Tissue and cellular specific expression of murine lysosomal acid lipase mRNA and protein

Impact of (intestinal) LAL deficiency on lipid metabolism and macrophage infiltration

OBJECTIVE

To date, the only enzyme known to be responsible for the hydrolysis of cholesteryl esters and triacylglycerols in the lysosome at acidic pH is lysosomal acid lipase (LAL). Lipid malabsorption in the small intestine (SI), accompanied by macrophage infiltration, is one of the most common pathological features of LAL deficiency. However, the exact role of LAL in intestinal lipid metabolism is still unknown.

METHODS

We collected three parts of the SI (duodenum, jejunum, ileum) from mice with a global (LAL KO) or intestine-specific deletion of LAL (iLAL KO) and corresponding controls.

RESULTS

We observed infiltration of lipid-associated macrophages into the lamina propria, where neutral lipids accumulate massively in the SI of LAL KO mice. In addition, LAL KO mice absorb less dietary lipids but have accelerated basolateral lipid uptake, secrete fewer chylomicrons, and have increased fecal lipid loss. Inflammatory markers and genes involved in lipid metabolism were overexpressed in the duodenum of old but not in younger LAL KO mice. Despite the significant reduction of LAL activity in enterocytes of enterocyte-specific (iLAL) KO mice, villous morphology, intestinal lipid concentrations, expression of lipid transporters and inflammatory genes, as well as lipoprotein secretion were comparable to control mice.

CONCLUSIONS

We conclude that loss of LAL only in enterocytes is insufficient to cause lipid deposition in the SI, suggesting that infiltrating macrophages are the key players in this process.

LAL deficiency induced myeloid-derived suppressor cells as targets and biomarkers for lung cancer

BACKGROUND

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells in tumor microenvironment, which suppress antitumor immunity. Expansion of various MDSC subpopulations is closely associated with poor clinical outcomes in cancer. Lysosomal acid lipase (LAL) is a key enzyme in the metabolic pathway of neutral lipids, whose deficiency (LAL-D) in mice induces the differentiation of myeloid lineage cells into MDSCs. These Lal -/- MDSCs not only suppress immune surveillance but also stimulate cancer cell proliferation and invasion. Understanding and elucidating the underlying mechanisms of MDSCs biogenesis will help to facilitate diagnosis/prognosis of cancer occurrence and prevent cancer growth and spreading.

METHODS

Single-cell RNA sequencing (scRNA-seq) was performed to distinguish intrinsic molecular and cellular differences between normal versus Lal -/- bone marrow-derived Ly6G+ myeloid populations in mice. In humans, LAL expression and metabolic pathways in various myeloid subsets of blood samples of patients with non-small cell lung cancer (NSCLC) were assessed by flow cytometry. The profiles of myeloid subsets were compared in patients with NSCLC before and after the treatment of programmed death-1 (PD-1) immunotherapy.

RESULTS

scRNA-seq of Lal -/- CD11b+Ly6G+ MDSCs identified two distinctive clusters with differential gene expression patterns and revealed a major metabolic shift towards glucose utilization and reactive oxygen species (ROS) overproduction. Blocking pyruvate dehydrogenase (PDH) in glycolysis reversed Lal -/- MDSCs' capabilities of immunosuppression and tumor growth stimulation and reduced ROS overproduction. In the blood samples of human patients with NSCLC, LAL expression was significantly decreased in CD13+/CD14+/CD15+/CD33+ myeloid cell subsets. Further analysis in the blood of patients with NSCLC revealed an expansion of CD13+/CD14+/CD15+ myeloid cell subsets, accompanied by upregulation of glucose-related and glutamine-related metabolic enzymes. Pharmacological inhibition of the LAL activity in the blood cells of healthy participants increased the numbers of CD13+ and CD14+ myeloid cell subsets. PD-1 checkpoint inhibitor treatment in patients with NSCLC reversed the increased number of CD13+ and CD14+ myeloid cell subsets and PDH levels in CD13+ myeloid cells.

CONCLUSION

These results demonstrate that LAL and the associated expansion of MDSCs could serve as targets and biomarkers for anticancer immunotherapy in humans.

Targeting the lysosome: Mechanisms and treatments for nonalcoholic fatty liver disease

The multiple functions of the lysosome, including degradation, nutrient sensing, signaling, and gene regulation, enable the lysosome to regulate lipid metabolism at different levels. In this review, I summarize the recent studies on lysosomal regulation of lipid metabolism and the alterations of the lysosome functions in the livers affected by nonalcoholic fatty liver disease (NAFLD). NAFLD is a highly prevalent lipid metabolic disorder. The progression of NAFLD leads to nonalcoholic steatohepatitis (NASH) and other severe liver diseases, and thus the prevention and treatments of NAFLD progression are critically needed. Targeting the lysosome is a promising strategy. I also discuss the current manipulations of the lysosome functions in the preclinical studies of NAFLD and propose my perspectives on potential future directions.

Lysosomal acid lipase deficiency: A rare inherited dyslipidemia but potential ubiquitous factor in the development of atherosclerosis and fatty liver disease

Lysosomal acid lipase (LAL), encoded by the gene LIPA, is the sole neutral lipid hydrolase in lysosomes, responsible for cleavage of cholesteryl esters and triglycerides into their component parts. Inherited forms of complete (Wolman Disease, WD) or partial LAL deficiency (cholesteryl ester storage disease, CESD) are fortunately rare. Recently, LAL has been identified as a cardiovascular risk gene in genome-wide association studies, though the directionality of risk conferred remains controversial. It has also been proposed that the low expression and activity of LAL in arterial smooth muscle cells (SMCs) that occurs inherently in nature is a likely determinant of the propensity of SMCs to form the majority of foam cells in atherosclerotic plaque. LAL also likely plays a potential role in fatty liver disease. This review highlights the nature of LAL gene mutations in WD and CESD, the association of LAL with prediction of cardiovascular risk from genome-wide association studies, the importance of relative LAL deficiency in SMC foam cells, and the need to further interrogate the pathophysiological impact and cell type-specific role of enhancing LAL activity as a novel treatment strategy to reduce the development and induce the regression of ischemic cardiovascular disease and fatty liver.

Lysosomal acid lipase, CSF1R, and PD-L1 determine functions of CD11c+ myeloid-derived suppressor cells

Lysosomal acid lipase (LAL) is a key enzyme in the metabolic pathway of neutral lipids. In the blood of LAL-deficient (Lal-/-) mice, increased CD11c+ cells were accompanied by upregulated programmed cell death ligand 1 (PD-L1) expression. Single-cell RNA sequencing of Lal-/- CD11c+ cells identified 2 distinctive clusters with a major metabolic shift toward glucose utilization and reactive oxygen species overproduction. Pharmacologically blocking pyruvate dehydrogenase in glycolysis not only reduced CD11c+ cells and their PD-L1 expression but also reversed their capabilities of T cell suppression and tumor growth stimulation. Colony-stimulating factor 1 receptor (CSF1R) played an essential role in controlling Lal-/- CD11c+ cell homeostasis and function and PD-L1 expression. Pharmacological inhibition of LAL activity increased CD11c, PD-L1, and CSF1R levels in both normal murine myeloid cells and human blood cells. Tumor-bearing mice and human patients with non-small cell lung cancer also showed CD11c+ cell expansion with PD-L1 and CSF1R upregulation and immunosuppression. There were positive correlations among CD11c, PD-L1, and CSF1R expression and negative correlations with LAL expression in patients with lung cancer or melanoma using The Cancer Genome Atlas database and patient samples. Therefore, CD11c+ cells switched their functions to immune suppression and tumor growth stimulation through CSF1R/PD-L1 upregulation and metabolic reprogramming.

Molecular markers of brain cholesterol homeostasis are unchanged despite a smaller brain mass in a mouse model of cholesteryl ester storage disease

Lysosomal acid lipase (LAL), encoded by the gene LIPA, facilitates the intracellular processing of lipids by hydrolyzing cholesteryl esters and triacylglycerols present in newly internalized lipoproteins. Loss-of-function mutations in LIPA result in cholesteryl ester storage disease (CESD) or Wolman disease when mutations cause complete loss of LAL activity. Although the phenotype of a mouse CESD model has been extensively characterized, there has not been a focus on the brain at different stages of disease progression. In the current studies, whole-brain mass and the concentrations of cholesterol in both the esterified (EC) and unesterified (UC) fractions were measured in Lal-/- and matching Lal+/+ mice (FVB-N strain) at ages ranging from 14 up to 280 days after birth. Compared to Lal+/+ controls at 50, 68-76, 140-142, and 230-280 days of age, Lal-/- mice had brain weights that averaged approximately 6%, 7%, 18%, and 20% less, respectively. Brain EC levels were higher in the Lal-/- mice at every age, being elevated 27-fold at 230-280 days. Brain UC concentrations did not show a genotypic difference at any age. The elevated brain EC levels in the Lal-/- mice did not reflect EC in residual blood. An mRNA expression analysis for an array of genes involved in the synthesis, catabolism, storage, and transport of cholesterol in the brains of 141-day old mice did not detect any genotypic differences although the relative mRNA levels for several markers of inflammation were moderately elevated in the Lal-/- mice. The possible sites of EC accretion in the central nervous system are discussed.

Impaired Bile Acid Metabolism and Gut Dysbiosis in Mice Lacking Lysosomal Acid Lipase

Lysosomal acid lipase (LAL) is the sole enzyme known to be responsible for the hydrolysis of cholesteryl esters and triglycerides at an acidic pH in lysosomes, resulting in the release of unesterified cholesterol and free fatty acids. However, the role of LAL in diet-induced adaptations is largely unexplored. In this study, we demonstrate that feeding a Western-type diet to Lal-deficient (LAL-KO) mice triggers metabolic reprogramming that modulates gut-liver cholesterol homeostasis. Induction of ileal fibroblast growth factor 15 (three-fold), absence of hepatic cholesterol 7α-hydroxylase expression, and activation of the ERK phosphorylation cascade results in altered bile acid composition, substantial changes in the gut microbiome, reduced nutrient absorption by 40%, and two-fold increased fecal lipid excretion in LAL-KO mice. These metabolic adaptations lead to impaired bile acid synthesis, lipoprotein uptake, and cholesterol absorption and ultimately to the resistance of LAL-KO mice to diet-induced obesity. Our results indicate that LAL-derived lipolytic products might be important metabolic effectors in the maintenance of whole-body lipid homeostasis.

Lysosomal Acid Lipase: From Cellular Lipid Handler to Immunometabolic Target

Lysosomal acid lipase (LAL) hydrolyzes cholesteryl esters (CEs) and triglycerides (TGs) to free cholesterol (FC) and free fatty acids (FFAs), which are then used for metabolic purposes in the cell. The process also occurs in immune cells that adapt their metabolic machinery to cope with the different energetic requirements associated with cell activation, proliferation, and polarization. LAL deficiency (LALD) causes severe lipid accumulation and affects the immunometabolic signature in animal models. In humans, LAL deficiency is associated with a peculiar clinical immune phenotype, secondary hemophagocytic lymphohistiocytosis. These observations suggest that LAL might play an important role in cellular immunometabolic modulation, and availability of an effective enzyme replacement strategy makes LAL an attractive target to rewire the metabolic machinery of immune cells beyond its role in controlling cellular lipid metabolism.

Lysosomal regulation of cholesterol homeostasis in tuberous sclerosis complex is mediated via NPC1 and LDL-R

Tuberous sclerosis complex (TSC) is a multisystem disease associated with hyperactive mTORC1. The impact of TSC1/2 deficiency on lysosome-mediated processes is not fully understood. We report here that inhibition of lysosomal function using chloroquine (CQ) upregulates cholesterol homeostasis genes in TSC2-deficient cells. This TSC2-dependent transcriptional signature is associated with increased accumulation and intracellular levels of both total cholesterol and cholesterol esters. Unexpectedly, engaging this CQ-induced cholesterol uptake pathway together with inhibition of de novo cholesterol synthesis allows survival of TSC2-deficient, but not TSC2-expressing cells. The underlying mechanism of TSC2-deficient cell survival is dependent on exogenous cholesterol uptake via LDL-R, and endosomal trafficking mediated by Vps34. Simultaneous inhibition of lysosomal and endosomal trafficking inhibits uptake of esterified cholesterol and cell growth in TSC2-deficient, but not TSC2-expressing cells, highlighting the TSC-dependent lysosome-mediated regulation of cholesterol homeostasis and pointing toward the translational potential of these pathways for the therapy of TSC.

Sebelipase alfa over 52 weeks reduces serum transaminases, liver volume and improves serum lipids in patients with lysosomal acid lipase deficiency

BACKGROUND & AIMS

Lysosomal acid lipase deficiency is an autosomal recessive enzyme deficiency resulting in lysosomal accumulation of cholesteryl esters and triglycerides. LAL-CL04, an ongoing extension study, investigates the long-term effects of sebelipase alfa, a recombinant human lysosomal acid lipase.

METHODS

Sebelipase alfa (1mg/kg or 3mg/kg) was infused every-other-week to eligible subjects. Safety and tolerability assessments, including liver function, lipid profiles and liver volume assessment, were carried out at regular intervals.

RESULTS

216 infusions were administered to eight adult subjects through week 52 during LAL-CL04. At week 52, mean alanine aminotransferase and aspartate aminotransferase levels were normal with mean change from baseline of -58% and -40%. Mean changes for low-density lipoprotein, total cholesterol, triglyceride and high-density lipoprotein were -60%, -39%, -36%, and +29%, respectively. Mean liver volume by magnetic resonance imaging and hepatic proton density fat fraction decreased (12% and 55%, respectively). Adverse events were mainly mild and unrelated to sebelipase alfa. Infusion-related reactions were uncommon: three events of moderate severity were reported in two subjects; one patient's event was suggestive of a hypersensitivity-like reaction, but additional testing did not confirm this, and the subject has successfully re-started sebelipase alfa. Of samples tested to date, no anti-drug antibodies have been detected.

CONCLUSIONS

Long-term dosing with sebelipase alfa in lysosomal acid lipase-deficient patients is well tolerated and produces sustained reductions in transaminases, improvements in serum lipid profile and reduction in the hepatic fat fraction. A randomized, placebo-controlled phase 3 trial in children and adults is underway (ARISE: NCT01757184).

The role of lipolysis in human orosensory fat perception

Taste perception elicited by food constituents and facilitated by sensory cells in the oral cavity is important for the survival of organisms. In addition to the five basic taste modalities, sweet, umami, bitter, sour, and salty, orosensory perception of stimuli such as fat constituents is intensely investigated. Experiments in rodents and humans suggest that free fatty acids represent a major stimulus for the perception of fat-containing food. However, the lipid fraction of foods mainly consists of triglycerides in which fatty acids are esterified with glycerol. Whereas effective lipolysis by secreted lipases (LIPs) liberating fatty acids from triglycerides in the rodent oral cavity is well established, a similar mechanism in humans is disputed. By psychophysical analyses of humans, we demonstrate responses upon stimulation with triglycerides which are attenuated by concomitant LIP inhibitor administration. Moreover, lipolytic activities detected in minor salivary gland secretions directly supplying gustatory papillae were correlated to individual sensitivities for triglycerides, suggesting that differential LIP levels may contribute to variant fat perception. Intriguingly, we found that the LIPF gene coding for lingual/gastric LIP is not expressed in human lingual tissue. Instead, we identified the expression of other LIPs, which may compensate for the absence of LIPF.

Cholesteryl ester storage disease: a rare and possibly treatable cause of premature vascular disease and cirrhosis

Cholesteryl ester storage disease (CESD) is an autosomal recessive lysosomal storage disorder caused by a variety of mutations of the LIPA gene. These cause reduced activity of lysosomal acid lipase, which results in accumulation of cholesteryl esters in lysosomes. If enzyme activity is very low/absent, presentation is in infancy with failure to thrive, malabsorption, hepatosplenomegaly and rapid early death (Wolman disease). With higher but still low enzyme activity, presentation is later in life with hepatic fibrosis, dyslipidaemia and early atherosclerosis.Identification of this rare disorder is difficult as it is essential to assay leucocyte acid phosphatase activity. An assay using specific inhibitors has now been developed that facilitates measurement in dried blood spots. Treatment of CESD has until now been limited to management of the dyslipidaemia, but this does not influence the liver effects. A new enzyme replacement therapy (Sebelipase) has now been developed that could change treatment options for the future.

Cloning, phylogenetic analysis and 3D modeling of a putative lysosomal acid lipase from the camel, Camelus dromedarius

Acid lipase belongs to a family of enzymes that is mainly present in lysosomes of different organs and the stomach. It is characterized by its capacity to withstand acidic conditions while maintaining high lipolytic activity. We cloned for the first time the full coding sequence of camel’s lysosomal acid lipase, cLIPA using RT-PCR technique (Genbank accession numbers JF803951 and AEG75815, for the nucleotide and aminoacid sequences respectively). The cDNA sequencing revealed an open reading frame of 1,197 nucleotides that encodes a protein of 399 aminoacids which was similar to that from other related mammalian species. Bioinformatic analysis was used to determine the aminoacid sequence, 3D structure and phylogeny of cLIPA. Bioinformatics analysis suggested the molecular weight of the translated protein to be 45.57 kDa, which could be decreased to 43.16 kDa after the removal of a signal peptide comprising the first 21 aminoacids. The deduced cLIPA sequences exhibited high identity with Equus caballus (86%), Numascus leucogenys (85%), Homo sapiens (84%), Sus scrofa (84%), Bos taurus (82%) and Ovis aries (81%). cLIPA shows high aminoacid sequence identity with human and dog-gastric lipases (58%, and 59% respectively) which makes it relevant to build a 3D structure model for cLIPA. The comparison confirms the presence of the catalytic triad and the oxyanion hole in cLIPA. Phylogenetic analysis revealed that camel cLIPA is grouped with monkey, human, pig, cow and goat. The level of expression of cLIPA in five camel tissues was examined using Real Time-PCR. The highest level of cLIPA transcript was found in the camel testis (162%), followed by spleen (129%), liver (100%), kidney (20.5%) and lung (17.4%).

Lipid metabolic effect of Korean red ginseng extract in mice fed on a high-fat diet

BACKGROUND

Ginseng saponin and ginsenosides exert anti-obesity effects via the modulation of physiological lipid metabolism in vivo or intracellular signalling in cell culture systems. However, the complicated relationship between the anti-obesity effects of ginseng and gene expression has yet to be defined under in vivo conditions. Therefore, we evaluated the relationship between the anti-obesity effects of Korean red ginseng extract (KRGE) and hepatic gene expression profiles in mice fed long-term on a high-fat diet (HFD) in this study.

RESULTS

KRGE reduces the levels of cholesterol, low-density lipoprotein-cholesterol (LDL-C), serum triglycerides, and atherogenic indices. Levels of leptin, adiponectin and insulin, which regulate glucose and lipid metabolism, were impaired profoundly by HFD. However, KRGE treatment brought these levels back to normal. KRGE was found to down-regulate genes associated with lipid metabolism or cholesterol metabolism (Lipa, Cyp7a1, Il1rn, Acot2, Mogat1, Osbpl3, Asah3l, Insig1, Anxa2, Vldlr, Hmgcs1, Sytl4, Plscr4, Pla2g4e, Slc27a3, Enpp6), all of which were up-regulated by HFD.

CONCLUSION

KRGE regulated the expression of genes associated with abnormal physiology via HFD. Leptin, insulin, and adiponectin, which carry out critical functions in energy and lipid metabolism, were shown to be modulated by KRGE. These results show that KRGE is effective in preventing obesity.

Inhibition of PPARγ in myeloid-lineage cells induces systemic inflammation, immunosuppression, and tumorigenesis

Peroxisome proliferator-activated receptor-γ (PPARγ) is an anti-inflammatory molecule. To study its biologic function in myeloid cells, dominant-negative PPARγ (dnPPARγ) was overexpressed in a myeloid-specific bitransgenic mouse model. In this bitransgenic system, overexpression of the dnPPARγ-Flag fusion protein in myeloid-lineage cells abnormally elevated frequencies and total numbers of IL-7Rα(-)Lin(-)c-Kit(+)Sca-1(-), Lin(-)/Scal(+)/c-Kit(+), common myeloid, and granulocyte-monocyte progenitor populations in the BM. dnPPARγ overexpression led to up-regulation of IL-1β, IL-6, and TNFα in the blood plasma. As a result, CD11b(+)Ly6G(+) cells were systemically increased in association with activation of Stat3, NF-κB, Erk1/2, and p38 molecules. Myeloid-derived suppressor cells (MDSCs) inhibited the proliferation and lymphokine production of wild-type CD4+ T cells in vitro. CD4+ T cells from doxycycline-treated bitransgenic mice displayed reduced proliferation and lymphokine release. Both CD4+ and CD8+ T-cell populations were decreased in doxycycline-treated bitransgenic mice. Multiple forms of carcinoma and sarcoma in the lung, liver, spleen, and lymph nodes were observed in doxycycline-treated bitransgenic mice. BM transplantation revealed that a myeloid-autonomous defect was responsible for MDSC expansion, immunosuppression, and tumorigenesis in these mice. These studies suggest that anti-inflammatory PPARγ in myeloid-lineage cells plays a key role in controlling pro-inflammatory cytokine synthesis, MDSC expansion, immunosuppression, and the development of cancer.

Genomics and proteomics of vertebrate cholesterol ester lipase (LIPA) and cholesterol 25-hydroxylase (CH25H)

Cholesterol ester lipase (LIPA; EC 3.1.1.13) and cholesterol 25-hydroxylase (CH25H; EC 1.14.99.48) play essential role in cholesterol metabolism in the body by hydrolysing cholesteryl esters and triglycerides within lysosomes (LIPA) and catalysing the formation of 25-hydroxycholesterol from cholesterol (CH25H) which acts to repress cholesterol biosynthesis. Bioinformatic methods were used to predict the amino acid sequences, structures and genomic features of several vertebrate LIPA and CH25H genes and proteins, and to examine the phylogeny of vertebrate LIPA. Amino acid sequence alignments and predicted subunit structures enabled the identification of key sequences previously reported for human LIPA and CH25H and transmembrane structures for vertebrate CH25H sequences. Vertebrate LIPA and CH25H genes were located in tandem on all vertebrate genomes examined and showed several predicted transcription factor binding sites and CpG islands located within the 5′ regions of the human genes. Vertebrate LIPA genes contained nine coding exons, while all vertebrate CH25H genes were without introns. Phylogenetic analysis demonstrated the distinct nature of the vertebrate LIPA gene and protein family in comparison with other vertebrate acid lipases and has apparently evolved from an ancestral LIPA gene which predated the appearance of vertebrates.

Comparative studies of mammalian acid lipases: Evidence for a new gene family in mouse and rat (Lipo)

At least six families of mammalian acid lipases (E.C. 3.1.1.-) catalyse the hydrolysis of triglycerides in the body, designated as LIPA (lysosomal), LIPF (gastric), LIPJ (testis) and LIPK, LIPM and LIPN (epidermal), which belong to the AB hydrolase superfamily. In this study, in silico methods were used to predict the amino acid sequences, secondary and tertiary structures, and gene locations for acid lipase genes and encoded proteins using data from several mammalian genome projects. Mammalian acid lipase genes were located within a gene cluster for each of the 8 mammalian genomes examined, including human (Homo sapiens), chimpanzee (Pons troglodytes), rhesus monkey (Macacca mulatta), mouse (Mus musculus), rat (Rattus norvegicus), cow (Bos taurus), horse (Equus caballus) and dog (Canis familaris), with each containing 9 coding exons. Human and mouse acid lipases shared 44-87% sequence identity and exhibited sequence alignments and identities for key amino acid residues and conservation of predicted secondary and tertiary structures with those previously reported for human gastric lipase (LIPF) (Roussel et al., 1999). Evidence for a new family of acid lipase genes is reported for mouse and rat genomes, designated as Lipo. Mouse acid lipase genes are subject to differential mRNA tissue expression, with Lipa showing wide tissue expression, while others have a more restricted tissue expression in the digestive tract (Lipf), salivary gland (Lipo) and epidermal tissues (Lipk, Lipm and Lipn). Phylogenetic analyses of the mammalian acid lipase gene families suggested that these genes are products of gene duplication events prior to eutherian mammalian evolution and derived from an ancestral vertebrate LIPA gene, which is present in the frog, Xenopus tropicalis.

Critical roles of lysosomal acid lipase in T cell development and function

Lysosomal acid lipase (LAL) cleaves cholesteryl esters and triglycerides to generate free fatty acids and cholesterol in lysosomes. In LAL gene-knockout (lal(-/-)) mice, blockage of cholesteryl ester and triglyceride metabolism led to abnormal organization of the thymus and spleen, as well as neutral lipid accumulation in these organs. LAL deficiency impaired T cell development in the thymus. Peripheral T cells were reduced dramatically in lal(-/-) mice, due largely to increased apoptosis and decreased proliferation of lal(-/-) T cells in the thymus and peripheral compartments. These lal(-/-) T cells lost the ability to respond to T cell receptor stimulation, including reduced expression of cell surface receptor CD69, abolishment of T cell proliferation, and decreased expression of T lymphokines after stimulation by either anti-CD3 plus anti-CD28 or phorbol-12-myristate-13-acetate and ionomycin. Differentiation of Th1 and Th2 CD4(+) effector lymphocytes by T cell receptor stimulation was blocked in lal(-/-) mice. The ratio of CD4(+)CD25(+)FoxP3(+) Tregs to CD4(+) T cells was increased in lal(-/-) spleens. Bone marrow chimeras demonstrated retardation of T cell development and maturation in lal(-/-) mice due to defects in T cell precursors. Therefore, LAL, its downstream genes, and lipid mediators all play essential roles in development, homeostasis, and function of T cells. The altered development and function of lal(-/-) T cells contributes to disease formation in various organs during LAL deficiency.

The role of mannosylated enzyme and the mannose receptor in enzyme replacement therapy

Lysosomal acid lipase (LAL) is the critical enzyme for the hydrolysis of triglycerides (TGs) and cholesteryl esters (CEs) in lysosomes. LAL defects cause Wolman disease (WD) and CE storage disease (CESD). An LAL null (lal-/-) mouse model closely mimics human WD/CESD, with hepatocellular, Kupffer cell and other macrophage, and adrenal cortical storage of CEs and TGs. The effect on the cellular targeting of high-mannose and complex oligosaccharide-type oligosaccharide chains was tested with human LAL expressed in Pichia pastoris (phLAL) and CHO cells (chLAL), respectively. Only chLAL was internalized by cultured fibroblasts, whereas both chLAL and phLAL were taken up by macrophage mannose receptor (MMR)-positive J774E cells. After intraperitoneal injection into lal-/- mice, phLAL and chLAL distributed to macrophages and macrophage-derived cells of various organs. chLAL was also detected in hepatocytes. Ten injections of either enzyme over 30 d into 2- and 2.5-mo-old lal-/- mice produced normalization of hepatic color, decreased liver weight (50%-58%), and diminished hepatic cholesterol and TG storage. Lipid accumulations in macrophages were diminished with either enzyme. Only chLAL cleared lipids in hepatocytes. Mice double homozygous for the LAL and MMR deficiences (lal-/-;MMR-/-) showed phLAL uptake into Kupffer cells and hepatocytes, reversal of macrophage histopathology and lipid storage in all tissues, and clearance of hepatocytes. These results implicate MMR-independent and mannose 6-phosphate receptor-independent pathways in phLAL uptake and delivery to lysosomes in vivo. In addition, these studies show specific cellular targeting and physiologic effects of differentially oligosaccharide-modified human LALs mediated by MMR and that lysosomal targeting of mannose-terminated glycoproteins occurs and storage can be eliminated effectively without MMR.

The pathophysiological function of peroxisome proliferator-activated receptor-gamma in lung-related diseases

Research into respiratory diseases has reached a critical stage and the introduction of novel therapies is essential in combating these debilitating conditions. With the discovery of the peroxisome proliferator-activated receptor and its involvement in inflammatory responses of cardiovascular disease and diabetes, attention has turned to lung diseases and whether knowledge of this receptor can be applied to therapy of the human airways. In this article, we explore the prospect of peroxisome proliferator-activated receptor-γ as a marker and treatment focal point of lung diseases such as asthma, chronic obstructive pulmonary disorder, lung cancer and cystic fibrosis. It is anticipated that peroxisome proliferator-activated receptor-γ ligands will provide not only useful mechanistic pathway information but also a possible new wave of therapies for sufferers of chronic respiratory diseases.

Alveolus formation: what have we learned from genetic studies?

The respiratory system has two basic functions: air exchange and pathogen clearance. The conducting airway and alveolar parenchyma are the basic structures to fulfill these functions during respiratory cycles. In humans, there are ∼40 cell types in the lung that coordinately work together through various structural and signaling molecules. These molecules are vital for maintaining normal lung functions in response to environmental changes. Aberrant expression of these molecules can jeopardize human health and cause various pulmonary diseases. In this article, we will review some recent progress made in the pulmonary field, using genetic animal model systems to elucidate molecular mechanisms that are important for alveolar formation and lung diseases.

Peroxisome proliferator-activated receptor gamma and ligands inhibit surfactant protein B gene expression in the lung

Pulmonary nonciliated bronchiolar epithelial cells (Clara cells) and alveolar type II (AT II) epithelial cells are responsible for surfactant synthesis and secretion. These cells are highly lipogenic with a high lipid turnover rate. Although only 10% of surfactant lipids are neutral lipids, they play very important roles in maintaining pulmonary surfactant homeostasis. Many metabolic intermediate products of neutral lipids serve as ligands for various nuclear receptors that bind to target genes to influence gene transcription. In this report, the functional role of the neutral lipid metabolites, 15-deoxy-Delta12,14-prostaglandin J2 and 9-hydroxyoctadecanoic acids, and peroxisome proliferator-activated receptor gamma was evaluated in surfactant protein B gene regulation. These reagents down-regulated surfactant protein B gene expression in respiratory epithelial cells at the transcriptional level in both cell line and whole lung explant systems. The studies support the concept that surfactant protein B homeostasis is influenced by neutral lipid metabolites in the lung.

Distinct endosomal compartments in early trafficking of low density lipoprotein-derived cholesterol

We previously studied the early trafficking of low density lipoprotein (LDL)-derived cholesterol in mutant Chinese hamster ovary cells defective in Niemann-Pick type C1 (NPC1) using cyclodextrin (CD) to monitor the arrival of cholesterol from the cell interior to the plasma membrane (PM) (Cruz, J. C., Sugii, S., Yu, C., and Chang, T.-Y. (2000) J. Biol. Chem. 275, 4013-4021). We found that newly hydrolyzed cholesterol derived from LDL first appears in certain CD-accessible pool(s), which we assumed to be the PM, before accumulating in the late endosome/lysosome, where NPC1 resides. To determine the identity of the early CD-accessible pool(s), in this study, we performed additional experiments, including the use of revised CD incubation protocols. We found that prolonged incubation with CD (>30 min) caused cholesterol in internal membrane compartment(s) to redistribute to the PM, where it became accessible to CD. In contrast, a short incubation with CD (5-10 min) did not cause such an effect. We also show that one of the early compartments contains acid lipase (AL), the enzyme required for liberating cholesterol from cholesteryl ester in LDL. Biochemical and microscopic evidence indicates that most of the AL is present in endocytic compartment(s) distinct from the late endosome/lysosome. Our results suggest that cholesterol is liberated from LDL cholesteryl ester in the hydrolytic compartment containing AL and then moves to the NPC1-containing late endosome/lysosome before reaching the PM or the endoplasmic reticulum.

Lysosomal amino acid transporter LYAAT-1 in the rat central nervous system: an in situ hybridization and immunohistochemical study

A first mammalian lysosomal transporter (LYAAT-1) was recently identified and functionally characterized. Preliminary immunocytochemical data revealed that LYAAT-1 localizes to lysosomes in some neurons. In order to determine whether it is expressed in specific neuron populations and other cell types, and to confirm whether it is localized at the membrane of lysosomes, we used in situ hybridization and immunohistochemistry methods in adult rat central nervous system (CNS). We found that LYAAT-1 is expressed in most areas of the CNS, specifically in neurons, but also in choroid plexus and ependymal epithelium cells. LYAAT-1-IR (immunoreactivity) levels varied among different neuroanatomical structures but were present in neurons independently of the neurotransmitter used (glutamate, GABA, acetylcholine, noradrenaline, serotonin, or glycine). Light and confocal microscopy demonstrated that LYAAT-1 and the lysosomal marker cathepsin D colocalized throughout the brain and electron microscopy showed that LYAAT-1-IR was associated with lysosomal membranes. In addition, LYAAT-1-IR was also found associated with other membranes belonging to the Golgi apparatus and lateral saccules and less frequently with multivesicular bodies, endoplasmic reticulum, and occasionally with the plasma membrane. The localization of LYAAT-1 at the lysosomal membrane is consistent with the view that it mediates amino acid efflux from lysosomes. Furthermore, its cell expression pattern suggests that it may contribute to specialized cellular function in the rat CNS such as neuronal metabolism, neurotransmission, and control of brain amino acid homeostasis.

Lysosomal acid lipase deficiency: correction of lipid storage by adenovirus-mediated gene transfer in mice

Lysosomal acid lipase (LAL) is the essential enzyme for hydrolysis of triglycerides (TGs) and cholesteryl esters (CEs) in lysosomes. Its deficiency produces two human phenotypes: Wolman disease (WD) and cholesteryl ester storage disease (CESD). The LAL null (lal(-/-)) mouse mimicks aspects of human WD and CESD. The potential for gene therapy of LAL deficiency was tested with first-generation adenoviral vectors containing human LAL cDNA (Ad-hLAL) by intravenous injection into lal(-/-) mice. Compared with phosphate-buffered saline-injected controls, the mice receiving Ad-hLAL had increased hepatic LAL activity, decreased hepatomegaly, and normalization of histopathology. hLAL protein and mRNA were detected by immunohistochemical staining and in situ hybridization in hepatic parenchymal and sinusoid lining cells, splenic sinusoidal cells, lung macrophages, and adrenal cortical cells. Mice showed TG reductions in liver, spleen, and small intestine of 68, 54, and 50%, respectively, and cholesterol reductions of 55, 52, and 34%, respectively, at 20 days postinjection. These studies provide the basis for the use of gene therapy, in the form of gene transfer via intravenously administered adenovirus, to correct deficiency states, such as WD and CESD, and histopathology of a variety of tissues.

Phenotypic correction of lipid storage and growth arrest in wolman disease fibroblasts by gene transfer of lysosomal acid lipase

Wolman disease is a lethal lysosomal storage disease due to deficiency of lysosomal acid lipase (LAL). Wolman disease is characterized by pronounced hepatic involvement while neurological symptoms are uncommon, making Wolman disease an attractive candidate for liver-directed gene therapy. This study was performed to test the effects of gene replacement in fibroblasts lacking LAL, using a recombinant adenovirus encoding the human LAL cDNA (AdhLAL). Human fibroblasts from a Wolman disease patient were infected with AdhLAL and showed a dose-dependent increase in LAL protein and activity up to 5-fold above levels in control fibroblasts. Furthermore, 72 hr after infection with AdhLAL there was a dose-dependent correction of the severe lipid storage phenotype of Wolman disease fibroblasts. Electron microscopy confirmed significant correction of the lysosomal lipid storage in AdhLAL-infected Wolman disease fibroblasts at the ultrastructural level. Intravenous injection of AdhLAL into wild-type mice resulted in a 13.5-fold increase in hepatic LAL activity, and overexpression of LAL was not associated with toxic side effects. These data demonstrate high-level lysosomal expression of recombinant LAL in vitro and in vivo and show the feasibility of gene therapeutic strategies for the treatment of Wolman disease.

Ectopic expression of alpha1,6 fucosyltransferase in mice causes steatosis in the liver and kidney accompanied by a modification of lysosomal acid lipase

The alpha1,6 fucosyltransferase (alpha1,6 FucT) catalyzes the transfer of a fucose from GDP-fucose to the innermost GlcNAc residue of N-linked glycans via an alpha1,6 linkage. alpha1,6 FucT was overexpressed in transgenic mice under the control of a combined cytomegalovirus and chicken beta-actin promoter. Histologically numerous small vacuoles, in which lipid droplets had accumulated, were observed in hepatocytes and proximal renal tubular cells. Electron microscopic studies showed that the lipid droplets were membrane-bound and apparently localized within the lysosomes. Cholesterol esters and triglycerides were significantly increased in liver and kidney of the transgenic mice. Liver lysosomal acid lipase (LAL) activity was significantly lower in the transgenic mice compared to the wild mice, whereas LAL protein level, which was detected immunochemically, was increased, indicating that the specific activity of LAL was much lower in the transgenic mice. In all of the transgenic and nontransgenic mice examined, the activity of liver LAL was negatively correlated with the level of alpha1,6 FucT activity. As evidenced by lectin and immunoblot analysis, LAL was found to be more fucosylated in the transgenic mice, suggesting that the aberrant fucosylation of LAL causes an accumulation of inactive LAL in the lysosomes. Such an accumulation of inactive LAL could be a likely cause for a steatosis in the lysosomes of the liver and kidney in the case of the alpha1,6 FucT transgenic mice.

Difference in substrate specificity between human and mouse lysosomal acid lipase: low affinity for cholesteryl ester in mouse lysosomal acid lipase

Lysosomal acid lipase (LAL) is essential for the intracellular degradation of cholesteryl esters (CE) and triacylglycerols (TG) that are delivered to lysosomes by low density lipoprotein (LDL) receptor mediated endocytosis. We have analysed the difference in the catalytic properties and substrate specificity of human and mouse LALs. LAL activities were measured in human and mouse fibroblasts and in HeLa cells transiently expressing wild-type or site-directed mutant LALs of the two species using the T7 vaccinia system. Cholesteryl esterase and triacylglycerol lipase activities were determined in cellular homogenates with a phospholipid/detergent vesicle assay, an assay frequently used to diagnose human LAL deficiency syndromes, and with LDL particles, a more physiological substrate. Characterisation of human and mouse LAL using these two assays demonstrated marked differences in their TG and CE hydrolysing activities. Compared to human LAL mouse LAL showed a much lower cholesteryl esterase activity in both assays used. The difference was more pronounced in the vesicle assay. The lower cholesteryl esterase activity of mouse LAL did not affect the LDL-CE degradation in intact fibroblasts. The analysis of site-directed mutants suggests a role of the non-conserved cysteine residue at position 240 in cholesteryl esterase activity in human LAL. Our results show a significant difference between human and mouse LAL in their specificity toward cholesteryl esters. The low cholesteryl esterase activity does not result in reduced LDL-cholesterol ester degradation in mouse fibroblasts in situ. In addition, this work emphasises the importance of the physical state of substrates in studies of the specificity and properties of lipolytic enzymes.

Lysosomal acid lipase mutations that determine phenotype in Wolman and cholesterol ester storage disease

Mechanisms producing the divergent phenotypes, Wolman disease (WD) and cholesterol ester storage disease (CESD), associated with the genetic deficiency of human lysosomal acid lipase/cholesterol ester hydrolase (hLAL) function were investigated with the determination of HLAL activity levels, mRNA and protein expression, and defects in structural gene sequences in cells from three WD and five CESD patients. Measured with natural substrates, HLAL activities were all below 2% of normal, regardless of phenotype. Immunoblotting showed a lack of detectable hLAL protein in all mutant fibroblasts. Four CESD, but no WD genomes contained at least one allele with a specific exon 8 splice junction mutation, c.894 G>A, that encodes a shortened form of hLAL mRNA. Other CESD mutations were identical in type to the WD defects: nucleotide deletions (positions 397, 684, 980), insertions (594), or substitutions (193, 347) that result in premature terminations precluding any function. The only exception was a substitution at nucleotide 866 in the CESD case without an exon 8 splicing mutation; expression of the predicted S289C change in a transfection assay produced a low, but clearly measurable, level of acid esterase activity. Although it is not easily demonstrated in conventional assays, CESD is distinct from WD in that at least one mutant allele has the potential to produce enough residual enzymatic function to ameliorate the phenotype; in the majority of CESD cases this may come from a single, easily detected, splicing mutation in one allele.

Murine acid alpha-glucosidase: cell-specific mRNA differential expression during development and maturation

Acid alpha-glucosidase (GAA) cleaves the alpha1-4 and alpha1-6 glycosidic linkages of glycogen and related alpha-glucosyl substrates within lysosomes. Its deficiency results in glycogen storage disease type II (GSDII) variants including Pompe disease. To gain insight into the tissue patterns of involvement by glycogen storage in GSDII, GAA mRNA expression in mouse tissues was evaluated by Northern blot and in situ hybridization analyses. Extensive temporal and spatial variation of GAA mRNA was observed. During preterm maturation, GAA mRNA levels of whole mice progressively increased as assessed by Northern analysis. By in situ hybridization with GAA antisense mRNA, low signals were detected in most tissues throughout gestation. However, increased expression in specific cell types of different tissues was observed beginning at 16 days post coitum in developing brain neurons, primitive inner ear cells, and seminiferous tubular epithelium. In adult mice, whole-organ GAA mRNA levels were highest in brain, moderate in heart, liver, and skeletal muscle, and lowest in the series kidney > lung > testis > spleen. By in situ hybridization, the highest-intensity signals were in neurons of the central and peripheral nervous systems whereas neuroglial cells had only low-level signal. Signals of moderate intensity were in cardiomyocytes whereas low signals were in hepatocytes and skeletal muscle myocytes and very low in cells of the lungs, thymus, pancreas, spleen, and adrenal glands. However, testicular Sertoli cells and kidney tubular epithelial cells had significant signals even though surrounding cells had very low signals. The discrete temporal and spatial variations of GAA mRNA during development indicate different physiological roles for this enzyme in various cell types and developmental stages.

Lack of PPCA expression only partially coincides with lysosomal storage in galactosialidosis mice: indirect evidence for spatial requirement of the catalytic rather than the protective function of PPCA

Protective protein/cathepsin A (PPCA) is a pleiotropic lysosomal enzyme that complexes with beta-galactosidase and neuraminidase, and possesses serine carboxypeptidase activity. Its deficiency in man results in the neurodegenerative lysosomal storage disorder galactosialidosis (GS). The mouse model of this disease resembles the human early onset phenotype and results in severe nephropathy and ataxia. To understand better the pathophysiology of the disease, we compared the occurrence of lysosomal PPCA mRNA and protein in normal adult mouse tissues with the incidence of lysosomal storage in PPCA(-/-) mice. PPCA expression was markedly variable among different tissues. Most sites that produced both mRNA and protein at high levels in normal mice showed extensive and overt storage in the knockout mice. However, this correlation was not consistent as some cells that normally expressed high levels of PPCA were unaffected in their storage capability in the PPCA(-/-) mice. In addition, some normally low expressing cells accumulated large amounts of undegraded products in the GS mouse. This apparent discrepancy may reflect a requirement for the catalytic rather than the protective function of PPCA and/or the presence of cell-specific substrates in certain cell types. A detailed map showing the cellular distribution of PPCA in nomal mouse tissues as well as the sites of lysosomal storage in deficient mice is critical for accurate assessment of the effects of therapeutic interventions.

Molecular and enzymatic analyses of lysosomal acid lipase in cholesteryl ester storage disease

Human lysosomal acid lipase (hLAL) is essential for the hydrolysis of cholesteryl esters and triglycerides in the lysosome. Defective hLAL activity leads to two autosomal recessive traits, Wolman disease (WD) or cholesteryl ester storage disease (CESD). Phenotypically, WD has accumulation of both triglycerides and cholesteryl esters, while CESD has mainly elevated cholesteryl esters. We characterized mutations in the hLAL gene from two CESD siblings. By reverse transcriptase-PCR (RT-PCR) and cDNA cloning and sequencing, we identified homozygous deletion mutations of nucleotides 863 to 934, in the hLAL transcript. Normal levels of LAL mRNA were detected. The deletion in mRNA is due to a G to A transition in the last nucleotide of exon 8 of the hLAL gene, a splice junction mutation (E8SJM) that resulted in exon skipping, and a predicted in-frame deletion of the 24 amino acids. [35S]Met metabolic labeling studies in fibroblasts showed a low level of E8SJM LAL ( approximately 38%) that was highly unstable. Heterologous expression of E8SJM LAL in insect cells gave an LAL with low catalytic activity toward cholesteryl oleate and triolein. The effects of this mutation are complex with the production of decreased amounts of an unstable LAL that is catalytically defective. The results suggest that E8SJM leads to essentially a null allele and that the differences in WD and CESD phenotype involve other factors.

Role of Sp proteins and RORalpha in transcription regulation of murine prosaposin

Prosaposin is the precursor of four low molecular weight sphingolipid-activating proteins (SAPs) or saposins. These four proteins function as intracellular activators of several lysosomal enzymes involved in the degradation of glycosphingolipids, and prosaposin itself has neurite outgrowth effects. Expression of prosaposin is regulated in a temporal and spatial manner with expression in specific brain neurons and visceral cell types. Here a major regulatory fragment was characterized within 310 bp 5' to the transcription start site. Using electrophoretic mobility shift assay (EMSA) and DNA footprinting, members of the Sp family (Sp1, Sp3, and Sp4), the orphan nuclear receptor (RORalpha), and an unknown transcription factor (U; TGGGGGAG) were shown to bind to this region. To evaluate the role of such transcription factor binding sites for this locus, a series of mutant constructs was generated within this region, and their function was evaluated in cultured NS20Y neuroblastoma cells. A 3' Sp1 site, a 5' Sp1/U cluster and the RORalpha binding sites were functional. The data are consistent with a model in which the factors that bind to the Sp1/U cluster and RORE site interact negatively to diminish promoter activity to a background level that is determined primarily by the 3' Sp1 site. These interactions depend on the tissue-specific repertoire of transcription factors leading to differential expression of this locus.

Mouse lysosomal acid lipase: characterization of the gene and analysis of promoter activity

Lysosomal acid lipase (LAL) is required for the hydrolysis of intracellular cholesteryl esters and triglycerides that are delivered to lysosomes by low density lipoprotein (LDL) receptor-mediated endocytosis. To understand that the expression of LAL mRNA and protein is tissue and cell specifically regulated in mice, genomic clones for the mouse lysosomal acid lipase (mLAL) gene were isolated and characterized. The 6.8 kb of the mLAL gene 5'-flanking region was sequenced. Comparisons of mouse and human LAL genes organization revealed identical intron/exon boundaries, except for intron 1 of the mouse gene, and identical exonic length of exons 3-9. The transcription start sites and exon 1 of mLAL were characterized by 5'-RACE-PCR and S1 nuclease mapping. Transfection of 5' flanking deletions of mLAL luciferase reporter gene construct identified positive and negative regulatory elements that varied with cell type. Transfection of three progressively smaller pieces of intron 1 inserted into an SV40 promoter and luciferase reporter gene revealed an enhancer-like activity in intron 1 that is also cell type specific. These studies provide insight into the basis for regulation of this critical enzyme in lipid metabolism.