A review on lecithin:cholesterol acyltransferase deficiency

A novel and diverse family of filamentous DNA viruses associated with parasitic wasps

Large dsDNA viruses from the Naldaviricetes class are currently composed of four viral families infecting insects and/or crustaceans. Since the 1970s, particles described as filamentous viruses (FVs) have been observed by electronic microscopy in several species of Hymenoptera parasitoids but until recently, no genomic data was available. This study provides the first comparative morphological and genomic analysis of these FVs. We analyzed the genomes of seven FVs, six of which were newly obtained, to gain a better understanding of their evolutionary history. We show that these FVs share all genomic features of the Naldaviricetes while encoding five specific core genes that distinguish them from their closest relatives, the Hytrosaviruses. By mining public databases, we show that FVs preferentially infect Hymenoptera with parasitoid lifestyle and that these viruses have been repeatedly integrated into the genome of many insects, particularly Hymenoptera parasitoids, overall suggesting a long-standing specialization of these viruses to parasitic wasps. Finally, we propose a taxonomical revision of the class Naldaviricetes in which FVs related to the Leptopilina boulardi FV constitute a fifth family. We propose to name this new family, Filamentoviridae.

Mildly elevated serum bilirubin and its correlations with lipid levels among male patients undergoing health checkups

BACKGROUND

Bilirubin's ability to lower lipid levels was confirmed by several studies, but those studies mainly focused on total bilirubin (TBil). The present study aimed to elucidate the correlations of the two subtypes of bilirubin with lipid levels.

METHODS

A total of 1732 male patients undergoing health checkups were categorized into three groups according to the levels of direct bilirubin (DBil) and indirect bilirubin (IBil). The differences in medical characteristics among the three groups were analysed.

RESULTS

Subjects in the elevated DBil group had the lowest serum alanine aminotransferase (ALT), total cholesterol (TC), blood urea nitrogen (BUN), γ-glutamyl transpeptidase (γ-GT), fasting blood glucose (FBG), haemoglobin (HGB), and triglyceride (TG) levels in contrast to the other groups (P < 0.01), while subjects in the elevated IBil group had the highest ALT, γ-GT, BUN, serum creatinine (SCR), HGB, TC, and TG levels among the three groups (P < 0.01). DBil levels exhibited a significant negative correlation with TC (r = -0.777, P < 0.01) and TG (r = -0.397, P < 0.01) levels, while IBil levels exhibited a significant positive correlation with TC (r = 0.790, P < 0.01) and TG (r = 0.302, P < 0.01) levels. The frequencies of abnormal TC, TG, HGB and BUN levels were the lowest in the elevated DBil group, while the levels of these four variables were the highest in the elevated IBil group. Mildly elevated DBil levels were related to lower TG (OR = 0.112, 95% CI = 0.027-0.458) and TC (OR = 0.097, 95% CI = 0.013-0.700), and mildly elevated IBil levels were connected with increased TC (OR = 3.436, 95% CI = 2.398-4.924) and TG (OR = 1.636, 95% CI = 1.163-2.303). DBil was an independent protective factor against increased TC (OR = 0.702, 95% CI = 0.602-0.817, P < 0.01) and TG (OR = 0.632, 95% CI = 0.541-0.739, P < 0.01) levels, and IBil was an independent risk factors for increased TC (OR = 1.251, 95% CI = 1.176-1.331, P < 0.01).

CONCLUSIONS

DBil was an independent protective factor against high TC and TG levels. IBil was an independent risk factors for elevated TC levels. The prognostic value of IBil levels warrants further attention.

A decreased level of high-density lipoprotein is a possible risk factor for type 2 diabetes mellitus: A review

Introduction

Type 2 diabetes mellitus (T2DM) is characterized primarily by dyslipidemia and hyperglycemia due to insulin resistance. High-density lipoprotein (HDL) play a significant role in preventing the incidence of dyslipidemia and its complications. HDL has different protective functions, such as reducing oxidation, vascular inflammation, and thrombosis; additionally, its anti-diabetic role is one of the most significant recent discoveries about HDL and some of its constituent lipoproteins.

Methods

This research reviews ongoing studies and preliminary investigations into the assessment of relation between decreased level of HDL and T2DM.

Results

The levels of HDL and its functions contribute to glucose hemostasis and the development of T2DM through four possible mechanisms, including insulin secretion by beta cells, peripheral insulin sensitivity, non-insulin-dependent glucose uptake, and adipose tissue metabolic activity. Additionally, the anti-oxidant properties of HDL protect beta cells from apoptosis caused by oxidative stress and inflammation induced by low-density lipoprotein, which facilitate insulin secretion.

Conclusion

Therefore, HDL and its compositions, especially Apo A-I, play an important role in regulating glucose metabolism, and decreased levels of HDL can be considered a risk factor for DM. Different factors, such as hypoalphalipoproteinemia that manifests as a consequence of genetic factors, such as Apo A-I deficiency, as well as secondary causes arising from lifestyle choices and underlying medical conditions that decrease the level of HDL, could be associated with DM. Moreover, intricate connections between HDL and diabetic complications extend beyond glucose metabolism to encompass complications like cardiovascular disease and kidney disease. Therefore, the exact interactions between HDL level and DM should be evaluated in future studies.

Regulation of cholesterol homeostasis in osteoporosis mechanisms and therapeutics

Osteoporosis is a metabolic bone disease that affects hundreds of millions of people worldwide and is characterized by excessive loss of bone protein and mineral content. The incidence and mortality of osteoporosis increase with age, creating a significant medical and economic burden globally. The importance of cholesterol levels has been reported in the development of diseases including osteoporosis. It is important to note that key enzymes and molecules involved in cholesterol homeostasis are closely related to bone formation. Excessive cholesterol may cause osteoporosis, cholesterol and its metabolites affect bone homeostasis by regulating the proliferation and stimulation of osteoblasts and osteoclasts. Therefore, antagonism of elevated cholesterol levels may be a potential strategy to prevent osteoporosis. There is sufficient evidence to support the use of bisphosphonates and statin drugs for osteoporosis in the clinic. Therefore, in view of the aggravation of the aging problem, we summarize the intracellular mechanism of cholesterol homeostasis and its relationship with osteoporosis (including cholesterol and cholesterol oxidation products (COPs) in osteoporosis). Furthermore, the current clinical cholesterol-lowering drugs for osteoporosis were also summarized, as are new and promising therapies (cell-based therapies (e.g., stem cells) and biomaterial-delivered target drug therapies for osteoporosis as well).

The Link between Magnesium Supplements and Statin Medication in Dyslipidemic Patients

Many investigations have discovered a connection between statins and magnesium supplements. On one hand, increasing research suggests that chronic hypomagnesemia may be an important factor in the etiology of some metabolic illnesses, including obesity and overweight, insulin resistance and type 2 diabetes mellitus, hypertension, alterations in lipid metabolism, and low-grade inflammation. Chronic metabolic problems seem to be prevented by a high Mg intake combined with diet and/or supplements. On the other hand, it is known that statins lower the frequency of cardiac events, stroke, and mortality, not by lowering LDL-C, but by the capacity to reduce mevalonate formation. That will enhance endothelial function, inhibit vascular smooth muscle cell proliferation and migration and encourage macrophages to promote plaque stability and regression while reducing inflammation. Taking these factors into consideration, we did an extensive analysis of the relevant literature, comparing the effects of Mg² and statin medications on lipoproteins and, implicitly, on the key enzymes involved in cholesterol metabolism.

Fully automated immunoassay for cholesterol uptake capacity to assess high-density lipoprotein function and cardiovascular disease risk

High-density lipoprotein (HDL) cholesterol efflux capacity (CEC), which is a conventional metric of HDL function, has been associated with coronary heart disease risk. However, the CEC assay requires cultured cells and takes several days to perform. We previously established a cell-free assay to evaluate cholesterol uptake capacity (CUC) as a novel measure of HDL functionality and demonstrated its utility in coronary risk stratification. To apply this concept clinically, we developed a rapid and sensitive assay system based on a chemiluminescent magnetic particle immunoassay. The system is fully automated, providing high reproducibility. Measurement of CUC in serum is completed within 20 min per sample without HDL isolation, a notably higher throughput than that of the conventional CEC assay. CUC decreased with myeloperoxidase-mediated oxidation of HDL or in the presence of N-ethylmaleimide, an inhibitor of lecithin: cholesterol acyltransferase (LCAT), whereas CUC was enhanced by the addition of recombinant LCAT. Furthermore, CUC correlated with CEC even after being normalized by ApoA1 concentration and was significantly associated with the requirement for revascularization due to the recurrence of coronary lesions. Therefore, our new assay system shows potential for the accurate measurement of CUC in serum and permits assessing cardiovascular health.

Very low HDL levels: clinical assessment and management

In individuals with very low high-density lipoprotein (HDL-C) cholesterol, such as Tangier disease, LCAT deficiency, and familial hypoalphalipoproteinemia, there is an increased risk of premature atherosclerosis. However, analyzes based on comparisons of populations with small variations in HDL-C mediated by polygenic alterations do not confirm these findings, suggesting that there is an indirect association or heterogeneity in the pathophysiological mechanisms related to the reduction of HDL-C. Trials that evaluated some of the HDL functions demonstrate a more robust degree of association between the HDL system and atherosclerotic risk, but as they were not designed to modify lipoprotein functionality, there is insufficient data to establish a causal relationship. We currently have randomized clinical trials of therapies that increase HDL-C concentration by various mechanisms, and this HDL-C elevation has not independently demonstrated a reduction in the risk of cardiovascular events. Therefore, this evidence shows that (a) measuring HDL-C as a way of estimating HDL-related atheroprotective system function is insufficient and (b) we still do not know how to increase cardiovascular protection with therapies aimed at modifying HDL metabolism. This leads us to a greater effort to understand the mechanisms of molecular action and cellular interaction of HDL, completely abandoning the traditional view focused on the plasma concentration of HDL-C. In this review, we will detail this new understanding and the new horizon for using the HDL system to mitigate residual atherosclerotic risk.

Influence of lecithin cholesterol acyltransferase alteration during different pathophysiologic conditions: A 45 years bibliometrics analysis

Background: Lecithin cholesterol acyltransferase (LCAT) is an important enzyme responsible for free cholesterol (FC) esterification, which is critical for high density lipoprotein (HDL) maturation and the completion of the reverse cholesterol transport (RCT) process. Plasma LCAT activity and concentration showed various patterns under different physiological and pathological conditions. Research on LCAT has grown rapidly over the past 50 years, but there are no bibliometric studies summarizing this field as a whole. This study aimed to use the bibliometric analysis to demonstrate the trends in LCAT publications, thus offering a brief perspective with regard to future developments in this field. Methods: We used the Web of Science Core Collection to retrieve LCAT-related studies published from 1975 to 2020. The data were further analyzed in the number of studies, the journal which published the most LCAT-related studies, co-authorship network, co-country network, co-institute network, co-reference and the keywords burst by CiteSpace V 5.7. Results: 2584 publications contained 55,311 references were used to analyzed. The number of included articles fluctuated in each year. We found that Journal of lipid research published the most LCAT-related studies. Among all the authors who work on LCAT, they tend to collaborate with a relatively stable group of collaborators to generate several major authors clusters which Albers, J. published the most studies (n = 53). The United States of America contributed the greatest proportion (n = 1036) of LCAT-related studies. The LCAT-related studies have been focused on the vascular disease, lecithin-cholesterol acyltransferase reaction, phospholipid, cholesterol efflux, chronic kidney disease, milk fever, nephrotic syndrome, platelet-activating factor acetylhydrolase, reconstituted lpa-i, reverse cholesterol transport. Four main research frontiers in terms of burst strength for LCAT-related studies including "transgenic mice", "oxidative stress", "risk", and "cholesterol metabolism "need more attention. Conclusion: This is the first study that demonstrated the trends and future development in LCAT publications. Further studies should focus on the accurate metabolic process of LCAT dependent or independent of RCT using metabolic marker tracking techniques. It was also well worth to further studying the possibility that LCAT may qualify as a biomarker for risk prediction and clinical treatment.

Developmental changes in proteins of casein micelles in goat milk using data-independent acquisition-based proteomics methods during the lactation cycle

Casein micelles (CM) play an important role in milk secretion, stability, and processing. The composition and content of milk proteins are affected by physiological factors, which have been widely investigated. However, the variation in CM proteins in goat milk throughout the lactation cycle has yet to be fully clarified. In the current study, milk samples were collected at d 1, 3, 30, 90, 150, and 240 of lactation from 15 dairy goats. The size of CM was determined using laser light scattering, and CM proteins were separated, digested, and identified using data-independent acquisition (DIA) and data-dependent acquisition (DDA)-based proteomics approaches. According to clustering and principal component analysis, protein profiles identified using DIA were similar to those identified using the DDA approach. Significant differences in the abundance of 115 proteins during the lactation cycle were identified using the DIA approach. Developmental changes in the CM proteome corresponding to lactation stages were revealed: levels of lecithin cholesterol acyltransferase, folate receptor α, and prominin 2 increased from 1 to 240 d, whereas levels of growth/differentiation factor 8, peptidoglycan-recognition protein, and 45 kDa calcium-binding protein decreased in the same period. In addition, lipoprotein lipase, glycoprotein IIIb, and α-lactalbumin levels increased from 1 to 90 d and then decreased to 240 d, which is consistent with the change in CM size. Protein-protein interaction analysis showed that fibronectin, albumin, and apolipoprotein E interacted more with other proteins at the central node. These findings indicate that changes in the CM proteome during lactation could be related to requirements of newborn development, as well as mammary gland development, and may thus contribute to elucidating the physical and chemical properties of CM.

LCAT- targeted therapies: Progress, failures and future

Lecithin: cholesterol acyltransferase (LCAT) is the only enzyme in plasma which is able to esterify cholesterol and boost cholesterol esterify with phospholipid-derived acyl chains. In order to better understand the progress of LCAT research, it is always inescapable that it is linked to high-density lipoprotein (HDL) metabolism and reverse cholesterol transport (RCT). Because LCAT plays a central role in HDL metabolism and RCT, many animal studies and clinical studies are currently aimed at improving plasma lipid metabolism by increasing LCAT activity in order to find better treatment options for familial LCAT deficiency (FLD), fish eye disease (FED), and cardiovascular disease. Recombinant human LCAT (rhLCAT) injections, cells and gene therapy, and small molecule activators have been carried out with promising results. Recently rhLCAT therapies have entered clinical phase II trials with good prospects. In this review, we discuss the diseases associated with LCAT and therapies that use LCAT as a target hoping to find out whether LCAT can be an effective therapeutic target for coronary heart disease and atherosclerosis. Also, probing the mechanism of action of LCAT may help better understand the heterogeneity of HDL and the action mechanism of dynamic lipoprotein particles.

Defects in a liver-bone axis contribute to hepatic osteodystrophy disease progression

Hepatic osteodystrophy (HOD) is a metabolic bone disease that is often associated with chronic liver disease and is marked by bone loss. Here, we demonstrate that hepatic expression of the phosphatase PP2Acα is upregulated during HOD, leading to the downregulation of expression of the hepatokine lecithin-cholesterol acyltransferase (LCAT). Loss of LCAT function markedly exacerbates the bone loss phenotype of HOD in mice. In addition, we found that alterations in cholesterol levels are involved in the regulation of osteoblast and osteoclast activities. We also found that LCAT improves liver function and relieves liver fibrosis in the mouse HOD model by promoting reversal of cholesterol transport from the bone to the liver. In summary, defects in a liver-bone axis occur during HOD that can be targeted to ameliorate disease progression.

A novel pathogenic variant in LCAT causing FLD. A case report

BACKGROUND

Fish-eye disease (FED) is due to a partial deficiency in LCAT activity. Nevertheless, Familial lecithin-cholesterol acyltransferase deficiency (FLD), also called Norum disease, appears when the deficiency is complete. They are both rare genetic disorders inherited in an autosomal recessive manner. Clinical signs include decreased circulating HDL cholesterol and dense corneal opacity. Kidney injuries also affect patients suffering from FLD. The diagnosis of FLD is based on the presence of characteristic signs and symptoms and confirmed by genetic testing.

CASE PRESENTATION

We present a case of a 63-year-old man showing an altered lipid profile with low HDL cholesterol, chronic kidney disease (CKD) and corneal disorders. He was referred to genetic counseling in order to discard genetic LCAT deficiency due to decreased visual acuity caused by corneal opacity. A massive DNA sequencing was conducted using a multigene panel associated with lipid metabolism disturbances.Results and genetic findings: Two likely pathogenic variants in LCAT were identified and later confirmed by Sanger sequencing. Both (c.491 G > A and c.496 G > A) were missense variants that originated an amino acid substitution (164Arginine for Histidine and 166Alanine for Threonine, respectively) modifying the protein sequence and its 3D structure.

CONCLUSIONS

FLD and FED sharing common biochemical features, and the existence of other diseases with similar clinical profiles underline the need for a timely differential diagnosis aiming to address patients to preventive programs and future available therapies. This case, added to the reduced number of publications previously reported regarding FLD and FED, contributes to better understanding the genetic characteristics, clinical features, and diagnosis of these syndromes.

LCAT deficiency and pregnancy: Case report

Lecithin-cholesterol acyltransferase (LCAT) deficiency is a rare autosomal recessive condition affecting lipid metabolism with a prevalence of less than 1:1,000,000. Described here is the case of a 29-year-old pregnant woman with a diagnosis of LCAT deficiency (c.140G>A in exon 4), who had three episodes of hypertriglyceridemia-induced pancreatitis and nephrotic-range proteinuria throughout the pregnancy. Furthermore, fetal ultrasounds carried out during the second and third trimester revealed a steady reduction in fetal growth rate, and fetal growth restriction (FGR) was diagnosed. The woman underwent an elective caesarean section at 33 weeks of gestation and delivered a healthy neonate. This case report adds knowledge of the natural history of LCAT deficiency during pregnancy and will be useful in future patient management.

Corneal thickness in the case of familial lecithin-cholesterol acyltransferase deficiency

Purpose

We report our findings of a patient with a definitive diagnosis of familial lecithin-cholesterol acyltransferase deficiency (FLD), whose corneal thickness was measured using swept-source optical coherence tomography (OCT) and who underwent an ophthalmologic therapeutic intervention.

Observations

The patient was a 78-year-old Japanese man diagnosed with FLD at the age of 52 years. This was his first ever visit to an ophthalmology clinic. Slit lamp microscopy revealed bilateral diffuse corneal opacities and cataracts, angioid streaks of the retina, and macular atrophy in the fundus. The central corneal thickness, measured with swept-source OCT, was within the normal range in both eyes. Deep lamellar keratoplasty, phacoemulsification, and intraocular lens insertion were performed simultaneously for the left eye. The right eye was treated only using deep lamellar keratoplasty.

Conclusions and importance

As seen in patients with fish-eye disease, the central corneal thickness in this patient with FLD was within the normal range. Since FLD is a rare disease, it is essential to collect and examine further data on corneal thickness.

Lipoprotein Proteomics and Aortic Valve Transcriptomics Identify Biological Pathways Linking Lipoprotein(a) Levels to Aortic Stenosis

Lipoprotein(a) (Lp(a)) is one of the most important risk factors for the development of calcific aortic valve stenosis (CAVS). However, the mechanisms through which Lp(a) causes CAVS are currently unknown. Our objectives were to characterize the Lp(a) proteome and to identify proteins that may be differentially associated with Lp(a) in patients with versus without CAVS. Our second objective was to identify genes that may be differentially regulated by exposure to high versus low Lp(a) levels in explanted aortic valves from patients with CAVS. We isolated Lp(a) from the blood of 21 patients with CAVS and 22 volunteers and performed untargeted label-free analysis of the Lp(a) proteome. We also investigated the transcriptomic signature of calcified aortic valves from patients who underwent aortic valve replacement with high versus low Lp(a) levels (n = 118). Proteins involved in the protein activation cascade, platelet degranulation, leukocyte migration, and response to wounding may be associated with Lp(a) depending on CAVS status. The transcriptomic analysis identified genes involved in cardiac aging, chondrocyte development, and inflammation as potentially influenced by Lp(a). Our multi-omic analyses identified biological pathways through which Lp(a) may cause CAVS, as well as key molecular events that could be triggered by Lp(a) in CAVS development.

LCAT deficiency: a systematic review with the clinical and genetic description of Mexican kindred

BACKGROUND

LCAT (lecithin-cholesterol acyltransferase) deficiency is characterized by two distinct phenotypes, familial LCAT deficiency (FLD) and Fish Eye disease (FED). This is the first systematic review evaluating the ethnic distribution of LCAT deficiency, with particular emphasis on Latin America and the discussion of three Mexican-Mestizo probands.

METHODS

A systematic review was conducted following the PRISMA (Preferred Reporting Items for Systematic review and Meta-Analysis) Statement in Pubmed and SciELO. Articles which described subjects with LCAT deficiency syndromes and an assessment of the ethnic group to which the subject pertained, were included.

RESULTS

The systematic review revealed 215 cases (154 FLD, 41 FED and 20 unclassified) pertaining to 33 ethnic/racial groups. There was no association between genetic alteration and ethnicity. The mean age of diagnosis was 42 ± 16.5 years, with fish eye disease identified later than familial LCAT deficiency (55 ± 13.8 vs. 41 ± 14.7 years respectively). The prevalence of premature coronary heart disease was significantly greater in FED vs. FLD. In Latin America, 48 cases of LCAT deficiency have been published from six countries (Argentina (1 unclassified), Brazil (38 FLD), Chile (1 FLD), Columbia (1 FLD), Ecuador (1 FLD) and Mexico (4 FLD, 1 FED and 1 unclassified). Of the Mexican probands, one showed a novel LCAT mutation.

CONCLUSIONS

The systematic review shows that LCAT deficiency syndromes are clinically and genetically heterogeneous. No association was confirmed between ethnicity and LCAT mutation. There was a significantly greater risk of premature coronary artery disease in fish eye disease compared to familial LCAT deficiency. In FLD, the emphasis should be in preventing both cardiovascular disease and the progression of renal disease, while in FED, cardiovascular risk management should be the priority. The LCAT mutations discussed in this article are the only ones reported in the Mexican- Amerindian population.

A Behavior-Manipulating Virus Relative as a Source of Adaptive Genes for Drosophila Parasitoids

Some species of parasitic wasps have domesticated viral machineries to deliver immunosuppressive factors to their hosts. Up to now, all described cases fall into the Ichneumonoidea superfamily, which only represents around 10% of hymenoptera diversity, raising the question of whether such domestication occurred outside this clade. Furthermore, the biology of the ancestral donor viruses is completely unknown. Since the 1980s, we know that Drosophila parasitoids belonging to the Leptopilina genus, which diverged from the Ichneumonoidea superfamily 225 Ma, do produce immunosuppressive virus-like structure in their reproductive apparatus. However, the viral origin of these structures has been the subject of debate. In this article, we provide genomic and experimental evidence that those structures do derive from an ancestral virus endogenization event. Interestingly, its close relatives induce a behavior manipulation in present-day wasps. Thus, we conclude that virus domestication is more prevalent than previously thought and that behavior manipulation may have been instrumental in the birth of such associations.

The role of high-density lipoprotein cholesterol, apolipoprotein A and paraoxonase-1 in the pathophysiology of neuroprogressive disorders

Lowered high-density lipoprotein (HDL) cholesterol has been reported in major depressive disorder, bipolar disorder, first episode of psychosis, and schizophrenia. HDL, its major apolipoprotein component, ApoA1, and the antioxidant enzyme paraoxonase (PON)1 (which is normally bound to ApoA1) all have anti-atherogenic, antioxidant, anti-inflammatory, and immunomodulatory roles, which are discussed in this paper. The paper details the pathways mediating the anti-inflammatory effects of HDL, ApoA1 and PON1 and describes the mechanisms leading to compromised HDL and PON1 levels and function in an environment of chronic inflammation. The molecular mechanisms by which changes in HDL, ApoA1 and PON1 might contribute to the pathophysiology of the neuroprogressive disorders are explained. Moreover, the anti-inflammatory actions of ApoM-mediated sphingosine 1-phosphate (S1P) signalling are reviewed as well as the deleterious effects of chronic inflammation and oxidative stress on ApoM/S1P signalling. Finally, therapeutic interventions specifically aimed at improving the levels and function of HDL and PON1 while reducing levels of inflammation and oxidative stress are considered. These include the so-called Mediterranean diet, extra virgin olive oil, polyphenols, flavonoids, isoflavones, pomegranate juice, melatonin and the Mediterranean diet combined with the ketogenic diet.

rHDL modeling and the anchoring mechanism of LCAT activation

Lecithin:cholesterol-acyl transferase (LCAT) plays a major role in cholesterol metabolism as it is the only extracellular enzyme able to esterify cholesterol. LCAT activity is required for lipoprotein remodeling and, most specifically, for the growth and maturation of HDLs. In fact, genetic alterations affecting LCAT functionality may cause a severe reduction in plasma levels of HDL-cholesterol with important clinical consequences. Although several hypotheses were formulated, the exact molecular recognition mechanism between LCAT and HDLs is still unknown. We employed a combination of structural bioinformatics procedures to deepen the insights into the HDL-LCAT interplay that promotes LCAT activation and cholesterol esterification. We have generated a data-driven model of reconstituted HDL (rHDL) and studied the dynamics of an assembled rHDL::LCAT supramolecular complex, pinpointing the conformational changes originating from the interaction between LCAT and apolipoprotein A-I (apoA-I) that are necessary for LCAT activation. Specifically, we propose a mechanism in which the anchoring of LCAT lid to apoA-I helices allows the formation of a hydrophobic hood that expands the LCAT active site and shields it from the solvent, allowing the enzyme to process large hydrophobic substrates.

Lipid Keratopathy: A Review of Pathophysiology, Differential Diagnosis, and Management

Lipid keratopathy is a disease in which fat deposits accumulate in the cornea, leading to opacification and decrease of visual acuity. This condition can be idiopathic without signs of previous corneal disease or secondary to ocular or systemic diseases. Lipid keratopathy is usually associated with abnormal vascularization of the cornea, and the lipid classically deposits adjacent to these vessels. Treatment of this condition usually aims to eliminate or prevent abnormal vessel formation, and several modalities have been described. In this review we summarize the etiology, pathophysiology, and clinical presentation of lipid keratopathy and describe current and emerging treatment regimens.

Combined liver-kidney transplantation for rare diseases

Combined liver and kidney transplantation (CLKT) is indicated in patients with failure of both organs, or for the treatment of end-stage chronic kidney disease (ESKD) caused by a genetic defect in the liver. The aim of the present review is to provide the most up-to-date overview of the rare conditions as indications for CLKT. They are major indications for CLKT in children. However, in some of them (e.g., atypical hemolytic uremic syndrome or primary hyperoxaluria), CLKT may be required in adults as well. Primary hyperoxaluria is divided into three types, of which type 1 and 2 lead to ESKD. CLKT has been proven effective in renal function replacement, at the same time preventing recurrence of the disease. Nephronophthisis is associated with liver fibrosis in 5% of cases and these patients are candidates for CLKT. In alpha 1-antitrypsin deficiency, hereditary C3 deficiency, lecithin cholesterol acyltransferase deficiency and glycogen storage diseases, glomerular or tubulointerstitial disease can lead to chronic kidney disease. Liver transplantation as a part of CLKT corrects underlying genetic and consequent metabolic abnormality. In atypical hemolytic uremic syndrome caused by mutations in the genes for factor H, successful CLKT has been reported in a small number of patients. However, for this indication, CLKT has been largely replaced by eculizumab, an anti-C5 antibody. CLKT has been well established to provide immune protection of the transplanted kidney against donor-specific antibodies against class I HLA, facilitating transplantation in a highly sensitized recipient.

Inborn errors of apolipoprotein A-I metabolism: implications for disease, research and development

PURPOSE OF REVIEW

We review current knowledge regarding naturally occurring mutations in the human apolipoprotein A-I (APOA1) gene with a focus on their clinical complications as well as their exploitation for the elucidation of structure-function-(disease) relationships and therapy.

RECENT FINDINGS

Bi-allelic loss-of-function mutations in APOA1 cause HDL deficiency and, in the majority of patients, premature atherosclerotic cardiovascular disease (ASCVD) and corneal opacities. Heterozygous HDL-cholesterol decreasing mutations in APOA1 were associated with increased risk of ASCVD in several but not all studies. Some missense mutations in APOA1 cause familial amyloidosis. Structure-function-reationships underlying the formation of amyloid as well as the manifestion of amyloidosis in specific tissues are better understood. Lessons may also be learnt from the progress in the treatment of amyloidoses induced by transthyretin variants. Infusion of reconstituted HDL (rHDL) containing apoA-I (Milano) did not cause regression of atherosclerosis in coronary arteries of patients with acute coronary syndrome. However, animal experiments indicate that rHDL with apoA-I (Milano) or apoA-I mimetic peptides may be useful for the treatment of heart failure of inflammatory bowel disease.

SUMMARY

Specific mutations in APOA1 are the cause of premature ASCVD or familial amyloidosis. Synthetic mimetics of apoA-I (mutants) may be useful for the treatment of several diseases beyond ASCVD.

Effects of obesity on cholesterol metabolism and its implications for healthy ageing

The last few decades have witnessed a global rise in the number of older individuals. Despite this demographic shift, morbidity within this population group is high. Many factors influence healthspan; however, an obesity pandemic is emerging as a significant determinant of older people's health. It is well established that obesity adversely affects several metabolic systems. However, due to its close association with overall cardiometabolic health, the impact that obesity has on cholesterol metabolism needs to be recognised. The aim of the present review is to critically discuss the effects that obesity has on cholesterol metabolism and to reveal its significance for healthy ageing.

Rare dyslipidaemias, from phenotype to genotype to management: a European Atherosclerosis Society task force consensus statement

Genome sequencing and gene-based therapies appear poised to advance the management of rare lipoprotein disorders and associated dyslipidaemias. However, in practice, underdiagnosis and undertreatment of these disorders are common, in large part due to interindividual variability in the genetic causes and phenotypic presentation of these conditions. To address these challenges, the European Atherosclerosis Society formed a task force to provide practical clinical guidance focusing on patients with extreme concentrations (either low or high) of plasma low-density lipoprotein cholesterol, triglycerides, or high-density lipoprotein cholesterol. The task force also recognises the scarcity of quality information regarding the prevalence and outcomes of these conditions. Collaborative registries are needed to improve health policy for the care of patients with rare dyslipidaemias.

Inherited metabolic disorders and dyslipidaemia

Monogenic dyslipidaemia is a diverse group of multisystem disorders. Patients may present to various specialities from early childhood to late in adult life, and it usually takes longer before the diagnosis is established. Increased awareness of these disorders among clinicians is imperative for early diagnosis. This best practice review provides an overview of primary dyslipidaemias, highlighting their clinical presentation, relevant biochemical and molecular tests. It also addresses the emerging role of genetics in the early diagnosis and prevention of these disorders.

[Inborn errors of high-density lipoprotein metabolism]

Both low and very high levels of high-density lipoprotein cholesterol (HDL-C) increase the risk of atherosclerotic cardiovascular disease (ASCVD) and shorten life expectancy. Low and high levels of HDL‑C are often caused by underlying diseases, lifestyle or medication, which should primarily be excluded. Much less frequently, monogenic diseases due to mutations in the APOA1, ABCA1 and LCAT genes are the cause of very low or unmeasurable HDL‑C levels or in the CETP, LIPC and SCARB1 genes for very high HDL‑C values. Genetic and detailed biochemical diagnostics should be considered, especially in cases of absolute HDL deficiency, early onset ASCVD or the presence of clinical symptoms or laboratory values characteristic for deficiencies of apolipoprotein A‑I (ApoA-I), lecithin cholesterol acyltransferase (LCAT) or Tangier disease. These included corneal opacities, xanthomas, large tonsils, hepatomegaly, peripheral neuropathy, proteinuria, anemia or thrombocytopenia. Sequencing of the APOA1 gene should also be considered in familial amyloidosis. There is no specific treatment for monogenic HDL diseases. Cholesterol and blood pressure lowering are indicated for the prevention of cardiovascular and renal complications.

Lipid Profile Rather Than the LCAT Mutation Explains Renal Disease in Familial LCAT Deficiency

Renal complications are the major cause of morbidity and mortality in patients with familial lecithin–cholesterol acyltransferase (LCAT) deficiency (FLD). We report three FLD patients, two of them siblings—only one of whom developed renal disease—and the third case being a young man with early renal disease. The aim of this study was to analyze the clinical characteristics and possible mechanisms associated with renal disease in these patients. Plasma lipid levels, LCAT activity, lipoprotein particle profile by NMR and FPLC, free and esterified cholesterol, presence of lipoprotein X (LpX) and DNA sequencing in the three FLD patients have been determined. The three cases presented clinical characteristics of FLD, although only one of the siblings developed renal disease, at 45 years of age, while the other patient developed the disease in his youth. Genetic analysis revealed new missense homozygous mutations, p.(Ile202Thr) in both siblings and p.(Arg171Glu) in the other patient. Lipoprotein particle analysis showed that the two patients with renal disease presented higher numbers of small very low-density lipoprotein (VLDL) and a higher concentration of triglycerides in VLDL. This study reports three new cases of LCAT deficiency, not previously described. Renal disease is not only dependent on LCAT deficiency, and could be due to the presence of VLDL particles, which are rich in triglycerides, free cholesterol and LpX.

Schnyder corneal dystrophy-associated UBIAD1 mutations cause corneal cholesterol accumulation by stabilizing HMG-CoA reductase

Schnyder corneal dystrophy (SCD) is a rare genetic eye disease characterized by corneal opacification resulted from deposition of excess free cholesterol. UbiA prenyltransferase domain-containing protein-1 (UBIAD1) is an enzyme catalyzing biosynthesis of coenzyme Q10 and vitamin K₂. More than 20 UBIAD1 mutations have been found to associate with human SCD. How these mutants contribute to SCD development is not fully understood. Here, we identified HMGCR as a binding partner of UBIAD1 using mass spectrometry. In contrast to the Golgi localization of wild-type UBIAD1, SCD-associated mutants mainly resided in the endoplasmic reticulum (ER) and competed with Insig-1 for HMGCR binding, thereby preventing HMGCR from degradation and increasing cholesterol biosynthesis. The heterozygous Ubiad1 G184R knock-in (Ubiad1^G184R/+) mice expressed elevated levels of HMGCR protein in various tissues. The aged Ubiad1^G184R/+ mice exhibited corneal opacification and free cholesterol accumulation, phenocopying clinical manifestations of SCD patients. In summary, these results demonstrate that SCD-associated mutations of UBIAD1 impair its ER-to-Golgi transportation and enhance its interaction with HMGCR. The stabilization of HMGCR by UBIAD1 increases cholesterol biosynthesis and eventually causes cholesterol accumulation in the cornea.

Schnyder corneal dystrophy (SCD) is a rare genetic eye disease caused by deposition of free cholesterol in the cornea. It is closely correlated with mutations in the UbiA prenyltransferase domain-containing protein-1 (UBIAD1) gene, which encodes an enzyme catalyzing biosynthesis of coenzyme Q10 and vitamin K₂. The underlying mechanism by which UBIAD1 mutations result in SCD development is unclear. Here, we report that SCD-associated mutations trap UBIAD1 in the ER and block Insig-1 mediated HMGCR degradation. We also generated a heterozygous mouse model (Ubiad1^G184R/+) that mimics human SCD. We conclude that SCD-associated UBIAD1 mutations decrease HMGCR degradation and subsequently increase cholesterol biosynthesis in the cornea.

Identification and functional analysis of missense mutations in the lecithin cholesterol acyltransferase gene in a Chilean patient with hypoalphalipoproteinemia

Background

Lecithin-cholesterol acyltransferase (LCAT) is a plasma enzyme that esterifies cholesterol in high- and low-density lipoproteins (HDL and LDL). Mutations in LCAT gene causes familial LCAT deficiency, which is characterized by very low plasma HDL-cholesterol levels (Hypoalphalipoproteinemia), corneal opacity and anemia, among other lipid-related traits. Our aim is to evaluate clinical/biochemical features of a Chilean family with a proband showing clinical signs of familial LCAT deficiency, as well as to identify and assess the functional effects of LCAT mutations.

Methods

An adult female proband with hypoalphalipoproteinemia, corneal opacity and mild anemia, as well as her first-degree relatives, were recruited for clinical, biochemical, genetic, in-silico and in-vitro LCAT analysis. Sequencing of exons and intron-exon boundaries was performed to identify mutations. Site-directed mutagenesis was carried out to generate plasmids containing cDNA with wild type or mutant sequences. Such expression vectors were transfected to HEK-239 T cells to asses the effect of LCAT variants in expression, synthesis, secretion and enzyme activity. In-silico prediction analysis and molecular modeling was also used to evaluate the effect of LCAT variants.

Results

LCAT sequencing identified rare p.V333 M and p.M404 V missense mutations in compound heterozygous state in the proband, as well the common synonymous p.L363 L variant. LCAT protein was detected in proband’s plasma, but with undetectable enzyme activity compared to control relatives. HEK-293 T transfected cells with vector expression plasmids containing either p.M404 V or p.V333 M cDNA showed detectable LCAT protein expression both in supernatants and lysates from cultured cells, but with much lower enzyme activity compared to cells transfected with the wild-type sequence. Bioinformatic analyses also supported a causal role of such rare variations in LCAT lack of function. Additionally, the proband carried the minor allele of the synonymous p.L363 L variant. However, this variant is unlikely to affect the clinical phenotype of the proband given its relatively high frequency in the Chilean population (4%) and its small putative effect on plasma HDL-cholesterol levels.

Conclusion

Genetic, biochemical, in vitro and in silico analyses indicate that the rare mutations p.M404 V and p.V333 M in LCAT gene lead to suppression of LCAT enzyme activity and cause clinical features of familial LCAT deficiency.

Electronic supplementary material

The online version of this article (10.1186/s12944-019-1045-0) contains supplementary material, which is available to authorized users.

The role of ghrelin and tumor necrosis factor alpha in diazinon-induced dyslipidemia: insights into energy balance regulation

The evidence shows that organophosphate compounds (OPCs), as toxic agents that stimulate the cholinergic system, can increase the incidence of metabolic disorders such as dyslipidemia. In the present study, we focused on the role of tumor necrosis factor alpha (TNF-α) and serum leptin and ghrelin in Diazinon (DZN)-induced dyslipidemia. The rats were randomly divided into five groups comprising eight animals, and all were treated via oral gavage for 28 consecutive days as follows: group one received only corn oil daily, while groups two through five received different doses of DZN dissolved in corn oil equal to 1/40, 1/20, 1/10 and 1/5 of the LD50 daily, respectively. The alteration of the serum lipid profile, such as triglycerides, high-density lipoprotein (HDL) and very-low-density lipoprotein (VLDL), was confirmed the occurrence of dyslipidemia in the range of doses 1/20-1/5 LD50 of DZN. Although no changes were found in the serum leptin levels, a significant increase was observed in the size of adipocytes, as well as in the TNF-α and ghrelin serum levels, and in the accumulation of epididymal fat, especially at a dose of 1/5 LD50 of DZN. It seems that interactions among the inflammatory reaction, cholinergic pathways and ghrelin secretion may be effective causes of DZN-induced dyslipidemia.

The P274S Mutation of Lecithin-Cholesterol Acyltransferase (LCAT) and Its Clinical Manifestations in a Large Kindred

RATIONALE & OBJECTIVE

Lecithin-cholesterol acyltransferase (LCAT) catalyzes the maturation of high-density lipoprotein. Homozygosity for loss-of-function mutations causes familial LCAT deficiency (FLD), characterized by corneal opacities, anemia, and renal involvement. This study sought to characterize kidney biopsy findings and clinical outcomes in a family with FLD.

STUDY DESIGN

Prospective observational study.

SETTING & PARTICIPANTS

2 (related) index patients with clinically apparent FLD were initially identified. 110 of 122 family members who consented to genetic analysis were also studied.

PREDICTORS

Demographic and laboratory parameters (including lipid profiles and LCAT activity) and full sequence analysis of the LCAT gene. Kidney histologic examination was performed with samples from 6 participants.

OUTCOMES

Cardiovascular and renal events during a median follow-up of 12 years. Estimation of annual rate of decline in glomerular filtration rate.

ANALYTICAL APPROACH

Analysis of variance, linear regression analysis, and Fine-Gray competing-risk survival analysis.

RESULTS

9 homozygous, 57 heterozygous, and 44 unaffected family members were identified. In all affected individuals, full sequence analysis of the LCAT gene revealed a mutation (c.820C>T) predicted to cause a proline to serine substitution at amino acid 274 (P274S). Homozygosity caused a complete loss of LCAT activity. Kidney biopsy findings demonstrated lipid deposition causing glomerular basement membrane thickening, mesangial expansion, and "foam-cell" infiltration of kidney tissue. Tubular atrophy, glomerular sclerosis, and complement fixation were associated with worse kidney outcomes. Estimated glomerular filtration rate deteriorated among homozygous family members at an average annual rate of 3.56 mL/min/1.73 m². The incidence of cardiovascular and renal complications was higher among homozygous family members compared with heterozygous and unaffected members. Mild thrombocytopenia was a common finding among homozygous participants.

LIMITATIONS

The presence of cardiovascular disease was mainly based on medical history.

CONCLUSIONS

The P274S LCAT mutation was found to cause FLD with renal involvement. Tubular atrophy, glomerular sclerosis, and complement fixation were associated with a worse renal prognosis.

Lipoprotein metabolism in liver diseases

PURPOSE OF REVIEW

The liver is the central hub of lipoprotein metabolism. A complex relationship exists between dyslipidemia and chronic liver diseases (CLDs). Recent advances in the genetics of nonalcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) exemplify the pivotal role of lipoprotein metabolism in the pathogenesis of CLD. We review these relationships in four quintessential forms of CLD: NAFLD, ALD, cholestatic liver disease and cirrhosis, with a focus on recent discoveries.

RECENT FINDINGS

An I148 M variant in patatin-like phospholipase domain-containing protein 3 (PNPLA3) and an E167K variant in transmembrane 6 superfamily 2 (TM6SF2) are major genetic risk factors for the development and progression of NAFLD. These genetic variants also increase the risk of ALD. Both PNPLA3 and TM6SF2 are involved in the hepatic assembly of very low-density lipoprotein. The discovery of these two genetic variants highlights the risk of CLD when environmental factors are combined with functional modifications in the lipoprotein metabolism pathway.

SUMMARY

The relationship between CLD and lipoprotein metabolism is reciprocal. On the one hand, the progression of CLD impairs lipoprotein metabolism; on the other hand, modifications in lipoprotein metabolism can substantially increase the risk of CLD. These relationships are at play among the most common forms of CLD affecting a significant proportion of the population.

A proteomic approach to identify novel disease biomarkers in LCAT deficiency

Genetic LCAT deficiency is a rare recessive autosomal disease due to loss-of-function mutations in the gene coding for the enzyme lecithin:cholesterol acyltransferase (LCAT). Homozygous carriers are characterized by corneal opacity, haemolytic anaemia and renal disease, which represent the first cause of morbidity and mortality in these subjects. Diagnostic and prognostic markers capable of early detecting declining kidney function in these subjects are not available, and the specific serum or urine proteomic signature of LCAT deficient carriers has never been assessed. Taking advantage of a proteomic approach, we performed 2-DE analysis of carriers' plasma and identified proteins present at different concentration in samples from homozygous carriers. Our data confirm the well-known alterations in the concentration of circulating apolipoproteins, with a statistically significant decrease of both apoA-I and apoA-II and a statistically significant increase of apoC-III. Furthermore, we observed increased level of alpha-1-antitrypsin, zinc-alpha-2-glycoprotein and retinol-binding protein 4, and reduced level of clusterin and haptoglobin. Interestingly, only beta but not alpha subunit of haptoglobin is significant reduced in homozygous subjects. Despite the limited sample size, our findings set the basis for assessing the identified protein in a larger population and for correlating their levels with clinical markers of renal function and anaemia. SIGNIFICANCE: This investigation defines the effects of LCAT deficiency on the level of the major plasma proteins in homozygous and heterozygous carriers. Increase for some proteins, with different function, together with a drop for haptoglobin, and specifically for haptoglobin beta chains, are reported for the first time as part of a coherent signature. We are glad to have the opportunity to report our findings on this subject, which is one of the main interests for our research group, when Journal of Proteomics celebrates its 10th anniversary. With its various sections devoted to different areas of research, this journal is a privileged forum for publishing proteomic investigations without restrictions either in sample type or in technical approach. It is as well a privileged forum for reviewing literature data on various topics related to proteomics investigation, as colleagues in our research group have done over the years; by the way, a good share of the reviewed papers were as well reports published in Journal of Proteomics itself. The journal also offers opportunities for focused surveys through thematic issues devoted to a variety of subjects, timely selected for their current relevance in research; it was an honour for colleagues in our group to recently act as editors of one of those. Out of this diverse experience, we express our appreciation for the endeavour of Journal of Proteomics in its first 10 years of life - and wish identical and possibly greater success for the time to come.

Identification of Secreted Proteins Involved in Nonspecific dsRNA-Mediated Lutzomyia longipalpis LL5 Cell Antiviral Response

Hematophagous insects transmit infectious diseases. Sand flies are vectors of leishmaniasis, but can also transmit viruses. We have been studying immune responses of Lutzomyia longipalpis, the main vector of visceral leishmaniasis in the Americas. We identified a non-specific antiviral response in L. longipalpis LL5 embryonic cells when treated with non-specific double-stranded RNAs (dsRNAs). This response is reminiscent of interferon response in mammals. We are investigating putative effectors for this antiviral response. Secreted molecules have been implicated in immune responses, including interferon-related responses. We conducted a mass spectrometry analysis of conditioned medium from LL5 cells 24 and 48 h after dsRNA or mock treatment. We identified 304 proteins. At 24 h, 19 proteins had an abundance equal or greater than 2-fold change, while the levels of 17 proteins were reduced when compared to control cells. At the 48 h time point, these numbers were 33 and 71, respectively. The two most abundant secreted peptides at 24 h in the dsRNA-transfected group were phospholipid scramblase, an interferon-inducible protein that mediates antiviral activity, and forskolin-binding protein (FKBP), a member of the immunophilin family, which mediates the effect of immunosuppressive drugs. The transcription profile of most candidates did not follow the pattern of secreted protein abundance.

The Interplay Between Cholesterol Metabolism and Intrinsic Ageing

The last few decades have witnessed remarkable progress in our understanding of ageing. From an evolutionary standpoint it is generally accepted that ageing is a non-adaptive process which is underscored by a decrease in the force of natural selection with time. From a mechanistic perspective ageing is characterized by a wide variety of cellular mechanisms, including processes such as cellular senescence, telomere attrition, oxidative damage, molecular chaperone activity, and the regulation of biochemical pathways by sirtuins. These biological findings have been accompanied by an unrelenting rise in both life expectancy and the number of older people globally. However, despite age being recognized demographically as a risk factor for healthspan, the processes associated with ageing are routinely overlooked in disease mechanisms. Thus, a central goal of biogerontology is to understand how diseases such as cardiovascular disease (CVD) are shaped by ageing. This challenge cannot be ignored because CVD is the main cause of morbidity in older people. A worthwhile way to examine how ageing intersects with CVD is to consider the effects ageing has on cholesterol metabolism, because dysregualted cholesterol metabolism is the key factor which underpins the pathology of CVD. The aim of this chapter is to outline a hypothesis which accounts for how ageing intersects with intracellular cholesterol metabolism. Moreover, we discuss the implications of this relationship for the onset of disease in the 'oldest old' (individuals ≥85 years of age). We conclude the chapter by discussing the important role mathematical modelling has to play in improving our understanding of cholesterol metabolism and ageing.

Dyslipidemia: Genetics, lipoprotein lipase and HindIII polymorphism

The direct link between lipid metabolism alterations and the increase of cardiovascular risk are well documented. Dyslipidemias, including isolated high LDL-c or mixed dyslipidemia, such as those seen in diabetes (hypertriglyceridemia, high LDL-c or low HDL-c), correlate with a significant risk of cardiovascular and cerebrovascular disease worldwide.  This review analyzes the current knowledge concerning the genetic basis of lipid metabolism alterations, emphasizing lipoprotein lipase gene mutations and the HindIII polymorphism, which are associated with decreased levels of triglycerides and LDL-c, as well as higher levels of HDL-c. These patterns would be associated with decreased global morbidity and mortality, providing protection against cardiovascular and cerebrovascular diseases.

Dyslipidemia: Genetics, lipoprotein lipase and HindIII polymorphism

The direct link between lipid metabolism alterations and the increase of cardiovascular risk are well documented. Dyslipidemias, including isolated high LDL-c or mixed dyslipidemia, such as those seen in diabetes (hypertriglyceridemia, high LDL-c or low HDL-c), correlate with a significant risk of cardiovascular and cerebrovascular disease worldwide.  This review analyzes the current knowledge concerning the genetic basis of lipid metabolism alterations, emphasizing lipoprotein lipase gene mutations and the HindIII polymorphism, which are associated with decreased levels of triglycerides and LDL-c, as well as higher levels of HDL-c. These patterns would be associated with decreased global morbidity and mortality, providing protection against cardiovascular and cerebrovascular diseases.

A novel homozygous mutation causing lecithin-cholesterol acyltransferase deficiency in a proband of Romanian origin with a record of extreme gestational hyperlipidemia

A patient from Romania with extraordinarily high total cholesterol levels and clinical and biochemical features consistent with familial lecithin-cholesterol acyltransferase deficiency is reported. The genetic analysis performed on our proband showed a novel homozygous mutation on codon 119 of lecithin-cholesterol acyltransferase gene that causes the substitution of glycine by aspartate. The same mutation, also in homozygosis, was observed in her older sister, whereas his brother presented it in heterozygosis.

HDL Cholesterol, LDL Cholesterol, and Triglycerides as Risk Factors for CKD: A Mendelian Randomization Study

BACKGROUND

High-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, and triglyceride concentrations are heritable risk factors for vascular disease, but their role in the progression of chronic kidney disease (CKD) is unclear.

STUDY DESIGN

2-sample Mendelian randomization analysis of data derived from the largest published lipid and CKD studies.

SETTING & PARTICIPANTS

Effect of independent genetic variants significantly associated with lipid concentrations was obtained from the Global Lipids Genetics Consortium (n=188,577), and the effect of these same variants on estimated glomerular filtration rate (eGFR), CKD (defined as eGFR<60mL/min/1.73m²), and albuminuria was obtained from the CKD Genetics Consortium (n=133,814).

FACTOR

Using conventional, multivariable, and Egger Mendelian randomization approaches, we assessed the causal association between genetically determined lipid concentrations and kidney traits.

OUTCOME

eGFR, dichotomous eGFR<60mL/min/1.73m², and albuminuria.

RESULTS

In multivariable analysis, a 17-mg/dL higher HDL cholesterol concentration was associated with an 0.8% higher eGFR (95% CI, 0.4%-1.3%; P=0.004) and lower risk for eGFR<60mL/min/1.73m² (OR, 0.85; 95% CI, 0.77-0.93; P<0.001), while Egger analysis showed no evidence of pleiotropy. There was no evidence for a causal relationship between LDL cholesterol concentration and any kidney disease measure. Genetically higher triglyceride concentrations appeared associated with higher eGFRs, but this finding was driven by a single pleiotropic variant in the glucokinase regulator gene (GCKR). After exclusion, genetically higher triglyceride concentration was not associated with any kidney trait.

LIMITATIONS

Individual patient-level phenotype and genotype information were unavailable.

CONCLUSIONS

2-sample Mendelian randomization analysis of data from the largest lipid and CKD cohorts supports genetically higher HDL cholesterol concentration as causally associated with better kidney function. There was no association between genetically altered LDL cholesterol or triglyceride concentration and kidney function. Further analysis of CKD outcomes in HDL cholesterol intervention trials is warranted.

The renal phenotype of allopurinol-treated HPRT-deficient mouse

Excess of uric acid is mainly treated with xanthine oxidase (XO) inhibitors, also called uricostatics because they block the conversion of hypoxanthine and xanthine into urate. Normally, accumulation of upstream metabolites is prevented by the hypoxanthine-guanine phosphoribosyltransferase (HPRT) enzyme. The recycling pathway, however, is impaired in the presence of HPRT deficiency, as observed in Lesch-Nyhan disease. To gain insights into the consequences of purine accumulation with HPRT deficiency, we investigated the effects of the XO inhibitor allopurinol in Hprt-lacking (HPRT^-/-) mice. Allopurinol was administered in the drinking water of E12-E14 pregnant mothers at dosages of 150 or 75 μg/ml, and mice sacrificed after weaning. The drug was well tolerated by wild-type animals and heterozygous HPRT^+/- mice. Instead, a profound alteration of the renal function was observed in the HPRT^-/- model. Increased hypoxanthine and xanthine concentrations were found in the blood. The kidneys showed a yellowish appearance, diffuse interstitial nephritis, with dilated tubules, inflammatory and fibrotic changes of the interstitium. There were numerous xanthine tubular crystals, as determined by HPLC analysis. Oil red O staining demonstrated lipid accumulation in the same location of xanthine deposits. mRNA analysis showed increased expression of adipogenesis-related molecules as well as profibrotic and proinflammatory pathways. Immunostaining showed numerous monocyte-macrophages and overexpression of alpha-smooth muscle actin in the tubulointerstitium. In vitro, addition of xanthine to tubular cells caused diffuse oil red O positivity and modification of the cell phenotype, with loss of epithelial features and appearance of mesenchymal characteristics, similarly to what was observed in vivo. Our results indicate that in the absence of HPRT, blockade of XO by allopurinol causes rapidly developing renal failure due to xanthine deposition within the mouse kidney. Xanthine seems to be directly involved in promoting lipid accumulation and subsequent phenotype changes of tubular cells, with activation of inflammation and fibrosis.

A case of acquired lecithin:cholesterol acyltransferase deficiency with sarcoidosis that remitted spontaneously

Familial lecithin:cholesterol acyltransferase (LCAT) deficiency is a rare inherited disorder that causes an extremely low high-density lipoprotein cholesterol concentration in serum. Recently, acquired LCAT deficiency caused by IgG antibodies to LCAT, without any LCAT gene mutation, was reported. Here we describe a case of acquired LCAT deficiency occurring in association with sarcoidosis. The patient was a Japanese female aged 70 years, had no mutation in the LCAT gene exon sequence, but had an LCAT inhibitor factor in her serum, detected using lipoprotein-deficient serum. She was diagnosed with acquired LCAT deficiency. Her abnormalities of serum lipoproteins improved spontaneously during three and a half years. Because they require different treatment strategies, distinction between familial lecithin:cholesterol acyltransferase deficiency (FLD) and acquired LCAT deficiency by gene sequencing is warranted, especially in cases without corneal clouding.

A Systematic Investigation of Structure/Function Requirements for the Apolipoprotein A-I/Lecithin Cholesterol Acyltransferase Interaction Loop of High-density Lipoprotein

The interaction of lecithin-cholesterol acyltransferase (LCAT) with apolipoprotein A-I (apoA-I) plays a critical role in high-density lipoprotein (HDL) maturation. We previously identified a highly solvent-exposed apoA-I loop domain (Leu(159)-Leu(170)) in nascent HDL, the so-called "solar flare" (SF) region, and proposed that it serves as an LCAT docking site (Wu, Z., Wagner, M. A., Zheng, L., Parks, J. S., Shy, J. M., 3rd, Smith, J. D., Gogonea, V., and Hazen, S. L. (2007) Nat. Struct. Mol. Biol. 14, 861-868). The stability and role of the SF domain of apoA-I in supporting HDL binding and activation of LCAT are debated. Here we show by site-directed mutagenesis that multiple residues within the SF region (Pro(165), Tyr(166), Ser(167), and Asp(168)) of apoA-I are critical for both LCAT binding to HDL and LCAT catalytic efficiency. The critical role for possible hydrogen bond interaction at apoA-I Tyr(166) was further supported using reconstituted HDL generated from apoA-I mutants (Tyr(166) → Glu or Asn), which showed preservation in both LCAT binding affinity and catalytic efficiency. Moreover, the in vivo functional significance of NO2-Tyr(166)-apoA-I, a specific post-translational modification on apoA-I that is abundant within human atherosclerotic plaque, was further investigated by using the recombinant protein generated from E. coli containing a mutated orthogonal tRNA synthetase/tRNACUA pair enabling site-specific insertion of the unnatural amino acid into apoA-I. NO2-Tyr(166)-apoA-I, after subcutaneous injection into hLCAT(Tg/Tg), apoA-I(-/-) mice, showed impaired LCAT activation in vivo, with significant reduction in HDL cholesteryl ester formation. The present results thus identify multiple structural features within the solvent-exposed SF region of apoA-I of nascent HDL essential for optimal LCAT binding and catalytic efficiency.

Structural Insights into High Density Lipoprotein: Old Models and New Facts

The physiological link between circulating high density lipoprotein (HDL) levels and cardiovascular disease is well-documented, albeit its intricacies are not well-understood. An improved appreciation of HDL function and overall role in vascular health and disease requires at its foundation a better understanding of the lipoprotein's molecular structure, its formation, and its process of maturation through interactions with various plasma enzymes and cell receptors that intervene along the pathway of reverse cholesterol transport. This review focuses on summarizing recent developments in the field of lipid free apoA-I and HDL structure, with emphasis on new insights revealed by newly published nascent and spherical HDL models constructed by combining low resolution structures obtained from small angle neutron scattering (SANS) with contrast variation and geometrical constraints derived from hydrogen-deuterium exchange (HDX), crosslinking mass spectrometry, electron microscopy, Förster resonance energy transfer, and electron spin resonance. Recently published low resolution structures of nascent and spherical HDL obtained from SANS with contrast variation and isotopic labeling of apolipoprotein A-I (apoA-I) will be critically reviewed and discussed in terms of how they accommodate existing biophysical structural data from alternative approaches. The new low resolution structures revealed and also provided some answers to long standing questions concerning lipid organization and particle maturation of lipoproteins. The review will discuss the merits of newly proposed SANS based all atom models for nascent and spherical HDL, and compare them with accepted models. Finally, naturally occurring and bioengineered mutations in apoA-I, and their impact on HDL phenotype, are reviewed and discuss together with new therapeutics employed for restoring HDL function.