Loss of lysosomal acid lipase results in mitochondrial dysfunction and fiber switch in skeletal muscles of mice

OBJECTIVE

Lysosomal acid lipase (LAL) is the only enzyme known to hydrolyze cholesteryl esters (CE) and triacylglycerols in lysosomes at an acidic pH. Despite the importance of lysosomal hydrolysis in skeletal muscle (SM), research in this area is limited. We hypothesized that LAL may play an important role in SM development, function, and metabolism as a result of lipid and/or carbohydrate metabolism disruptions.

RESULTS

Mice with systemic LAL deficiency (Lal-/-) had markedly lower SM mass, cross-sectional area, and Feret diameter despite unchanged proteolysis or protein synthesis markers in all SM examined. In addition, Lal-/- SM showed increased total cholesterol and CE concentrations, especially during fasting and maturation. Regardless of increased glucose uptake, expression of the slow oxidative fiber marker MYH7 was markedly increased in Lal-/-SM, indicating a fiber switch from glycolytic, fast-twitch fibers to oxidative, slow-twitch fibers. Proteomic analysis of the oxidative and glycolytic parts of the SM confirmed the transition between fast- and slow-twitch fibers, consistent with the decreased Lal-/- muscle size due to the "fiber paradox". Decreased oxidative capacity and ATP concentration were associated with reduced mitochondrial function of Lal-/- SM, particularly affecting oxidative phosphorylation, despite unchanged structure and number of mitochondria. Impairment in muscle function was reflected by increased exhaustion in the treadmill peak effort test in vivo.

CONCLUSION

We conclude that whole-body loss of LAL is associated with a profound remodeling of the muscular phenotype, manifested by fiber type switch and a decline in muscle mass, most likely due to dysfunctional mitochondria and impaired energy metabolism, at least in mice.

Metabolic changes and propensity for inflammation, fibrosis, and cancer in livers of mice lacking lysosomal acid lipase

Lysosomal acid lipase (LAL) is the sole lysosomal enzyme responsible for the degradation of cholesteryl esters and triacylglycerols at acidic pH. Impaired LAL activity leads to LAL deficiency (LAL-D), a severe and fatal disease characterized by ectopic lysosomal lipid accumulation. Reduced LAL activity also contributes to the development and progression of non-alcoholic fatty liver disease (NAFLD). To advance our understanding of LAL-related liver pathologies, we performed comprehensive proteomic profiling of livers from mice with systemic genetic loss of LAL (Lal-/-) and from mice with hepatocyte-specific LAL-D (hepLal-/-). Lal-/- mice exhibited drastic proteome alterations, including dysregulation of multiple proteins related to metabolism, inflammation, liver fibrosis, and cancer. Global loss of LAL activity impaired both acidic and neutral lipase activities and resulted in hepatic lipid accumulation, indicating a complete metabolic shift in Lal-/- livers. Hepatic inflammation and immune cell infiltration were evident, with numerous upregulated inflammation-related gene ontology biological process terms. In contrast, both young and mature hepLal-/- mice displayed only minor changes in the liver proteome, suggesting that loss of LAL solely in hepatocytes does not phenocopy metabolic alterations observed in mice globally lacking LAL. These findings provide valuable insights into the mechanisms underlying liver dysfunction in LAL-D and may help in understanding why decreased LAL activity contributes to NAFLD. Our study highlights the importance of LAL in maintaining liver homeostasis and demonstrates the drastic consequences of its global deficiency on the liver proteome and liver function.

Recent insights into lysosomal acid lipase deficiency

Lysosomal acid lipase (LAL) is the sole enzyme known to degrade neutral lipids in the lysosome. Mutations in the LAL-encoding LIPA gene lead to rare lysosomal lipid storage disorders with complete or partial absence of LAL activity. This review discusses the consequences of defective LAL-mediated lipid hydrolysis on cellular lipid homeostasis, epidemiology, and clinical presentation. Early detection of LAL deficiency (LAL-D) is essential for disease management and survival. LAL-D must be considered in patients with dyslipidemia and elevated aminotransferase concentrations of unknown etiology. Enzyme replacement therapy, sometimes in combination with hematopoietic stem cell transplantation (HSCT), is currently the only therapy for LAL-D. New technologies based on mRNA and viral vector gene transfer are recent efforts to provide other effective therapeutic strategies.

Monoglyceride Lipase Deficiency Is Associated with Altered Thrombogenesis in Mice

Monoglyceride lipase (MGL) hydrolyzes monoacylglycerols (MG) to glycerol and one fatty acid. Among the various MG species, MGL also degrades 2-arachidonoylglycerol, the most abundant endocannabinoid and potent activator of the cannabinoid receptors 1 and 2. We investigated the consequences of MGL deficiency on platelet function using systemic (Mgl-/-) and platelet-specific Mgl-deficient (platMgl-/-) mice. Despite comparable platelet morphology, loss of MGL was associated with decreased platelet aggregation and reduced response to collagen activation. This was reflected by reduced thrombus formation in vitro, accompanied by a longer bleeding time and a higher blood volume loss. Occlusion time after FeCl3-induced injury was markedly reduced in Mgl-/- mice, which is consistent with contraction of large aggregates and fewer small aggregates in vitro. The absence of any functional changes in platelets from platMgl-/- mice is in accordance with lipid degradation products or other molecules in the circulation, rather than platelet-specific effects, being responsible for the observed alterations in Mgl-/- mice. We conclude that genetic deletion of MGL is associated with altered thrombogenesis.

Dysregulation of Placental Lipid Hydrolysis by High-Fat/High-Cholesterol Feeding and Gestational Diabetes Mellitus in Mice

Advanced maternal age and obesity are the main risk factors to develop gestational diabetes mellitus (GDM). Obesity is a consequence of the increased storage of triacylglycerol (TG). Cytosolic and lysosomal lipid hydrolases break down TG and cholesteryl esters (CE) to release fatty acids (FA), free cholesterol, and glycerol. We have recently shown that intracellular lipases are present and active in the mouse placenta and that deficiency of lysosomal acid lipase alters placental and fetal lipid homeostasis. To date, intracellular lipid hydrolysis in GDM has been poorly studied despite the important role of FA in this condition. Therefore, we hypothesized that intracellular lipases are dysregulated in pregnancies complicated by maternal high-fat/high-cholesterol (HF/HCD) feeding with and without GDM. Placentae of HF/HCD-fed mice with and without GDM were more efficient, indicating increased nutrient transfer to the fetus. The increased activity of placental CE but not TG hydrolases in placentae of dams fed HF/HCD with or without GDM resulted in upregulated cholesterol export to the fetus and placental TG accumulation. Our results indicate that HF/HCD-induced dysregulation of placental lipid hydrolysis contributes to fetal hepatic lipid accumulation and possibly to fetal overgrowth, at least in mice.

Off-target effects of the lysosomal acid lipase inhibitors Lalistat-1 and Lalistat-2 on neutral lipid hydrolases

OBJECTIVES

Lysosomal acid lipase (LAL) is the key enzyme, which degrades neutral lipids at an acidic pH in lysosomes. The role of LAL in various cellular processes has mostly been studied in LAL-knockout mice, which share phenotypical characteristics with humans suffering from LAL deficiency. In vitro, the cell-specific functions of LAL have been commonly investigated by using the LAL inhibitors Lalistat-1 and Lalistat-2.

METHODS

We performed lipid hydrolase activity assays and serine hydrolase-specific activity-based labeling combined with quantitative proteomics to investigate potential off-target effects of Lalistat-1 and -2.

RESULTS

Pharmacological LAL inhibition but not genetic loss of LAL impairs isoproterenol-stimulated lipolysis as well as neutral triglyceride and cholesteryl ester hydrolase activities. Apart from LAL, Lalistat-1 and -2 also inhibit major cytosolic lipid hydrolases responsible for lipid degradation in primary cells at neutral pH through off-target effects. Their binding to the active center of the enzymes leads to a decrease in neutral lipid hydrolase activities in cells overexpressing the respective enzymes.

CONCLUSIONS

Our findings are critically important since they demonstrate that commonly used concentrations of these inhibitors are not suitable to investigate the role of LAL-specific lipolysis in lysosomal function, signaling pathways, and autophagy. The interpretation of their effects on lipid metabolism should be taken with caution and the applied inhibitor concentrations in cell culture studies should not exceed 1 μM.

ATG7 is dispensable for LC3-PE conjugation in thioglycolate-elicited mouse peritoneal macrophages

Thioglycolate-elicited macrophages exhibit abundant conjugation of LC3 with PE (LC3-II). Among other autophagy-related (ATG) proteins, it is proposed that, like in yeast, both ATG5 and ATG7 are essential for LC3 conjugation. Using atg5-deficient (-/-) and atg7-/-macrophages, we provide evidence that loss of ATG5 but not of ATG7 resulted in LC3-II depletion. Accumulation of LC3-II in elicited atg7-/- macrophages in response to bafilomycin A1 validated these data. Furthermore, complete loss of ATG3 in atg7-/- macrophages demonstrated that ATG7 and ATG3 are dispensable for LC3-PE conjugation. In contrast to thioglycolate-elicited macrophages, naïve peritoneal and bone marrow-derived atg7-/- macrophages exhibited no LC3-II, even under inflammatory stimuli in vitro. Hence, the macrophage metabolic status dictates the level of LC3-PE conjugation with a supportive but nonessential role of ATG7, disclosing the eukaryotic exception from the LC3 lipidation model based on yeast data. Abbreviations: ATG: autophagy-related; BM: bone marrow; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; PE: phosphatidylethanolamine.

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.

Urolithiasis in childhood: surgery and lithotripsy

From 1982 through 1993, 174 interventions in 160 infants and children with urolithiasis were performed at our department. There were 101 boys and 59 girls, mean age 8.9 years. The main causes of the interventions were congenital malformations in 62, followed by recurrent urinary tract infections in 29, previous operations in 17, and hypercalciuria in 35 patients. In 17 children, the cause of urolithiasis remained unknown. As a therapeutic option, extracorporeal shock-wave lithotripsy (ESWL) has become available since 1988. The malformations and postoperative conditions are surgically corrected, and the calculi removed in the same act. For post-infectious, idiopathic or hypercalciuric calculi, ESWL has been used in the majority of patients since 1988. Thus, a total of 129 calculi were removed by operation and 47 by ESWL, whereas 18 calculi were endoscopically extracted. There were no complications after either ESWL or open surgery. Calculi in congenital malformations or as a result of operation are still removed by open surgery. In other cases, ESWL is the method of choice.

Our 10-year experience with embolized Wilms' tumor

In the Department of Pediatric Surgery, Clinical Hospital Center Rebro in Zagreb, during the last 10 years a new method of invasive diagnostic and at the same time therapeutic procedure for the treatment of Wilms' tumor has been introduced. The treatment is preoperative Percutaneous Transcatheter Intraarterial Embolization (PTIE) of the renal artery. The aim of this procedure is to reduce vascularization, to decrease the mass of kidney affected by the tumor, to separate it from the surrounding tissue, to decrease intraoperative spillage of malignant cells into the blood stream and their metastasizing. As a result nephrectomy is easier to perform. It has been confirmed that it is best to perform nephrectomy 48 hours after embolization. The authors present their own experience with 33 patients, ranging from 1 to 16 years of age.

[Modern diagnosis and treatment of pheochromocytoma in children]

Pheochromocytoma is a rare tumor of chromaffin tissue of the adrenal gland that synthesizes, stores and releases cathecolamines. In 10% of the patients it arises outside the adrenal gland, and has been called paraganglioma. The following study describes our experience in the diagnostic process and treatment of pheochromocytoma in two children, a 8-year-old boy with the right ureteral paraganglioma, and a 8-year-old girl with pheo-chromocytoma of the leftsuprarenal gland. Characteristic clinical features with predominant signs of hypertension, as well as the diagnostic flow diagram, have been presented. We have analysed recent diagnostic possibilities, sensitivity of diagnostic methods (ultrasonography, CT, selective angiography and J131 MIBG scintigraphy), indications for their use, and the importance of appropriate preoperative management. The major role of the J131-metaiodobenzilguanidine scintigraphy in diagnostic assessment, especially in precise preoperative localization and postoperative verification of tumour removal, has been stressed.

Cloacal exstrophy: a case report

A case of an extremely rare type of cloacal exstrophy in a male infant with a normally developed subvesical part of the urinary system and external genitalia but absent distal colon segment is presented. The patient also had omphalocele, upper urinary tract anomalies and sacrococcygeal teratoma.

Congenital pulmonary arteriovenous fistula: a rare cause of cyanosis in childhood

Two children (both females) aged 15 months and 4 years are described as very rare cases of central cyanosis in childhood being caused by a congenital pulmonary arteriovenous fistula. The initial diagnosis was made based on cyanosis and chest radiographs, with normal physical, ECG, and radiological findings of the heart. They had no family history of the Rendu-Weber-Osler syndrome. The patients underwent cardiac catheterization and pulmonary angiography, where the diagnosis was confirmed. After the surgery, both were symptom-free, and had no evidence of the disease.

[The present status of treatment of splenic injuries in children]

Small but very dangerous risk of postsplenectomic sepses gave rise to the examination of surgical attitudes of medical treatment of damaged and ruptured spleen. Some new ideas of immunology revealed the importance of the spleen in the protection of the host and serious defect of immunologic system if the spleen is removed. According to those ideas, ruptured spleen is to be retained by all means. Some minor lesions and hemorrhages that are easily controlled by conservative measures, are not to be operated. In case of serious ruptures and massive hemorrhages necessitating more than 20 ml/kg of fresh blood to replace lost volume, penetrated abdominal injuries and with polytraumatic patients, laparotomy, surgical hemostasis and preservation of the spleen are indicated if possible. In the period of the last eight years, 90 children were treated because of the possibility they had injured spleen. Thirty-eight patients (42%) were under observation. Hemodynamic indicators were normal, so we did not make any aggressive diagnostic examinations. Other 47 patients had splenic scintigraphy, computed tomography (CT) of the abdomen or ultrasound examination. The findings were positive with 32 (69%) patients. Of those patients, 14 (44%) were immediately operated since serious rupture of the spleen was diagnosed and clinical signs suggested the presence of severe abdominal bleeding. To this number of operated patients, four polytraumatic patients and one suffering from penetrated injury are to be added. They were indicated the exploration of the abdomen without previous diagnostics. There were 19 surgical treatments of ruptured spleen; three of them included splenectomy while the other patients underwent splenic preservation.(ABSTRACT TRUNCATED AT 250 WORDS)

Congenital ureteric diverticula in children and adults: classification, radiological and clinical features

To date, about 100 cases of a blind-ending branch of a bifid ureter have been reported. We present 13 clinically, radiologically and histologically evaluated cases of congenital ureteric diverticulum. We believe this anomaly is not as rare as hitherto believed and suggest the term congenital ureteric diverticulum for a blind-ending branch of a bifid ureter.

Primary vesicoureteric reflux treated by antireflux ureterocystostomy at the vertex of the bladder. A 12-year follow-up and analysis of operative failure

A total of 618 children with primary vesicoureteric reflux (VUR) were examined preoperatively and 6, 9 and 24 months after an antireflux ureterocystostomy of the vertex of the bladder (AUVB); 206 children were operated on bilaterally, so that 824 AUVBs were performed. Most patients had grade 3 or 4 reflux and only 5% had grade 2 reflux. Successful results were noted in 792 ureteric units; in 10 cases of post-operative stenosis and 17 cases of recurrent VUR a second AUVB was performed. The following causes of operative failure were found: obstruction of the submucosal ureter after tailoring (5 cases), stricture of the new ureteric orifice (3), necrosis of the terminal part of the ureter (2), submucosal ureter too short or too wide (12) and fibrosis of the detrusor muscle over the submucosal ureter (5); a success rate of 84% was noted after the second procedure.

Bladder diverticula in children - a clinical, radiologic and endoscopic study

We have described the clinical, radiologic and endoscopic findings in 84 children with bladder diverticula and 9 children with posterolateral pouch-like protrusions of the bladder wall. Cystoscopically, a new bladder diverticulum is described, resembling a walnutshell. The majority of children had symptoms of urinary tract infection, the walnutshell-like diverticula was frequently associated with haematuria. In 66 or 84 children with bladder diverticula and in 9 children with posterolateral pouches no obstruction of the lower urinary tract was found. Diverticula caused by obstruction were found in 18 cases. Vesicoureteral reflux was present in 34 of 66 children with diverticula without obstruction of the lower urinary tract, in 20 of these there were saccules (diverticula smaller than 2 cm in diameter). Vesicoureteral reflux was found in 8 of 9 children with posterolateral pouches of the bladder wall. Long term follow-up suggests that any protrusion of the bladder wall, regardless of the size of cavity and the shape of the opening, may become a diverticulum associated with further abnormalities of the urinary tract. In 3 patients with postero lateral pouches a transformation from pouches into true diverticula together with the development of vesicoureteral reflux was observed.

Cystitis cystica: characteristics of the disease in children

Cystitis cystica was found at cystoscopy in 157 children between the ages of 9 1/2 months and 14 years. Girls were affected much more often than boys, the proportion being 153 to 4. Urinary infection, most commonly caused by E. coli, was almost invariable. Urinary tract anomalies, in particular vesico-ureteric reflux, were frequently present. Histologically, the cysts were composed of submucous aggregations of lymphoid tissue. Cystitis cystica affecting the ureteric orifices may contribute to the occurence of reflux and involvement of the bladder neck may produce some degree of vesical outlet obstruction.

Antireflux ureterocystostomy at the vertex of the bladder

This is the first report on the technique and the results of an antireflux ureterocystostomy in the vault of the bladder. During the last 3 years, a total of 106 antireflux ureterocystostomies at the vertex of the urinary bladder has been performed. In 93 cases without another preceding antireflux operation, only 2 (2-1%) recurrent refluxes were found, whereas in 13 cases where an antireflux operation had been performed previously, 4 cases of recurrent reflux were seen, making a 30% rate of operative failure in this particular group. In all other cases the end result was excellent; the urine has become negative on culture and the dilatation of the ureter has subsided.