a-filtration-based-method-preparing-high-quality-nuclei-from-cross

A Filtration-based Method of Preparing High-quality Nuclei from Cross-linked Skeletal Muscle for Chromatin Immunoprecipitation

Chromatin immunoprecipitation (ChIP) is a powerful method to determine protein binding to chromatin DNA. Fiber-rich skeletal muscle, however, has been a ...

University of Texas Health Science Center at Houston

The mechanism of induction of apoptosis by dolichyl phosphate (Dol-P) was investigated in U937 cells. Studies using isolated mitochondria revealed that the respiratory complex II activity was almost completely inhibited by 20 microg/ml of Dol-P but not by the same concentration of dolichol. Activities of complex I and III were also inhibited by Dol-P, but nearly 50% of activity still remained at 20 microg/ml. Dol-P induced release of cytochrome-c from the isolated mitochondria. Fluorometric microtiter plate assay revealed that generation of reactive oxygen species (ROS) increased in a time-dependent manner. Flow cytometric analysis also indicated that Dol-P caused loss of mitochondrial membrane potential (Deltapsi(m)) and increased ROS generation. The addition of the antioxidant pyrrolidine dithiocarbamate (PDTC) significantly inhibited Dol-P-induced ROS generation and activation of caspase-3. A specific inhibitor of respiratory complex II, thenoyltrifluoroacetone (TTFA), increased ROS generation, potentially mimicking the consequence of inhibition of electron flow at complex II by Dol-P in U937 cells. Electron microscopy revealed that mitochondria became swollen and spherical in shape by the treatment with Dol-P. Neither the tyrosine kinase inhibitor k252a nor mitogen activated protein kinase/extracellular signal-regulated kinase kinase (MEK) inhibitors PD98059 and U0126 inhibited the Dol-P-induced apoptosis. Together, these results suggest that the direct disruption of mitochondrial respiratory complexes and the consequent ROS generation play a critical role in the initiation of Dol-P-induced apoptosis.

Generation of reactive oxygen species is an early event in dolichyl phosphate-induced apoptosis.

T-2 toxin, which belongs to a group of mycotoxins synthesized by Fusarium fungi that are widely encountered as natural contaminants, induced apoptosis with distinct morphological and biological features in U937 cells. The concentration of more than 10nM T-2 toxin affected cell viability, induced nuclear and DNA fragmentation and caspase-3 activation. Caspase-2, -3, -8, and -9 were activated during T-2 toxin-induced apoptosis. T-2 toxin neither inhibited mitochondrial respiratory chain complexes I-IV in isolated mitochondria nor decreased ATP levels in U937 cells. Both enzyme activity assay and Western blot analysis revealed that T-2 toxin activated caspase-2 earlier than caspase-3, -8, and -9. Caspase-2 inhibitor (VDVAD-CHO/fmk) and caspase-8 inhibitor (IETD-CHO/fmk) completely blocked the T-2 toxin-induced process of procaspase-3, while caspase-9 inhibitor (LEHD-CHO/fmk) did so less effectively. Caspase-2 inhibitor entirely blocked T-2 toxin-induced caspase-8, and -9 activation. These results clearly indicate that activation of caspase-2 is essential to T-2 toxin-induced apoptosis and that apoptotic signals are mainly transmitted via caspase-8 and caspase-3 rather than mitochondrial pathway.

T-2 toxin initially activates caspase-2 and induces apoptosis in U937 cells.

Butyrate, a short chain fatty acid, exhibits a wide variety of biological effects including the inhibition of cell growth, change of cellular morphology and the induction of apoptosis. Sodium butyrate-induced apoptosis has been reported to associate with the up-regulation of pro-apoptotic Bax expression, and the down-regulation of anti-apoptotic Bcl-2 and Bcl-XL expressions. However, in some cases, butyrate has also been shown to cause apoptosis without change in Bcl-2, Bcl-XL and/or Bax. This study investigates the detailed mechanisms of sodium butyrate-induced apoptosis. The effect of sodium butyrate was analyzed in the induction of caspase activities, formation of caspase active forms and mRNA levels in human breast cancer cell line MRK-nu-1. Induction of activities of caspase-3, -10 and, to some extent, -8 and formation of DNA fragmentation were observed with sodium butyrate in a dose- and/or time-dependent manner. The levels of caspase-10 mRNA expression markedly increased in a time-dependent manner by the treatment of sodium butyrate, whereas caspase-8 mRNA expression was not changed. Inhibitors of caspase-8 and caspase-10 reduced caspase-3 activity and subsequent DNA fragmentation induced by sodium butyrate. These caspase inhibitors also inhibited the cleavage of pro-caspase-3 to the active forms indicated by Western blotting analysis. Pyrrolidine dithiocarbamate also inhibited the induction of caspase-10 mRNA expression and caspase-3 activation. Contrary to other reports, levels of Bcl-2, Bcl-XL and Bax mRNA expressions were not distinctly changed by even 5 mM sodium butyrate treatment. Our results suggest that sodium butyrate may trigger apoptosis via the induction of the caspase-10 expression.

The important role of caspase-10 in sodium butyrate-induced apoptosis.

In mammals, males consume more food, which is considered a masculinized behavior, but the underlying mechanism of this sex-specific feeding behavior is unknown. In mice, neonatal testosterone (NT) is critical to masculinize the developing brain, leading to sex differences in reproductive physiology. The proopiomelanocortin (POMC) neurons of the hypothalamic arcuate nucleus (ARC) are critical to suppress energy intake and POMC innervation of hypothalamic feeding circuits develops to a large extent neonatally. We hypothesized that NT programs the masculinization of energy intake by programming POMC neurons. We tested this hypothesis by comparing control females and control males (CMs) with female mice neonatally androgenized with testosterone (NTFs). We show that increased food intake in CMs is associated with reduced POMC expression and decreased intensity of neuronal projections from POMC neurons within the ARC compared with control females. We found that NTFs display a masculinized energy intake and ARC POMC expression and innervation as observed in CMs, which can be mimicked by neonatal exposure to the androgen receptor agonist dihydrotestosterone (DHT). NTFs also exhibit hyperleptinemia and a decreased ability of leptin to up-regulate POMC, suppress food intake, and prevent adipose tissue accumulation, independent of signal transducer and activator of transcription 3. However, this leptin resistance is specific to NTFs, is not a consequence of masculinization, and is reproduced by neonatal exposure to estrogen but not DHT. Thus, NT programs a sexual differentiation of POMC neurons in female mice via DHT but also predisposes to leptin resistance and obesity in an estrogen-dependent manner.

Early-life exposure to testosterone programs the hypothalamic melanocortin system.

Among women, the polycystic ovarian syndrome (PCOS) is considered a form of metabolic syndrome with reproductive abnormalities. Women with PCOS show increased sympathetic tone, visceral adiposity with enlarged adipocytes, hypoadiponectinemia, insulin resistance, glucose intolerance, increased inactive osteocalcin, and hypertension. Excess fetal exposure to androgens has been hypothesized to play a role in the pathogenesis of PCOS. Previously, we showed that neonatal exposure to the androgen testosterone (NT) programs leptin resistance in adult female mice. Here, we studied the impact of NT on lean and adipose tissues, sympathetic tone in cardiometabolic tissues, and the development of metabolic dysfunction in mice. Neonatally androgenized adult female mice (NTF) displayed masculinization of lean tissues with increased cardiac and skeletal muscle as well as kidney masses. NTF mice showed increased and dysfunctional white adipose tissue with increased sympathetic tone in both visceral and subcutaneous fat as well as increased number of enlarged and insulin-resistant adipocytes that displayed altered expression of developmental genes and hypoadiponectinemia. NTF exhibited dysfunctional brown adipose tissue with increased mass and decreased energy expenditure. They also displayed decreased undercarboxylated and active osteocalcin and were predisposed to obesity during chronic androgen excess. NTF showed increased renal sympathetic tone associated with increased blood pressure, and they developed glucose intolerance and insulin resistance. Thus, developmental exposure to testosterone in female mice programs features of cardiometabolic dysfunction, as can be observed in women with PCOS, including increased sympathetic tone, visceral adiposity, insulin resistance, prediabetes, and hypertension.

Developmental androgen excess programs sympathetic tone and adipose tissue dysfunction and predisposes to a cardiometabolic syndrome in female mice.

Polycystic ovary syndrome is a common endocrine disorder in females of reproductive age and is believed to have a developmental origin in which gestational androgenization programs reproductive and metabolic abnormalities in offspring. During gestation, both male and female fetuses are exposed to potential androgen excess. In this study, we determined the consequences of developmental androgenization in male mice exposed to neonatal testosterone (NTM). Adult NTM displayed hypogonadotropic hypogonadism with decreased serum testosterone and gonadotropin concentrations. Hypothalamic KiSS1 neurons are believed to be critical to the onset of puberty and are the target of leptin. Adult NTM exhibited lower hypothalamic Kiss1 expression and a failure of leptin to upregulate Kiss1 expression. NTM displayed an early reduction in lean mass, decreased locomotor activity, and decreased energy expenditure. They displayed a delayed increase in subcutaneous white adipose tissue amounts. Thus, excessive neonatal androgenization disrupts reproduction and energy homeostasis and predisposes to hypogonadism and obesity in adult male mice.

Developmental androgen excess disrupts reproduction and energy homeostasis in adult male mice.

Androgen excess in women is associated with visceral adiposity. However, little is known on the mechanism through which androgen promotes visceral fat accumulation.

Central mechanisms of adiposity in adult female mice with androgen excess.

Modernization of human society parallels an epidemic of metabolic disorders including obesity. Apart from excess caloric intake, a 24/7 lifestyle poses another important challenge to our metabolic health. Recent research under both laboratory and epidemiological settings has indicated that abnormal temporal organization of sleep and wakeful activities including food intake is a significant risk factor for metabolic disease. The circadian clock system is our intrinsic biological timer that regulates internal rhythms such as the sleep/wake cycle and also responses to external stimuli including light and food. Initially thought to be mainly involved in the timing of sleep, the clock, and/or clock genes may also play a role in sleep architecture and homeostasis. Importantly, an extensive body of evidence has firmly established a master regulatory role of the clock in energy balance. Together, a close relationship between well-timed circadian/sleep cycles and metabolic health is emerging. Exploiting this functional connection, an important holistic strategy toward curbing the epidemic of metabolic disorders (e.g., obesity) involves corrective measures on the circadian clock and sleep. In addition to behavioral and environmental interventions including meal timing and light control, pharmacological agents targeting sleep and circadian clocks promise convenient and effective applications. Recent studies, for example, have reported small molecules targeting specific clock components and displaying robust beneficial effects on sleep and metabolism. Furthermore, a group of clock-amplitude-enhancing small molecules (CEMs) identified via high-throughput chemical screens are of particular interest for future in vivo studies of their metabolic and sleep efficacies. Elucidating the functional relationship between clock, sleep, and metabolism will also have far-reaching implications for various chronic human diseases and aging.

Manipulating the circadian and sleep cycles to protect against metabolic disease.

Dietary fibers are increasingly appreciated as beneficial nutritional components. However, a requisite role of gut microbiota in fiber function and the overall impact of fibers on metabolomic flux remain unclear. We herein showed enhancing effects of a soluble resistant maltodextrin (RM) on glucose homeostasis in mouse metabolic disease models. Remarkably, fecal microbiota transplantation (FMT) caused pronounced and time-dependent improvement in glucose tolerance in RM recipient mice, indicating a causal relationship between microbial remodeling and metabolic efficacy. Microbial 16S sequencing revealed transmissible taxonomic changes correlated with improved metabolism, notably enrichment of probiotics and reduction of Alistipes and Bacteroides known to associate with high fat/protein diets. Metabolomic profiling further illustrated broad changes, including enrichment of phenylpropionates and decreases in key intermediates of glucose utilization, cholesterol biosynthesis and amino acid fermentation. These studies elucidate beneficial roles of RM-dependent microbial remodeling in metabolic homeostasis, and showcase prevalent health-promoting potentials of dietary fibers.

Transmissible microbial and metabolomic remodeling by soluble dietary fiber improves metabolic homeostasis.

Ammonia detoxification is essential for physiological well-being, and the urea cycle in liver plays a predominant role in ammonia disposal. Nobiletin (NOB), a natural dietary flavonoid, is known to exhibit various physiological efficacies. In the current study, we investigated a potential role of NOB in ammonia control and the underlying cellular mechanism.

Ammonia-lowering activities and carbamoyl phosphate synthetase 1 (Cps1) induction mechanism of a natural flavonoid.

Circadian clocks orchestrate essential physiology in response to various cues, yet their mechanistic and functional plasticity remains unclear. Here, we investigated Clock(Δ19/+) heterozygous (Clk/+) mice, known to display lengthened periodicity and dampened amplitude, as a model of partially perturbed clocks. Interestingly, Clk/+ mice exhibited improved glycemic control and resistance to circadian period lengthening under high-fat diet (HFD). Furthermore, BMAL1 protein levels in Clk/+ mouse liver were upregulated compared with wild-type (WT) mice under HFD. Pharmacological and molecular studies showed that BMAL1 turnover entailed proteasomal and autophagic activities, and CLOCKΔ19 attenuated both processes. Consistent with an important role of BMAL1 in glycemic control, enhanced activation of insulin signaling was observed in Clk/+ mice relative to WT in HFD. Finally, transcriptome analysis revealed reprogramming of clock-controlled metabolic genes in Clk/+ mice. Our results demonstrate a novel role of autophagy in circadian regulation and reveal an unforeseen plasticity of circadian and metabolic networks.

Dual attenuation of proteasomal and autophagic BMAL1 degradation in Clock Δ19/+ mice contributes to improved glucose homeostasis.

Dysregulation of circadian rhythms is associated with metabolic dysfunction, yet it is unclear whether enhancing clock function can ameliorate metabolic disorders. In an unbiased chemical screen using fibroblasts expressing PER2::Luc, we identified Nobiletin (NOB), a natural polymethoxylated flavone, as a clock amplitude-enhancing small molecule. When administered to diet-induced obese (DIO) mice, NOB strongly counteracted metabolic syndrome and augmented energy expenditure and locomotor activity in a Clock gene-dependent manner. In db/db mutant mice, the clock is also required for the mitigating effects of NOB on metabolic disorders. In DIO mouse liver, NOB enhanced clock protein levels and elicited pronounced gene expression remodeling. We identified retinoid acid receptor-related orphan receptors as direct targets of NOB, revealing a pharmacological intervention that enhances circadian rhythms to combat metabolic disease via the circadian gene network.

Kazunari Nohara

Department of Biochemistry and Molecular Biology

University of Texas Health Science Center at Houston

A Filtration-based Method of Preparing High-quality Nuclei from Cross-linked Skeletal Muscle for Chromatin Immunoprecipitation

Kazunari Nohara

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Biochemistry and Molecular Biology

University of Texas Health Science Center at Houston

A Filtration-based Method of Preparing High-quality Nuclei from Cross-linked Skeletal Muscle for Chromatin Immunoprecipitation

Department of Biochemistry and Molecular Biology