Localization of lipoprotein lipase mRNA in selected rat tissues

Correlation of lipoprotein lipase gene polymorphism and mRNA expression with intramuscular fat content in Baicheng-Oil chicken

Lipoprotein lipase (LPL) was often taken as a candidate gene for investigating fat metabolism. However, there are few studies on the effect of LPL on intramuscular fat (IMF) deposition in Baicheng oil chicken (BOC) and Three-yellow Chicken (TYC). In this study, we studied the relationship between polymorphism and messenger RNA (mRNA) expression of LPL with IMF deposition in the chest muscle (CM) and leg muscle (LM) of TYC and BOC. Sixty TYCs and 60 BOCs were raised from 1 d and slaughtered by avascularization at their slaughtering age. IMF contents of the CM and LM in the BOC were markedly higher than those in the TYC. Three genotypes following AA, AB and BB were found by the method of polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP). The synonymous mutation C12315T was detected. The content of IMF with the AA genotype was significantly higher than the AB genotype in the LM of TYC. The mRNA expression both of CM and LM in BOC was prominently higher than those in TYC, and there was a positive significant correlation between LM and CM in both BOC and TYC. These results suggested that the SNPs polymorphism and mRNA expression of the LPL gene might be helpful for selective breeding in IMF of the chicken.

Performance and muscle lipogenesis of calves born to Nellore cows with different residual feed intake classification

This study aimed to evaluate relationships among maternal residual feed intake (RFI) with growth performance and expression of genes involved in lipid metabolism in offspring of Nellore cattle. Fifty-three cows classified as negative or positive RFI by genomic prediction were exposed to fixed-time artificial insemination (FTAI) protocols at 2 and 3 years of age using semen from the same bull. In the first year, cows gestated under grazing conditions and nursed their calves in the feedlot. In the second year, the opposite occurred. Cows were weighed every 28 days during pregnancy and calves were weighed at birth and every 28 days until weaning. Ultrasound images were collected from the carcass of cows and calves. Muscle gene expression was evaluated in calves at birth and weaning. Data were analyzed by year considering the fixed effects of RFI class and FTAI protocol for variables measured in cows, and RFI class, FTAI protocol and sex for variables measured in calves. There was no effect of maternal RFI on calves performance in the first year. Lower expression of FABP4 gene and trend towards lower expression of SREBF1 and LPL genes were detected in samples collected after birth from calves born to negative RFI cows, indicating that adipogenesis was reduced during the fetal and neonatal period. In the second year, negative RFI cows had greater subcutaneous fat thickness than positive RFI cows, and their calves tended to be heavier at birth and to have less rump fat thickness at weaning. No significant differences in expression of genes studied were detected between cow RFI classes. Nellore cows classified as negative RFI consume less feed and produce calves whose growth potential is similar to that of calves produced by positive RFI cows.

Lipoprotein Lipase Regulates Microglial Lipid Droplet Accumulation

Microglia become increasingly dysfunctional with aging and contribute to the onset of neurodegenerative disease (NDs) through defective phagocytosis, attenuated cholesterol efflux, and excessive secretion of pro-inflammatory cytokines. Dysfunctional microglia also accumulate lipid droplets (LDs); however, the mechanism underlying increased LD load is unknown. We have previously shown that microglia lacking lipoprotein lipase (LPL KD) are polarized to a pro-inflammatory state and have impaired lipid uptake and reduced fatty acid oxidation (FAO). Here, we also show that LPL KD microglia show excessive accumulation of LD-like structures. Moreover, LPL KD microglia display a pro-inflammatory lipidomic profile, increased cholesterol ester (CE) content, and reduced cholesterol efflux at baseline. We also show reduced expression of genes within the canonical cholesterol efflux pathway. Importantly, PPAR agonists (rosiglitazone and bezafibrate) rescued the LD-associated phenotype in LPL KD microglia. These data suggest that microglial-LPL is associated with lipid uptake, which may drive PPAR signaling and cholesterol efflux to prevent inflammatory lipid distribution and LD accumulation. Moreover, PPAR agonists can reverse LD accumulation, and therefore may be beneficial in aging and in the treatment of NDs.

Eckel R. Genetic Variants of Lipoprotein Lipase and Regulatory Factors Associated with Alzheimer's Disease Risk

Lipoprotein lipase (LPL) is a key enzyme in lipid and lipoprotein metabolism. The canonical role of LPL involves the hydrolysis of triglyceride-rich lipoproteins for the provision of FFAs to metabolic tissues. However, LPL may also contribute to lipoprotein uptake by acting as a molecular bridge between lipoproteins and cell surface receptors. Recent studies have shown that LPL is abundantly expressed in the brain and predominantly expressed in the macrophages and microglia of the human and murine brain. Moreover, recent findings suggest that LPL plays a direct role in microglial function, metabolism, and phagocytosis of extracellular factors such as amyloid- beta (Aβ). Although the precise function of LPL in the brain remains to be determined, several studies have implicated LPL variants in Alzheimer's disease (AD) risk. For example, while mutations shown to have a deleterious effect on LPL function and expression (e.g., N291S, HindIII, and PvuII) have been associated with increased AD risk, a mutation associated with increased bridging function (S447X) may be protective against AD. Recent studies have also shown that genetic variants in endogenous LPL activators (ApoC-II) and inhibitors (ApoC-III) can increase and decrease AD risk, respectively, consistent with the notion that LPL may play a protective role in AD pathogenesis. Here, we review recent advances in our understanding of LPL structure and function, which largely point to a protective role of functional LPL in AD neuropathogenesis.

Circulating Triglycerides Gate Dopamine-Associated Behaviors through DRD2-Expressing Neurons

Energy-dense food alters dopaminergic (DA) transmission in the mesocorticolimbic (MCL) system and can promote reward dysfunctions, compulsive feeding, and weight gain. Yet the mechanisms by which nutrients influence the MCL circuitry remain elusive. Here, we show that nutritional triglycerides (TGs), a conserved post-prandial metabolic signature among mammals, can be metabolized within the MCL system and modulate DA-associated behaviors by gating the activity of dopamine receptor subtype 2 (DRD2)-expressing neurons through a mechanism that involves the action of the lipoprotein lipase (LPL). Further, we show that in humans, post-prandial TG excursions modulate brain responses to food cues in individuals carrying a genetic risk for reduced DRD2 signaling. Collectively, these findings unveil a novel mechanism by which dietary TGs directly alter signaling in the reward circuit to regulate behavior, thereby providing a new mechanistic basis by which energy-rich diets may lead to (mal)adaptations in DA signaling that underlie reward deficit and compulsive behavior.

GPIHBP1 expression in gliomas promotes utilization of lipoprotein-derived nutrients

GPIHBP1, a GPI-anchored protein of capillary endothelial cells, binds lipoprotein lipase (LPL) within the subendothelial spaces and shuttles it to the capillary lumen. GPIHBP1-bound LPL is essential for the margination of triglyceride-rich lipoproteins (TRLs) along capillaries, allowing the lipolytic processing of TRLs to proceed. In peripheral tissues, the intravascular processing of TRLs by the GPIHBP1-LPL complex is crucial for the generation of lipid nutrients for adjacent parenchymal cells. GPIHBP1 is absent from the capillaries of the brain, which uses glucose for fuel; however, GPIHBP1 is expressed in the capillaries of mouse and human gliomas. Importantly, the GPIHBP1 in glioma capillaries captures locally produced LPL. We use NanoSIMS imaging to show that TRLs marginate along glioma capillaries and that there is uptake of TRL-derived lipid nutrients by surrounding glioma cells. Thus, GPIHBP1 expression in gliomas facilitates TRL processing and provides a source of lipid nutrients for glioma cells.

The application of gene marker-assisted selection and proteomics for the best meat quality criteria and body measurements in Qinchuan cattle breed

In the past few decades, enhancement of animal productivity has been gaining increasing attention among decisions-makers, politicians, mangers, and breeders, because of the increasing of world population and shortage of natural resources. The selection of high productivity animals is the main goal, through the application of genetic improvement programs. The use of molecular genetics has conferred significant breeding advantages over conventional breeding techniques. In this regard, many economic characteristics are controlled by a small number of multiple gene loci, each of which is responsible for trait diversity and hence they are referred to as quantitative trait loci (QTL). Single-nucleotide polymorphisms (SNPs), which have recently been discovered through DNA sequencing, are considered one of the most useful types of genetic marker. SNPs are found where different nucleotides occur at the same position in the DNA sequence. They are found in both coding and noncoding regions of the genome and are present at one SNP in every 1000 b. Strategies for the identification and application of markers are based on reference to examples of loci that can control various traits. Furthermore, markers for growth, body measurements, and meat quality traits are preferred, because they can be used to predict the performance of animals, via blood samples, in the first few days of animal life. Marker-assisted selection using SNPs, such asSIRT1, SIRT2, LPL, CRTC2, SIX4, UCPs, and ZBTB38as selection criteria of body measurements and meat traits in beef cattle, will be beneficial in selection and breeding programs. The proteomic is a novel marker and a new approache of biotechnology which increases the understanding of the biological processes, besides being a remarkable biomarker that interrelated to growth and meat quality traits. Proteomics is a vigorous tool as usage for deduces molecular processes between quality traits and muscle proteins, which are helpful in analyzing the mechanisms of biochemistry that influence quality. So they could be potential biomarker for some meat quality traits. Among them, Actin, Myosin, Heat shock proteins are used a novel approaches in the field of biotechnology to understand the proteomics changes. This review article highlights the novel findings on the potential use of MAS and proteomics as biomarker for the selection for meat quality and carcass traits in Qinchuan cattle breed.

Lipoprotein Lipase Is a Feature of Alternatively-Activated Microglia and May Facilitate Lipid Uptake in the CNS During Demyelination

Severe demyelinating disorders of the central nervous system (CNS) such as multiple sclerosis (MS), can be devastating for many young lives. To date, the factors resulting in poor remyelination and repair are not well understood, and reparative therapies that benefit MS patients have yet to be developed. We have previously shown that the activity and abundance of Lipoprotein Lipase (LPL)—the rate-limiting enzyme in the hydrolysis of triglyceride-rich lipoproteins—is increased in Schwann cells and macrophages following nerve crush injury in the peripheral nervous system (PNS), suggesting that LPL may help scavenge myelin-derived lipids. We hypothesized that LPL may play a similar role in the CNS. To test this, mice were immunized with MOG_35–55 peptide to induce experimental allergic encephalomyelitis (EAE). LPL activity was increased (p < 0.05) in the brain at 30 days post-injection, coinciding with partial remission of clinical symptoms. Furthermore, LPL abundance and activity was up-regulated (p < 0.05) at the transition between de- and re-myelination in lysolecithin-treated ex vivo cerebellar slices. Since microglia are the key immune effector cells of the CNS we determined the role of LPL in microglia. Lipid uptake was decreased (p < 0.001) in LPL-deficient BV-2 microglial cells compared to WT. In addition, LPL-deficient cells showed dramatically reduced expression of anti-inflammatory markers, YM1 (−22 fold, p < 0.001), and arginase 1 (Arg1; −265 fold, p < 0.001) and increased expression of pro-inflammatory markers, such as iNOS compared to WT cells (+53 fold, p < 0.001). This suggests that LPL is a feature of reparative microglia, further supported by the metabolic and inflammatory profile of LPL-deficient microglia. Taken together, our data strongly suggest that LPL expression is a novel feature of a microglial phenotype that supports remyelination and repair through the clearance of lipid debris. This mechanism may be exploited to develop future reparative therapies for MS and primary neurodegenerative disorders (Alzheimer’s disease (AD) and Parkinson’s disease).

Lipoprotein lipase reaches the capillary lumen in chickens despite an apparent absence of GPIHBP1

In mammals, GPIHBP1 is absolutely essential for transporting lipoprotein lipase (LPL) to the lumen of capillaries, where it hydrolyzes the triglycerides in triglyceride-rich lipoproteins. In all lower vertebrate species (e.g., birds, amphibians, reptiles, fish), a gene for LPL can be found easily, but a gene for GPIHBP1 has never been found. The obvious question is whether the LPL in lower vertebrates is able to reach the capillary lumen. Using purified antibodies against chicken LPL, we showed that LPL is present on capillary endothelial cells of chicken heart and adipose tissue, colocalizing with von Willebrand factor. When the antibodies against chicken LPL were injected intravenously into chickens, they bound to LPL on the luminal surface of capillaries in heart and adipose tissue. LPL was released rapidly from chicken hearts with an infusion of heparin, consistent with LPL being located inside blood vessels. Remarkably, chicken LPL bound in a specific fashion to mammalian GPIHBP1. However, we could not identify a gene for GPIHBP1 in the chicken genome, nor could we identify a transcript for GPIHBP1 in a large chicken RNA-seq data set. We conclude that LPL reaches the capillary lumen in chickens - as it does in mammals - despite an apparent absence of GPIHBP1.

Candidate Gene Identification of Feed Efficiency and Coat Color Traits in a C57BL/6J × Kunming F2 Mice Population Using Genome-Wide Association Study

Feed efficiency (FE) is a very important trait in livestock industry. Identification of the candidate genes could be of benefit for the improvement of FE trait. Mouse is used as the model for many studies in mammals. In this study, the candidate genes related to FE and coat color were identified using C57BL/6J (C57) × Kunming (KM) F2 mouse population. GWAS results showed that 61 and 2 SNPs were genome-wise suggestive significantly associated with feed conversion ratio (FCR) and feed intake (FI) traits, respectively. Moreover, the Erbin, Msrb2, Ptf1a, and Fgf10 were considered as the candidate genes of FE. The Lpl was considered as the candidate gene of FI. Further, the coat color trait was studied. KM mice are white and C57 ones are black. The GWAS results showed that the most significant SNP was located at chromosome 7, and the closely linked gene was Tyr. Therefore, our study offered useful target genes related to FE in mice; these genes may play similar roles in FE of livestock. Also, we identified the major gene of coat color in mice, which would be useful for better understanding of natural mutation of the coat color in mice.

Kidney triglyceride accumulation in the fasted mouse is dependent upon serum free fatty acids

Lipid accumulation is a pathological feature of every type of kidney injury. Despite this striking histological feature, physiological accumulation of lipids in the kidney is poorly understood. We studied whether the accumulation of lipids in the fasted kidney are derived from lipoproteins or NEFAs. With overnight fasting, kidneys accumulated triglyceride, but had reduced levels of ceramide and glycosphingolipid species. Fasting led to a nearly 5-fold increase in kidney uptake of plasma [¹⁴C]oleic acid. Increasing circulating NEFAs using a β adrenergic receptor agonist caused a 15-fold greater accumulation of lipid in the kidney, while mice with reduced NEFAs due to adipose tissue deficiency of adipose triglyceride lipase had reduced triglycerides. Cluster of differentiation (Cd)36 mRNA increased 2-fold, and angiopoietin-like 4 (Angptl4), an LPL inhibitor, increased 10-fold. Fasting-induced kidney lipid accumulation was not affected by inhibition of LPL with poloxamer 407 or by use of mice with induced genetic LPL deletion. Despite the increase in CD36 expression with fasting, genetic loss of CD36 did not alter fatty acid uptake or triglyceride accumulation. Our data demonstrate that fasting-induced triglyceride accumulation in the kidney correlates with the plasma concentrations of NEFAs, but is not due to uptake of lipoprotein lipids and does not involve the fatty acid transporter, CD36.

Emerging strategies of targeting lipoprotein lipase for metabolic and cardiovascular diseases

Although statins and other pharmacological approaches have improved the management of lipid abnormalities, there exists a need for newer treatment modalities especially for the management of hypertriglyceridemia. Lipoprotein lipase (LPL), by promoting hydrolytic cleavage of the triglyceride core of lipoproteins, is a crucial node in the management of plasma lipid levels. Although LPL expression and activity modulation is observed as a pleiotropic action of some the commonly used lipid lowering drugs, the deliberate development of drugs targeting LPL has not occurred yet. In this review, we present the biology of LPL, highlight the LPL modulation property of currently used drugs and review the novel emerging approaches to target LPL.

Association studies on the bovine lipoprotein lipase gene polymorphism with growth and carcass quality traits in Qinchuan cattle

Lipoprotein lipase (LPL) is considered as an essential enzyme in lipid deposition and tissue metabolism. It has been proposed to be a lead candidate gene for genetic markers of lipid deposition and energy balance. In this paper, polymorphisms in the LPL gene were investigated in 554 Chinese Qinchuan cattle by PCR-RFLP and DNA sequencing. Seven single nucleotide polymorphisms (SNPs) were identified, which included one mutation (g.91C > T) in the 5'untranslated region (UTR), four synonymous mutations (g.17015A > G, g.18362G > A, g.18377T > C and g.19873T > C) and two mutations (g.25225A > G and g.25316T > G) in the 3'UTR. The frequencies of SNP g.18377T > C and g.25316T > G were skewed from Hardy-Weinberg equilibrium in all the samples (chi-square test, P < 0.05). An association analysis showed that five loci (except for g.91C > T and g.18377T > C) were significantly correlated with some growth and carcass quality traits. These results demonstrate that LPL might be a potential candidate gene for marker-assisted selection (MAS).

New molecular insights in diabetic nephropathy

Diabetes mellitus represents one of the major causes of functional kidney impairment. The review highlights the most significant steps made over the last decades in understanding the molecular basis of diabetic nephropathy (DN), which may provide reliable biomarkers for early diagnosis and prognosis, along with new molecular targets for personalized medicine. There is an increased interest in developing new therapeutic strategies to slow DN progression for improving patients' quality of life and reducing all-cause morbidity and disease-associated mortality. It is highly important to have a science-based medical attitude when facing diabetic patients with associated comorbidities and risk of rapid evolution toward end-stage renal disease. The data discussed herein were mainly from MEDLINE and PubMed articles published in English from 1990 to 2015 and from up-to-date. The search term was "diabetic nephropathy and oxidative stress".

Lipoprotein lipase is an important modulator of lipid uptake and storage in hypothalamic neurons

LPL is the rate-limiting enzyme for uptake of TG-derived FFA in peripheral tissues, and the enzyme is expressed in the brain and CNS. We previously created a mouse which lacks neuronal LPL. This animal becomes obese on a standard chow, and we observed reduced lipid uptake in the hypothalamus at 3 months preceding obesity. In our present study, we replicated the animal phenotype in an immortalized mouse hypothalamic cell line (N41) to examine how LPL affects expression of AgRP as well as entry and storage of lipids into neurons. We show that LPL is able to modulate levels of the orexigenic peptide AgRP. LPL also exerts effects on lipid uptake into culture neurons, and that uptake of neutral lipid can be enhanced even by mutant LPL lacking catalytic activity. N41 cells also accumulate neutral lipid in droplets, and this is at least in part regulated by LPL. These data in addition to those published in mice with neuron-specific deletion of LPL suggest that neuronal LPL is an important regulator of lipid homeostasis in neurons and that alterations in LPL levels may have important effects on systemic metabolism and neuronal lipid biology.

The evolving understanding of the contribution of lipid metabolism to diabetic kidney disease

Although diabetes is mainly diagnosed based on elevated glucose levels, dyslipidemia is also observed in these patients. Chronic kidney disease (CKD), a frequent occurrence in patients with diabetes, is associated with major abnormalities in circulating lipoproteins and renal lipid metabolism. At baseline, most renal epithelial cells rely on fatty acids as their energy source. CKD, including that which occurs in diabetes, is characterized by tubule epithelial lipid accumulation. Whether this is due to increased uptake or greater local fatty acid synthesis is unknown. We have recently shown that CKD also leads to decreased fatty acid oxidation, which might be an additional mechanism leading to lipid accumulation. Defective fatty acid utilization causes energy depletion resulting in increased apoptosis and dedifferentiation, which in turn contributes to fibrosis and CKD progression. Enhanced fatty acid oxidation in the kidney induced by fenofibrate, a peroxisomal proliferator-activated receptor (PPAR)-α agonist, showed benefit in mouse models of CKD. Fenofibrate treatment also reduced albuminuria in patients with diabetes in multiple clinical trials. Taken together, these findings suggest that further understanding of lipid metabolism in diabetic kidney disease may lead to novel therapeutic approaches.

JCL Roundtable: Hypertriglyceridemia due to defects in lipoprotein lipase function

In this Roundtable, our intent is to discuss those rare genetic disorders that impair the function of lipoprotein lipase. These cause severe hypertriglyceridemia that appears in early childhood with Mendelian inheritance and usually with full penetrance in a recessive pattern. Dr Ira Goldberg from New York University School of Medicine and Dr Stephen Young from the University of California, Los Angeles have agreed to answer my questions about this topic. Both have done fundamental work in recent years that has markedly altered our views on lipoprotein lipase function. I am going to start by asking them to give us a brief history of this enzyme system as a clinical entity.

Differential effects of angiopoietin-like 4 in brain and muscle on regulation of lipoprotein lipase activity

OBJECTIVE

Lipoprotein lipase (LPL) is a key regulator of circulating triglyceride rich lipoprotein hydrolysis. In brain LPL regulates appetite and energy expenditure. Angiopoietin-like 4 (Angptl4) is a secreted protein that inhibits LPL activity and, thereby, triglyceride metabolism, but the impact of Angptl4 on central lipid metabolism is unknown.

METHODS

We induced type 1 diabetes by streptozotocin (STZ) in whole-body Angptl4 knockout mice (Angptl4(-/-) ) and their wildtype littermates to study the role of Angptl4 in central lipid metabolism.

RESULTS

In type 1 (streptozotocin, STZ) and type 2 (ob/ob) diabetic mice, there is a ~2-fold increase of Angptl4 in the hypothalamus and skeletal muscle. Intracerebroventricular insulin injection into STZ mice at levels which have no effect on plasma glucose restores Angptl4 expression in hypothalamus. Isolation of cells from the brain reveals that Angptl4 is produced in glia, whereas LPL is present in both glia and neurons. Consistent with the in vivo experiment, in vitro insulin treatment of glial cells causes a 50% reduction of Angptl4 and significantly increases LPL activity with no change in LPL expression. In Angptl4(-/-) mice, LPL activity in skeletal muscle is increased 3-fold, and this is further increased by STZ-induced diabetes. By contrast, Angptl4(-/-) mice show no significant difference in LPL activity in hypothalamus or brain independent of diabetic and nutritional status.

CONCLUSION

Thus, Angptl4 in brain is produced in glia and regulated by insulin. However, in contrast to the periphery, central Angptl4 does not regulate LPL activity, but appears to participate in the metabolic crosstalk between glia and neurons.

Liver X receptor regulation of thyrotropin-releasing hormone transcription in mouse hypothalamus is dependent on thyroid status

Reversing the escalating rate of obesity requires increased knowledge of the molecular mechanisms controlling energy balance. Liver X receptors (LXRs) and thyroid hormone receptors (TRs) are key physiological regulators of energetic metabolism. Analysing interactions between these receptors in the periphery has led to a better understanding of the mechanisms involved in metabolic diseases. However, no data is available on such interactions in the brain. We tested the hypothesis that hypothalamic LXR/TR interactions could co-regulate signalling pathways involved in the central regulation of metabolism. Using in vivo gene transfer we show that LXR activation by its synthetic agonist GW3965 represses the transcriptional activity of two key metabolic genes, Thyrotropin-releasing hormone (Trh) and Melanocortin receptor type 4 (Mc4r) in the hypothalamus of euthyroid mice. Interestingly, this repression did not occur in hypothyroid mice but was restored in the case of Trh by thyroid hormone (TH) treatment, highlighting the role of the triiodothyronine (T₃) and TRs in this dialogue. Using shLXR to knock-down LXRs in vivo in euthyroid newborn mice, not only abrogated Trh repression but actually increased Trh transcription, revealing a potential inhibitory effect of LXR on the Hypothalamic-Pituitary-Thyroid axis. In vivo chromatin immunoprecipitation (ChIP) revealed LXR to be present on the Trh promoter region in the presence of T₃ and that Retinoid X Receptor (RXR), a heterodimerization partner for both TR and LXR, was never recruited simultaneously with LXR. Interactions between the TR and LXR pathways were confirmed by qPCR experiments. T₃ treatment of newborn mice induced hypothalamic expression of certain key LXR target genes implicated in metabolism and inflammation. Taken together the results indicate that the crosstalk between LXR and TR signalling in the hypothalamus centres on metabolic and inflammatory pathways.

Physiological regulation of lipoprotein lipase

The enzyme lipoprotein lipase (LPL), originally identified as the clearing factor lipase, hydrolyzes triglycerides present in the triglyceride-rich lipoproteins VLDL and chylomicrons. LPL is primarily expressed in tissues that oxidize or store fatty acids in large quantities such as the heart, skeletal muscle, brown adipose tissue and white adipose tissue. Upon production by the underlying parenchymal cells, LPL is transported and attached to the capillary endothelium by the protein GPIHBP1. Because LPL is rate limiting for plasma triglyceride clearance and tissue uptake of fatty acids, the activity of LPL is carefully controlled to adjust fatty acid uptake to the requirements of the underlying tissue via multiple mechanisms at the transcriptional and post-translational level. Although various stimuli influence LPL gene transcription, it is now evident that most of the physiological variation in LPL activity, such as during fasting and exercise, appears to be driven via post-translational mechanisms by extracellular proteins. These proteins can be divided into two main groups: the liver-derived apolipoproteins APOC1, APOC2, APOC3, APOA5, and APOE, and the angiopoietin-like proteins ANGPTL3, ANGPTL4 and ANGPTL8, which have a broader expression profile. This review will summarize the available literature on the regulation of LPL activity in various tissues, with an emphasis on the response to diverse physiological stimuli.

Lipoprotein lipase (LPL) is associated with neurite pathology and its levels are markedly reduced in the dentate gyrus of Alzheimer's disease brains

Lipoprotein lipase (LPL) is involved in regulation of fatty acid metabolism, and facilitates cellular uptake of lipoproteins, lipids and lipid-soluble vitamins. We evaluated LPL distribution in healthy and Alzheimer’s disease (AD) brain tissue and its relative levels in cerebrospinal fluid. LPL immunostaining is widely present in different neuronal subgroups, microglia, astrocytes and oligodendroglia throughout cerebrum, cerebellum and spinal cord. LPL immunoreactivity is also present in leptomeninges, small blood vessels, choroid plexus and ependymal cells, Schwann cells associated with cranial nerves, and in anterior and posterior pituitary. In vitro studies have shown presence of secreted LPL in conditioned media of human cortical neuronal cell line (HCN2) and neuroblastoma cells (SK-N-SH), but not in media of cultured primary human astrocytes. LPL was present in cytoplasmic and nuclear fractions of neuronal cells and astrocytes in vitro. LPL immunoreactivity strongly associates with AD-related pathology, staining diffuse plaques, dystrophic and swollen neurites, possible Hirano bodies and activated glial cells. We observed no staining associated with neurofibrillary tangles or granulovacuolar degeneration. Granule cells of the dentate gyrus and the associated synaptic network showed significantly reduced staining in AD compared to control tissue. LPL was also reduced in AD CSF samples relative to those in controls.

Biochemistry and pathophysiology of intravascular and intracellular lipolysis

All organisms use fatty acids (FAs) for energy substrates and as precursors for membrane and signaling lipids. The most efficient way to transport and store FAs is in the form of triglycerides (TGs); however, TGs are not capable of traversing biological membranes and therefore need to be cleaved by TG hydrolases ("lipases") before moving in or out of cells. This biochemical process is generally called "lipolysis." Intravascular lipolysis degrades lipoprotein-associated TGs to FAs for their subsequent uptake by parenchymal cells, whereas intracellular lipolysis generates FAs and glycerol for their release (in the case of white adipose tissue) or use by cells (in the case of other tissues). Although the importance of lipolysis has been recognized for decades, many of the key proteins involved in lipolysis have been uncovered only recently. Important new developments include the discovery of glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 (GPIHBP1), the molecule that moves lipoprotein lipase from the interstitial spaces to the capillary lumen, and the discovery of adipose triglyceride lipase (ATGL) and comparative gene identification-58 (CGI-58) as crucial molecules in the hydrolysis of TGs within cells. This review summarizes current views of lipolysis and highlights the relevance of this process to human disease.

Glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 and the intravascular processing of triglyceride-rich lipoproteins

Lipoprotein lipase (LPL) is produced by parenchymal cells, mainly adipocytes and myocytes, but is involved in hydrolysing triglycerides in plasma lipoproteins at the capillary lumen. For decades, the mechanism by which LPL reaches its site of action in capillaries was unclear, but this mystery was recently solved. Glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 (GPIHBP1), a glycosylphosphatidylinositol-anchored protein of capillary endothelial cells, 'picks up' LPL from the interstitial spaces and shuttles it across endothelial cells to the capillary lumen. When GPIHBP1 is absent, LPL is mislocalized to the interstitial spaces, leading to severe hypertriglyceridaemia. Some cases of hypertriglyceridaemia in humans are caused by GPIHBP1 mutations that interfere with the ability of GPIHBP1 to bind to LPL, and some are caused by LPL mutations that impair the ability of LPL to bind to GPIHBP1. Here, we review recent progress in understanding the role of GPIHBP1 in health and disease and discuss some of the remaining unresolved issues regarding the processing of triglyceride-rich lipoproteins.

Brain region-specific immunolocalization of the lipolysis-stimulated lipoprotein receptor (LSR) and altered cholesterol distribution in aged LSR+/- mice

Brain lipid homeostasis is important for maintenance of brain cell function and synaptic communications, and is intimately linked to age-related cognitive decline. Because of the blood-brain barrier's limiting nature, this tissue relies on a complex system for the synthesis and receptor-mediated uptake of lipids between the different networks of neurons and glial cells. Using immunofluorescence, we describe the region-specific expression of the lipolysis-stimulated lipoprotein receptor (LSR), in the mouse hippocampus, cerebellum Purkinje cells, the ependymal cell interface between brain parenchyma and cerebrospinal fluid, and the choroid plexus. Colocalization with cell-specific markers revealed that LSR was expressed in neurons, but not astrocytes. Latency in arms of the Y-maze exhibited by young heterozygote LSR(+/-) mice was significantly different as compared to control LSR(+/+), and increased in older LSR(+/-) mice. Filipin and Nile red staining revealed membrane cholesterol content accumulation accompanied by significantly altered distribution of LSR in the membrane, and decreased intracellular lipid droplets in the cerebellum and hippocampus of old LSR(+/-) mice, as compared to control littermates as well as young LSR(+/-) animals. These data therefore suggest a potential role of LSR in brain cholesterol distribution, which is particularly important in preserving neuronal integrity and thereby cognitive functions during aging.

Lipoprotein lipase in the brain and nervous system

Lipoprotein lipase (LPL) is rate limiting in the provision of triglyceride-rich lipoprotein-derived lipids into tissues. LPL is also present in the brain, where its function has remained elusive. Recent evidence implicates a role of LPL in the brain in two processes: (a) the regulation of energy balance and body weight and (b) cognition. Mice with neuron-specific deletion of LPL have increases in food intake that lead to obesity, and then reductions in energy expenditure that further contribute to and sustain the phenotype. In other mice with LPL deficiency rescued from neonatal lethality by somatic gene transfer wherein LPL in the brain remains absent, altered cognition ensues. Taking into consideration data that associate LPL mutations with Alzheimer's disease, a role for LPL in learning and memory seems likely. Overall, the time is ripe for new insights into how LPL-mediated lipoprotein metabolism in the brain impacts CNS processes and systems biology.

New wrinkles in lipoprotein lipase biology

PURPOSE OF REVIEW

We summarize recent progress on GPIHBP1, a molecule that transports lipoprotein lipase (LPL) to the capillary lumen, and discuss several newly studied molecules that appear important for the regulation of LPL activity.

RECENT FINDINGS

LPL, the enzyme responsible for the lipolytic processing of triglyceride-rich lipoproteins, interacts with multiple proteins and is regulated at multiple levels. Several regulators of LPL activity have been known for years and have been investigated thoroughly, but several have been identified only recently, including an endothelial cell protein that transports LPL to the capillary lumen, a microRNA that reduces LPL transcript levels, a sorting protein that targets LPL for uptake and degradation, and a transcription factor that increases the expression of apolipoproteins that regulate LPL activity.

SUMMARY

Proper regulation of LPL is important for controlling the delivery of lipid nutrients to tissues. Recent studies have identified GPIHBP1 as the molecule that transports LPL to the capillary lumen, and have also identified other molecules that are potentially important for regulating LPL activity. These new discoveries open new doors for understanding basic mechanisms of lipolysis and hyperlipidemia.

GPIHBP1, an endothelial cell transporter for lipoprotein lipase

Interest in lipolysis and the metabolism of triglyceride-rich lipoproteins was recently reignited by the discovery of severe hypertriglyceridemia (chylomicronemia) in glycosylphosphatidylinositol-anchored high density lipoprotein-binding protein 1 (GPIHBP1)-deficient mice. GPIHBP1 is expressed exclusively in capillary endothelial cells and binds lipoprotein lipase (LPL) avidly. These findings prompted speculation that GPIHBP1 serves as a binding site for LPL in the capillary lumen, creating "a platform for lipolysis." More recent studies have identified a second and more intriguing role for GPIHBP1-picking up LPL in the subendothelial spaces and transporting it across endothelial cells to the capillary lumen. Here, we review the studies that revealed that GPIHBP1 is the LPL transporter and discuss which amino acid sequences are required for GPIHBP1-LPL interactions. We also discuss the human genetics of LPL transport, focusing on cases of chylomicronemia caused by GPIHBP1 mutations that abolish GPIHBP1's ability to bind LPL, and LPL mutations that prevent LPL binding to GPIHBP1.

Deficiency of lipoprotein lipase in neurons modifies the regulation of energy balance and leads to obesity

Free fatty acids (FFAs) suppress appetite when injected into the hypothalamus. To examine whether lipoprotein lipase (LPL), a serine hydrolase that releases FFAs from circulating triglyceride (TG)-rich lipoproteins, might contribute to FFA-mediated signaling in the brain, we created neuron-specific LPL-deficient mice. Homozygous mutant (NEXLPL-/-) mice were hyperphagic and became obese by 16 weeks of age. These traits were accompanied by elevations in the hypothalamic orexigenic neuropeptides, AgRP and NPY, and were followed by reductions in metabolic rate. The uptake of TG-rich lipoprotein fatty acids was reduced in the hypothalamus of 3-month-old NEXLPL-/- mice. Moreover, deficiencies in essential fatty acids in the hypothalamus were evident by 3 months, with major deficiencies of long-chain n-3 fatty acids by 12 months. These results indicate that TG-rich lipoproteins are sensed in the brain by an LPL-dependent mechanism and provide lipid signals for the central regulation of body weight and energy balance.

Lipoprotein lipase is a novel amyloid beta (Abeta)-binding protein that promotes glycosaminoglycan-dependent cellular uptake of Abeta in astrocytes

Lipoprotein lipase (LPL) is a member of a lipase family known to hydrolyze triglyceride molecules in plasma lipoprotein particles. LPL also plays a role in the binding of lipoprotein particles to cell-surface molecules, including sulfated glycosaminoglycans (GAGs). LPL is predominantly expressed in adipose and muscle but is also highly expressed in the brain where its specific roles are unknown. It has been shown that LPL is colocalized with senile plaques in Alzheimer disease (AD) brains, and its mutations are associated with the severity of AD pathophysiological features. In this study, we identified a novel function of LPL; that is, LPL binds to amyloid β protein (Aβ) and promotes cell-surface association and uptake of Aβ in mouse primary astrocytes. The internalized Aβ was degraded within 12 h, mainly in a lysosomal pathway. We also found that sulfated GAGs were involved in the LPL-mediated cellular uptake of Aβ. Apolipoprotein E was dispensable in the LPL-mediated uptake of Aβ. Our findings indicate that LPL is a novel Aβ-binding protein promoting cellular uptake and subsequent degradation of Aβ.

Altered PPARgamma expression and activation after transient focal ischemia in rats

Stroke is a devastating disease with limited treatment options. Recently, we found that the peroxisome proliferator-activated receptor-gamma (PPARgamma) agonists troglitazone and pioglitazone reduce injury and inflammation in a rat model of transient cerebral ischemia. The mechanism of this protection is unclear, as these agents can act through PPAR-gamma activation or through PPAR-gamma-independent mechanisms. Therefore, we examined PPAR-gamma expression, DNA binding and transcriptional activity following stroke. In addition, we used a PPAR-gamma antagonist, T0070907, to determine the role of PPAR-gamma during ischemia. Using immunohistochemical techniques and real-time PCR, we found low levels of PPAR-gamma mRNA and PPAR-gamma immunoreactivity in nonischemic brain; however, PPAR-gamma expression dramatically increased in ischemic neurons, peaking 24 h following middle cerebral artery occlusion. Interestingly, we found that in both vehicle- and agonist-treated brains, DNA binding was reduced in the ischemic hemisphere relative to the contralateral hemisphere. Expression of a PPAR-gamma target gene, lipoprotein lipase, was also reduced in ischemic relative to nonischemic brain. Both DNA binding and lipoprotein lipase expression were increased by the addition of the PPAR-gamma agonist rosiglitazone. Finally, we found that rosiglitazone-mediated protection after stroke was reversed by the PPAR-gamma antagonist T0070907. Interestingly, infarction size was also increased by T0070907 in the absence of PPAR-gamma agonist, suggesting that endogenous PPAR-gamma ligands may mitigate the effects of cerebral ischemia.

A polymorphism in lipoprotein lipase affects the severity of Alzheimer's disease pathophysiology

Emerging evidences indicate a role for lipoprotein lipase (LPL) in degenerative states. Genetic variations in the LPL gene were previously associated to lipid imbalance and coronary artery disease (CAD) risk and severity, a condition that shares pathological features with common Alzheimer's disease (AD). To evaluate whether these genetic variations associate with the risk and pathophysiology of common AD, autopsy-confirmed patients (242 controls, 153 AD) were genotyped for a PvuII single nucleotide polymorphism (SNP; rs285; referred to as the P+ allele) of LPL. Brain LPL mRNA levels, cholesterol levels, amyloid concentration, senile plaques and neurofibrillary tangles density counts were measured and contrasted with specific LPL genotypes. When adjusted for age and sex, homozygosity for the P+ allele resulted in an odds ratio of 2.3 for the risk of developing AD. More importantly, we report that the presence of the P+ allele of LPL significantly affects its mRNA expression level (n = 51; P = 0.026), brain tissue cholesterol levels (n = 55; P = 0.0013), neurofibrillary tangles (n = 52; P = 0.025) and senile plaque (n = 52; P = 0.022) densities. These results indicate that a common polymorphism in the lipoprotein lipase gene modulates the risk level for sporadic AD in the eastern Canadian population but more importantly, indirectly modulates the pathophysiology of the brain in autopsy-confirmed cases.

Adipogenic effect of alcohol on human bone marrow-derived mesenchymal stem cells

BACKGROUND

In addition to a decrease in bone mass in alcoholics their osteopenic skeletons show an increase in bone marrow adiposity. Human bone marrow mesenchymal stem cells (hMSC) in vivo differentiate into several phenotypes including osteogenic and adipogenic cells, both of which remain as resident populations of bone marrow. In vitro, the lineage commitment and differentiation of hMSC toward the adipogenic pathway can be promoted by alcohol.

METHODS

Human male and female mesenchymal stem cells from joint replacement surgery were cultured. Cells were grouped as: 1) Control (no additions to the culture medium), 2) EtOH (50 mm alcohol added to the culture medium), 3) OS (osteogenic inducers added to the culture medium), and 4) OS + EtOH (osteogenic inducers and 50 mm alcohol added to the culture medium). Cultures stained with Nile Red confirmed the development of differentiated adipocytes. Population analysis was performed using fluorescence-activated cell sorting. Gene expression of early, middle, late, and terminal differentiation stage markers (PPAR)gamma2, lipoprotein lipase, adipsin, leptin, and adipocyte P2 (aP2)] was studied by Northern hybridization, and protein synthesis of aP2 was determined by Western analysis.

RESULTS

Nile red staining confirmed increased adipocyte development 10 days after the onset of treatment with 50 mm alcohol and osteogenic induction. By day 21 the number of adipocytes increased to 13.6% of the total population. Alcohol up-regulated the gene expression of PPARgamma2 whereas no up-regulation was observed for the other genes. Protein production of aP2 was significantly increased in hMSC cells by culture in the presence of alcohol.

CONCLUSIONS

The data suggest that alcohol's adipogenic effect on cultured hMSC is through up-regulation of PPARgamma2 at the point of lineage commitment as well as through enhancement of lipid transport and storage through increased aP2 synthesis. The alcohol-induced expression and synthesis changes account for the increased Nile red staining of cultured hMSC.

Requirement for enzymatically active lipoprotein lipase in neuronal differentiation: a site-directed mutagenesis study

Lipoprotein lipase (LPL) is well known for its role in the catabolism of plasma triglyceride (Tg)-rich lipoproteins, such as very low density lipoproteins (VLDL) and chylomicrons. The action of LPL on Tg-rich lipoproteins provides free fatty acids to skeletal muscle and adipose tissues, the main sites of LPL synthesis. Several studies have demonstrated that LPL is widely expressed in the parenchyma of brain tissues. We have recently shown that LPL expression is essential for promoting VLDL-stimulated differentiation of Neuro-2A cells. In the present study, we have generated stably transfected Neuro-2A cell lines expressing either wild-type LPL or various LPL mutants, including three enzymatically inactive variants (Asp156Asn, Gly188Glu and Pro207Leu), an enzymatically defective variant (Asn291Ser) and a variant known to express increased LPL activity (Ser447Ter). In Neuro-2A cells expressing enzymatically inactive LPL variants, VLDL-stimulated differentiation and neurite extension were not observed. However, in Neuro-2A cells expressing partially active or overactive LPL variants, VLDL added to the cultured medium was able to induce the phenotypic differentiation similar to that observed in Neuro-2A cells expressing wild-type LPL. In summary, these data show that the availability of fatty acids, resulting from the catabolism of VLDL by LPL, is required to promote the phenotypical differentiation of neuroblastoma cells. These findings may have significant relevance to lipoprotein metabolism in the brain as well as to the maturation and regeneration of nervous tissues in carriers of mutant LPL.

Peroxisome proliferator-activated receptor (PPAR) agonists decrease lipoprotein lipase secretion and glycated LDL uptake by human macrophages

Lipoprotein lipase (LPL) acts independently of its function as triglyceride hydrolase by stimulating macrophage binding and uptake of native, oxidized and glycated LDL. Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors expressed in monocyte/macrophages, where they control cholesterol homeostasis. Here we study the role of PPARs in the regulation of LPL expression and activity in human monocytes and macrophages. Incubation of human monocytes or macrophages with PPARalpha or PPARgamma ligands increases LPL mRNA and intracellular protein levels. By contrast, PPAR activators decrease secreted LPL mass and enzyme activity in differentiated macrophages. These actions of PPAR activators are associated with a reduced uptake of glycated LDL and could influence atherosclerosis development associated with diabetes.

Differentiation of human marrow stromal precursor cells: bone morphogenetic protein-2 increases OSF2/CBFA1, enhances osteoblast commitment, and inhibits late adipocyte maturation

Because regulation of the differentiation to osteoblasts and adipocytes from a common progenitor in bone marrow stroma is poorly understood, we assessed effects of bone morphogenetic protein-2 (BMP-2) on a conditionally immortalized human marrow stromal cell line, hMS(2-6), which is capable of differentiation to either lineage. BMP-2 did not affect hMS(2-6) cell proliferation but enhanced osteoblast differentiation as assessed by a 1.8-fold increase in expression of OSF2/CBFA1 (a gene involved in commitment to the osteoblast pathway), by increased mRNA expression and protein secretion for alkaline phosphatase (ALP), type I procollagen and osteocalcin (OC) (except for OC protein), and by increased mineralized nodule formation. Transient transfection with Osf2/Cbfa1 antisense oligonucleotide substantially reduced BMP-2-stimulated expression of ALP mRNA and protein. The effects of BMP-2 on adipocyte differentiation varied: expression of peroxisome proliferator-activated receptor gamma2 (a gene involved in commitment to the adipocyte pathway) was unchanged, mRNA expression of the early differentiation marker, lipoprotein lipase, was increased, and mRNA and protein levels of the late differentiation marker, leptin, and the formation of cytoplasmic lipid droplets were decreased. Thus, by enhancing osteoblast commitment and by inhibiting late adipocyte maturation, BMP-2 acts to shunt uncommitted marrow stromal precursor cells from the adipocyte to the osteoblast differentiation pathway.

Mouse very low-density lipoprotein receptor (VLDLR): gene structure, tissue-specific expression and dietary and developmental regulation

The very low density lipoprotein receptor (VLDLR) is a multifunctional apolipoprotein (apo) E receptor that shares a common structural feature as well as some ligand specificity to apo E with members of the low density lipoprotein receptor gene family. We have isolated and characterized the mouse VLDLR gene. The mouse VLDLR gene contains 19 exons spanning approximately 50 kb. The exon-intron organization of the gene is completely conserved between mouse and human. Since the 5'-flanking region of the mouse VLDLR gene contains two copies of a sterol regulatory element-1 like sequence (SRE-1), we next studied regulation of the VLDLR mRNA expression in heart, skeletal muscle and adipose tissue in C57BL/6, LDLR-/-, apo E-/- and LDLR-/-apo E-/- mice fed normal chow or atherogenic diet. The VLDLR mRNA expression was down-regulated 3-fold by feeding atherogenic diet in heart and skeletal muscle only in LDLR-/- mice. In contrast, VLDLR mRNA expression was up-regulated by atherogenic diet in adipose tissue in all animal models except double knockout mice. These results suggest that SRE-1 may be functional and VLDLR plays a role in cholesterol homeostasis in heart and skeletal muscle when LDLR is absent and that apo E is required for this modulation. Developmental regulation of the VLDLR mRNA expression was also tissue-specific. VLDLR mRNA expression in heart displayed significant up and down regulation during development. Maximal level was detected on post-natal day 3. However, the VLDLR mRNA levels in skeletal muscle remained relatively constant except a slight dip on post-natal day 7. In kidney and brain, VLDLR mRNA also peaked on post-natal day 3 but remained relatively constant thereafter. In liver, VLDLR mRNA expression was very low; it was barely detectable at day 19 of gestation and was decreased further thereafter. In adipose tissue, the VLDLR mRNA level showed an increase on post-natal day 13, went down again during weaning and then continued to increase afterwards. This developmental pattern as well as dietary regulation in adipose tissue supports the notion that VLDLR plays a role in lipid accumulation in this tissue. Although the primary role of VLDLR in heart, muscle and adipose tissue is likely in lipid metabolism, developmental pattern of this receptor in other tissues suggests that VLDLR has functions that are unrelated to lipid metabolism.

Three independent lines of evidence suggest retinoids as causal to schizophrenia

Retinoid dysregulation may be an important factor in the etiology of schizophrenia. This hypothesis is supported by three independent lines of evidence that triangulate on retinoid involvement in schizophrenia: (i) congenital anomalies similar to those caused by retinoid dysfunction are found in schizophrenics and their relatives; (ii) those loci that have been suggestively linked to schizophrenia are also the loci of the genes of the retinoid cascade (convergent loci); and (iii) the transcriptional activation of the dopamine D2 receptor and numerous schizophrenia candidate genes is regulated by retinoic acid. These findings suggest a close causal relationship between retinoids and the underlying pathophysiological defects in schizophrenia. This leads to specific strategies for linkage analyses in schizophrenia. In view of the heterodimeric nature of the retinoid nuclear receptor transcription factors, e.g., retinoid X receptor beta at chromosome 6p21.3 and retinoic acid receptor beta at 3p24.3, two-locus linkage models incorporating genes of the retinoid cascade and their heterodimeric partners, e.g., peroxisome proliferator-activated receptor alpha at chromosome 22q12-q13 or nuclear-related receptor 1 at chromosome 2q22-q23, are proposed. New treatment modalities using retinoid analogs to alter the downstream expression of the dopamine receptors and other genes that are targets of retinoid regulation, and that are thought to be involved in schizophrenia, are suggested.

Expression and regulation of the lipoprotein lipase gene in human adrenal cortex

Lipoprotein lipase (LPL), an enzyme which hydrolyzes triglycerides and participates in the catabolism of remnant lipoproteins, plays a crucial role in energy and lipid metabolism. The goal of this study was to analyze the expression and regulation of the LPL gene in human adrenals. Reverse transcriptase-polymerase chain reaction amplification and sequence analysis demonstrated the presence of LPL mRNA in fetal and adult human adrenal cortex. Furthermore, the human adrenocortical carcinoma cell line, NCI-H295, expresses LPL mRNA and protein, which is localized to the outer cellular membrane as demonstrated by immunofluorescence confocal microscopy and can be released in the medium by heparin addition. To asses whether the LPL gene is regulated by agents regulating adrenal steroidogenesis, NCI-H295 cells were treated with activators of second messenger systems. Whereas the calcium-ionophore A23187 did not affect LPL gene expression, treatment with phorbol 12-myristate 13-acetate decreased LPL mRNA levels in a time- and dose-dependent manner. This decrease after phorbol 12-myristate 13-acetate was associated with diminished heparin-releasable LPL mass and activity in the culture medium. Addition of the cAMP analog 8-Br-cAMP to NCI-H295 cells resulted in a rapid, but transient dose-dependent induction of LPL mRNA. Treatment with the protein synthesis inhibitor cycloheximide gradually induced, whereas simultaneous addition of cAMP and cycloheximide superinduced LPL mRNA levels. Nuclear run-on analysis indicated that the effects of cAMP and cycloheximide occurred at the transcriptional and post-transcriptional level, respectively. Transient co-transfection assays demonstrated that the first 230 base pairs of the proximal LPL promoter contain a cAMP-responsive element activated by protein kinase A and transcription factors belonging to the CREB/CREM family. These data indicate that LPL is expressed in human adrenal cortex and regulated in NCI-H295 adrenocortical carcinoma cells by activators of the protein kinase A and protein kinase C second messenger pathways in a manner comparable to P450scc, which catalyzes the first step in adrenal steroidogenesis. These observations suggest a role for LPL in adrenal energy and/or lipid metabolism and possibly in steroidogenesis.

Expression in mouse embryos and in adult mouse brain of three members of the amyloid precursor protein family, of the alpha-2-macroglobulin receptor/low density lipoprotein receptor-related protein and of its ligands apolipoprotein E, lipoprotein lipase, alpha-2-macroglobulin and the 40,000 molecular weight receptor-associated protein

We have analysed by northern blotting and by in situ hybridization the expression patterns of eight different genes during the second half of mouse embryonic development and in adult mouse brain: we compared the messenger RNA levels of amyloid precursor protein and of the two amyloid precursor protein-like proteins 1 and 2 and we have analysed expression of apolipoprotein E and of its main receptor in brain, the alpha-2-macroglobulin/low density lipoprotein receptor-related protein and three other ligands: the proteinase inhibitor alpha-2-macroglobulin, the modifying enzyme lipoprotein lipase and the 44,000 molecular weight heparin binding protein, a ligand of unknown function. During embryogenesis the temporal expression pattern differs considerably for the three members of the amyloid precursor proteins. Total embryo messenger RNA levels of amyloid precursor protein and amyloid precursor protein-like protein 2 increased progressively, while amyloid precursor protein-like protein 1 messenger RNA showed a burst of synthesis between days 10 and 13 post-coitum. Significantly, expression of the alpha-2-macroglobulin/low density lipoprotein receptor-related protein and of its associated protein, the 44,000 molecular weight heparin binding protein, exhibited their most important increase very similar to that of amyloid precursor protein-like protein 1, between days 10 and 13 post-coitum. Apolipoprotein E, lipoprotein lipase and alpha-2-macroglobulin messenger RNA levels in total embryos increased progressively, beginning most pronounced at days 13, 15 and 17, respectively. In mouse embryos, in situ hybridization established amyloid precursor protein, amyloid precursor protein-like protein 2 and alpha-2-macroglobulin/low density lipoprotein receptor-related protein messenger RNA to be expressed in most organs, with the notable exception of the liver, while expression of the other studied proteins was much more restricted. Among adult mouse tissues, the genes investigated were expressed very prominently in brain, except for lipoprotein lipase and for the complete absence of alpha-2-macroglobulin messenger RNA. In adult mouse brain, the cortex and hippocampus exhibited strong signals for most genes analysed. Exceptions are lipoprotein lipase and apolipoprotein E messenger RNAs, and the absent alpha-2-macroglobulin messenger RNA. Several interesting features, similarities as well as differences, between brain tissue sections hybridized with probes for amyloid precursor protein, amyloid precursor protein-like proteins 1 and 2 and between alpha-2-macroglobulin/low density lipoprotein receptor-related protein and heparin binding protein-44 were observed and are described. The results are further discussed in view of the known or anticipated physiological functions of the proteins examined and of their possible role in the etiology of Alzheimer's disease.

Regulation of expression of the lipoprotein lipase gene in brown adipose tissue

The regulation of lipoprotein lipase gene expression in brown adipose tissue was studied. Rats were preacclimated to 21 degrees C. Exposure to cold (4 degrees C) resulted in a rapid increase in the level of lipoprotein lipase mRNA in the tissue. The level peaked (expressed per microgram total RNA) after approximately 8 h and then slowly declined. The increased lipoprotein lipase mRNA level was not due to an increased stability of the mRNA, but, in a transition event from a high to a low expression of the lipoprotein lipase gene, a transcription-dependent process was recruited that accelerated the breakdown of lipoprotein lipase mRNA. Norepinephrine injections increased lipoprotein lipase mRNA levels in the tissue; this effect was mediated via a beta-adrenergic receptor. The effect of cold could be mimicked by norepinephrine injections, and these two effects were not additive, indicating that the cold effect was mediated by norepinephrine. The lipoprotein lipase mRNA level was also increased by insulin injections (into fasted animals); thus an increase in lipoprotein lipase gene expression in brown adipose tissue may be induced via two different stimuli, which, intracellularly, would be mediated via different signaling systems. In all investigated conditions, the changes in lipoprotein lipase mRNA levels observed here were parallelled by alterations in lipoprotein lipase activity reported earlier from this laboratory. It was therefore concluded that, under the conditions studied, lipoprotein lipase activity in brown adipose tissue was primarily regulated at the transcriptional level.

Developmental regulation of lipoprotein lipase in rats

To evaluate changes in lipoprotein lipase (LPL) expression during development, levels of LPL mRNA, protein, and enzyme activity were measured in heart, epididymal fat, kidney, and brain of rats, from late gestation through 24 mo. LPL mRNA, protein, and enzyme activity were low in fetal and neonatal hearts. LPL mRNA increased 11-fold by 60 days and remained at this level thereafter; LPL protein and enzyme activity increased 10-fold by weaning, before declining to low values by 3 mo. LPL mRNA levels, protein, and enzyme activity did not change in epididymal fat from 3 wk to 21 mo. In the kidney, LPL mRNA levels were high at the end of gestation but fluctuated during the first month. LPL protein and activity were low at day 1 and rose eightfold to peak values by day 7 before decreasing to low levels by weaning. LPL mRNA levels were relatively high in fetal brains and then fell 60% during the neonatal period. LPL protein peaked at day 7 before falling 95% by weaning. Thus LPL is under complex tissue-specific regulation involving transcriptional and posttranscriptional mechanisms.

Apolipoproteins in rat cerebrospinal fluid: a comparison with plasma lipoprotein metabolism and effect of aging

Cerebrospinal fluid (CSF) apo E concentrations, determined by a sensitive sandwich ELISA, were 411.3 +/- 76.0 and 454.3 +/- 51.8 micrograms/dl (mean +/- S.D.) for young rats (8-12 weeks old, n = 7) and old rats (36-40 weeks old, n = 10), respectively. Age-related increase, which was conspicuous in serum apo E (21.2 +/- 2.4 vs 60.9 +/- 14.1 mg/dl for young and old rats, respectively), was not observed in CSF apo E. CSF apo A-I concentrations, determined by ELISA, were extremely low in the both groups (less than 10 micrograms/dl). Neither CSF apo A-I nor CSF apo E correlated to any of the plasma lipoprotein components, indicating the presence of largely independent lipoprotein metabolism in the rat central nervous system. Apo E is present in CSF in the form of apo E-rich HDL1 with particle sizes similar to those of plasma E-rich HDL1.