N-acetylaspartate catabolism determines cytosolic acetyl-CoA levels and histone acetylation in brown adipocytes.

Histone acetylation depends on the abundance of nucleo-cytoplasmic acetyl-CoA. Here, we present a novel route for cytoplasmic acetyl-CoA production in brown adipocytes. N-acetylaspartate (NAA) is a highly abundant brain metabolite catabolized by aspartoacylase yielding aspartate and acetate. The latter can be further used for acetyl-CoA production. Prior to this work, the presence of NAA has not been described in adipocytes. Here, we show that accumulation of NAA decreases the brown adipocyte phenotype. We increased intracellular NAA concentrations in brown adipocytes via media supplementation or knock-down of aspartoacylase and measured reduced lipolysis, thermogenic gene expression, and oxygen consumption. Combinations of approaches to increase intracellular NAA levels showed additive effects on lipolysis and gene repression, nearly abolishing the expression of Ucp1, Cidea, Prdm16, and Ppara. Transcriptome analyses of aspartoacylase knock-down cells indicate deficiencies in acetyl-CoA and lipid metabolism. Concordantly, cytoplasmic acetyl-CoA levels and global histone H3 acetylation were decreased. Further, activating histone marks (H3K27ac and H3K9ac) in promoters/enhancers of brown marker genes showed reduced acetylation status. Taken together, we present a novel route for cytoplasmic acetyl-CoA production in brown adipocytes. Thereby, we mechanistically connect the NAA pathway to the epigenomic regulation of gene expression, modulating the phenotype of brown adipocytes.

Molecular aspects of adipoepithelial transdifferentiation in mouse mammary gland.

The circular, reversible conversion of the mammary gland during pregnancy and involution is a paradigm of physiological tissue plasticity. The two most prominent cell types in mammary gland, adipocytes and epithelial cells, interact in an orchestrated way to coordinate this process. Previously, we showed that this conversion is at least partly achieved by reciprocal transdifferentiation between mammary adipocytes and lobulo-alveolar epithelial cells. Here, we aim to shed more light on the regulators of mammary transdifferentiation. Using immunohistochemistry with cell type-specific lipid droplet-coating markers (Perilipin1 and 2), we show that cells with an intermediate adipoepithelial phenotype exist during and after pregnancy. Nuclei of cells with similar transitional structural characteristics are highly positive for Elf5, a master regulator of alveologenesis. In cultured adipocytes, we could show that transient and stable ectopic expression of Elf5 induces expression of the milk component whey acidic protein, although the general adipocyte phenotype is not affected suggesting that additional pioneering factors are necessary. Furthermore, the lack of transdifferentiation of adipocytes during pregnancy after clearing of the epithelial compartment indicates that transdifferentiation signals must emanate from the epithelial part. To explore candidate genes potentially involved in the transdifferentiation process, we devised a high-throughput gene expression study to compare cleared mammary fat pads with developing, contralateral controls at several time points during pregnancy. Incorporation of bioinformatic predictions of secretory proteins provides new insights into possible paracrine signaling pathways and downstream transdifferentiation factors. We discuss a potential role for osteopontin (secreted phosphoprotein 1 [Spp1]) signaling through integrins to induce adipoepithelial transdifferentiation.

Adenovirus-mediated rescue of lipoprotein lipase-deficient mice. Lipolysis of triglyceride-rich lipoproteins is essential for high density lipoprotein maturation in mice.

Lipoprotein lipase (LPL) is the rate-limiting enzyme for the hydrolysis of triglycerides and the subsequent uptake of free fatty acids in extrahepatic tissues. Deficiency of LPL in humans (Type I hyperlipoproteinemia) is associated with massive chylomicronemia, low high density lipoprotein (HDL) cholesterol levels, and recurrent attacks of pancreatitis when not controlled by a strict diet. In contrast to humans, homozygous LPL knock-out mice (L0) do not survive suckling and die between 18 and 24 h after birth. In this study, an adenovirus-based protocol was utilized for the transient expression of LPL during the suckling period in an effort to rescue L0 mice. After a single intraperitoneal injection of 5x10(9) plaque-forming units of LPL-expressing virus immediately after birth, more than 90% of L0 mice survived the first days of life. 3% of L0 mice survived the entire suckling period and lived for up to 20 months, although LPL activity in mouse tissues and postheparin plasma was undetectable in all animals after 6 weeks of age. Adult LPL-deficient mice were smaller than their littermates until 2-3 months of age and exhibited very high triglyceride levels in the fed (4997 +/- 1102 versus 113.4 +/- 18.7 mg/dl) and fasted state (2007 +/- 375 versus 65.5 +/- 7.4 mg/dl). Plasma total cholesterol levels, free fatty acids, and ketone bodies were elevated in L0 mice, whereas plasma glucose was normal. Most strikingly, L0 mice lacked apoA-I-containing prebeta-HDL particles as well as mature HDL resulting in undetectable HDL cholesterol and HDL-apoA-I levels. HDL deficiency in plasma was evident despite normal apoA-I mRNA levels in the liver and normal apoA-I protein levels in plasma, which were predominantly found in the chylomicron fraction. The absence of prebeta-HDL and mature HDL particles supports the concept that the lipolysis of triglyceride-rich lipoproteins is an essential step for HDL maturation.

Tissue-specific activity of lipoprotein lipase in skeletal muscle regulates the expression of uncoupling protein 3 in transgenic mouse models.

Uncoupling protein (UCP)-2 and UCP-3 are two recently discovered proteins similar to UCP-1, which regulates thermogenesis in brown adipose tissue (BAT). Whereas UCP-1 expression is restricted to BAT, UCP-2 is widely expressed. UCP-3 is found mainly in skeletal muscle and BAT. A large body of evidence exists that the expression of UCP-2 and UCP-3 in skeletal muscle of mice is regulated by feeding/fasting, and some studies have suggested that this effect might be caused by the changing concentration of plasma non-esterified fatty acids (NEFAs). In an attempt to determine whether the increased import of triacylglycerol-derived NEFAs can also affect UCP expression, we determined the mRNA levels of UCP-1, UCP-2 and UCP-3 in BAT and muscle of induced mutant mouse lines that overexpressed or lacked lipoprotein lipase (LPL) in these tissues. The expression levels of UCP-1 and UCP-2 in BAT and in skeletal and cardiac muscle respectively were not affected by variations in tissue LPL activities. In contrast, UCP-3 mRNA levels were induced 3.4-fold in mice with high levels of LPL in skeletal muscle, and down-regulated in mice that lacked LPL in skeletal muscle. The presence or absence of LPL in BAT had no effect on UCP-3 expression levels. The response of UCP-3 mRNA expression to variations in LPL activity in skeletal muscle was independent of the feeding status or of plasma NEFA concentrations. These findings indicated that NEFAs as lipolytic products of LPL-mediated triacylglycerol hydrolysis markedly affect UCP-3 expression and that increased LPL activities occurring during fasting in skeletal muscle contribute to the induction of UCP-3 expression by promoting the increased uptake of NEFAs. In addition, our results demonstrate that UCP-2 and UCP-3 are differentially regulated in response to LPL-mediated NEFA uptake in skeletal muscle of mice.

The paediatric emergency ward--do mothers want to stay?

The attitudes of parents towards staying with their children in the medical emergency ward at the Red Cross War Memorial Children's Hospital, Cape Town, are reported on. A randomly selected sample of 80 parents or caretakers attending children in the ward were interviewed. The interviews were semi-structured and included open-ended questions. Data were recorded on interview schedules. Of the respondents, 96% wanted to stay with their acutely ill children, although 20% of these were anxious about the effect of this on events at home or at work. Based on the finding that mothers want to stay, even in view of difficulties regarding the situation at home and at work, improved facilities for parents should receive high priority. Recommendations arising from the study include the provision of more comfortable sleeping accommodation for parents, availability of refreshments on a 24-hour basis and provision of a regular supply of books and magazines to the ward.