Anti-obesity effect of sulforaphane involves inhibition of HDAC8 but not Nrf2

Abstract

Obesity is rising worldwide leading the increase of the risks of metabolic diseases such as type 2 diabetes, hypertension, and cardiovascular diseases. The causes of obesity is not simple because various environmental factors such as diet, sedentary time, even stress influence the development of obesity and obesity-related diseases. Since, there are always obesogenic environment surrounding us, sustainable, and effective long-term strategies for control obesity is required. Currently, there are several interventions of obesity including lifestyle and habit modification, bariatric surgery, and pharmacotherapy with anti-obesity drugs. However, some of them have some limitations in terms of safety, and difficulty for durability. In this context, dietary foods has some benefits because their safety is proved through the historical long-term intake, and easy to maintain continuous intervention by daily intake. Recent findings show that epigenetic alteration can be induced by several dietary food components as well as various obesogenic environmental factors. Therefore, in perspectives of epigenetics, pharmacotherapy with natural epigenetic regulators or daily intake of natural epigenetic regulators enrich dietary food can be suggested for newly strategies for prevention or treatment of obesity. Sulforaphane (SFN) is a natural compound enriched in daily intake available cruciferous vegetables such as broccoli sprout. There are many previous studies about the beneficial effect of SFN on various diseases including obesity and diabetes mellitus. In general, it is widely believed that these beneficial effects are mainly attributed to the activation of nuclear factor E2-related factor 2 (Nrf2), thereby, SFN is frequently utilized as Nrf2 activating agent. However, there are some conflicting evidences about the role of Nrf2 in metabolic diseases. It indicates that it is required to investigate the role of Nrf2 in the beneficial effects of SFN on obesity and obesity-related metabolic diseases such as type 2 diabetes. SFN newly received attention as a natural histone deacetylase (HDAC) inhibitor beyond Nrf2 mechanism especially in cancer biology. However, there is few study identifying the role of SFN as a HDAC inhibitor in obesity and related metabolic diseases. Moreover, the selectivity of SFN on HDAC families is unclear even in cancer biology. Here, I utilized Nrf2-KO mice to determine whether the anti-obesity effect of SFN depends on Nrf2. I found that SFN suppressed high fat diet (HFD)-induced increases in body weight and improved insulin sensitivity in both Nrf2-WT and Nrf2-KO mice. These reduction was not due to alteration of food intake or lipid excretion. Therefore, to further investigate the mechanism of SFN, I examined the effect of SFN on lipid metabolism in each peripheral tissues such as white adipose tissue (WAT), liver, skeletal muscle, and brown adipose tissue (BAT) in high fat diet (HFD)-fed mice. As results, SFN induced the expression of lipases such as adipose triglyceride lipase (ATGL), and hormone sensitive lipase (HSL) in WAT resulting in the reduction of epididymal WAT weight and the increase of circulating fatty acids. SFN also promoted the consumption of fatty acids to produce energy by increasing the expression of either mitochondrial biogenesis-related proteins such as nuclear respiratory factor 1 (NRF1) in liver or mitochondrial fatty acid oxidation-related proteins such as peroxisome proliferator-activated receptor (PPAR) families in skeletal muscle, thermogenesis-related proteins such as uncoupling protein 1 (UCP1) in BAT, which are mainly regulated by Peroxisome proliferator-activated receptor gamma coactivator 1α (PGC1α), a key protein in energy metabolism. For definite understanding of regulation of PGC1α by SFN, I investigated the regulatory mechanism of SFN against PGC1α. I found while there were no changes on the expression of transcription factors such as myocyte enhancer factor 2C (MEF2C), and cAMP-response element binding protein (CREB), SFN increased the transcription of PGC1α in oxidation-related organ such as liver, and skeletal muscle. However, SFN increased the global histone acetylation on histone H3 in skeletal muscle. Thereafter, I identified that SFN only selectively inhibited the HDAC8 activity rather than other classical HDAC isoforms in vitro, and there was no change on HDAC8 expression in skeletal muscle. To further examine the relevance between HDAC8 and PGC1α, I deleted HDAC8 with leti viral system in HeLa cell. I found that knockdown of HDAC8 increased the PGC1α expression, and the increase of PGC1α by SFN disappeared in shHDAC8 HeLa cell compared to shCont HeLa cells. Overall, for the first time, I have demonstrated that SFN suppresses HFD-induced obesity regulating PGC1α-mediated lipid metabolism in several peripheral tissues by inhibiting HDAC8 activity, which is independent of Nrf2 system unlikely previous premise. These observations imply that SFN has an advantages in sustainable, and long-term intervention effect for obesity through the daily intake of broccoli or pharmacotherapy with single natural compound in perspectives of epigenetic regulation over the lifetime.