Sang Gwon Seo

Piceatannol, Natural Polyphenolic Stilbene, Inhibits Adipogenesis via Modulation of Mitotic Clonal Expansion and Insulin Receptor-dependent Insulin Signaling in Early Phase of Differentiation

Background: Adipogenesis contributes to the increase in adipose tissue mass. Results: Preadipocytes treated with piceatannol showed reduced adipogenesis with impairment of the early cell cycle progress and insulin-signaling pathway. Conclusion: The anti-adipogenic function of piceatannol is through inhibition of mitotic clonal expansion and insulin receptor activity in the early phase of adipogenesis. Significance: Piceatannol is a novel anti-adipogenic compound that could modulate development of adipose tissue. Piceatannol, a natural stilbene, is an analog and a metabolite of resveratrol. Despite a well documented health benefit of resveratrol in intervention of the development of obesity, the role of piceatannol in the development of adipose tissue and related diseases is unknown. Here, we sought to determine the function of piceatannol in adipogenesis and elucidate the underlying mechanism. We show that piceatannol inhibits adipogenesis of 3T3-L1 preadipocytes in a dose-dependent manner at noncytotoxic concentrations. This anti-adipogenic property of piceatannol was largely limited to the early event of adipogenesis. In the early phase of adipogenesis, piceatannol-treated preadipocytes displayed a delayed cell cycle entry into G2/M phase at 24 h after initiation of adipogenesis. Furthermore, the piceatannol-suppressed mitotic clonal expansion was accompanied by reduced activation of the insulin-signaling pathway. Piceatannol dose-dependently inhibited differentiation mixture-induced phosphorylation of insulin receptor (IR)/insulin receptor substrate-1 (IRS-1)/Akt pathway in the early phase of adipogenesis. Moreover, we showed that piceatannol is an inhibitor of IR kinase activity and phosphatidylinositol 3-kinase (PI3K). Our kinetics study of IR further identified a Km value for ATP of 57.8 μm and a Ki value for piceatannol of 28.9 μm. We also showed that piceatannol directly binds to IR and inhibits IR kinase activity in a mixed noncompetitive manner to ATP, through which piceatannol appears to inhibit adipogenesis. Taken together, our study reveals an anti-adipogenic function of piceatannol and highlights IR and its downstream insulin signaling as novel targets for piceatannol in the early phase of adipogenesis.

An inhibitory effect of resveratrol in the mitotic clonal expansion and insulin signaling pathway in the early phase of adipogenesis

Resveratrol is known as a potent antiobesity compound that acts partly through inhibition of adipogenesis. However, the direct targets responsible for its antiadipogenic action are unclear. Our hypothesis is that resveratrol inhibits adipogenesis through modulation of mitotic clonal expansion (MCE) and cell signaling pathways in the early phase of differentiation. To test this, we examined the effects of resveratrol on MCE and insulin signaling pathway in the early phase of adipogenesis in murine preadipocytes. We observed that the antiadipogenic action of resveratrol is largely limited to the early phase of adipogenesis. Specifically, the presence of resveratrol in the first 24 hours of adipogenesis was required for its antiadipogenic effect. During the first 24 hours of adipogenesis, resveratrol impaired the progression of MCE by suppressing the cell cycle entry of preadipocytes to G2/M phase, and expression of cell cycle regulators cyclin A and cyclin-dependent kinase 2. Concomitantly, resveratrol inhibited insulin signaling pathway in the early phase of adipogenesis. Furthermore, we revealed an inhibitory effect of resveratrol on insulin receptor (IR) activity, and this is likely through a direct physical interaction between resveratrol and IR. The antiadipogenic effect of resveratrol is through inhibition of the MCE and IR-dependent insulin signaling pathway in the early phase of adipogenesis.

Sulforaphane alleviates scopolamine-induced memory impairment in mice

Sulforaphane, an organosulfur compound present in cruciferous vegetables, has been shown to exert neuroprotective effects in experimental in vitro and in vivo models of neurodegeneration. To determine whether sulforaphane can preserve cognitive function, we examined its effects on scopolamine-induced memory impairment in mice using the Morris water maze test. Sulforaphane (10 or 50mg/kg) was administered to C57BL/6 mice by oral gavage for 14 days (days 1-14), and memory impairment was induced by intraperitoneal injection of scopolamine (1mg/kg) for 7 days (days 8-14). Mice that received scopolamine alone showed impaired learning and memory retention and considerably decreased cholinergic system reactivity in the hippocampus and frontal cortex, as indicated by a decreased acetylcholine (ACh) level and an increased acetylcholinesterase (AChE) activity. Sulforaphane significantly attenuated the scopolamine-induced memory impairment and improved cholinergic system reactivity, as indicated by an increased ACh level, decreased AChE activity, and increased choline acetyltransferase (ChAT) expression in the hippocampus and frontal cortex. These effects of sulforaphane on cholinergic system reactivity were confirmed in vitro. Sulforaphane (10 or 20μM) increased the ACh level, decreased the AChE activity, and increased ChAT expression in scopolamine-treated primary cortical neurons. These observations suggest that sulforaphane might exert a significant neuroprotective effect on cholinergic deficit and cognitive impairment.

Eupatilin, a major flavonoid of Artemisia, attenuates aortic smooth muscle cell proliferation and migration by inhibiting PI3K, MKK3/6, and MKK4 activities.

Eupatilin, a major flavonoid of plants in the genus Artemisia, has been shown to exhibit anti-inflammatory, anti-oxidative, and anti-tumor effects. However, the potential anti-atherogenic effects of eupatilin and any underlying mechanisms have not been investigated. In the present study, we sought to determine the effects of eupatilin on phenotypes induced by the growth factor PDGF-BB in human aortic smooth muscle cells. Here we show that aortic sprouting as well as PDGF-BB-induced proliferation and migration of human aortic smooth muscle cells were significantly inhibited by eupatilin. We found that eupatilin inhibited PI3K activity, causing a direct effect on phosphorylation of the downstream kinases Akt and p70S6K. In parallel, eupatilin also inhibited the phosphorylation of MKK3/6-p38 MAPK and the MKK4-JNK pathway. Moreover we found that eupatilin exhibited stronger inhibition effects on PDGF-BB-induced proliferation and migration of human aortic smooth muscle cells than PI3K, p38 MAPK, and JNK pathway inhibitors. Taken together, our results indicate that eupatilin is a potent anti-atherogenic agent that inhibits PDGF-BB-induced proliferation and migration in HASMCs as well as aortic sprouting, which is likely mediated through the attenuation of PI3K, MKK3/6, and MKK4 activation.

Licochalcone A, a Polyphenol Present in Licorice, Suppresses UV-Induced COX-2 Expression by Targeting PI3K, MEK1, and B-Raf

Licorice is a traditional botanical medicine, and has historically been commonly prescribed in Asia to treat various diseases. Glycyrrhizin (Gc), a triterpene compound, is the most abundant phytochemical constituent of licorice. However, high intake or long-term consumption of Gc has been associated with a number of side effects, including hypertension. However, the presence of alternative bioactive compounds in licorice with anti-carcinogenic effects has long been suspected. Licochalcone A (LicoA) is a prominent member of the chalcone family and can be isolated from licorice root. To date, there have been no reported studies on the suppressive effect of LicoA against solar ultraviolet (sUV)-induced cyclooxygenase (COX)-2 expression and the potential molecular mechanisms involved. Here, we show that LicoA, a major chalcone compound of licorice, effectively inhibits sUV-induced COX-2 expression and prostaglandin E2 PGE2 generation through the inhibition of activator protein 1 AP-1 transcriptional activity, with an effect that is notably more potent than Gc. Western blotting analysis shows that LicoA suppresses sUV-induced phosphorylation of Akt/ mammalian target of rapamycin (mTOR) and extracellular signal-regulated kinases (ERK)1/2/p90 ribosomal protein S6 kinase (RSK) in HaCaT cells. Moreover, LicoA directly suppresses the activity of phosphoinositide 3-kinase (PI3K), mitogen-activated protein kinase kinase (MEK)1, and B-Raf, but not Raf-1 in cell-free assays, indicating that PI3K, MEK1, and B-Raf are direct molecular targets of LicoA. We also found that LicoA binds to PI3K and B-Raf in an ATP-competitive manner, although LicoA does not appear to compete with ATP for binding with MEK1. Collectively, these results provide insight into the biological action of LicoA, which may have potential for development as a skin cancer chemopreventive agent.

Essential role of Cenexin1, but not Odf2, in ciliogenesis.

Primary cilia are microtubule-based solitary sensing structures on the cell surface that play crucial roles in cell signaling and development. Abnormal ciliary function leads to various human genetic disorders, collectively known as ciliopathies. Outer dense fiber protein 2 (Odf2) was initially isolated as a major component of sperm-tail fibers. Subsequent studies have demonstrated the existence of many splicing variants of Odf2, including Cenexin1 (Odf2 isoform 9), which bears an unusual C-terminal extension. Strikingly, Odf2 localizes along the axoneme of primary cilia, whereas Cenexin1 localizes to basal bodies in cultured mammalian cells. Whether Odf2 and Cenexin1 contribute to primary cilia assembly by carrying out either concerted or distinct functions is unknown. By taking advantage of odf2−/− cells lacking endogenous Odf2 and Cenexin1, but exogenously expressing one or both of these proteins, we showed that Cenexin1, but not Odf2, was necessary and sufficient to induce ciliogenesis. Furthermore, the Cenexin1-dependent primary cilia assembly pathway appeared to function independently of Odf2. Consistently, Cenexin1, but not Odf2, interacted with GTP-loaded Rab8a, localized to the distal/subdistal appendages of basal bodies, and facilitated the recruitment of Chibby, a centriolar component that is important for proper ciliogenesis. Taken together, our results suggest that Cenexin1 plays a critical role in ciliogenesis through its C-terminal extension that confers a unique ability to mediate primary cilia assembly. The presence of multiple splicing variants hints that the function of Odf2 is diversified in such a way that each variant has a distinct role in the complex cellular and developmental processes.

Quercetin suppresses invasion and migration of H-Ras-transformed MCF10A human epithelial cells by inhibiting phosphatidylinositol 3-kinase.

Quercetin is a major flavonoid compound found in red wine at a much higher concentration than the phytoalexin resveratrol. In this study, we examined potential anti-metastatic effects and found that compared to resveratrol, quercetin more potently inhibits H-Ras-induced invasion and migration in MCF10A human epithelial cells, an effect likely mediated by the mitigation of matrix metalloproteinase (MMP)-2 activation. We then measured Akt phosphorylation to investigate whether the decreased MMP-2 activation was attributable to the inhibition of phosphatidylinositol 3-kinase (PI3K)/Akt signalling. Quercetin, but not resveratrol at equivalent concentrations, suppressed the phosphorylation of Akt and was a more potent inhibitor of PI3K activity than resveratrol. An ex vivo binding assay further revealed that quercetin directly binds to PI3K. Collectively, these results suggest that PI3K is a molecular target of quercetin for the inhibition of H-Ras-induced invasion and migration of MCF10A cells.

Caffeic Acid Phenethyl Ester, a Major Component of Propolis, Suppresses High Fat Diet-Induced Obesity through Inhibiting Adipogenesis at the Mitotic Clonal Expansion Stage

In the present study, we aimed to investigate the antiobesity effect of CAPE in vivo, and the mechanism by which CAPE regulates body weight in vitro. To confirm the antiobesity effect of CAPE in vivo, mice were fed with a high fat diet (HFD) with different concentrations of CAPE for 5 weeks. CAPE significantly reduced body weight gain and epididymal fat mass in obese mice fed a HFD. In accordance with in vivo results, Oil red O staining results showed that CAPE significantly suppressed MDI-induced adipogenesis of 3T3-L1 preadipocytes. FACS analysis results showed that CAPE delayed MDI-stimulated cell cycle progression, thereby contributing to inhibit mitotic clonal expansion (MCE), which is a prerequisite step for adipogenesis. Also, CAPE regulated the expression of cyclin D1 and the phosphorylation of ERK and Akt, which are upstream of cyclin D1. These results suggest that CAPE exerts an antiobesity effect in vivo, presumably through inhibiting adipogenesis at an early stage of adipogenesis.

Dehydroglyasperin C Suppresses TPA-Induced Cell Transformation Through Direct Inhibition of MKK4 and PI3K

Bioactive natural compounds from plant‐derived sources have received substantial interest due to their potential therapeutic and preventive effects toward various human diseases. Licorice (Glycyrrhiza), a frequently‐used component in traditional oriental medicines, has been incorporated into recipes not only to enhance taste, but also to treat various conditions including inflammation, chronic fatigue syndrome, and even cancer. Dehydroglyasperin C (DGC) is a major isoflavone found in the root of licorice. In the present study, we investigated the cancer chemopreventive effect of DGC and the underlying molecular mechanisms involved, by analyzing its effects on 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA)‐induced neoplastic cell transformation and cyclooxygenase (COX)‐2 expression in JB6 P+ mouse epidermal cells. DGC treatment attenuated TPA‐induced activator protein‐1 (AP‐1) and nuclear factor‐κB (NF‐κB) transcriptional activation, two major regulators of TPA‐induced cell transformation, and COX‐2 expression. TPA‐induced phosphorylation of p38, JNK1/2 and Akt was also suppressed by DGC. Kinase assay data revealed that DGC inhibited the kinase activity of MKK4 and PI3K and this outcome was due to direct physical binding with DGC. Notably, DGC bound directly to MKK4 and PI3K in an ATP‐competitive manner. Taken together, these results suggest that DGC exhibits cancer chemopreventive potential via its inhibitory effect on TPA‐induced neoplastic cell transformation and COX‐2 modulation through regulation of the MKK4 and PI3K pathways.

Persimmon peel extract attenuates PDGF-BB-induced human aortic smooth muscle cell migration and invasion through inhibition of c-Src activity.

The unregulated migration and invasion of human aortic smooth muscle cells (HASMCs) into the intima is a crucial step in the development of atherosclerosis. Recently, the oriental persimmon extract (Diospyros kaki Thunb. cv. Fuyu) has been investigated for its anti-atherogenic properties, but the molecular mechanisms involved remain unclear. We investigated the inhibitory effects of persimmon peel and flesh extract on the platelet-derived growth factor (PDGF) BB-induced MMP-1 expression using Western blot, and abnormal migration and invasion of HASMCs using a modified Boyden chamber assay and a wound healing assay. We also evaluated the inhibitory effects of persimmon peel extract on aortic vessel thickening using a rat aortic sprouting assay. Persimmon peel (PPE), but not flesh extract (PFE), inhibited PDGF-BB-induced MMP-1 expression, cell migration and invasion in HASMCs, while suppressing the rat aortic sprouting. Western blot and in vitro kinase assay data demonstrated that PPE inhibited Src kinase activity and subsequently attenuated PDGF-BB-induced phosphorylation of MAPK and Akt signalling pathways. Taken together, our results indicate that persimmon peel might possess a potential anti-atherogenic effect through attenuation of ASMCs migration and invasion and aortic sprouting by direct inhibition of the c-Src kinase activity.