Lipoprotein glomerulopathy. Report of a normolipidemic case and review of the literature

Clinicopathological characteristics and gene mutations in 11 patients with lipoprotein glomerulopathy

OBJECTIVE

Lipoprotein glomerulopathy (LPG) is a rare disorder characterized by the development of glomerular lipoprotein thrombosis. LPG exhibits familial aggregation, with mutations in the apolipoprotein E (APOE) gene identified as the leading cause of this disease. This study aimed to investigate APOE gene mutations and the clinicopathological features in eleven LPG patients.

METHODS

Clinicopathological and follow-up data were obtained by extracting DNA, followed by APOE coding region sequencing analysis. This study analyzed clinical and pathological manifestations, gene mutations, treatment and prognosis.

RESULTS

The mean age of the eleven patients was 33.82 years. Among them, five had a positive family history for LPG, ten presented with proteinuria, four exhibited nephrotic syndrome, and six presented with microscopic hematuria. Dyslipidemia was identified in ten patients. In all renal specimens, there was evident dilation of glomerular capillary lumens containing lipoprotein thrombi, and positive oil red O staining was observed in frozen sections of all samples. APOE gene testing revealed that one patient had no mutations, while the remaining ten patients exhibited mutations in the APOE gene, with three patients presenting with multiple mutations simultaneously. Following the confirmation of LPG diagnosis, treatment with angiotensin-converting enzyme inhibitor (ACEI)/angiotensin receptor blocker (ARB) was initiated, and the disease progressed slowly.

CONCLUSION

LPG is histologically characterized by lamellated lipoprotein thrombi in glomeruli, and kidney biopsy is essential for diagnosis. Mutations in the APOE gene are the leading cause of LPG. This study revealed clinicopathological characteristics and APOE gene mutations in patients with LPG, which helps us better understand the disease.

Lipoprotein Glomerulopathy With Complete Resolution With Fenofibrate: Report of First Case From Pakistan

Background: Lipoprotein glomerulopathy is an infrequent glomerular disorder that culminates in nephrotic syndrome and often progresses to kidney failure. Whereas most patients have been reported in Japan and China, limited reports have been documented outside these regions. This patient represents the first report of lipoprotein glomerulopathy in Pakistan. Case Presentation: A 25-year-old male patient, hypertensive for 2 years, presented with progressive body edema, frothy urine, and fatigue. Examination revealed elevated blood pressure, bilateral pedal edema, and positive shifting dullness. Laboratory results showed significant proteinuria and elevated cholesterol and triglyceride levels. Renal biopsy revealed enlarged glomeruli with a dilated capillary lumen filled with pale-staining mesh-like material "lipoprotein thrombi." Mild tubular atrophy and interstitial inflammation were observed. No interstitial fibrosis was evident. Electron microscopy detailed the lipoprotein thrombi with lipid granules and vacuoles of various sizes. A diagnosis of lipoprotein glomerulopathy was rendered. Treatment with fenofibrate, rosuvastatin, and captopril led to notable improvements in symptoms, blood pressure, and lipid levels during a 6-month follow-up. Subsequent biopsy showed complete resolution of the lipoprotein thrombi and a significant reduction in subendothelial granular densities. However, the flocculent subendothelial material persisted to some extent despite the complete resolution of lipoprotein thrombi. Conclusion: This report underscores the rarity of lipoprotein glomerulopathy in Pakistan and contributes valuable insights into its histopathologic features and global epidemiology. This unique instance aims to raise awareness among healthcare professionals, aiding in improved recognition of this rare entity. The favorable response to fenofibrate treatment underscores its effectiveness in managing lipoprotein glomerulopathy.

The Association between Apolipoprotein E Genotypes and Serum Malondialdehyde Level with End-Stage Renal Disease

Background

The Apolipoprotein E (ApoE) polymorphism plays an important role in the pathophysiology of end-stage renal disease (ESRD). Additionally, ApoE may contribute to the progression of oxidative stress. Thus, this study aimed to determine the ApoE gene polymorphism and evaluate the malondialdehyde (MDA) level in ESRD patients and healthy individuals.

Methods

The present cross-sectional study was conducted at 2010 at Kermanshah University of Medical Sciences (Kermanshah, Iran). The study population comprised ESRD patients (n=136) and healthy individuals (n=137). The MDA level was assessed using high-performance liquid chromatography (HPLC), and the frequencies of ApoE gene alleles were analyzed using restriction fragment length polymorphism-polymerase chain reaction (RFLP-PCR). The data were analyzed using Statistical Package for Social Sciences (SPSS), version 13. The significant differences of ApoE genotypes in case and control groups were assessed using Pearson's Chi square tests, and two-tailed Student's tests. A logistic regression model was used to calculate the odd ratio. P<0.05 was considered statistically significant.

Results

According to the results, ESRD patients had a higher frequency of the E2/E3 genotype than the healthy group (P<0.001). The results indicated that E3/E4 genotype frequency in the patients' group was higher than that of the control group (P=0.026). Furthermore, the E3/E2 (OR=5.7, 95% CI=2.68-12.14) (P<0.001) and E3/E4 (OR=1.57, 95% CI=1.05-2.34) (P=0.029) genotypes were found to increase the risk of ESRD. Moreover, the MDA level in ESRD patients was higher than the healthy individuals (P<0.001). The patients with E3/E2 (P<0.001) and E3/E4 (P<0.001) genotypes had a higher level of MDA than the control group.

Conclusion

According to the findings, patients with ESRD had higher genotypes of E3/E2 and E3/E4, which suggests a higher risk of developing ESRD.

Case Report: A Pediatric Case of Lipoprotein Glomerulopathy in China and Literature Review

Background: Lipoprotein glomerulopathy is a rare kidney disease characterized by lipoprotein thrombi in the glomerulus. Here, we report a case of lipoprotein glomerulopathy in a Chinese pediatric patient. Furthermore, we summarized the clinical features and genetic characteristics of lipoprotein glomerulopathy in China. Case Presentation: An 11-year-old Chinese girl presented with nephrotic syndrome with anemia (98 g/L). After excluding secondary causes, primary nephrotic syndrome was considered. Treatment with prednisone (60 mg/day) did not improve her condition. Renal biopsy showed marked dilation of the capillary lumen with lipoprotein thrombi and positive oil red O staining. Genetic testing revealed the genetic variant c.127C > T (p.R43C), known as the Kyoto mutation of the APOE gene. These findings are consistent with the diagnosis of lipoprotein glomerulopathy. Prednisone was gradually tapered and captopril was initiated. A 2-year follow-up revealed elevated urine protein and serum creatinine levels. We also reviewed 17 pediatric and 156 adult cases of lipoprotein glomerulopathy reported in China from the year of creation to 2021. The most common clinical features were edema, hematuria, hypertriglyceridemia, and increased serum apoE levels. Extra-renal manifestations included anemia, splenomegaly, and cardiac lipoprotein deposition. Conclusion: APOE Kyoto is the most common mutation in patients with lipoprotein glomerulopathy. In China, homozygosity for E3 (E3/3) is the most common isoform.

Apolipoprotein E-related glomerular disorders

Of the glomerular disorders that occur due to apolipoprotein E (apoE) mutations, apoE2 homozygote glomerulopathy and lipoprotein glomerulopathy (LPG) have been characterized. ApoE2 homozygote glomerulopathy has been found in individuals expressing homozygous apoE2/2. This was characterized histologically by glomerulosclerosis with marked infiltration of foam cells derived from macrophages, and occasionally with non-lamellated lipoprotein thrombi. Recently, several cases of apoE Toyonaka (Ser197Cys) combined with homozygous apoE2/2 have been reported, in which non-immune membranous nephropathy-like features were observed in glomeruli. Interestingly, in these cases, apoE accumulation was identified by tandem mass spectrometry. Therefore, it is speculated that these findings may arise from apoE molecules without lipids, which result from hinge damage by apoE Toyonaka and may cross the glomerular basement membrane as small molecules. LPG is primarily associated with heterozygous apoE mutations surrounding the low-density lipoprotein-receptor binding site, and it is histologically characterized by lamellated lipoprotein thrombi that lack foam cells. Recent studies have suggested that LPG can be induced by thermodynamic destabilization, hydrophobic surface exposure, and the aggregation of apoE resulting from the incompatibility of apoE mutated residues within helical regions. Additionally, apoE5 may play a supporting role in the development of LPG and in lipid-induced kidney diseases via hyperlipoproteinemia. Thus, it is interesting that many apoE mutations contribute to characteristic glomerular disorders through various mechanisms. In particular, macrophages may uptake lipoproteins into the cytoplasm and contribute to the development of apoE2 homozygote glomerulopathy as foam cells, and their dysfunction may contribute to the accumulation of lipoproteins in the glomerulus, causing lipoprotein thrombi in LPG.

A young Chinese man with nephrotic syndrome due to lipoprotein glomerulopathy

Lipoprotein glomerulopathy (LPG) is a rare autosomal dominant renal disease with incomplete penetrance, associated with specific protein-modifying mutations in the APOE gene. LPG is associated with poor renal prognosis, in which lipoprotein thrombi are seen in the glomerular capillaries. Dyslipidemia in LPG generally resembles type III hyperlipoproteinemia with elevated serum apolipoprotein E level. Fibrate is the most frequently reported lipid-lowering therapy in LPG as hypertriglyceridemia is common in these individuals. There are few existing case reports on effectiveness of statin monotherapy for LPG. We report a 32-year-old Chinese man who presented with nephrotic syndrome, renal impairment, severe hypercholesterolemia without hypertriglyceridemia, and hypertension. Renal biopsy confirmed lipoprotein glomerulopathy. Genetic testing confirmed APOE Kyoto mutation. Anti-hypertensive therapy, including angiotensin receptor blocker, and statin were initiated. Concomitant with normalization of lipid profile, his proteinuria markedly improved, and his renal function has remained stable up to 3 years, demonstrating sustained benefit with statin monotherapy in LPG.

Membranous Nephropathy-Like Apolipoprotein E Deposition Disease with Apolipoprotein E Toyonaka (Ser197Cys) and a Homozygous Apolipoprotein E2/2

A 20-year-old female student underwent renal biopsy because of chance proteinuria and hematuria. Histological study revealed a membranous nephropathy-like appearance by light microscopy. But immunoglobulins and complements were negative in the glomerulus by immunofluorescence study. On the other hand, plasma apolipoprotein E (ApoE) concentration was elevated to more than 2 times the normal range, and the phenotype, genotype, and DNA sequence studies of her ApoE showed homozygous ApoE2/2 and a heterozygous novel missense mutation called ApoE Toyonaka (Ser197Cys). Detailed immunohistochemical studies found that the dense deposits in subepithelial, subendothelial, and mesangial areas contained ApoE. Tandem mass spectrometry also proved a large amount of ApoE in the glomerulus. These findings suggest that ApoE Toyonaka with a homozygous ApoE2/2 may cause a new form of ApoE-related glomerular disease resembling membranous nephropathy.

The Novel Apolipoprotein E Mutation ApoE Chengdu (c.518T＞C, p.L173P) in a Chinese Patient with Lipoprotein Glomerulopathy

Aims: Lipoprotein glomerulopathy (LPG) is a rare inherited renal disease. Several apolipoprotein E (apoE) mutations have been reported to be related to LPG. Herein, we report a case of a LPG patient with a novel apoE mutation.

Methods: A 45-year-old Chinese female was diagnosed as LPG by renal biopsy. APOE gene was sequenced. Clinical and genetic studies were conducted.

Results: The patient presented with nephrotic syndrome and hypertension. A fasting lipid panel showed mild hyperlipidemia and elevated serum apoE (5.6 mg/dL). Renal biopsy revealed typical LPG lesions with whorled, mesh-like material in dilated glomerular capillary lumens that stained positive for Sudan III and apoE. apoE gene analysis revealed a T-to-C point mutation at amino acid 173 that caused a substitution of a proline residue for a leucine residue, which has not been reported previously. We named this mutation apoE Chengdu (c.518T> C, p.L173P). Two of five of the family members carried this mutation, including the patient's brother who was receiving hemodialysis, and her sister, whose urine protein levels were normal. All mutation carriers were heterozygotes with the apoE genotype ε3/ε3. This mutation was not found among 200 of the local people. Fenofibrate treatment for one year induced clinical improvement.

Conclusions: ApoE Chengdu (p.L173P) is a novel mutation causing LPG. This case supports the hypothesis that the substitution of proline in or near the LDL receptor-binding area contributes to the development of LPG. The detailed mechanism of action of this variant remains to be elucidated.

Macrophage Infiltration into the Glomeruli in Lipoprotein Glomerulopathy

Lipoprotein glomerulopathy (LPG) is characterized by histopathological features showing intra-glomerular lipoprotein thrombi and type III hyperlipoproteinemia (HLP), with heterozygote mutation of apolipoprotein (apo) E gene. On the other hand, as another renal lipidosis with type III HLP, apoE2 homozygote-related glomerulopathy (apoE2-GN) showing foamy macrophages has been reported. The case of a 25-year-old man who had LPG by clinical behavior and gene analysis, but demonstrated atypical histopathological features with a substantial amount of foamy macrophage infiltration in the glomeruli, is presented. The combination of alleles for apoE Tokyo/Maebashi and classical apoE2 (Arg158Cys) was inferred to be the leading cause of the unique renal pathology with lipoprotein thrombi and foamy macrophages. In addition, foamy macrophages infiltrated some part of the apoE-positive region within the glomerulus, but did not exist in lipoprotein thrombi despite apoE positivity, suggesting that properties of apoE are crucial in the development of LPG rather than macrophage function. This case provides important information related to the pathogenesis of LPG and apoE2-GN.

Long-term outcome of kidney transplantation in a patient with coexisting lipoprotein glomerulopathy and fibrillary glomerulonephritis

Both lipoprotein glomerulopathy (LPG) and fibrillary glomerulonephritis (FGN) are rare causes of end-stage renal disease (ESRD), and the literature concerning the outcome of kidney transplant in patients with LPG or FGN is scarce. We report a patient who suffered from ESRD with coexisting FGN and LPG and received deceased kidney transplant >10 years ago did not reveal any clinical features of disease recurrence during follow-up. Our case shows that the prognosis of patients with LPG component who received kidney transplant can be good. Kidney transplantation remains a viable therapeutic option for patients with ESRD secondary to FGN with LPG.

Apolipoprotein E gene variants on the risk of end stage renal disease

Objective

End-stage renal disease (ESRD) is a severe health concern over the world. Associations between apolipoprotein E (apoE) gene polymorphisms and the risk of ESRD remained inconclusive. This study aimed to investigate the association between apoE gene polymorphisms and ESRD susceptibility.

Methods

Databases including PubMed, Embase, Web of Science and the Cochrane Library were searched to find relevant studies. Meta-analysis method was used synthesize the eligible studies.

Results

Sixteen pertinent case-control studies which included 3510 cases and 13924 controls were analyzed. A significant association was found between ε2 allele and the ESRD risk (odds ratio (OR) = 1.30, 95% confidence interval (CI) 1.15–1.46, P < 0.0001; I² = 18%, P for heterogeneity = 0.24). The ε2ε3, ε2ε4, ε3ε3, ε3ε4, ε4ε4, ε3 and ε4 were not associated with the susceptibility of ESRD. In the subgroup analysis by ethnicity, there was a statistically significant association between ε2ε3 or ε2 allele and ESRD risk in East Asians (OR = 1.66, 95% CI 1.31–2.10, P < 0.0001; OR = 1.62, 95% CI 1.31–2.01, P < 0.0001, respectively), but not in Caucasians. E2 carriers had higher plasma apoE (mean difference = 16.24 mg/L, 95% CI 7.76-24.73, P = 0.0002) than the (ε3 + ε4) carriers in patients with ESRD. The publication bias was not significant.

Conclusion

The ε2 allele of apoE gene might increase the risk of ESRD. E2 carriers expressed higher level of plasma apoE in patients with ESRD. More well-designed studies are needed to confirm these associations in the future.

Macrophage impairment produced by Fc receptor gamma deficiency plays a principal role in the development of lipoprotein glomerulopathy in concert with apoE abnormalities

BACKGROUND

To obtain a clear understanding of the pathogenesis of lipoprotein glomerulopathy (LPG), we studied the role of the deficiency of Fc receptor gamma chain (FcRγ) for the development of LPG in concert with apolipoprotein E (apoE) abnormalities.

METHODS

We generated apoE and FcRγ double-knockout (FcRγ/apoE-KO) mice, and subsequently introduced several kinds of human recombinant apoE genes. At 21 days after infection, the mice were sacrificed and histologically examined. Peritoneal macrophages were evaluated for their response to modified lipids.

RESULTS

In the FcRγ/apoE-KO mice, the human apoE3-injected mice showed the most drastic LPG-like changes, as well as prominent hypertriglyceridemia. Meanwhile, relative to the human apoE3-injected mice, the FcRγ/apoE-KO mice showed greater lipoprotein deposition and less macrophage infiltration into the mesangial area. Moreover, the peritoneal macrophages in the apoE/FcRγ-KO mice were impaired in lipid uptake and secretion of the cytokines monocyte chemotactic protein-1 and regulated upon activation, normal T-cell expressed and secreted, after the uptake of oxidized low-density lipoprotein.

CONCLUSIONS

These results suggest that the impairment of macrophage function resulting from FcRγ deficiency plays a principal role in the development of LPG in the presence of apoE abnormalities.

Lipoprotein glomerulopathy induced by ApoE-Sendai is different from glomerular lesions in aged apoE-deficient mice

OBJECTIVE

A mutant of apolipoproteinE (apoE), ApoE-Sendai (Arg145Pro), is one of the major causative factors of human lipoprotein glomerulopathy (LPG). An apoE-deficient mouse with introduced ApoE-Sendai gene (ApoE-Sendai mouse) developed a murine counterpart of LPG, whereas it was also reported that apoE-deficient mouse (apoE KO mouse) spontaneously developed LPG-like lesion regardless of introduction of ApoE-Sendai gene. In the present study, we differentiated renal lesions between these two models by detailed analyses of histology and lipoprotein profile, and clarified the role of apoE variants.

METHOD

ApoE-Sendai mice were induced by injection of adenovirus vectors. The kidneys showing LPG-like lesions in apoE-Sendai and apoE KO mice were histopathologically evaluated. Plasma lipids and lipoproteins of both mice were also examined.

RESULTS

Histological alteration of the kidney in ApoE-Sendai mice was observed with light microscopy (in 40 out of 50 mice; mild 24, moderate 13, severe 3). Characteristic lesions were dilated vascular lumens mimicking lipoprotein thrombi in human LPG. Similar changes were found in hematoxylin-eosin stained sections of aged apoE KO mice. Meanwhile, periodic acid-Schiff, Azan Mallory, and Oil red O/Sudan III stained sections revealed that the dilated lumens of ApoE-Sendai mice mainly contained lipids and lipoproteins but those of aged apoE KO mice contained much other materials, e.g., proteins and fibrils. These findings were supported by electron micrographs, in which round-shaped droplets indicating lipoproteins were observed in ApoE-Sendai mice but not in aged apoE KO mice. In the kidney of apoE KO mice many anti-mouse CD68 Ab positive cells were detected. This contrasts with the result seen in ApoE-Sendai mice. The plasma lipoprotein compositions of the two types of mice were totally different.

CONCLUSION

It was certain that the kidneys of aged apoE KO mice showed morphological alteration, but the histological findings of glomerular lesions were different from those seen in the kidneys of ApoE-Sendai mice. According to the histological findings and plasma lipoprotein profile, ApoE-Sendai mice, not apoE KO mice, is a murine model for human LPG. This means that apoE variants are essential to LPG.

Identification of apolipoprotein E Guangzhou (arginine 150 proline), a new variant associated with lipoprotein glomerulopathy

BACKGROUND/AIMS

Lipoprotein glomerulopathy (LPG) is a rare disease characterized by thrombus-like substances in markedly dilated glomerular capillaries and elevated plasma levels of apolipoprotein E (apoE). Previous studies have shown that genetic disorders of apoE may contribute to the pathogenesis of LPG, but LPG may not be caused by apoE gene mutations in Chinese patients. This study investigated the association of a new variant of apoE with LPG in a Chinese family.

METHODS

The apoE gene in a family with 4 LPG patients was sequenced. The polymerase chain reaction product of coding region of apoE exon 4 was cloned into pMD 18-T vector and then sequenced.

RESULTS

A novel point mutation in exon 4 of the apoE gene was identified in all 4 LPG patients and 1 asymptomatic family member. Sequence analysis confirmed a nucleotide G to C point mutation in exon 4 (base 308) of the apoE gene in all patients and the asymptomatic family member. This missense mutation denotes amino acid substitution of the proline residue for arginine residue at position 150 of apoE. Those patients were all heterozygotes with apoE Guangzhou. One of 2 grandsons was a heterozygous carrier of apoE Guangzhou, although he did not have proteinuria.

CONCLUSION

The results of this study suggest that apoE (arginine 150 proline) is a novel apoE variant that etiologically related to LPG. This variant (apoE Guangzhou) may cause a marked molecular conformational change of the apoE and thus impair its binding ability to lipids.

Lipoprotein glomerulopathy: a new apolipoprotein E mutation with enhanced glomerular binding

We describe a case of lipoprotein glomerulopathy, the second ever reported from the United States, in a Mexican man with a hitherto undescribed mutation in the apolipoprotein E gene (substitution of proline for arginine at position 147 [Arg147Pro]). In this patient, glomerular basement membranes showed double contours and circumferential mesangial extensions, suggesting that deposition of lipids could be injurious to endothelial cells. Immunofluorescence staining of thrombi was positive for apolipoprotein E and B. To study the reason for lipid deposition in glomeruli, we incubated normal human kidney sections with serum from the patient and a healthy control. Apolipoprotein E from the patient's serum showed binding to the glomerular capillary wall, but the control did not, suggesting enhanced binding of the mutated apolipoprotein E to glomerular capillaries. Apolipoprotein E genotyping by means of restriction endonuclease digestion of polymerase chain reaction-amplified genomic DNA showed it to be of the wild-type E3/E3.

Impact of Lipoprotein Glomerulopathy on the Relationship Between Lipids and Renal Diseases

Lipoprotein glomerulopathy (LPG) is a unique entity of renal lipidosis characterized by peculiar histopathologic characteristics of lipoprotein thrombi and an abnormal plasma lipoprotein profile resembling type III hyperlipoproteinemia, with a marked increase in serum apolipoprotein E (apoE) concentrations. At present, 65 cases have been reported worldwide, although most patients are found in Japan and east Asian countries. Recently, we identified 4 types of novel apoE mutations associated with LPG. In particular, a mutation designated apoE Sendai, in which arginine 145 is substituted with proline, occurs in the majority of Japanese patients. The virus-mediated transduction of apoE Sendai resulting in the development of LPG in apoE-deficient mice confirms the etiologic role of apoE mutation in LPG. Conversely, experimental graft-versus-host disease induced in Fc receptor gamma-chain-deficient mice showed LPG-like lesions in glomeruli without apoE mutations. Considered together, we believe that intrinsic factors in the kidney also contribute to the induction of LPG. Today, apoE and related lipid abnormalities are reported to have an important role in the development of various renal diseases, eg, diabetic nephropathy and immunoglobulin A nephropathy. In this article, we review clinical and histopathologic features of LPG, describe the etiologic role of apoE variants and intrinsic renal factors, and discuss the impact of LPG on mechanisms of other renal diseases.

Apolipoprotein E and renal disease

Apolipoprotein E (ApoE) is a major constituent of plasma lipoproteins with many biological actions of great significance. Beyond the known influence of ApoE polymorphisms on serum lipid profile, the pathogenesis of atherosclerosis, and the development of neurodegenerative disorders, ApoE also has a major role in the pathogenesis and progression of a variety of renal diseases, as well as in the atherosclerotic complications associated with them. Briefly, the polymorphisms of ApoE are major determinants of plasma lipid levels in uremic patients. They may affect the risk for cardiovascular disease in this population, predispose to the development of diabetic nephropathy, influence the severity of certain glomerulopathies, and regulate mesangial and glomerular functions locally in the kidney microenvironment. Finally, certain mutations of the ApoE gene are associated with a recently described nephropathy, termed lipoprotein glomerulopathy.

Etiological significance of apolipoprotein E mutations in lipoprotein glomerulopathy

Lipoprotein glomerulopathy (LPG) is a newly recognized renal disease characterized by thrombus-like lipoproteins in the glomerular capillaries and abnormal lipoprotein profiles similar to those in type III hyperlipoproteinemia. Recently, these conditions have been shown to be associated with some apolipoprotein E (apoE) mutations. We found an apoE mutation (designated apoE-Sendai) that substitutes arginine 145 with proline. This mutation occurs most frequently in Japanese patients with LPG. To elucidate the etiological role of this mutation in the apoE gene, we established an experimental model for LPG by transducing apoE-Sendai in apoE knockout mice with the use of an adenovirus vector. Based on the findings in patients with LPG and its animal model, we suggest that the glomerular lesions are not only caused by hyperlipidemia, but also by in situ interaction between lipoprotein-containing mutant apoE with the glomerulus. In this review, we outline the clinical features of LPG and discuss the relationship between apoE mutations and LPG.

Novel glomerular lipoprotein deposits associated with apolipoprotein E2 homozygosity

BACKGROUND

Hyperlipoproteinemia is occasionally associated with severe glomerular injury caused by abnormal accumulation of lipid in glomeruli, which occurs in conditions such as lipoprotein glomerulopathy (LPG). This study investigates the cases of two siblings with homozygous apolipoprotein (apo) E2 who show unique histologic features, massive proteinuria, and dysbetalipoproteinemia.

METHODS

Histologic studies were performed using renal biopsy specimens. Plasma lipoproteins were extensively characterized. The exons of the apo E genes were sequenced to avoid missing any mutations.

RESULTS

Histologically, the siblings' condition resembled LPG by light microscopy studies. Electron microscopy studies revealed large lipoid deposits in the paramesangium, subendothelium, and subepithelium of the glomeruli, which were different from LPG in terms of not forming the layered structure resembling a fingerprint even in large lipoprotein thrombi, and mesangial foam cells. Immunohistochemically, the lipoid deposits contained apo E and apo B. These patients did not have either diabetic nephropathy or other known forms of glomerulonephritis. The sequence of exons of the apo E genes revealed homozygosity for apo E2 in both cases.

CONCLUSION

The extensive lipoprotein deposition in glomeruli, which resembles LPG, can also occur in apo E2 homozygous individuals, but in a distinct fashion. Because the two cases were siblings, they may have other shared alleles, in addition to the apo E2 allele, that negatively affect processing of lipoproteins and lead to abnormal accumulation of lipoprotein deposits in glomeruli.

Diminished LDL receptor and high heparin binding of apolipoprotein E2 Sendai associated with lipoprotein glomerulopathy

Variants of apolipoprotein E (apoE) have been linked to lipoprotein glomerulopathy, a new glomerular disease characterized by the deposition of lipoproteins in mesangial capillaries. One third of affected patients are heterozygous for apoE2 Sendai (Arg(145) Pro). Variants of apoE can also produce type III hyperlipoproteinemia (HLP). Recessive type III HLP is caused by apoE2 (Arg(158) Cys), a mutant with diminished low-density lipoprotein (LDL) receptor binding but halfnormal heparin binding. Dominant type III HLP is caused by mutations that markedly alter heparin binding but modestly reduce receptor binding. This study examined whether apoE2 Sendai (Arg(145) Pro) was functionally different from type III HLP-producing apoE variants by expressing apoE3, apoE2 (Arg(158) Cys), apoE1 (Arg(146) Glu), a dominant apoE variant, and apoE2 Sendai (Arg(145) Pro) in the baculovirus system. LDL receptor binding was studied using recombinant apoE complexed to phospholipid vesicles and to very lowdensity lipoprotein from a patient with familiar apoE deficiency. Compared with apoE3, receptor-binding activities of apoE2 (Arg(158) Cys), apoE1 (Arg(146) Glu), and apoE2 Sendai (Arg(145) Pro) all were less than 5%. Heparin-binding activities were 53%, 23%, and 66%, respectively, of apoE3. The distribution of apoE2 Sendai among the major plasma lipoprotein fractions was similar to that of apoE3 and apoE2 (Arg(158) Cys). ApoE2 Sendai (Arg(145) Pro) represents the only known mutation within the heparin-binding domain of apoE (residues 142 through 147), revealing diminished receptor binding and almost normal heparin binding. These unique characteristics of apoE2 Sendai (Arg(145) Pro) may relate to the development of lipoprotein glomerulopathy.

Hypertriglyceridaemia and hyperuricaemia are risk factors for progression of IgA nephropathy

BACKGROUND

The prognosis of IgA nephropathy (IgAN) is variable and about 10-20% of patients progress to end-stage renal disease (ESRD) in 10 years. Hypertension, proteinuria and renal insufficiency at the time of diagnosis are risk factors associated with poor prognosis. Lipid abnormalities may have a role in the progression of glomerulonephritides, and glomerulosclerosis and atherosclerosis may have similar pathophysiological mechanisms. We therefore evaluated factors associated with cardiovascular diseases, especially hypercholesterolaemia, hypertriglyceridaemia, and hyperuricaemia, as predictors of the progression of IgAN.

METHODS

A total of 223 patients with IgAN (141 men, 82 women; median age 41 years, range 8-78 years) were studied. The following parameters were recorded at the time of renal biopsy: presence of hypertension or diabetes, smoking habits, body mass index (BMI), serum creatinine, total and HDL-cholesterol, triglycerides, and urate and 24-h urinary protein excretion. The patients were followed up for 0.2-17 years (median 10 years) with respect to progression of renal disease defined as elevation of serum creatinine above 125 micromol/l in men or 105 micromol/l in women, and over 20% elevation from baseline.

RESULTS

Forty-one patients (18%) showed progression. Hypertriglyceridaemia and hyperuricaemia were significantly more common at the time of renal biopsy in patients with progressive than in those with stable disease. In patients with normal renal function at the time of diagnosis initial hypertriglyceridaemia, hyperuricaemia, hypertension and proteinuria were independent risk factors for progression of IgAN in the Cox regression hazard model.

CONCLUSIONS

Our results show that hypertriglyceridaemia and hyperuricaemia at the time of diagnosis are important, previously underestimated predictors of poor outcome in IgAN, although causality between these factors and progression cannot be inferred from the present study.

Apolipoprotein E and atherosclerosis: insight from animal and human studies

Major advances have been made in our understanding of the role of apolipoprotein E (apoE) in the onset and development of atherosclerosis. Increasing evidence from both animal and human studies suggests that apoE is able to protect against atherosclerosis by: a) promoting efficient uptake of triglyceride-rich lipoproteins from the circulation; b) maintaining normal macrophage lipid homeostasis; c) playing a role in cellular cholesterol efflux and reverse cholesterol transport; d) acting as an antioxidant; e) inhibiting platelet aggregation; and f) modulating immune function. In humans, apoE is polymorphic, and this genetic variation has a strong effect on its antiatherogenic characteristics. Thus, compared to the epsilon3 allele, the epsilon4 allele promotes atherosclerosis, whereas the epsilon2 allele is either pro- or anti-atherogenic, depending on the influence of both environmental and genetic factors. ApoE and its gene are prime targets for therapeutic intervention aimed at preventing or treating atherosclerotic vascular disease.

A novel apolipoprotein E mutation, E2 (Arg25Cys), in lipoprotein glomerulopathy

BACKGROUND

Lipoprotein glomerulopathy (LPG) is characterized by intraglomerular lipoprotein thrombosis and high plasma concentrations of apolipoprotein (apo) E. An apo E variant, apo E2 (Arg145Pro) Sendai, was recently identified in three patients with LPG. We detected a novel point mutation in the apo E gene in a patient with LPG, and we characterized the mutant apo E.

METHODS

The propositus was a 32-year-old male patient on maintenance hemodialysis because of LPG. The mutation was detected by sequencing of genomic DNA from the patient and was confirmed by restriction fragment length polymorphism (RFLP) with Aor51HI. Recombinant apo E2 (Arg25Cys) Kyoto and normal apo E3 were expressed from COS-1 cells. Low-density lipoprotein (LDL) receptor-binding activities of the variants were determined in an in vitro competition assay.

RESULTS

The propositus had the apo E phenotype E2/E4, as determined by isoelectric focusing, and the genotype epsilon3/epsilon4, as determined by RFLP with HhaI. Sequence analysis of amplified DNA showed a C to T transition, changing the codon for residue 25 from arginine to cysteine. The proband was a heterozygous carrier for apo E2 (Arg25Cys) Kyoto. A family study showed that the mother was a heterozygous carrier of apo E2 Kyoto and had dysbetalipoproteinemia, but no LPG. The pathophysiological effect of this mutation was investigated in vitro by binding studies of recombinant apo E2 Kyoto to LDL receptors on human fibroblasts. The ability of recombinant apo E2 Kyoto to displace LDL was reduced to 10% compared with recombinant apo E3.

CONCLUSIONS

Apo E2 (Arg25Cys) Kyoto is a novel mutation of apo E that is etiologically related to LPG. However, our case indicates that the development of LPG may involve other genetic or environmental factors. Furthermore, our data suggest that arginine-25 of apo E plays an important functional role by influencing the receptor-binding ability of apo E.

Lipoprotein glomerulopathy: significance of lipoprotein and ultrastructural features

BACKGROUND

Lipoprotein glomerulopathy (LPG) is a unique disease characterized by intraglomerular lipoprotein thrombi and type III hyperlipoproteinemia. Recently, we have demonstrated that LPG is associated with inherited apolipoprotein E (apoE) variants including apoE Sendai. On the other hand electron microscopy shows that intraglomerular lipoprotein thrombi consist of lipid granules of various sizes. To elucidate the relationship between the peculiar histology and abnormal lipid metabolism related to apoE Sendai, we studied lipoprotein profiles and ultrastructural features.

METHODS

The subjects were 11 patients with LPG. Four patients were nephrotic, and two others became nephrotic within six months following the biopsy. Eight patients underwent apoE gene analysis and showed apoE Sendai. The other three were presumed to have apoE Sendai because this mutation was demonstrated in their kindreds. Under electron microscopy, diameters of more than 1000 lipid granules were measured in several glomeruli, and a mean value was calculated in each case. Lipoprotein profiles were analyzed by the ultracentrifugation methods.

RESULTS

The mean diameter of intraglomerular lipid granules correlated inversely with the levels of plasma triglyceride (TG; rs = -0.73, P < 0.05), TG (rs = -0.77, P < 0.01) and cholesterol (Chol; rs = -0.75, P < 0.05) in very low-density lipoprotein (VLDL) fraction and TG in high-density lipoprotein (HDL) fraction (rs = -0.75, P < 0.05). The inverse correlation was also seen between the mean lipid diameter and TG/Chol ratios in whole plasma (rs = -0.80, P < 0.01) and in HDL (rs = -0.80, P < 0.01). In addition, the cases showing smaller lipid granules and higher TG/Chol ratios in plasma and in HDL were nephrotic or became nephrotic within six months.

CONCLUSION

These results suggest that the size of lipid granules in LPG may become smaller under the influence of hypertriglyceridemia and particularly elevated plasma VLDL and HDL-TG, which may lead to heavy proteinuria.

Genetics of lipoprotein disorders

The study of lipoprotein metabolism has led to major breakthroughs in the fields of cellular physiology, molecular genetics, and protein chemistry. These advances in basic science are reflected in medicine in the form of improved diagnostic methods and better therapeutic tools. Perhaps the greatest benefit is the improved ability to identify at an early stage patients who are at high risk for atherosclerosis, providing clinicians the opportunity to proceed swiftly with intensive lipid-lowering therapy for the prevention of cardiovascular complications. Recent clinical trials have shown that such an approach is not only cost-effective but saves lives while improving the quality of life. They also emphasize the important role physicians can have in prevention. More than half of patients with premature CAD have a familial form of dyslipoproteinemia. This review of the genetics of atherogenic lipoprotein disorders underscores the importance of identifying major genetic defects. It also stresses the need to take into account multifactorial etiologies and clustering of risk factors, as well as gene-gene and gene-environment interactions in assessing the atherogenic potential of a lipid transport disorder. Table 2 summarizes the key points in the diagnosis, clinical implications, and treatment of the major inherited atherogenic dyslipidemias.

Abnormal lipid metabolism and renal disorders

Abnormal renal diseases including nephrotic syndrome and chronic renal failure are associated with hyperlipidemia, significance of abnormal lipid metabolism has been thought to be limited in some inherited renal diseases. However, recent studies have postulated that glomerulosclerosis is induced by hyperlipidemia and is in common with atherosclerosis. This involvement is found in the progressive renal disorders, e.g., focal glomerular sclerosis, diabetic nephropathy and glycogen storage disease. Interaction between macrophages and mesangial cells may play an important role in such conditions. This evidence is supported by experimental models with hyperlipidemia. On the other hand, discovery and new hereditary metabolic disorders, such as type III hyperlipoproteinemia and lipoprotein glomerulopathy, shows that apolipoprotein (apo) E abnormalities are responsible for the glomerular lesions. Especially, lipoprotein glomerulopathy has specific features different from those of lipid-induced renal diseases. In this disease, apo E Sendai which results from new substitution (Arginine 145-->Proline) may induce intraglomerular lipoprotein thrombi characteristic of lipoprotein glomerulopathy.