Characterization of lysosomal acid lipase by site-directed mutagenesis and heterologous expression

ABHD5 regulates midgut-specific lipid homeostasis in Bombyx mori

Lipids are an important energy source and are utilized as substrates for various physiological processes in insects. Comparative gene identification 58 (CGI-58), also known as α/β hydrolase domain-containing 5 (ABHD5), is a highly conserved and multifunctional gene involved in regulating lipid metabolism and cellular energy balance in many organisms. However, the biological functions of ABHD5 in insects are poorly understood. In the current study, we describe the identification and characterization of the ABHD5 gene in the lepidopteran model insect, Bombyx mori. The tissue expression profile investigated using quantitative reverse transcription polymerase chain reaction (RT-qPCR) reveals that BmABHD5 is widely expressed in all tissues, with particularly high levels found in the midgut and testis. A binary transgenic CRISPR/Cas9 system was employed to conduct a functional analysis of BmABHD5, with the mutation of BmABHD5 leading to the dysregulation of lipid metabolism and excessive lipid accumulation in the larval midgut. Histological and physiological analysis further reveals a significant accumulation of lipid droplets in the midgut of mutant larvae. RNA-seq and RT-qPCR analysis showed that genes related to metabolic pathways were significantly affected by the absence of BmABHD5. Altogether, our data prove that BmABHD5 plays an important role in regulating tissue-specific lipid metabolism in the silkworm midgut.

The resolution of phagosomes

Phagocytosis is a fundamental immunobiological process responsible for the removal of harmful particulates. While the number of phagocytic events achieved by a single phagocyte can be remarkable, exceeding hundreds per day, the same phagocytic cells are relatively long-lived. It should therefore be obvious that phagocytic meals must be resolved in order to maintain the responsiveness of the phagocyte and to avoid storage defects. In this article, we discuss the mechanisms involved in the resolution process, including solute transport pathways and membrane traffic. We describe how products liberated in phagolysosomes support phagocyte metabolism and the immune response. We also speculate on mechanisms involved in the redistribution of phagosomal metabolites back to circulation. Finally, we highlight the pathologies owed to impaired phagosome resolution, which range from storage disorders to neurodegenerative diseases.

Lysosomal acid lipase promotes endothelial proliferation in cold-activated adipose tissue

Oxidative tissues such as brown adipose tissue and muscle internalize large amounts of circulating lipids and glucose as energy source. Endothelial cells (ECs) provide a platform for regulated transport and processing of blood-borne nutrients. Next to this role, it has become recognized that intercellular crosstalk between ECs and underlying parenchymal cells is indispensable for maintenance of tissue homoeostasis. Here, we comment on our recent observation that capillary ECs in thermogenic adipose tissues take up and metabolize entire triglyceride-rich lipoprotein (TRL) particles in response to cold exposure. This process is dependent on CD36, lipoprotein lipase (LPL) and lysosomal acid lipase (LAL). Remarkably, loss of LAL specifically in endothelial cells results in impaired endothelial proliferation and diminished thermogenic adaptation. Mechanistically, cell culture experiments indicate that LAL-mediated TRL processing leads to the generation of reactive oxygen species, which in turn activate hypoxia-induced factor (HIF)-mediated proliferative responses. In the current manuscript, we provide in vivo evidence that LAL-deficiency impairs proliferation of endothelial cells in thermogenic adipose tissue. In addition, we show uptake of nanoparticle-labelled TRL and LAL expression in cardiac endothelial cells, suggesting a physiological function of endothelial lipoprotein processing not only in thermogenic adipose tissue but also in cardiac muscle.

Therapeutic efficacy of rscAAVrh74.miniCMV.LIPA gene therapy in a mouse model of lysosomal acid lipase deficiency

Lysosomal acid lipase deficiency (LAL-D) presents as one of two rare autosomal recessive diseases: Wolman disease (WD), a severe disorder presenting in infancy characterized by absent or very low LAL activity, and cholesteryl ester storage disease (CESD), a less severe, later onset disease form. Recent clinical studies have shown efficacy of enzyme replacement therapy for both forms of LAL-D; however, no gene therapy approach has yet been developed for clinical use. Here, we show that rscAAVrh74.miniCMV.LIPA gene therapy can significantly improve disease symptoms in the Lipa^−/− mouse model of LAL-D. Treatment dramatically lowered hepatosplenomegaly, liver and spleen triglyceride and cholesterol levels, and serum expression of markers of liver damage. Measures of liver inflammation and fibrosis were also reduced. Treatment of young adult mice was more effective than treatment of neonates, and enzyme activity was elevated in serum, consistent with possible bystander effects. These results demonstrate that adeno associated virus (AAV)-mediated LIPA gene-replacement therapy may be a viable option to treat patients with LAL-D, particularly patients with CESD.

Adaptive and maladaptive roles of lipid droplets in health and disease

Advances in the understanding of lipid droplet biology have revealed essential roles for these organelles in mediating proper cellular homeostasis and stress response. Lipid droplets were initially thought to play a passive role in energy storage. However, recent studies demonstrate that they have substantially broader functions, including protection from reactive oxygen species, endoplasmic reticulum stress, and lipotoxicity. Dysregulation of lipid droplet homeostasis is associated with various pathologies spanning neurological, metabolic, cardiovascular, oncological, and renal diseases. This review provides an overview of the current understanding of lipid droplet biology in both health and disease.

Lipophagy: a new player in CNS disorders

Lipophagy is the process of selective degradation of lipid droplets (LDs) by autophagy. Several studies have highlighted the importance of lipophagy in regulating cellular lipid levels in various tissues and disease conditions. In recent years, disruption of autophagy and accumulation of LDs have been reported as pathological hallmarks in several neurodegenerative and neuroinflammatory diseases, raising the question whether lipophagy is a process that is important in the progression of these disorders. This supports the growing interest in lipid metabolism as a major player in neurodegeneration, and the emerging understanding of several neurological pathologies as not only proteinopathies but also lipidopathies. In this review we discuss the importance of lipophagy in the most common central nervous system diseases. We examine the latest evidence for the reported interplay between abnormalities in lipid accumulation and autophagy, and propose lipophagy as a potentially important mechanism in neurodegeneration.

Lipolysis: cellular mechanisms for lipid mobilization from fat stores

The perception that intracellular lipolysis is a straightforward process that releases fatty acids from fat stores in adipose tissue to generate energy has experienced major revisions over the last two decades. The discovery of new lipolytic enzymes and coregulators, the demonstration that lipophagy and lysosomal lipolysis contribute to the degradation of cellular lipid stores and the characterization of numerous factors and signalling pathways that regulate lipid hydrolysis on transcriptional and post-transcriptional levels have revolutionized our understanding of lipolysis. In this review, we focus on the mechanisms that facilitate intracellular fatty-acid mobilization, drawing on canonical and noncanonical enzymatic pathways. We summarize how intracellular lipolysis affects lipid-mediated signalling, metabolic regulation and energy homeostasis in multiple organs. Finally, we examine how these processes affect pathogenesis and how lipolysis may be targeted to potentially prevent or treat various diseases.

Hepatic Lysosomal Acid Lipase Overexpression Worsens Hepatic Inflammation in Mice Fed a Western Diet

Nonalcoholic fatty liver disease (NAFLD) is characterized by the accumulation of lipid droplets in hepatocytes. NAFLD development and progression is associated with an increase in hepatic cholesterol levels and decreased autophagy and lipophagy flux. Previous studies have shown that the expression of lysosomal acid lipase (LAL), encoded by the gene LIPA, which can hydrolyze both triglyceride and cholesteryl esters, is inversely correlated with the severity of NAFLD. In addition, ablation of LAL activity results in profound NAFLD. Based on this, we predicted that overexpressing LIPA in the livers of mice fed a Western diet would prevent the development of NAFLD. As expected, mice fed the Western diet exhibited numerous markers of NAFLD, including hepatomegaly, lipid accumulation, and inflammation. Unexpectedly, LAL overexpression did not attenuate steatosis and had only minor effects on neutral lipid composition. However, LAL overexpression exacerbated inflammatory gene expression and infiltration of immune cells in mice fed the Western diet. LAL overexpression also resulted in abnormal phagosome accumulation and lysosomal lipid accumulation depending upon the dietary treatment. Overall, we found that hepatic overexpression of LAL drove immune cell infiltration and inflammation and did not attenuate the development of NAFLD, suggesting that targeting LAL expression may not be a viable route to treat NAFLD in humans.

Defective Lysosomal Lipolysis Causes Prenatal Lipid Accumulation and Exacerbates Immediately after Birth

Cholesterol and fatty acids are essential lipids that are critical for membrane biosynthesis and fetal organ development. Cholesteryl esters (CE) are degraded by hormone-sensitive lipase (HSL) in the cytosol and by lysosomal acid lipase (LAL) in the lysosome. Impaired LAL or HSL activity causes rare pathologies in humans, with HSL deficiency presenting less severe clinical manifestations. The infantile form of LAL deficiency, a lysosomal lipid storage disorder, leads to premature death. However, the importance of defective lysosomal CE degradation and its consequences during early life are incompletely understood. We therefore investigated how defective CE catabolism affects fetus and infant maturation using Lal and Hsl knockout (-/-) mouse models. This study demonstrates that defective lysosomal but not neutral lipolysis alters placental and fetal cholesterol homeostasis and exhibits an initial disease pathology already in utero as Lal-/- fetuses accumulate hepatic lysosomal lipids. Immediately after birth, LAL deficiency exacerbates with massive hepatic lysosomal lipid accumulation, which continues to worsen into young adulthood. Our data highlight the crucial role of LAL during early development, with the first weeks after birth being critical for aggravating LAL deficiency.

Loss of function of lysosomal acid lipase (LAL) profoundly impacts osteoblastogenesis and increases fracture risk in humans

Lysosomal acid lipase (LAL) is essential for cholesteryl ester (CE) and triacylglycerol (TAG) hydrolysis in the lysosome. Clinically, an autosomal recessive LIPA mutation causes LAL deficiency (LALD), previously described as Wolman Disease or Cholesteryl Ester Storage Disease (CESD). LAL-D is associated with ectopic lipid accumulation in the liver, small intestine, spleen, adrenal glands, and blood. Considering the importance of unesterified cholesterol and fatty acids in bone metabolism, we hypothesized that LAL is essential for bone formation, and ultimately, skeletal health. To investigate the role of LAL in skeletal homeostasis, we used LAL-deficient (^-/-) mice, in vitro osteoblast cultures, and novel clinical data from LAL-D patients. Both male and female LAL^-/- mice demonstarted lower trabecular and cortical bone parameters , which translated to reduced biomechanical properties. Further histological analyses revealed that LAL^-/- mice had fewer osteoblasts, with no change in osteoclast or marrow adipocyte numbers. In studying the cell-autonomous role of LAL, we observed impaired differentiation of LAL^-/- calvarial osteoblasts and in bone marrow stromal cells treated with the LAL inhibitor lalistat. Consistent with LAL's role in other tissues, lalistat resulted in profound lipid puncta accumulation and an altered intracellular lipid profile. Finally, we analyzed a large de-identified national insurance database (i.e. 2016/2017 Optum Clinformatics®) which revealed that adults (≥18 years) with CESD (n = 3076) had a higher odds ratio (OR = 1.21; 95% CI = 1.03-1.41) of all-cause fracture at any location compared to adults without CESD (n = 13.7 M) after adjusting for demographic variables and osteoporosis. These data demonstrate that alterations in LAL have significant clinical implications related to fracture risk and that LAL's modulation of lipid metabolism is a critical for osteoblast function.

Low LAL (Lysosomal Acid Lipase) Expression by Smooth Muscle Cells Relative to Macrophages as a Mechanism for Arterial Foam Cell Formation

[Figure: see text].

Crystal structure of human lysosomal acid lipase and its implications in cholesteryl ester storage disease

Lysosomal acid lipase (LAL) is a serine hydrolase that hydrolyzes cholesteryl ester (CE) and TGs delivered to the lysosomes into free cholesterol and fatty acids. LAL deficiency due to mutations in the LAL gene (LIPA) results in accumulation of TGs and cholesterol esters in various tissues of the body leading to pathological conditions such as Wolman's disease and CE storage disease (CESD). Here, we present the first crystal structure of recombinant human LAL (HLAL) to 2.6 Å resolution in its closed form. The crystal structure was enabled by mutating three of the six potential glycosylation sites. The overall structure of HLAL closely resembles that of the evolutionarily related human gastric lipase (HGL). It consists of a core domain belonging to the classical α/β hydrolase-fold family with a classical catalytic triad (Ser-153, His-353, Asp-324), an oxyanion hole, and a "cap" domain, which regulates substrate entry to the catalytic site. Most significant structural differences between HLAL and HGL exist at the lid region. Deletion of the short helix, 238NLCFLLC244, at the lid region implied a possible role in regulating the highly hydrophobic substrate binding site from self-oligomerization during interfacial activation. We also performed molecular dynamic simulations of dog gastric lipase (lid-open form) and HLAL to gain insights and speculated a possible role of the human mutant, H274Y, leading to CESD.

Macrophage polarisation associated with atherosclerosis differentially affects their capacity to handle lipids

BACKGROUND AND AIMS

Lipid-rich foam cell macrophages drive atherosclerosis via several mechanisms, including inflammation, lipid uptake, lipid deposition and plaque vulnerability. The atheroma environment shapes macrophage function and phenotype; anti-inflammatory macrophages improve plaque stability while pro-inflammatory macrophages promote rupture. Current evidence suggests a variety of macrophage phenotypes occur in atherosclerotic plaques with local lipids, cytokines, oxidised phospholipids and pathogenic stimuli altering their phenotype. In this study, we addressed differential functioning of macrophage phenotypes via a systematic analysis of in vitro polarised, human monocyte-derived macrophage phenotypes, focussing on molecular events that regulate foam-cell formation.

METHODS

We examined transcriptomes, protein levels and functionally determined lipid handling and foam cell formation capacity in macrophages polarised with IFNγ+LPS, IL-4, IL-10, oxPAPC and CXCL4.

RESULTS

RNA sequencing of differentially polarised macrophages revealed distinct gene expression changes, with enrichment in atherosclerosis and lipid-associated pathways. Analysis of lipid processing activity showed IL-4 and IL-10 macrophages have higher lipid uptake and foam cell formation activities, while inflammatory and oxPAPC macrophages displayed lower foam cell formation. Inflammatory macrophages showed low lipid uptake, while higher lipid uptake in oxPAPC macrophages was matched by increased lipid efflux capacity.

CONCLUSIONS

Atherosclerosis-associated macrophage polarisation dramatically affects lipid handling capacity underpinned by major transcriptomic changes and altered protein levels in lipid-handling gene expression. This leads to phenotype-specific differences in LDL uptake, cellular cholesterol levels and cholesterol efflux, informing how the plaque environment influences atherosclerosis progression by influencing macrophage phenotypes.

Lysosomal acid lipase is the major acid retinyl ester hydrolase in cultured human hepatic stellate cells but not essential for retinyl ester degradation

Vitamin A is stored as retinyl esters (REs) in lipid droplets of hepatic stellate cells (HSCs). To date, two different pathways are known to facilitate the breakdown of REs: (i) Hydrolysis of REs by neutral lipases, and (ii) whole lipid droplet degradation in autolysosomes by acid hydrolysis. In this study, we evaluated the contribution of neutral and acid RE hydrolases to the breakdown of REs in human HSCs. (R)-Bromoenol lactone (R-BEL), inhibitor of adipose triglyceride lipase (ATGL) and patatin-like phospholipase domain-containing 3 (PNPLA3), the hormone-sensitive lipase (HSL) inhibitor 76-0079, as well as the serine-hydrolase inhibitor Orlistat reduced neutral RE hydrolase activity of LX-2 cell-lysates between 20 and 50%. Interestingly, in pulse-chase experiments, R-BEL, 76-0079, as well as Orlistat exerted little to no effect on cellular RE breakdown of LX-2 cells as well as primary human HSCs. In contrast, Lalistat2, a specific lysosomal acid lipase (LAL) inhibitor, virtually blunted acid in vitro RE hydrolase activity of LX-2 cells. Accordingly, HSCs isolated from LAL-deficient mice showed RE accumulation and were virtually devoid of acidic RE hydrolase activity. In pulse-chase experiments however, LAL-deficient HSCs, similar to LX-2 cells and primary human HSCs, were not defective in degrading REs. In summary, results demonstrate that ATGL, PNPLA3, and HSL contribute to neutral RE hydrolysis of human HSCs. LAL is the major acid RE hydrolase in HSCs. Yet, LAL is not limiting for RE degradation under serum-starvation. Together, results suggest that RE breakdown of HSCs is facilitated by (a) so far unknown, non-Orlistat inhibitable RE-hydrolase(s).

Functional Characterization of LIPA (Lysosomal Acid Lipase) Variants Associated With Coronary Artery Disease

OBJECTIVE

LIPA (lysosomal acid lipase) mediates cholesteryl ester hydrolysis, and patients with rare loss-of-function mutations develop hypercholesterolemia and severe disease. Genome-wide association studies of coronary artery disease have identified several tightly linked, common intronic risk variants in LIPA which unexpectedly associate with increased mRNA expression. However, an exonic variant (rs1051338 resulting in T16P) in linkage with intronic variants lies in the signal peptide region and putatively disrupts trafficking. We sought to functionally investigate the net impact of this locus on LIPA and whether rs1051338 could disrupt LIPA processing and function to explain coronary artery disease risk. Approach and Results: In monocytes isolated from a large cohort of healthy individuals, we demonstrate both exonic and intronic risk variants are associated with increased LIPA enzyme activity coincident with the increased transcript levels. To functionally isolate the impact of rs1051338, we studied several in vitro overexpression systems and consistently observed no differences in LIPA expression, processing, activity, or secretion. Further, we characterized a second common exonic coding variant (rs1051339), which is predicted to alter LIPA signal peptide cleavage similarly to rs1051338, yet is not linked to intronic variants. rs1051339 also does not impact LIPA function in vitro and confers no coronary artery disease risk.

CONCLUSIONS

Our findings show that common LIPA exonic variants in the signal peptide are of minimal functional significance and suggest coronary artery disease risk is instead associated with increased LIPA function linked to intronic variants. Understanding the mechanisms and cell-specific contexts of LIPA function in the plaque is necessary to understand its association with cardiovascular risk.

Emerging Roles of Lipophagy in Health and Disease

The term lipophagy is used to describe the autophagic degradation of lipid droplets, the main lipid storage organelles of eukaryotic cells. Ever since its discovery in 2009, lipophagy has emerged as a significant component of lipid metabolism with important implications for organismal health. This review aims to provide a brief summary of our current knowledge on the mechanisms that are responsible for regulating lipophagy and the impact the process has under physiological and pathological conditions.

Cyclodextrin triggers MCOLN1-dependent endo-lysosome secretion in Niemann-Pick type C cells

In specialized cell types, lysosome-related organelles support regulated secretory pathways, whereas in nonspecialized cells, lysosomes can undergo fusion with the plasma membrane in response to a transient rise in cytosolic calcium. Recent evidence also indicates that lysosome secretion can be controlled transcriptionally and promote clearance in lysosome storage diseases. In addition, evidence is also accumulating that low concentrations of cyclodextrins reduce the cholesterol-storage phenotype in cells and animals with the cholesterol storage disease Niemann-Pick type C, via an unknown mechanism. Here, we report that cyclodextrin triggers the secretion of the endo/lysosomal content in nonspecialized cells and that this mechanism is responsible for the decreased cholesterol overload in Niemann-Pick type C cells. We also find that the secretion of the endo/lysosome content occurs via a mechanism dependent on the endosomal calcium channel mucolipin-1, as well as FYCO1, the AP1 adaptor, and its partner Gadkin. We conclude that endo-lysosomes in nonspecialized cells can acquire secretory functions elicited by cyclodextrin and that this pathway is responsible for the decrease in cholesterol storage in Niemann-Pick C cells.

N-acetylaspartate pathway is nutrient responsive and coordinates lipid and energy metabolism in brown adipocytes

The discovery of significant amounts of metabolically active brown adipose tissue (BAT) in adult humans renders it a promising target for anti-obesity therapies by inducing weight loss through increased energy expenditure. The components of the N-acetylaspartate (NAA) pathway are highly abundant in BAT. Aspartate N-acetyltransferase (Asp-NAT, encoded by Nat8l) synthesizes NAA from acetyl-CoA and aspartate and increases energy expenditure in brown adipocytes. However, the exact mechanism how the NAA pathway contributes to accelerated mobilization and oxidation of lipids and the physiological regulation of the NAA pathway remained elusive. Here, we demonstrate that the expression of NAA pathway genes corresponds to nutrient availability and specifically responds to changes in exogenous glucose. NAA is preferentially produced from glucose-derived acetyl-CoA and aspartate and its concentration increases during adipogenesis. Overexpression of Nat8l drains glucose-derived acetyl-CoA into the NAA pool at the expense of cellular lipids and certain amino acids. Mechanistically, we elucidated that a combined activation of neutral and lysosomal (acid) lipolysis is responsible for the increased lipid degradation. Specifically, translocation of the transcription factor EB to the nucleus activates the biosynthesis of autophagosomes and lysosomes. Lipid degradation within lysosomes accompanied by adipose triglyceride lipase-mediated lipolysis delivers fatty acids for the support of elevated mitochondrial respiration. Together, our data suggest a crucial role of the NAA pathway in energy metabolism and metabolic adaptation in BAT.

Hepatocyte-specific lysosomal acid lipase deficiency protects mice from diet-induced obesity but promotes hepatic inflammation

Lysosomal acid lipase (LAL) hydrolyzes cholesteryl esters (CE) and triglycerides (TG) to generate fatty acids (FA) and cholesterol. LAL deficiency (LAL-D) in both humans and mice leads to hepatomegaly, hypercholesterolemia, and shortened life span. Despite its essential role in lysosomal neutral lipid catabolism, the cell type-specific contribution of LAL to disease progression is still elusive. To investigate the role of LAL in the liver in more detail and to exclude the contribution of LAL in macrophages, we generated hepatocyte-specific LAL-deficient mice (Liv-Lipa^−/−) and fed them either chow or high fat/high cholesterol diets (HF/HCD). Comparable to systemic LAL-D, Liv-Lipa^−/− mice were resistant to diet-induced obesity independent of food intake, movement, and energy expenditure. Reduced body weight gain was mainly due to reduced white adipose tissue depots. Furthermore, Liv-Lipa^−/− mice exhibited improved glucose clearance during glucose and insulin tolerance tests compared to control mice. Analysis of hepatic lipid content revealed a massive reduction of TG, whereas CE concentrations were markedly increased, leading to CE crystal formation in the livers of Liv-Lipa^−/− mice. Elevated plasma transaminase activities, increased pro-inflammatory cytokines and chemokines as well as hepatic macrophage infiltration indicated liver inflammation. Our data provide evidence that hepatocyte-specific LAL deficiency is sufficient to alter whole-body lipid and energy homeostasis in mice. We conclude that hepatic LAL plays a pivotal role by preventing liver damage and maintaining lipid and energy homeostasis, especially during high lipid availability.

Quantitative Analysis of the Proteome Response to the Histone Deacetylase Inhibitor (HDACi) Vorinostat in Niemann-Pick Type C1 disease

Niemann-Pick type C (NPC) disease is an inherited, progressive neurodegenerative disorder principally caused by mutations in the NPC1 gene. NPC disease is characterized by the accumulation of unesterified cholesterol in the late endosomes (LE) and lysosomes (Ly) (LE/Ly). Vorinostat, a histone deacetylase inhibitor (HDACi), restores cholesterol homeostasis in fibroblasts derived from NPC patients; however, the exact mechanism by which Vorinostat restores cholesterol level is not known yet. In this study, we performed comparative proteomic profiling of the response of NPC1^I1061T fibroblasts to Vorinostat. After stringent statistical criteria to filter identified proteins, we observed 202 proteins that are differentially expressed in Vorinostat-treated fibroblasts. These proteins are members of diverse cellular pathways including the endomembrane dependent protein folding-stability-degradation-trafficking axis, energy metabolism, and lipid metabolism. Our study shows that treatment of NPC1^I1061T fibroblasts with Vorinostat not only enhances pathways promoting the folding, stabilization and trafficking of NPC1 (I1061T) mutant to the LE/Ly, but alters the expression of lysosomal proteins, specifically the lysosomal acid lipase (LIPA) involved in the LIPA->NPC2->NPC1 based flow of cholesterol from the LE/Ly lumen to the LE/Ly membrane. We posit that the Vorinostat may modulate numerous pathways that operate in an integrated fashion through epigenetic and post-translational modifications reflecting acetylation/deacetylation balance to help manage the defective NPC1 fold, the function of the LE/Ly system and/or additional cholesterol metabolism/distribution pathways, that could globally contribute to improved mitigation of NPC1 disease in the clinic based on as yet uncharacterized principles of cellular metabolism dictating cholesterol homeostasis.

The role of sebelipase alfa in the treatment of lysosomal acid lipase deficiency

Lysosomal acid lipase deficiency (LALD) is a lysosomal storage disorder (LSD) characterized either by infantile onset with fulminant clinical course and very poor prognosis or childhood/adult-onset disease with an attenuated phenotype. The disorder is often misdiagnosed or remains undiagnosed in children and adults due to a rather unspecific clinical presentation with dyslipidemia and steatohepatitis. Until recently, no good treatment options were available for LALD. Despite supportive and symptomatic therapies, death occurred before 1 year of age in patients with infantile-onset disease and patients with childhood/adult-onset LALD suffered from significant complications, such as liver cirrhosis, requiring liver transplantation and early-onset cardiovascular disease. With the recent approval of sebelipase alfa for clinical use in infantile- as well as childhood/adult-onset LALD, a new treatment era for this disorder has begun. Sebelipase alfa is a recombinant human lysosomal acid lipase (LAL), which is administered via the intravenous route. Clinical trials have shown significant improvement of disease parameters such as liver transaminases, hepatomegaly, and dyslipidemia in childhood/adult-onset LALD patients. Treatment of infants with the severe infantile-onset form of the disease has led to improved survival beyond the age of 1 year, and also showed improvement of hepatic and gastrointestinal symptoms, as well as growth. Overall, sebelipase alfa has a favorable safety profile and promises to be a good long-term treatment option for patients with LALD, with significant reduction of disease burden and increased life expectancy.

Lysosomal lipid hydrolysis provides substrates for lipid mediator synthesis in murine macrophages

Degradation of lysosomal lipids requires lysosomal acid lipase (LAL), the only intracellular lipase known to be active at acidic pH. We found LAL to be expressed in murine immune cells with highest mRNA expression in macrophages and neutrophils. Furthermore, we observed that loss of LAL in mice caused lipid accumulation in white blood cells in the peripheral circulation, which increased in response to an acute inflammatory stimulus. Lal-deficient (-/-) macrophages accumulate neutral lipids, mainly cholesteryl esters, within lysosomes. The cholesteryl ester fraction is particularly enriched in the PUFAs 18:2 and 20:4, important precursor molecules for lipid mediator synthesis. To investigate whether loss of LAL activity affects the generation of lipid mediators and to eliminate potential systemic effects from other cells and tissues involved in the pronounced phenotype of Lal-/- mice, we treated macrophages from Wt mice with the LAL-specific inhibitor LAListat-2. Acute inhibition of LAL resulted in reduced release of 18:2- and 20:4-derived mediators from macrophages, indicating that lipid hydrolysis by LAL is an important source for lipid mediator synthesis in macrophages. We conclude that lysosomes should be considered as organelles that provide precursor molecules for lipid mediators such as eicosanoids.

Managing Cardiovascular Risk in Lysosomal Acid Lipase Deficiency

Lysosomal acid lipase deficiency (LAL-D) is a rare, life-threatening, autosomal recessive, lysosomal storage disease caused by mutations in the LIPA gene, which encodes for lysosomal acid lipase (LAL). This enzyme is necessary for the hydrolysis of cholesteryl ester and triglyceride in lysosomes. Deficient LAL activity causes accumulation of these lipids in lysosomes and a marked decrease in the cytoplasmic free cholesterol concentration, leading to dysfunctional cholesterol homeostasis. The accumulation of neutral lipid occurs predominantly in liver, spleen, and macrophages throughout the body, and the aberrant cholesterol homeostasis causes a marked dyslipidemia. LAL-D is characterized by accelerated atherosclerotic cardiovascular disease (ASCVD) and hepatic microvesicular or mixed steatosis, leading to inflammation, fibrosis, cirrhosis and liver failure. LAL-D presents as a clinical continuum with two phenotypes: the infantile-onset phenotype, formally referred to as Wolman disease, and the later-onset phenotype, formerly referred to as cholesteryl ester storage disease. Infants with LAL-D present within the first few weeks of life with vomiting, diarrhea, hepatosplenomegaly, failure to thrive and rapid progression to liver failure and death by 6-12 months of age. Children and young adults with LAL-D generally present with marked dyslipidemia, hepatic enzyme elevation, hepatomegaly and mixed steatosis by liver biopsy. The average age of the initial signs and symptoms of the later-onset phenotype is about 5 years old. The typical dyslipidemia is a significantly elevated low-density lipoprotein cholesterol (LDL-C) concentration and a low high-density lipoprotein cholesterol (HDL-C) concentration, placing these individuals at heightened risk for premature ASCVD. Diagnosis of the later-onset phenotype of LAL-D requires a heightened awareness of the disease because the dyslipidemia and hepatic transaminase elevation combination are common and overlap with other metabolic disorders. LAL-D should be considered in the differential diagnosis of healthy weight children and young adults with unexplained hepatic transaminase elevation accompanied by an elevated LDL-C level (>160 mg/dL) and low HDL-C level (<35 mg/dL) that is not caused by monogenic and polygenic lipid disorders or secondary factors. Treatment of LAL-D with sebelipase alfa (LAL replacement enzyme) should be considered as the standard of treatment in all individuals diagnosed with LAL-D. Other ASCVD risk factors that may be present (hypertension, tobacco use, diabetes mellitus, etc.) should be managed appropriately, consistent with secondary prevention goals.

Lysosomal acid lipase deficiency in all siblings of the same parents

We present 4 normal-weight sibling children with lysosomal acid lipase deficiency (LAL-D). LAL-D was considered in the differential diagnosis based on the absence of secondary causes and primary inherited traits for their marked hyperlipidemia, together with unexplained hepatic transaminase elevation. Residual lysosomal acid lipase activity confirmed the diagnosis. DNA sequencing of LIPA indicated that the siblings were compound heterozygotes (c.894G>A and c.428+1G>A). This case describes the unusual occurrence of all offspring from the same nonconsanguineous mother and father inheriting compound heterozygosity of a recessive trait and the identification of an apparently unique LIPA mutation (c.428+1G>A). It highlights the collaborative effort between a lipidologist and gastroenterologist in developing a differential diagnosis leading to the confirmatory diagnosis of this rare, life-threatening disease. With the availability of an effective enzyme replacement therapy (sebelipase alfa), LAL-D should be entertained in the differential diagnosis of children, adolescents, and young adults with idiopathic hyperlipidemia and unexplained hepatic transaminase elevation.

Monoglyceride lipase as a drug target: At the crossroads of arachidonic acid metabolism and endocannabinoid signaling

Monoglyerides (MGs) are short-lived, intermediary lipids deriving from the degradation of phospho- and neutral lipids, and monoglyceride lipase (MGL), also designated as monoacylglycerol lipase (MAGL), is the major enzyme catalyzing the hydrolysis of MGs into glycerol and fatty acids. This distinct function enables MGL to regulate a number of physiological and pathophysiological processes since both MGs and fatty acids can act as signaling lipids or precursors thereof. The most prominent MG species acting as signaling lipid is 2-arachidonoyl glycerol (2-AG) which is the most abundant endogenous agonist of cannabinoid receptors in the body. Importantly, recent observations demonstrate that 2-AG represents a quantitatively important source for arachidonic acid, the precursor of prostaglandins and other inflammatory mediators. Accordingly, MGL-mediated 2-AG degradation affects lipid signaling by cannabinoid receptor-dependent and independent mechanisms. Recent genetic and pharmacological studies gave important insights into MGL's role in (patho-)physiological processes, and the enzyme is now considered as a promising drug target for a number of disorders including cancer, neurodegenerative and inflammatory diseases. This review summarizes the basics of MG (2-AG) metabolism and provides an overview on the therapeutic potential of MGL.

From Loci to Biology: Functional Genomics of Genome-Wide Association for Coronary Disease

Genome-wide association studies have provided a rich collection of ≈ 58 coronary artery disease (CAD) loci that suggest the existence of previously unsuspected new biology relevant to atherosclerosis. However, these studies only identify genomic loci associated with CAD, and many questions remain even after a genomic locus is definitively implicated, including the nature of the causal variant(s) and the causal gene(s), as well as the directionality of effect. There are several tools that can be used for investigation of the functional genomics of these loci, and progress has been made on a limited number of novel CAD loci. New biology regarding atherosclerosis and CAD will be learned through the functional genomics of these loci, and the hope is that at least some of these new pathways relevant to CAD pathogenesis will yield new therapeutic targets for the prevention and treatment of CAD.

Lysosomal Acid Lipase Hydrolyzes Retinyl Ester and Affects Retinoid Turnover

Lysosomal acid lipase (LAL) is essential for the clearance of endocytosed cholesteryl ester and triglyceride-rich chylomicron remnants. Humans and mice with defective or absent LAL activity accumulate large amounts of cholesteryl esters and triglycerides in multiple tissues. Although chylomicrons also contain retinyl esters (REs), a role of LAL in the clearance of endocytosed REs has not been reported. In this study, we found that murine LAL exhibits RE hydrolase activity. Pharmacological inhibition of LAL in the human hepatocyte cell line HepG2, incubated with chylomicrons, led to increased accumulation of REs in endosomal/lysosomal fractions. Furthermore, pharmacological inhibition or genetic ablation of LAL in murine liver largely reduced in vitro acid RE hydrolase activity. Interestingly, LAL-deficient mice exhibited increased RE content in the duodenum and jejunum but decreased RE content in the liver. Furthermore, LAL-deficient mice challenged with RE gavage exhibited largely reduced post-prandial circulating RE content, indicating that LAL is required for efficient nutritional vitamin A availability. In summary, our results indicate that LAL is the major acid RE hydrolase and required for functional retinoid homeostasis.

Development of a selective activity-based probe for glycosylated LIPA

Loss of LIPA activity leads to diseases such as Wolman's Disease and Cholesterol Ester Storage Disease. While it is possible to measure defects in LIPA protein levels, it is difficult to directly measure LIPA activity in cells. In order to measure LIPA activity directly we developed a LIPA specific activity based probe. LIPA is heavily glycosylated although it is unclear how glycosylation affects LIPA activity or function. Our probe is specific for a glycosylated form of LIPA in cells, although it labels purified LIPA regardless of glycosylation.

Cholesterol ester storage disease with a novel LIPA mutation (L264P) that presented massive hepatomegaly: A case report

Cholesterol ester storage disease (CESD) is an autosomal recessive disorder caused by deficient lysosomal acid lipase (LAL) activity, resulting in cholesteryl ester (CE) accumulation. CESD patients have liver disease associated with mixed dyslipidemia leading to liver failure. We here report the case of an 11-year-old male CESD patient with a novel mutation who had the chief complaint of massive hepatomegaly. The patient's liver reached to his pelvis, and his spleen was 2 cm below the costal margin. The patient had elevated serum liver enzymes and mixed dyslipidemia. The liver biopsy tissue showed characteristic CESD pathology, which included microvesicular steatosis, mild fibrosis and foamy macrophages. Electron microscopy showed a remnant cleft of CE crystals, and dried blood spot testing showed reduced LAL activity. We identified compound heterozygous mutations in the LIPA gene in this patient, namely, c.607G>C and c.791T>C. The former mutation was previously reported only in a Japanese patient, whereas the latter mutation is novel. The findings of this study suggest that LIPA gene mutations in Japanese CESD patients are different from those in Western patients. Although CESD is rare, it is likely that many patients are unrecognized or misdiagnosed, and thus the possibility of CESD should be considered in patients with hepatosplenomegaly and dyslipidemia.

Novel functions of PXR in cardiometabolic disease

Cardiometabolic disease emerges as a worldwide epidemic and there is urgent need to understand the molecular mechanisms underlying this chronic disease. The chemical environment to which we are exposed has significantly changed in the past few decades and recent research has implicated its contribution to the development of many chronic human diseases. However, the mechanisms of how exposure to chemicals contributes to the development of cardiometabolic disease are poorly understood. Numerous chemicals have been identified as ligands for the pregnane X receptor (PXR), a nuclear receptor functioning as a xenobiotic sensor to coordinately regulate xenobiotic metabolism via transcriptional regulation of xenobiotic-detoxifying enzymes and transporters. In the past decade, the function of PXR in the regulation of xenobiotic metabolism has been extensively studied by many laboratories and the role of PXR as a xenobiotic sensor has been well-established. The identification of PXR as a xenobiotic sensor has provided an important tool for the study of new mechanisms through which xenobiotic exposure impacts human chronic diseases. Recent studies have revealed novel and unexpected roles of PXR in modulating obesity, insulin sensitivity, lipid homeostasis, atherogenesis, and vascular functions. These studies suggest that PXR signaling may contribute significantly to the pathophysiological effects of many known xenobiotics on cardiometabolic disease in humans. The discovery of novel functions of PXR in cardiometabolic disease not only contributes to our understanding of "gene-environment interactions" in predisposing individuals to chronic diseases but also provides strong evidence to inform future risk assessment for relevant chemicals. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.

Monocyte-Derived Dendritic Cells Upregulate Extracellular Catabolism of Aggregated Low-Density Lipoprotein on Maturation, Leading to Foam Cell Formation

OBJECTIVE

Although dendritic cells are known to play a role in atherosclerosis, few studies have examined the contribution of the wide variety of dendritic cell subsets. Accordingly, their roles in atherogenesis remain largely unknown. We investigated the ability of different dendritic cell subsets to become foam cells after contact with aggregated low-density lipoprotein (LDL; the predominant form of LDL found in atherosclerotic plaques).

APPROACH AND RESULTS

We demonstrate that both murine and human monocyte-derived dendritic cells use exophagy to degrade aggregated LDL, leading to foam cell formation, whereas monocyte-independent dendritic cells are unable to clear LDL aggregates by this mechanism. Exophagy is a catabolic process in which objects that cannot be internalized by phagocytosis (because of their size or association with extracellular structures) are initially digested in an extracellular acidic lytic compartment. Surprisingly, we found that monocyte-derived dendritic cells upregulate exophagy on maturation. This contrasts various forms of endocytic internalization in dendritic cells, which decrease on maturation. Finally, we show that our in vitro results are consistent with dendritic cell lipid accumulation in plaques of an ApoE(-/-) mouse model of atherosclerosis.

CONCLUSIONS

Our results show that monocyte-derived dendritic cells use exophagy to degrade aggregated LDL and become foam cells, whereas monocyte-independent dendritic cells are unable to clear LDL deposits. Furthermore, we find that exophagy is upregulated on dendritic cell maturation. Thus, exophagy-mediated foam cell formation in monocyte-derived dendritic cells could play a significant role in atherogenesis.

Lysosomal acid lipase: at the crossroads of normal and atherogenic cholesterol metabolism

Unregulated cellular uptake of apolipoprotein B-containing lipoproteins in the arterial intima leads to the formation of foam cells in atherosclerosis. Lysosomal acid lipase (LAL) plays a crucial role in both lipoprotein lipid catabolism and excess lipid accumulation as it is the primary enzyme that hydrolyzes cholesteryl esters derived from both low density lipoprotein (LDL) and modified forms of LDL. Evidence suggests that as atherosclerosis progresses, accumulation of excess free cholesterol in lysosomes leads to impairment of LAL activity, resulting in accumulation of cholesteryl esters in the lysosome as well as the cytosol in foam cells. Impaired metabolism and release of cholesterol from lysosomes can lead to downstream defects in ATP-binding cassette transporter A1 regulation, needed to offload excess cholesterol from plaque foam cells. This review focuses on the role LAL plays in normal cholesterol metabolism and how the associated changes in its enzymatic activity may ultimately contribute to atherosclerosis progression.

Cell-intrinsic lysosomal lipolysis is essential for alternative activation of macrophages

Alternative (M2) activation of macrophages driven via the α-chain of the receptor for interleukin 4 (IL-4Rα) is important for immunity to parasites, wound healing, the prevention of atherosclerosis and metabolic homeostasis. M2 polarization is dependent on fatty acid oxidation (FAO), but the source of the fatty acids that support this metabolic program has not been clear. We found that the uptake of triacylglycerol substrates via the scavenger receptor CD36 and their subsequent lipolysis by lysosomal acid lipase (LAL) was important for the engagement of elevated oxidative phosphorylation, enhanced spare respiratory capacity (SRC), prolonged survival and expression of genes that together define M2 activation. Inhibition of lipolysis suppressed M2 activation during infection with a parasitic helminth and blocked protective responses to this pathogen. Our findings delineate a critical role for cell-intrinsic lysosomal lipolysis in M2 activation.

Lysosomal acid lipase is critical for myeloid-derived suppressive cell differentiation, development, and homeostasis

Lysosomal acid lipase (LAL) cleaves cholesteryl esters (CE) and triglycerides (TG) to generate cholesterol and free fatty acid in lysosomes of cells. The downstream metabolic products of fatty acids are ligands for activation of peroxisome proliferator-activated receptor gamma (PPARγ). Accumulation of CEs and TGs is resulted from lack of functional LAL in lysosomes of cells, especially in myeloid cells. One characteristic phenotype in LAL knock-out (lal-/-) mice is systemic elevation of myeloid-derived suppressive cells (MDSCs). MDSCs infiltrate into multiple distal organs, alter T cell development, and suppress T cell proliferation and lymphokine production in lal-/- mice, which lead to severe pathogeneses in multiple organs. The gene transcriptional profile analysis in MDSCs from the bone marrow has identified multiple defects responsible for MDSCs malformation and malfunction in lal-/- mice, including G protein signaling, cell cycles, glycolysis metabolism, mitochondrial bioenergetics, mTOR pathway etc. In a separate gene transcriptional profile analysis in the lung of lal-/- mice, matrix metalloproteinase 12 (MMP12) and apoptosis inhibitor 6 (Api6) are highly overexpressed due to lack of ligand synthesis for PPARγ. PPARγ negatively regulates MMP12 and Api6. Blocking the PPAR signaling by overexpression of a dominant negative PPARγ (dnPPARγ) form, or overexpressing MMP12 or Api6 in myeloid or lung epithelial cells in inducible transgenic mouse models results in elevated MDSCs and inflammation-induced tumorigenesis. These studies demonstrate that LAL and its downstream effectors are critical for MDSCs development, differentiation and malfunction.

Memory CD8(+) T cells use cell-intrinsic lipolysis to support the metabolic programming necessary for development

Generation of CD8(+) memory T cells requires metabolic reprogramming that is characterized by enhanced mitochondrial fatty-acid oxidation (FAO). However, where the fatty acids (FA) that fuel this process come from remains unclear. While CD8(+) memory T cells engage FAO to a greater extent, we found that they acquired substantially fewer long-chain FA from their external environment than CD8(+) effector T (Teff) cells. Rather than using extracellular FA directly, memory T cells used extracellular glucose to support FAO and oxidative phosphorylation (OXPHOS), suggesting that lipids must be synthesized to generate the substrates needed for FAO. We have demonstrated that memory T cells rely on cell intrinsic expression of the lysosomal hydrolase LAL (lysosomal acid lipase) to mobilize FA for FAO and memory T cell development. Our observations link LAL to metabolic reprogramming in lymphocytes and show that cell intrinsic lipolysis is deterministic for memory T cell fate.

Calpain-1 inhibitors for selective treatment of rheumatoid arthritis: what is the future?

Effective small-molecule treatment of inflammatory diseases remains an unmet need in medicine. Current treatments are either limited in effectiveness or invasive. The latest biologics prevent influx of inflammatory cells to damaged tissue. Calpain-1 is a calcium-activated cysteine protease that plays an important role in neutrophil motility. It is, therefore, a potential target for intervention in inflammatory disease. Many inhibitors of calpains have been developed but most are unselective and so unsuitable for drug use. However, recent series of α-mercaptoacrylate inhibitors target regulatory domains of calpain-1 and are much more specific. These compounds are effective in impairing the cell spreading mechanism of neutrophils in vitro and raise the possibility of treating rheumatoid arthritis with a pill; however, challenges still remain. Improved bioavailability is needed and solution of their precise mode of action should prompt the development of specific calpain-1 screens for novel classes of inhibitors.

Pregnane X receptor mediates dyslipidemia induced by the HIV protease inhibitor amprenavir in mice

Human immunodeficiency virus (HIV) protease inhibitors (PIs) have been used successfully in extending the life span of people infected with HIV. The use of PIs has also been associated with dyslipidemia and an increased risk of cardiovascular disease, but the underlying mechanisms remain elusive. Several PIs have been implicated in activating the nuclear receptor pregnane X receptor (PXR), which acts as a xenobiotic sensor to regulate xenobiotic metabolism in the liver and intestine. Recent studies indicate that PXR may also play an important role in the regulation of lipid homeostasis. In the present study, we identified amprenavir, a widely used HIV PI, as a potent PXR-selective agonist. Computational docking studies combined with site-direct mutagenesis identified several key residues within the ligand-binding pocket of PXR that constitute points of interaction with amprenavir. Amprenavir efficiently activated PXR and induced PXR target gene expression in vitro and in vivo. Short-term exposure to amprenavir significantly increased plasma total cholesterol and atherogenic low-density lipoprotein cholesterol levels in wild-type mice, but not in PXR-deficient mice. Amprenavir-mediated PXR activation stimulated the expression of several key intestinal genes involved in lipid homeostasis. These findings provide critical mechanistic insight for understanding the impact of PIs on cardiovascular disease and demonstrate a potential role of PXR in mediating the adverse effects of HIV PIs in humans.

Plasmin promotes foam cell formation by increasing macrophage catabolism of aggregated low-density lipoprotein

OBJECTIVE

The plasmin/plasminogen system is involved in atherosclerosis. However, the mechanisms by which it stimulates disease are not fully defined. A key event in atherogenesis is the deposition of low-density lipoprotein (LDL) on arterial walls where it is modified, aggregated, and retained. Macrophages are recruited to clear the lipoproteins, and they become foam cells. The goal of this study was to assess the role of plasmin in macrophage uptake of aggregated LDL and foam cell formation.

APPROACH AND RESULTS

Plasminogen treatment of macrophages catabolizing aggregated LDL significantly accelerated foam cell formation. Macrophage interaction with aggregated LDL increased the surface expression of urokinase-type plasminogen activator receptor and plasminogen activator activity, resulting in increased ability to generate plasmin at the cell surface. The high local level of plasmin cleaves cell-associated aggregated LDL, allowing a portion of the aggregate to become sequestered in a nearly sealed, yet extracellular, acidic compartment. The low pH in the plasmin-induced compartment allows lysosomal enzymes, delivered via lysosome exocytosis, greater activity, resulting in more efficient cholesteryl ester hydrolysis and delivery of a large cholesterol load to the macrophage, thereby promoting foam cell formation.

CONCLUSIONS

These findings highlight a critical role for plasmin in the catabolism of aggregated LDL by macrophages and provide a new context for considering the atherogenic role of plasmin.

Fasting energy homeostasis in mice with adipose deficiency of desnutrin/adipose triglyceride lipase

Adipose triglyceride lipase (ATGL) catalyzes the first step of lipolysis of cytoplasmic triacylglycerols in white adipose tissue (WAT) and several other organs. We created adipose-specific ATGL-deficient (ATGLAKO) mice. In these mice, in vivo lipolysis, measured as the increase of plasma nonesterified fatty acid and glycerol levels after injection of a β3-adrenergic agonist, was undetectable. In isolated ATGLAKO adipocytes, β3-adrenergic-stimulated glycerol release was 10-fold less than in controls. Under fed conditions, ATGLAKO mice had normal viability, mild obesity, low plasma nonesterified fatty acid levels, increased insulin sensitivity, and increased daytime food intake. After 5 h of fasting, ATGLAKO WAT showed phosphorylation of the major protein kinase A-mediated targets hormone-sensitive lipase and perilipin A and ATGLAKO liver showed low glycogen and triacylglycerol contents. During a 48-h fast, ATGLAKO mice developed striking and complex differences from controls: progressive reduction of oxygen consumption, high respiratory exchange ratio, consistent with reduced fatty acid availability for energy production, lethargy, hypothermia, and undiminished fat mass, but greater loss of lean mass than controls. Plasma of 48 h-fasted ATGLAKO mice had a unique pattern: low 3-hydroxybutyrate, insulin, adiponectin, and fibroblast growth factor 21 with elevated leptin and corticosterone. ATGLAKO WAT, liver, skeletal muscle, and heart showed increased levels of mRNA related to autophagy and proteolysis. In murine ATGL deficiency, adipose lipolysis is critical for fasting energy homeostasis, and fasting imposes proteolytic stress on many organs, including heart and skeletal muscle.

Lysosomal lipase deficiency: molecular characterization of eleven patients with Wolman or cholesteryl ester storage disease

Wolman Disease (WD) and cholesteryl ester storage disease (CESD) represent two distinct phenotypes of the same recessive disorder caused by the complete or partial deficiency of lysosomal acidic lipase (LAL), respectively. LAL, encoded by the LIPA gene, hydrolyzes cholesteryl esters derived from cell internalization of plasma lipoproteins. WD is a rapidly progressive and lethal disease characterized by intestinal malabsorption, hepatic and adrenal failure. CESD is characterized by hepatic fibrosis, hyperlipidemia and accelerated atherosclerosis. Aim of the study was the identification of LIPA mutations in three WD and eight CESD patients. The WD patients, all deceased before the first year of age, were homozygous for two novel mutations (c.299+1G>A and c.419G>A) or a mutation (c.796G>T) previously reported as compound heterozygosity in a CESD patient. The two mutations (c.419G>A and c.796G>T) resulting in truncated proteins (p.W140* and p.G266*) and the splicing mutation (c.229+1G>A) were associated with undetectable levels of LIPA mRNA in fibroblasts. All eight CESD patients carried the common mutation c.894G>A known to result not only in a major non-functional transcript with the skipping of exon 8 (p.S275_Q298del), but also in a minor normally spliced transcript producing 5-10% residual LAL activity. The c.894G>A mutation was found in homozygosity in four patients and, as compound heterozygosity, in association with a known (p.H295Y and p.G342R) or a novel (p.W140*) mutation in four other CESD patients. Segregation analysis performed in all patients harboring c.895G>A showed its occurrence on the same haplotype suggesting a common founder ancestor. The other WD and CESD mutations were associated with different haplotypes.

Structural bases of Wolman disease and cholesteryl ester storage disease

To elucidate the bases of Wolman disease (WD) and cholesteryl ester storage disease (CESD) from the viewpoint of enzyme structure, we constructed a structural model of human lysosomal acid lipase (LAL) using molecular modeling software Modeller. The results revealed that the residues responsible for WD/CESD tend to be less solvent-accessible than others. Then, we examined the structural changes in the LAL protein caused by the WD/CESD mutations, using molecular modeling software TINKER. The results indicated that conformational changes of the functionally important residues and/or large conformational changes tend to cause the severe clinical phenotype (WD), whereas small conformational changes tend to cause the mild clinical phenotype (CESD), although there have been several exceptions. Further structural analysis is required to clarify the relationship between the three-dimensional structural changes and clinical phenotypes.