Dysregulation of lipid homeostasis is a common feature of several major human diseases, including type 2 diabetes and cardiovascular disease. However, because of the complex nature of lipid metabolism, the regulatory mechanisms remain poorly defined at the molecular level. As the key transcriptional activators of lipogenic genes, such as fatty acid synthase (FAS), sterol regulatory element-binding proteins (SREBPs) play a pivotal role in stimulating lipid biosynthesis. Several studies have shown that SREBPs are regulated by the NAD(+)-dependent histone deacetylase SIRT1, which forms a complex with the lysine-specific histone demethylase LSD1. Here, we show that LSD1 plays a role in regulating SREBP1-mediated gene expression. Multiple lines of evidence suggest that LSD1 is required for SREBP1-dependent activation of the FAS promoter in mammalian cells. LSD1 knockdown decreases SREBP-1a at the transcription level. Although LSD1 affects nuclear SREBP-1 abundance indirectly through SIRT1, it is also required for SREBP1 binding to the FAS promoter. As a result, LSD1 knockdown decreases triglyceride levels in hepatocytes. Taken together, these results show that LSD1 plays a role in regulating lipogenic gene expression, suggesting LSD1 as a potential target for treating dysregulation of lipid metabolism.
Dysregulation of lipid homeostasis is intimately associated with obesity, type 2 diabetes, and cardiovascular diseases. Sterol regulatory-element binding proteins (SREBPs) are the master regulators of lipid biosynthesis. Previous studies have shown that the conserved transcriptional cofactor Mediator complex is critically required for the SREBP transcriptional activity, and recruitment of the Mediator complex to the SREBP transactivation domains (TADs) is through the MED15-KIX domain. Recently, we have synthesized several boron-containing small molecules. Among these novel compounds, BF175 can specifically block the binding of MED15-KIX to SREBP1a-TAD in vitro, resulting in an inhibition of the SREBP transcriptional activity and a decrease of SREBP target gene expression in cultured hepatocytes. Furthermore, BF175 can improve lipid homeostasis in the mouse model of diet-induced obesity. Compared with the control, BF175 treatment decreased the expression of SREBP target genes in mouse livers and decreased hepatic and blood levels of lipids. These results suggest that blocking the interaction between SREBP-TADs and the Mediator complex by small molecules may represent a novel approach for treating diseases with aberrant lipid homeostasis.
Mice treated with the antidepressant trans-2-phenylcyclopropylamine (2-PCPA) were protected against diet-induced-obesity, and adiposity was reversed in pre-established diet-induced obese mice. Contrary to a recent report that inhibition of lysine-specific demethylase-1 by 2-PCPA results in increased energy expenditure, long-term 2-PCPA treatment had no such effect but its protection against obesity was associated with increased spontaneous locomotor activity, Moreover, pair feeding to assure equal caloric intake in wild type mice as well as in genetic hyperphagic mice (ob/ob) also resulted in weight reduction in 2-PCPA treated mice that correlated with increased activity but no change in energy expenditure. Similarly, short-term intraperitoneal injections of 2-PCPA did not affect food intake but caused a substantial increase in locomotor activity in the light cycle that correlated with increased energy expenditure, whereas activity and energy expenditure were unchanged in the dark cycle. Lastly, 2-PCPA was also effective in reducing obesity in genetic UCP1 null mice. These data suggest that 2-PCPA can reduce obesity by decreasing food intake in the long term while increasing activity in the short-term. However, the protective and weight loss effects of 2-PCPA are independent of UCP1-regulated thermogenesis or basal energy expenditure.
Natural polyphenols, such as resveratrol, have beneficial functions on major human diseases such as cancer, diabetes, and cardiovascular disease. Besides acting as antioxidants, some of these polyphenols can also target proteins to modulate specific biological pathways. The lysine-specific histone demethylase LSD1 plays important roles in cell growth, differentiation and nutrient metabolism. Here, we studied the effect of natural polyphenols resveratrol, curcumin, quercetin and analogs on LSD1. Using in vitro LSD1 enzymatic assays, we show that resveratrol, curcumin and quercetin displayed a potent inhibitory effect on the LSD1 activity and were more potent than the known LSD1 inhibitor trans-2-phenylcyclopropylamine (TCP). The new function of resveratrol, curcumin and quercetin is independent of their antioxidant properties, as other antioxidants had no effect on LSD1 under the similar conditions. In C2C12 fibroblasts, resveratrol and curcumin can efficiently inhibit myogenic expression and differentiation, for which LSD1 is required. Thus, our study has identified LSD1 as a novel target of bioactive natural compounds, such as resveratrol, curcumin and quercetin, and such finding suggests that LSD1 inhibition can at least partially contribute to some of the previously observed beneficial effects of these compounds.
Two-photon microscopy has advanced fluorescence imaging of cellular processes in living animals. Fluorescent proteins in the blue-green wavelength range are widely used in two-photon microscopy; however, the use of red fluorescent proteins is limited by the low power output of Ti-Sapphire lasers above 1,000 nm. To overcome this limitation we have developed two red fluorescent proteins, LSS-mKate1 and LSS-mKate2, which possess large Stokes shifts with excitation/emission maxima at 463/624 and 460/605 nm, respectively. These LSS-mKates are characterized by high pH stability, photostability, rapid chromophore maturation, and monomeric behavior. They lack absorbance in the green region, providing an additional red color to the commonly used red fluorescent proteins. Substantial overlap between the two-photon excitation spectra of the LSS-mKates and blue-green fluorophores enables multicolor imaging using a single laser. We applied this approach to a mouse xenograft model of breast cancer to intravitally study the motility and Golgi-nucleus alignment of tumor cells as a function of their distance from blood vessels. Our data indicate that within 40 mum the breast cancer cells show significant polarization towards vessels in living mice.
Altered lipid metabolism underlies several major human diseases, including obesity and type 2 diabetes. However, lipid metabolism pathophysiology remains poorly understood at the molecular level. Insulin is the primary stimulator of hepatic lipogenesis through activation of the SREBP-1c transcription factor. Here we identified cyclin-dependent kinase 8 (CDK8) and its regulatory partner cyclin C (CycC) as negative regulators of the lipogenic pathway in Drosophila, mammalian hepatocytes, and mouse liver. The inhibitory effect of CDK8 and CycC on de novo lipogenesis was mediated through CDK8 phosphorylation of nuclear SREBP-1c at a conserved threonine residue. Phosphorylation by CDK8 enhanced SREBP-1c ubiquitination and protein degradation. Importantly, consistent with the physiologic regulation of lipid biosynthesis, CDK8 and CycC proteins were rapidly downregulated by feeding and insulin, resulting in decreased SREBP-1c phosphorylation. Moreover, overexpression of CycC efficiently suppressed insulin and feeding-induced lipogenic gene expression. Taken together, these results demonstrate that CDK8 and CycC function as evolutionarily conserved components of the insulin signaling pathway in regulating lipid homeostasis.
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