis; AU, arbitrary units. *p≤0.05 versus adult specimens.

Figure 3.

Metalloproteinase9 (MMP9) skin evaluation—Representative skin photomicrographs of MMP9 immunostaining of adult specimens (A–D) and elderly specimens (E–H). MMP9-negative control—elderly skin specimens (I). Bars 40 µm (A, C, E, G, I) and 80 µm (B, D, F, H). The plot (J) summarizes the MMP9 immunomorphometrics. Abbreviations: E, epidermis; D, dermis; AU, arbitrary units. *p≤0.05 versus adult specimens.

Figure 4.

Transient receptor potential vanilloid1 (TRPV1) skin evaluation—Representative skin photomicrographs of TRPV1 immunostaining in adult specimens (A–D) and in elderly specimens (E–H). TRPV1-negative control—elderly skin specimens (I). Bars 40 µm (A, C, E, G, I) and 80 µm (B, D, F, H). The plots summarize the TRPV1 immunomorphometric measurement (J) and the skin TRPV1 ELISA evaluation (K). Abbreviations: E, epidermis; D, dermis; AU, arbitrary units. *p≤0.05 versus adult specimens.

Figure 5.

Mast cell assessment in the dermis—Representative skin photomicrographs after toluidine blue staining of adult specimens (A, B) and elderly specimens (C, D). The black circles indicate intact (A) and degranulated (C) mast cells; the arrows show the mast cells granules. Bars 40 µm (A, C) and 80 µm (B,D). *p≤0.05 versus adult specimens. Plot (E) summarizes the number of intact and degranulated mast cells per mm² in adult and elderly specimens and plot (F) summarizes the total number of mast cells (intact plus degranulated mast cells) per mm² in adult and elderly specimens. Abbreviations: E, epidermis; D, dermis; MCs, mast cells.

Figure 6.

Evaluation of COX-2 expression in skin—Representative skin photomicrographs of COX-2 immunostaining in adult specimens (A–D) and elderly specimens (E–H). COX-2-negative control—adult skin specimens (I). Bars: Bars 60 µm (A, C, E, G, I) and 90 µm (B, D, F, H). The plot (J) summarizes the COX-2 immunomorphometric measurements. Abbreviations: E, epidermis; D, dermis; AU, arbitrary units. *p≤0.05 versus adult specimens.

Figure 7.

Aging-related injury in skin—Schematic representation of how host, environmental, and extrinsic factors act on the skin introducing aging-related alterations and leading to possible dermatological diseases. Superoxide dismutase-1 (SOD-1) increases its expression in both dermis and epidermis; it acts as an antioxidant molecule by playing a protective role against ROS production. Abbreviations: MC, mast cell; ECM, extracellular matrix; TRPV1, transient receptor potential vanilloid1; ROS, reactive oxygen species; SOD-1, superoxide dismutase1; MMP9, metalloproteinase9; COX-2, cyclooxygenase-2; Ca²⁺, calcium²⁺.