Abstract
Ultraviolet (UV) B irradiation decreases blood adiponectin levels, but the mechanism is not well understood. This study investigated how UVB irradiation reduces adiponectin expression in ovarial adipose tissues. Female Hos:HR-1 hairless mice were exposed to UVB (1.6 J/cm2) irradiation and were killed 24 h later. UVB irradiation decreased the adiponectin protein level in the serum and the adiponectin mRNA level in ovarial adipose tissues. UVB irradiation also decreased the mRNA levels of peroxisome proliferator-activated receptor (PPAR) γ, CCAAT/enhancer binding protein (C/EBP) α, C/EBPβ, and fatty acid binding protein 4 (aP2) in ovarial adipose tissues. In contrast, UVB irradiation increased the mRNA levels of interleukin (IL)-6 and monocyte chemoattractant protein (MCP)-1 in ovarial adipose tissues. In the serum and liver, the levels of serum amyloid A (SAA), involved in PPARγ, C/EBPα, C/EBPβ, aP2, IL-6, and MCP-1 regulation, increased after UVB irradiation. The SAA gene is regulated by IL-1β, IL-6, and tumor necrosis factor-α, but only IL-6 expression increased in the liver after UVB irradiation. Additionally, in the liver, hypothalamus, and epidermis, UVB irradiation increased the expression of calcitonin gene-related peptide (CGRP), which upregulates SAA in the liver. Collectively, our results suggest that the CGRP signal induced by skin exposure to UVB transfers to the liver, possibly through the brain, and increases SAA production via IL-6 in the liver. In turn, serum SAA acts in an endocrine manner to decreases the serum adiponectin level by downregulating factors that regulate adiponectin expression in adipose tissues.
Highlights
Ultraviolet (UV) B irradiation is a major environmental factor that affects the structure and function of the skin
Kim et al reported that UVB irradiation of the skin reduced the expression of peroxisome proliferator-activated receptor (PPAR) c and CCAAT/enhancer binding protein (C/EBP) a, which participate in adipocyte differentiation, in the subcutaneous adipose tissues [1]
The adipose mRNA levels of IL-6 and monocyte chemoattractant protein (MCP)-1, factors associated with adipocyte hypertrophy, were significantly higher in the UVB (+) group than in the UVB (2) groups (Fig. 2E and F)
Summary
Ultraviolet (UV) B irradiation is a major environmental factor that affects the structure and function of the skin. Recent studies showed that UVB irradiation affects the skin, and the subcutaneous adipose tissues. Kim et al reported that UVB irradiation of the skin reduced the expression of peroxisome proliferator-activated receptor (PPAR) c and CCAAT/enhancer binding protein (C/EBP) a, which participate in adipocyte differentiation, in the subcutaneous adipose tissues [1]. Meeran et al demonstrated that UVB irradiation reduced the plasma adiponectin level by affecting visceral adipose tissues [2]. Adiponectin is abundant in the plasma of healthy humans (8.965.4 mg/mL) [3], whereas obese and overweight patients have low circulating levels of adiponectin. A low circulating level of adiponectin contributes to the pathogenesis of metabolic syndrome, acts as a risk factor for type 2 diabetes mellitus, and plays a role in the development of cardiovascular disease caused by abdominal obesity and insulin resistance [4,5]. UVB irradiation decreases the level of plasma adiponectin [2], but the mechanism by which UVB irradiation decreases the expression of adiponectin in ovarial adipose tissues is still unclear
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