Abstract
Chronological aging is characterized by an alteration in the genes’ regulatory network. In human skin, epidermal keratinocytes fail to differentiate properly with aging, leading to the weakening of the epidermal function. MiR-30a is particularly overexpressed with epidermal aging, but the downstream molecular mechanisms are still uncovered. The aim of this study was to decipher the effects of miR-30a overexpression in the human epidermis, with a focus on keratinocyte differentiation. We formally identified the mitophagy receptor BNIP3L as a direct target of miR-30a. Using a 3D organotypic model of reconstructed human epidermis overexpressing miR-30a, we observed a strong reduction in BNIP3L expression in the granular layer. In human epidermal sections of skin biopsies from donors of different ages, we observed a similar pattern of BNIP3L decreasing with aging. Moreover, human primary keratinocytes undergoing differentiation in vitro also showed a decreased expression of BNIP3L with age, together with a retention of mitochondria. Moreover, aging is associated with altered mitochondrial metabolism in primary keratinocytes, including decreased ATP-linked respiration. Thus, miR-30a is a negative regulator of programmed mitophagy during keratinocytes terminal differentiation, impairing epidermal homeostasis with aging.
Highlights
Aging is a natural and inexorable biological evolution associated with a progressive decline in tissue homeostasis
Another putative binding site of miR-30a-5p and two putative binding sites of miR-30a-3p were found, even though the conservation of these sites among vertebrates is less important. Since both strands of miR-30a are overexpressed in keratinocytes from aged skin, we tested the in vitro ability of miRNA mimics to decrease the mRNA levels of BNIP3L in keratinocytes (Figure 1B)., Both mimics of miR-30a-3p and miR-30a-5p induced a significant decrease in BNIP3L mRNA levels, by 28% and 36%, respectively, 24 h after the transient transfection of proliferating human keratinocytes
We found that BNIP3L is a direct target of miR-30a and we have previously reported that miR-30a expression levels substantially increase with aging in human keratinocytes [6]
Summary
Aging is a natural and inexorable biological evolution associated with a progressive decline in tissue homeostasis. Skin is an excellent model of aging: during the natural aging process, the skin undergoes a typical age-related tissue dysfunction, including epidermis atrophy, barrier dysfunction and delayed wound healing. Multiple epigenetic changes are considered to be reliable hallmarks of tissue aging, such as modification of DNA methylation patterns, histone posttranslational modifications and modulation of non-coding RNA expression [1,2]. The latter is an emerging scientific domain, in which a number of studies have been published over the last decade. The control of skin homeostasis largely depends on the fine-tuning of signalling pathways by long non-coding RNAs, circular non-coding RNAs and micro-RNAs (miRNAs) [3–5]
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