Regular Light-dark Cycle Research Articles

Light modulates glucose and lipid homeostasis via the sympathetic nervous system.

Light is an important environmental factor for vision, and for diverse physiological and psychological functions. Light can also modulate glucose metabolism. Here, we show that in mice, light is critical for glucose and lipid homeostasis by regulating the sympathetic nervous system, independent of circadian disruption. Light deprivation from birth elicits insulin hypersecretion, glucagon hyposecretion, lower gluconeogenesis, and reduced lipolysis by 6-8 weeks, in male, but not, female mice. These metabolic defects are consistent with blunted sympathetic activity, and indeed, sympathetic responses to a cold stimulus are significantly attenuated in dark-reared mice. Further, long-term dark rearing leads to body weight gain, insulin resistance, and glucose intolerance. Notably, metabolic dysfunction can be partially alleviated by 5 weeks exposure to a regular light-dark cycle. These studies provide insight into circadian-independent mechanisms by which light directly influences whole-body physiology and inform new approaches for understanding metabolic disorders linked to aberrant environmental light conditions.

The analysis of the histomorphometric characteristics and ultrastructural features of the liver in response to environmental cycle desynchronization in the wild desert rodent (Gerbillus tarabuli)

The architecture of the hepatic tissue in the nocturnal wild desert rodent (Gerbillus tarabuli) subjected to a shifted LD (Light/Dark) cycle was investigated using transmission electron microscopy and histomorphometry. Investigation involved two groups: the control group (n = 5), exposed to the regular LD cycle (LD: 12:12), and the shifted group (n = 5), exposed to the LD regimen with a prolonged light phase of 8 h, in a day by day alternation with regular LD cycle (LD: 12:12 / LD: 20:4) during 12 weeks. Histological examination showed in the shifted group disorganization of hepatocyte trabeculae, sinusoidal dilatation, and inflammatory cell infiltration around the portal tracts. Morphometric results revealed hypertrophy of hepatocytes with a size of 29.83 ± 1.69 μm vs. 17.52 ± 0.81 μm and of their nuclei diameter with 8.69 ± 0.25 μm vs. 6.55 ± 0.15 μm. This increase is highly significant (p<0.001) and represents an increase of 70.17% and 32.67%, respectively. We also noticed a significant increase in the number of binucleated cells compared to the control group with an average of 9.73 ± 0.98 vs. 5.53 ± 0.38 binucleated hepatocytes per area unit, respectively. Ultrastructural analysis corroborated the histological findings, confirming the installation of inflammatory foci, characterized by portal and intraparenchymal infiltration of leukocytes, proliferation of Kupffer cells and stellate cells, as well as an expansion of collagen fiber deposits. Electron microscopy also revealed in the shifted group some hepatocytic lesional features represented by vacuolar or liquefied cytoplasm associated with degenerative mitochondria and a rarefaction of organelles in addition to an abundance of lysosomes. Additionally, strong glycogen depletion was observed at the metabolic level. This study showed that 12 weeks of lengthening the light phase of the LD cycle, corresponding to the gerbil's resting period, had a discernible impact on hepatocellular activity, making G. tarabuli an interesting model to study the influence of artificial light at night as a circadian rhythm disruptor.

Rest phase snacking increases energy resorption and weight gain in male mice

ObjectiveSnacking, i.e., the intake of small amounts of palatable food items, is a common behavior in modern societies, promoting overeating and obesity. Shifting food intake into the daily rest phase disrupts circadian rhythms and is also known to stimulate weight gain. We therefore hypothesized that chronic snacking in the inactive phase may promote body weight gain and that this effect is based on disruption of circadian clocks. MethodsMale mice were fed a daily chocolate snack either during their rest or their active phase and body weight development and metabolic parameters were investigated. Snacking experiments were repeated in constant darkness and in clock-deficient mutant mice to examine the role of external and internal time cues in mediating the metabolic effects of snacking. ResultsChronic snacking in the rest phase increased body weight gain and disrupted metabolic circadian rhythms in energy expenditure, body temperature, and locomotor activity. Additionally, these rest phase snacking mice assimilated more energy during the inactive phase. Body weight remained increased in rest phase snacking wildtype mice in constant darkness as well as in clock-deficient mutant mice under a regular light–dark cycle compared to mice snacking in the active phase. Weight gain effects were abolished in clock-deficient mice in constant darkness. ConclusionsOur data suggest that mistimed snacking increases energy resorption and promotes body weight gain. This effect requires a functional circadian clock at least under constant darkness conditions.

Abstract 106: Assessing the impact of staggered light exposure on breast cancer risk and metabolism

Abstract Background: Numerous epidemiological studies, including the Nurses' Health Study II, found that shift workers have a higher risk for breast cancer. These studies hypothesize that suppressed melatonin and disrupted clock gene expression likely lead to an immune compromised, proliferative phenotype. However, the majority of studies to date rely on correlative evidence. With the onset of the COVID-19 pandemic, shift work has become increasingly prevalent, making the need to understand the mechanisms promoting disease, including breast cancer, even more important. Objective: The objective of this study is to analyze the impact of staggered light exposure on the immune function and breast tissue gene expression in order to identify how breast cancer risk is mediated. Methods: An 18-week study with 10 C57BL/6 female mice was conducted whereby half of the mice were exposed to a staggered light/dark (LD) cycle, as would be experienced by shift workers, and half were exposed to a regular LD cycle. Body weight was monitored weekly and sera and mammary tissues were collected at termination. The sera from each group was pooled and cytokine levels assessed using an antibody-pair-based assay. Results: Intriguingly, although the mice from the two study groups did not significantly differ in average body weight, the staggered LD exposure group had higher levels of inflammatory cytokines indicative of chronic, low-grade inflammation. Notably, the staggered LD group had 75% higher IL-6 levels, 157% higher IL-10 levels, and 49% higher TNF-alpha levels compared to the control group. To determine the impact of staggered light exposure on localized breast tissue gene expression, qPCR arrays of breast cancer risk and inflammatory genes will be done comparing expression levels between the control and staggered LD groups. IHC techniques will be used to determine Ki67 and macrophage subtype infiltration in the breast tissue of the two groups. Conclusion: Our data show that staggered LD exposure induces chronic, low-grade inflammation independent from body mass, which can be indicative of increased breast cancer risk. These data help elucidate the metabolic and immune responses induced by staggered light exposure, helping to define the mechanisms promoting health risks imposed by shift work, with the ultimate goal to develop preventive measures to limit breast cancer development. Citation Format: Lauren Palluth, Brittany Harlow, Bryan McCellan, Christopher Jolly, Molly Bray, Linda deGraffenried. Assessing the impact of staggered light exposure on breast cancer risk and metabolism [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 106.

REV-ERB in GABAergic neurons controls diurnal hepatic insulin sensitivity.

SUMMARY PARAGRAPHSystemic insulin sensitivity shows diurnal rhythm with a peak at wakening1,2. The molecular mechanism underlying such a temporal pattern is unclear. Here we demonstrate that nuclear receptors Rev-erbα/β in the GABAergic neurons in the suprachiasmatic nucleus (SCNGABA) control the diurnal rhythm of insulin-mediated suppression of hepatic glucose production in mice, without affecting diurnal eating or locomotor behaviors under the regular light-dark cycles. Rev-erb regulates the rhythmic expression of genes involved in neurotransmission in the SCN and modulates the oscillatory firing activity of SCNGABA neurons. Chemogenetic stimulation of SCNGABA neurons at wakening causes glucose intolerance, while restoration of the temporal pattern of either SCNGABA neuron firing or Rev-erb expression rescues the time-dependent glucose metabolic phenotype due to Rev-erb depletion. The elevated blood glucose level after awakening is a defining feature of the extended dawn phenomenon (DP) in diabetes patients3,4. Type 2 diabetes (T2D) patients with the extended DP display a differential temporal pattern of Rev-erb gene expression compared to T2D patients without DP. These findings provide mechanistic insights into how the central circadian clock regulates the diurnal rhythm of hepatic insulin sensitivity, which has implications in the extended DP in T2D.

Group housing and social dominance hierarchy affect circadian activity patterns in mice.

In this study, we investigated the effect of social environment on circadian patterns in activity by group housing either six male or six female mice together in a cage, under regular light–dark cycles. Based on the interactions among the animals, the social dominance rank of individual mice was quantitatively established by calculating Elo ratings. Our results indicated that, during our experiment, the social dominance hierarchy was rapidly established, stable yet complex, often showing more than one dominant mouse and several subordinate mice. Moreover, we found that especially dominant male mice, but not female mice, displayed a significantly higher fraction of their activity during daytime. This resulted in reduced rhythm amplitude in dominant males. After division into separate cages, male mice showed an enhancement of their 24 h rhythm, due to lower daytime activity. Recordings of several physiological parameters showed no evidence for reduced health as a potential consequence of reduced rhythm amplitude. For female mice, transfer to individual housing did not affect their daily activity pattern. We conclude that 24 h rhythms under light–dark cycles are influenced by the social environment in males but not in females, and lead to a decrement in behavioural rhythm amplitude that is larger in dominant mice.

Continuous Light Does Not Affect Atherosclerosis in APOE*3-Leiden.CETP Mice.

Artificial light exposure is associated with dyslipidemia in humans, which is a major risk factor for the development of atherosclerotic cardiovascular disease. However, it remains unclear whether artificial light at night can exacerbate atherosclerosis. In this study, we exposed female APOE*3-Leiden.CETP mice, a well-established model for human-like lipid metabolism and atherosclerosis, to either a regular light-dark cycle or to constant bright light for 14 weeks. Mice exposed to constant light demonstrated a minor reduction in food intake, without any effect on body weight, body composition, or the weight of metabolic organs. Constant light increased the plasma levels of proatherogenic non–high-density lipoprotein (HDL) cholesterol but did not increase the size or severity of atherosclerotic lesions in the aortic root. Mice exposed to constant light did show lower immune cell counts, which could explain the absence of an effect of atherosclerosis despite increased non–HDL cholesterol levels. Behavioral analysis demonstrated variability in the response of mice to the light intervention. Constant light completely blunted behavioral rhythms in some mice, while others extended their behavioral period. However, rhythm strength was not an important determinant of atherosclerosis. Altogether, these results demonstrate that constant bright light does not affect atherosclerosis in APOE*3-Leiden.CETP mice. Whether artificial light exposure contributes to cardiovascular disease risk in humans remains to be investigated.

Constant light exposure causes oocyte meiotic defects and quality deterioration in mice

Artificial light at night (ALAN) exposes us to prolonged illumination, that adversely affects female reproduction. However, it remains to be clarified how prolonged light exposure affects oocyte meiotic maturation and quality. To this end, we exposed female mice to a constant light (CL) of 250 lux for different durations. Our findings showed that CL exposure for 7 weeks reduced the oocyte maturation rate. Meanwhile, CL exposure caused greater abnormalities in spindle assembly and chromosome alignment and a higher rate of oocyte aneuploidy than the regular light dark cycle. CL exposure also induced oxidative stress and caused mitochondrial dysfunction, which resulted in oocyte apoptosis and autophagy. Notably, our results showed that CL exposure reduced the levels of α-tubulin acetylation, DNA methylation at 5 mC, RNA methylation at m6A and histone methylation at H3K4me2 but increased the levels of histone methylation at H3K27me2 in oocytes. In summary, our findings demonstrate that constant bright light exposure causes oocyte meiotic defects and reduces cytoplasmic quality. These results extend the current understanding of ALAN-mediated defects in female reproduction.

Disruption of circadian rhythm by alternating light-dark cycles aggravates atherosclerosis development in APOE*3-Leiden.CETP mice.

Disruption of circadian rhythm by means of shift work has been associated with cardiovascular disease in humans. However, causality and underlying mechanisms have not yet been established. In this study, we exposed hyperlipidemic APOE*3‐Leiden.CETP mice to either regular light‐dark cycles, weekly 6 hours phase advances or delays, or weekly alternating light‐dark cycles (12 hours shifts), as a well‐established model for shift work. We found that mice exposed to 15 weeks of alternating light‐dark cycles displayed a striking increase in atherosclerosis, with an approximately twofold increase in lesion size and severity, while mice exposed to phase advances and delays showed a milder circadian disruption and no significant effect on atherosclerosis development. We observed a higher lesion macrophage content in mice exposed to alternating light‐dark cycles without obvious changes in plasma lipids, suggesting involvement of the immune system. Moreover, while no changes in the number or activation status of circulating monocytes and other immune cells were observed, we identified increased markers for inflammation, oxidative stress, and chemoattraction in the vessel wall. Altogether, this is the first study to show that circadian disruption by shifting light‐dark cycles directly aggravates atherosclerosis development.

Sex and estrous cycle dependent changes in locomotor activity, anxiety and memory performance in aged mice after exposure of light at night.

Light-at-night (LAN) can affect mammalian behaviour. But, the effects of LAN on aged rodents remain undefined yet. In the present investigation, aged Swiss Albino mice, habituated in regular light-dark cycle, were exposed to bright-light-pulse (1-h) at night on the day of study followed by experimentations for assessment of locomotor activities in the open field, anxiety in the elevated plus maze and short-term memory for novel object recognition (NOR) in the habituated field. Under without-bright-light exposure, (a) aged proestrous females showed greater locomotor activities and less anxiety than in aged diestrous females, (b) aged males showed locomotor activities and anxiety level similar to aged diestrous females and aged proestrous females respectively and (c) all animals failed to retain in object discrimination memory. LAN exposure exhibited the continual failure of such retention of memory while animals showed free and spontaneous exploration with thigmotactic behaviour having no object bias and/or phobia, but time stay in objects by animals altered variably among sexes and stages of estrous cycle. Overall, the LAN caused (a) diminution in locomotor activities, rise in anxiety and failure of memory for recognition of both familiar and novel objects in aged proestrous females, (b) hyperlocomotor activities and reduction in anxiety in both males and diestrous females with the failure of memory for recognition of novel objects only in aged males while diestrous females showed enhanced exploration time to both objects during NOR. Thus, nocturnal behaviour of aged mice varies with sex and estrous cycle and light acts differentially on them.

Effect of different light-dark schedules on estrous cycle in mice, and implications for mitigating the adverse impact of night work.

Approximately 20% of workers in developed countries are involved in night work. Nevertheless, many studies have strongly suggested that night-work-induced chronic circadian misalignment increases the risk of a diverse range of health problems. Although a relation between night work and irregular menstrual cycles has been indicated epidemiologically, a direct causal link remains elusive. Here, we report that repetitive reversal of light-dark (LD) cycles triggers irregular estrous cycles in mice. The findings showed that the estrous cycle remained irregular for more than four weeks after the mice were returned to regular LD cycles. Importantly, the magnitude of the negative impact of reversed LD cycles on the estrous cycle, or more specifically the decreased number of normal estrous cycles during the observation period, was dependent on the difference in the frequency of LD reversal. Presently, no clear solution to prevent night-work-mediated menstrual abnormalities is available, and reducing night work in modern society is difficult. Our findings indicate that optimizing work schedules could significantly prevent menstrual problems without reducing total night-work time.

Circadian disruption promotes tumor growth by anabolic host metabolism; experimental evidence in a rat model

BackgroundLight at night creates a conflicting signal to the biological clock and disrupts circadian physiology. In rodents, light at night increases the risk to develop mood disorders, overweight, disrupted energy metabolism, immune dysfunction and cancer. We hypothesized that constant light (LL) in rats may facilitate tumor growth via disrupted metabolism and increased inflammatory response in the host, inducing a propitious microenvironment for tumor cells.MethodsMale Wistar rats were exposed to LL or a regular light-dark cycle (LD) for 5 weeks. Body weight gain, food consumption, triglycerides and glucose blood levels were evaluated; a glucose tolerance test was also performed. Inflammation and sickness behavior were evaluated after the administration of intravenous lipopolysaccharide. Tumors were induced by subcutaneous inoculation of glioma cells (C6). In tumor-bearing rats, the metabolic state and immune cells infiltration to the tumor was investigated by using immunohistochemistry and flow cytometry. The mRNA expression of genes involved metabolic, growth, angiogenes and inflammatory pathways was measured in the tumor microenvironment by qPCR. Tumor growth was also evaluated in animals fed with a high sugar diet.ResultsWe found that LL induced overweight, high plasma triglycerides and glucose levels as well as reduced glucose clearance. In response to an LPS challenge, LL rats responded with higher pro-inflammatory cytokines and exacerbated sickness behavior. Tumor cell inoculation resulted in increased tumor volume in LL as compared with LD rats, associated with high blood glucose levels and decreased triglycerides levels in the host. More macrophages were recruited in the LL tumor and the microenvironment was characterized by upregulation of genes involved in lipogenesis (Acaca, Fasn, and Pparγ), glucose uptake (Glut-1), and tumor growth (Vegfα, Myc, Ir) suggesting that LL tumors rely on these processes in order to support their enhanced growth. Genes related with the inflammatory state in the tumor microenvironment were not different between LL and LD conditions. In rats fed a high caloric diet tumor growth was similar to LL conditions.ConclusionsData indicates that circadian disruption by LL provides a favorable condition for tumor growth by promoting an anabolic metabolism in the host.

Day-Time Isoflurane Administration Suppresses Circadian Gene Expressions in Both the Brain and a Peripheral Organ, Liver.

The aim of this study is to investigate the effects of light and administration time of isoflurane on circadian gene expression in the brains and liver tissues of rats kept in light-dark cycle. Seventy two 15-days-old rats pups were divided into four groups. All animals were exposed to 1.5% concentration of isoflurane or to 6 L min-1 O2 for six hours between Zeitgeber Time (ZT) 0-ZT06 (day-time administration) or ZT12-ZT18 (night-time administration). Rats were sacrificed after six hours of anaesthesia with four-hour time intervals. Total RNA was isolated from brains and liver tissues. Circadian gene expression was examined using quantitative real-time Reverse transcription polymerase chain reaction (RT-PCR). BMAL1, CLOCK, PER2 and CRY2 gene expression levels were markedly suppressed after day-time anaesthesia in the both brain and liver, but night-time administration caused only temporary suppression of gene expression. The effect of isoflurane on the circadian clock is time-dependent, and administered isoflurane anaesthesia at night had minimal effect on clock gene expression. Additionally, when the treated animals were kept in a regular light-dark cycle, isoflurane-induced phase shift was not observed, possibly because of the light.

Shifts in the light-dark cycle increase unpredictability of the cardiovascular system.

Physiological variables such as heart rate (HR) and blood pressure (BP) exhibit long-term circadian rhythms, which can be disturbed by shift work. On the other hand, short-term oscillations in HR and BP have a high prognostic value. Therefore, we aimed to determine if the short-term variability, complexity and entropy of HR and BP would be affected by a regular light/dark (LD) cycle and phase delay shifts of the LD cycle, leading to chronodisruption. Telemetry-monitored rats were exposed first to the regular LD cycle and then to shifts in LD for 8weeks. On the basis of long-term HR and BP recording and evaluation, we found circadian rhythms in HR and BP variability, complexity and entropy under regular LD cycles. Short-term exposure to shifts disturbed circadian rhythms of HR and BP variability, complexity and entropy, indicating chronodisruption. The power of circadian rhythms was suppressed after 8weeks of phase delay shifts. Long-term exposure to shifts increased variability (p=0.007), complexity (p<0.001) and dark-time entropy (p=0.006) of HR but not BP. This is the first study demonstrating long-term recording and estimation of HR and BP variability, complexity and entropy in conscious rats exposed to irregular lighting conditions. After long-term phase delay shifts, short-term variability of HR was less predictable than in controls. This study suggests that changes in short-term HR and BP oscillations induced by long-term shift work can negatively affect cardiovascular health.

Influence of light exposure at nighttime on sleep development and body growth of preterm infants.

Previous studies have demonstrated that a light-dark cycle has promoted better sleep development and weight gain in preterm infants than constant light or constant darkness. However, it was unknown whether brief light exposure at night for medical treatment and nursing care would compromise the benefits brought about by such a light-dark cycle. To examine such possibility, we developed a special red LED light with a wavelength of >675 nm which preterm infants cannot perceive. Preterm infants born at <36 weeks’ gestational age were randomly assigned for periodic exposure to either white or red LED light at night in a light-dark cycle after transfer from the Neonatal Intensive Care Unit to the Growing Care Unit, used for supporting infants as they mature. Activity, nighttime crying and body weight were continuously monitored from enrolment until discharge. No significant difference in rest-activity patterns, nighttime crying, or weight gain was observed between control and experimental groups. The data indicate that nursing care conducted at 3 to 4-hour intervals exposing infants to light for <15 minutes does not prevent the infants from developing circadian rest-activity patterns, or proper body growth as long as the infants are exposed to regular light-dark cycles.

Impact of Various Stress Conditions on Poly-β-Hydroxybutyrate (PHB) Accumulation in Aulosira fertilissima CCC 444

Background: Poly-β-hydroxybutyrate (PHB) from cyanobacteria is considered to be a potentially viable source for degradable plastic. Yet, to date, only a modest level of research has been reported in this area. PHB has variety of properties such as natural origin, biocompatibility, biodegradability, piezoelectricity, streospecificity, thermoplasticity and optical activity, which make it suitable for various applications in health industry. Methods: This article elucidates comprehensive information and knowledge with regard to several stress conditions (e.g., salt stress, heat and chilling stresses, heavy metal supplementation, limitation of gas exchange and nutrient deficiency) to enhance PHB production from a diazotrophic cyanobacterium, Aulosira fertilissima CCC 444. Results: The results showed that cultures reached a maximum biomass concentration of 631 mg l-1, regardless of initial inoculum levels. However, with an initial inoculum of 80 mg dry cell weight (dcw) l-1, maximum PHB accumulation was achieved under regular light-dark cycles. A. fertilissima supplemented with heavy metals showed enhancement in PHB accumulation up to 18.7% of dcw in 1.0 mg l-1 Ni-supplemented medium for 7 days, followed by 17.6% (dcw) in 1.5 mg l-1 Cu-supplemented medium. NaCl stress, heat and chilling stresses and deficiencies of potassium, calcium, and magnesium had negative effects on PHB accumulation. Interestingly, supplementation of 0.5% acetate at the initiation of gas exchange limitation boosted the accumulation of PHB to 48.7% (dcw) on 14 days of incubation, a value 7-fold higher compared to the control. Conclusion: Gas exchange limitation with carbon supplementation found to be an appropriate condition for enhanced PHB accumulation in cyanobacteria. Thus, using cyanobacteria for PHB production is one of the most promising ecofriendly ways as these are oxygen evolving photoautotrophic organisms; require minimal inorganic nutrients for growth and due to aquatic in nature, cyanobacteria do not compete for arable land for their cultivation. Currently, intensive research is essential in this area for ingenious utilization of cyanobacterial biomass to produce environmentally affordable bioplastic. Keywords: Aulosira fertilissima, gas exchange limitation, heavy metals, poly-β-hydroxybutyrate.

Effects of light-dark cycle manipulation on critical velocity and anaerobic running capacity in Wistar rats

The aim of the study was to assess the effect of the light-dark cycle on the critical velocity (CV) and the anaerobic capacity (ARC) of running rats. The entire experiment utilised two separate groups under two conditions: a regular light-dark cycle 12/12 hours (light on from 6:00 to 18:00 - RC group) and an altered light-dark cycle 12/12 hours (light on from 18:00 to 6:00 - AC group). First, running rat groups were selected. The animals were submitted to four exercise tests (25, 30, 35 and 40 m/min) performed until exhaustion. The times to exhaustion for each running intensity were recorded (tlim). The CV and ARC were estimated from the linear regression of ‘velocity vs. 1/tlim’, where the CV and ARC were the linear and slope coefficients, respectively. The running rat groups showed a significant difference in percent selection under the two light cycles (16.4% and 28.9% of running rats in the RC and AC groups, respectively). The CV was highest in the AC condition (CVRC = 22.7±0.8 m/min and CVAC = 25.5±0.4 m/min), but the ARC (ARCRC = 22.80±2.76 m and ARCAC = 21.80±4.93 m) and the linear fit (R2 RC = 0.88±0.03 and R2 AC = 0.85±0.02) were not different in both conditions These results indicate that caution is necessary when varying the circadian rhythm of rats submitted to running exercise, especially because their aerobic condition is improved when an altered light-dark cycle is used.

Cholesteryl ester hydrolase activity is abolished in HSL macrophages but unchanged in macrophages lacking KIAA1363

Cholesteryl ester (CE) accumulation in macrophages represents a crucial event during foam cell formation, a hallmark of atherogenesis. Here we investigated the role of two previously described CE hydrolases, hormone-sensitive lipase (HSL) and KIAA1363, in macrophage CE hydrolysis. HSL and KIAA1363 exhibited marked differences in their abilities to hydrolyze CE, triacylglycerol (TG), diacylglycerol (DG), and 2-acetyl monoalkylglycerol ether (AcMAGE), a precursor for biosynthesis of platelet-activating factor (PAF). HSL efficiently cleaved all four substrates, whereas KIAA1363 hydrolyzed only AcMAGE. This contradicts previous studies suggesting that KIAA1363 is a neutral CE hydrolase. Macrophages of KIAA1363−/− and wild-type mice exhibited identical neutral CE hydrolase activity, which was almost abolished in tissues and macrophages of HSL−/− mice. Conversely, AcMAGE hydrolase activity was diminished in macrophages and some tissues of KIAA1363−/− but unchanged in HSL−/− mice. CE turnover was unaffected in macrophages lacking KIAA1363 and HSL, whereas cAMP-dependent cholesterol efflux was influenced by HSL but not by KIAA1363. Despite decreased CE hydrolase activities, HSL−/− macrophages exhibited CE accumulation similar to wild-type (WT) macrophages. We conclude that additional enzymes must exist that cooperate with HSL to regulate CE levels in macrophages. KIAA1363 affects AcMAGE hydrolase activity but is of minor importance as a direct CE hydrolase in macrophages.

Adipose triglyceride lipase plays a key role in the supply of the working muscle with fatty acids

FAs are mobilized from triglyceride (TG) stores during exercise to supply the working muscle with energy. Mice deficient for adipose triglyceride lipase (ATGL-ko) exhibit defective lipolysis and accumulate TG in adipose tissue and muscle, suggesting that ATGL deficiency affects energy availability and substrate utilization in working muscle. In this study, we investigated the effect of moderate treadmill exercise on blood energy metabolites and liver glycogen stores in mice lacking ATGL. Because ATGL-ko mice exhibit massive accumulation of TG in the heart and cardiomyopathy, we also investigated a mouse model lacking ATGL in all tissues except cardiac muscle (ATGL-ko/CM). In contrast to ATGL-ko mice, these mice did not accumulate TG in the heart and had normal life expectancy. Exercise experiments revealed that ATGL-ko and ATGL-ko/CM mice are unable to increase circulating FA levels during exercise. The reduced availability of FA for energy conversion led to rapid depletion of liver glycogen stores and hypoglycemia. Together, our studies suggest that ATGL-ko mice cannot adjust circulating FA levels to the increased energy requirements of the working muscle, resulting in an increased use of carbohydrates for energy conversion. Thus, ATGL activity is required for proper energy supply of the skeletal muscle during exercise.

Identification of Mouse Prp19p as a Lipid Droplet-associated Protein and Its Possible Involvement in the Biogenesis of Lipid Droplets

Prp19p is an integral component of the heteromeric protein complex (the NineTeen complex) in the nucleus, and it is essential for the structural integrity of NineTeen complex and its subsequent activation of the spliceosome. We identified Prp19p, which has never been reported in relation to any function outside of the nucleus, as a member of proteins associated with lipid droplets. Down-regulation of Prp19p expression with RNA interference in 3T3-L1 cells repressed lipid droplet formation with the reduction in the level of expression of perilipin and S3-12. The levels of expression of SCD1 (stearoyl-CoA desaturase-1), DGAT-1 (acyl-CoA diacylglycerol acyltransferase-1), and glycerol-3-phosphate acyltransferase were also reduced in Prp19p down-regulated cells, and a significant decrease in triglycerides was observed. Unlike perilipin, which is one of the most extensively studied lipid droplet-associated proteins, Prp19p is not essential for cAMP- and hormone-sensitive lipase-dependent lipolysis pathways, even though Prp19p is a component of the lipid droplet phospholipid monolayer, and down-regulation of Prp19p represses fat accretion significantly. These results suggest that Prp19p or Prp19-interacting proteins during lipid droplet biogenesis in adipocytes may be considered as another class of potential targets for attacking obesity and obesity-related problems.