Browsing by Author "Liu, Longhua"
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- Coordinated Upregulation of Mitochondrial Biogenesis and Autophagy in Breast Cancer Cells: The Role of Dynamin Related Protein-1 and Implication for Breast Cancer TreatmentZou, Peng; Liu, Longhua; Zheng, Louise D.; Payne, Kyle K.; Manjili, Masoud H.; Idowu, Michael O.; Zhang, Jinfeng; Schmelz, Eva M.; Cheng, Zhiyong (Hindawi, 2016-09-26)Overactive mitochondrial fission was shown to promote cell transformation and tumor growth. It remains elusive how mitochondrial quality is regulated in such conditions. Here, we show that upregulation of mitochondrial fission protein, dynamin related protein-1 (Drp1), was accompanied with increased mitochondrial biogenesis markers (PGC1α, NRF1, and Tfam) in breast cancer cells. However, mitochondrial number was reduced, which was associated with lower mitochondrial oxidative capacity in breast cancer cells. This contrast might be owing to enhanced mitochondrial turnover through autophagy, because an increased population of autophagic vacuoles engulfing mitochondria was observed in the cancer cells. Consistently, BNIP3 (a mitochondrial autophagy marker) and autophagic flux were significantly upregulated, indicative of augmented mitochondrial autophagy (mitophagy). The upregulation of Drp1 and BNIP3 was also observed in vivo (human breast carcinomas). Importantly, inhibition of Drp1 significantly suppressed mitochondrial autophagy, metabolic reprogramming, and cancer cell viability. Together, this study reveals coordinated increase of mitochondrial biogenesis and mitophagy in which Drp1 plays a central role regulating breast cancer cell metabolism and survival. Given the emerging evidence of PGC1α contributing to tumor growth, it will be of critical importance to target both mitochondrial biogenesis and mitophagy for effective cancer therapeutics.
- FoxO1 in the regulation of adipocyte autophagy and biologyLiu, Longhua (Virginia Tech, 2016-12-08)Obesity is a rapidly growing epidemic in the USA and worldwide. While the molecular and cellular mechanism of obesity is incompletely understood, studies have shown that excess adiposity may arise from increased adipogenesis (hyperplasia) and adipocyte size (hypertrophy) . Emerging evidence underscores autophagy as an important mediator of adipogenesis and adiposity. We are interested in the upstream regulator of adipocyte autophagy and how it impacts adipocyte biology. Given that metabolic stress activates transcription factor FoxO1 in obesity, my dissertation project is designed to depict the role of FoxO1 in adipocyte autophagy and biology. We found that FoxO1 upregulation was concomitant with elevation of autophagy activity during adipogenesis. Inhibition of FoxO1 suppressed autophagy flux and almost completely prevented adipocyte differentiation. For the first time, we found that the kinetics of FoxO1 activation followed a series of sigmoid curves that showed multiple activation-inactivation transitions during adipogenesis. Our study provides critical evidence casting light on the controversy in the literature that either persistent inhibition or activation of FoxO1 suppresses adipogenesis. In addition, we identified two central pathways that FoxO1-mediated autophagy regulated adipocyte biology: (1) to control lipid droplet growth via fat specific protein 27 (FSP27) in adipocytes; and (2) to differentially regulate mitochondrial uncoupling proteins (UCP) that have been implicated in browning of white adipose tissue and redox homeostasis. Mechanistically, FoxO1 appears to induce autophagy through the transcription factor EB (Tfeb), which was previously shown to regulate both autophagosome and lysosome. Chromatin immunoprecipitation assay demonstrated that FoxO1 directly bound to the promoter of Tfeb, and inhibition of FoxO1 attenuated the binding, which resulted in reduced Tfeb expression. To investigate the role of FoxO1 in vivo, we have developed mouse models to modulate FoxO1 in adipose tissue using an inducible Cre-loxP system. Tamoxifen is widely used to activate the inducible Cre recombinase that spatiotemporally control target gene expression in animal models, but it was unclear whether tamoxifen itself may affect adiposity and confounds phenotyping. Part of my dissertation work was to address this important question. We found that tamoxifen led to reduced fat mass independent of Cre, which lasted for 4-5 weeks. Mechanistically, Tamoxifen induced reactive oxygen species (ROS) and augmented apoptosis. Our data reveals a critical period of recovery following tamoxifen treatment in the study of inducible knockout mice. Together, my dissertation work demonstrates FoxO1 as a critical regulator of adipocyte autophagy via Tfeb during adipogenesis. FoxO1-mediated autophagy controls FSP27, lipid droplet growth, and mitochondrial uncoupling proteins. Further study of FoxO1-autophagy axis in obese subjects is of physiological significance, and the investigation is under way.
- FoxO1 interacts with transcription factor EB and differentially regulates mitochondrial uncoupling proteins via autophagy in AdipocytesLiu, Longhua; Tao, Zhipeng; Zheng, Louise D.; Brooke, Joseph P.; Smith, Cayleen M.; Liu, Dongmin; Long, Yun Chau; Cheng, Zhiyong (Nature, 2016-10-03)Mitochondrial uncoupling proteins (UCPs) are inducible and play an important role in metabolic and redox homeostasis. Recent studies have suggested that FoxO1 controls mitochondrial biogenesis and morphology, but it remains largely unknown how FoxO1 may regulate mitochondrial UCPs. Here we show that FoxO1 interacted with transcription factor EB (Tfeb), a key regulator of autophagosome and lysosome, and mediated the expression of UCP1, UCP2 and UCP3 differentially via autophagy in adipocytes. UCP1 was down-regulated but UCP2 and UCP3 were upregulated during adipocyte differentiation, which was associated with increased Tfeb and autophagy activity. However, inhibition of FoxO1 suppressed Tfeb and autophagy, attenuating UCP2 and UCP3 but increasing UCP1 expression. Pharmacological blockade of autophagy recapitulated the effects of FoxO1 inhibition on UCPs. Chromatin immunoprecipitation assay demonstrated that FoxO1 interacted with Tfeb by directly binding to its promoter, and silencing FoxO1 led to drastic decrease in Tfeb transcript and protein levels. These data provide the first line of evidence that FoxO1 interacts with Tfeb to regulate autophagy and UCP expression in adipocytes. Dysregulation of FoxO1→autophagy→UCP pathway may account for metabolic changes in obesity.
- Insulin resistance is associated with epigenetic and genetic regulation of mitochondrial DNA in obese humansZheng, Louise D.; Linarelli, Leah E.; Liu, Longhua; Wall, Sarah S.; Greenawald, Mark H.; Seidel, Richard W.; Estabrooks, Paul A.; Almeida, Fabio A.; Cheng, Zhiyong (2015-06-10)Background Mitochondrial alterations have been observed in subjects with metabolic disorders such as obesity and diabetes. Studies on animal models and cell cultures suggest aberrant glucose and lipid levels, and impaired insulin signaling might lead to mitochondrial changes. However, the molecular mechanism underlying mitochondrial aberrance remains largely unexplored in human subjects. Results Here we show that the mitochondrial DNA copy number (mtDNAn) was significantly reduced (6.9-fold lower, p < 0.001) in the leukocytes from obese humans (BMI >30). The reduction of mtDNAn was strongly associated with insulin resistance (HOMA-IR: −0.703, p < 0.05; fasting insulin level: −0.015, p < 0.05); by contrast, the correlation between fasting glucose or lipid levels and mtDNAn was not significant. Epigenetic study of the displacement loop (D-loop) region of mitochondrial genome, which controls the replication and transcription of the mitochondrial DNA as well as organization of the mitochondrial nucleoid, revealed a dramatic increase of DNA methylation in obese (5.2-fold higher vs. lean subjects, p < 0.05) and insulin-resistant (4.6-fold higher vs. insulin-sensitive subjects, p < 0.05) individuals. Conclusions The reduction of mtDNAn in obese human subjects is associated with insulin resistance and may arise from increased D-loop methylation, suggesting an insulin signaling-epigenetic-genetic axis in mitochondrial regulation.
- Tamoxifen reduces fat mass by boosting reactive oxygen speciesLiu, Longhua; Zou, Peng; Zheng, Louise; Linarelli, Leah E.; Amarell, Sarah M.; Passaro, Austin; Liu, Dongmin; Cheng, Zhiyong (Nature Publishing Group, 2015-01-08)As the pandemic of obesity is growing, a variety of animal models have been generated to study the mechanisms underlying the increased adiposity and development of metabolic disorders. Tamoxifen (Tam) is widely used to activate Cre recombinase that spatiotemporally controls target gene expression and regulates adiposity in laboratory animals. However, a critical question remains as to whether Tam itself affects adiposity and possibly confounds the functional study of target genes in adipose tissue. Here we administered Tam to Cre-absent forkhead box O1 (FoxO1) floxed mice (f-FoxO1) and insulin receptor substrate Irs1/Irs2 double floxed mice (df-Irs) and found that Tam induced approximately 30% reduction (P<0.05) in fat mass with insignificant change in body weight. Mechanistically, Tam promoted reactive oxygen species (ROS) production, apoptosis and autophagy, which was associated with downregulation of adipogenic regulator peroxisome proliferator-activated receptor gamma and dedifferentiation of mature adipocytes. However, normalization of ROS potently suppressed Tam-induced apoptosis, autophagy and adipocyte dedifferentiation, suggesting that ROS may account, at least in part, for the changes. Importantly, Tam-induced ROS production and fat mass reduction lasted for 4-5 weeks in the f-FoxO1 and df-Irs mice. Our data suggest that Tam reduces fat mass via boosting ROS, thus making a recovery period crucial for posttreatment study.
- Targeting FoxO1 with AS1842856 Suppresses AdipogenesisZou, Peng; Liu, Longhua; Zheng, Louise; Liu, Lu; Stoneman, Rebecca E.; Cho, Alicia; Emery, Ashley; Gilbert, Elizabeth R.; Cheng, Zhiyong (Taylor & Francis, 2014-12-01)Hyperplasia (i.e., increased adipogenesis) contributes to excess adiposity, the hallmark of obesity that can trigger metabolic complications. As FoxO1 has been implicated in adipogenic regulation, we investigated the kinetics of FoxO1 activation during adipocyte differentiation, and tested the effects of FoxO1 antagonist (AS1842856) on adipogenesis. We found for the first time that the kinetics of FoxO1 activation follows a series of sigmoid curves, and reveals the phases relevant to clonal expansion, cell cycle arrest, and the regulation of PPAR?, adiponectin, and mitochondrial proteins (complexes I and III). In addition, multiple activation-inactivation transitions exist in the stage of terminal differentiation. Importantly, persistent inhibition of FoxO1 with AS1842856 almost completely suppressed adipocyte differentiation, while selective inhibition in specific stages had differential effects on adipogenesis. Our data present a new view of FoxO1 in adipogenic regulation, and suggest AS1842856 can be an anti-obesity agent that warrants further investigation.