A new variant of apolipoprotein E (apo E Maebashi) in lipoprotein glomerulopathy

Lipoprotein Glomerulopathy, First Case Report from Canada

Lipoprotein glomerulopathy (LPG) is caused by a mutation in the apolipoprotein E gene (APOE) gene and is characterized by lipoprotein thrombi in glomerular capillaries. Here, we describe a case of LPG, the first to be reported from Canada and the first case of LPG in North America to be associated with the APOE Tokyo/Maebashi mutation (p.Leu162_Lys164del, traditional nomenclature 142_144del). A 49-year-old man of Chinese descent with a previous diagnosis of dyslipidemia and a new diagnosis of hypertension was found to have proteinuria on routine urinalysis. Renal biopsy showed markedly dilated glomerular capillaries filled with pale staining mesh-like material that stained positive for Oil-Red-O, consistent with lipoprotein thrombi. APOE gene sequencing confirmed the diagnosis of LPG. The patient was treated with fenofibrate and perindopril. His lipid profile normalized and proteinuria dropped to minimal levels. Repeat renal biopsy 2 years after the first showed resolution of lipoprotein thrombi but with rare residual granular densities by electron microscopy consistent with lipoprotein in the subendothelial space, supporting the hypothesis that this subendothelial material contains precursors to lipoprotein thrombi.

APOE gene variants in primary dyslipidemia

Apolipoprotein E (apoE) is a major apolipoprotein involved in lipoprotein metabolism. It is a polymorphic protein and different isoforms are associated with variations in lipid and lipoprotein levels and thus cardiovascular risk. The isoform apoE4 is associated with an increase in LDL-cholesterol levels and thus a higher cardiovascular risk compared to apoE3. Whereas, apoE2 is associated with a mild decrease in LDL-cholesterol levels. In the presence of other risk factors, apoE2 homozygotes could develop type III hyperlipoproteinemia (familial dysbetalipoproteinemia or FD), an atherogenic disorder characterized by an accumulation of remnants of triglyceride-rich lipoproteins. Several rare APOE gene variants were reported in different types of dyslipidemias including FD, familial combined hyperlipidemia (FCH), lipoprotein glomerulopathy and bona fide autosomal dominant hypercholesterolemia (ADH). ADH is characterized by elevated LDL-cholesterol levels leading to coronary heart disease, and due to molecular alterations in three main genes: LDLR, APOB and PCSK9. The identification of the APOE-p.Leu167del variant as the causative molecular element in two different ADH families, paved the way to considering APOE as a candidate gene for ADH. Due to non mendelian interacting factors, common genetic and environmental factors and perhaps epigenetics, clinical presentation of lipid disorders associated with APOE variants often strongly overlap. More studies are needed to determine the spectrum of APOE implication in each of the diseases, notably ADH, in order to improve clinical and genetic diagnosis, prognosis and patient management. The purpose of this review is to comment on these APOE variants and on the molecular and clinical overlaps between dyslipidemias.

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 novel apolipoprotein E mutation caused by a five amino acid deletion in a Chinese family with lipoprotein glomerulopathy: a case report

BACKGROUND

Lipoprotein glomerulopathy (LPG) is a rare kidney disease with a poor prognosis that is related to mutation of the apoE gene. More than 10 variants of apoE associated with LPG have currently been identified.

CASE PRESENTATION

A male and his mother presented with proteinuria during a health examination. They went to hospital for further examination. Renal biopsy was performed, and the diagnosis was lipoprotein glomerulopathy (LPG), which is a rare, inherited renal disease. Medical histories were collected from the 2 LPG patients and their family members. The patients and family members underwent a routine urine test, and their renal function, blood lipids, and lipoprotein levels were examined. Genomic DNA was extracted from the peripheral blood of 7 family members, and exon 2, exon 3 and exon 4 of apoE were amplified by polymerase chain reaction (PCR). The purified PCR products were sequenced. Sequence analysis identified a 15 bp deletion (GCGCAAGCTGCGTAA) in exon 4 of the apoE gene that results in a novel 5 amino acid deletion in apoE (143 K-147R → 0). No mutations were found in exon 2 and exon 3 of the apoE gene.

CONCLUSIONS

This family study suggests that a novel ApoE mutation (143 K-147R → 0) may be etiologically related to LPG, and other genetic or environmental factors may be associated with the occurrence of LPG.

Endocytosis of lipoproteins

During their metabolism, all lipoproteins undergo endocytosis, either to be degraded intracellularly, for example in hepatocytes or macrophages, or to be re-secreted, for example in the course of transcytosis by endothelial cells. Moreover, there are several examples of internalized lipoproteins sequestered intracellularly, possibly to exert intracellular functions, for example the cytolysis of trypanosoma. Endocytosis and the subsequent intracellular itinerary of lipoproteins hence are key areas for understanding the regulation of plasma lipid levels as well as the biological functions of lipoproteins. Indeed, the identification of the low-density lipoprotein (LDL)-receptor and the unraveling of its transcriptional regulation led to the elucidation of familial hypercholesterolemia as well as to the development of statins, the most successful therapeutics for lowering of cholesterol levels and risk of atherosclerotic cardiovascular diseases. Novel limiting factors of intracellular trafficking of LDL and the LDL receptor continue to be discovered and to provide drug targets such as PCSK9. Surprisingly, the receptors mediating endocytosis of high-density lipoproteins or lipoprotein(a) are still a matter of controversy or even new discovery. Finally, the receptors and mechanisms, which mediate the uptake of lipoproteins into non-degrading intracellular itineraries for re-secretion (transcytosis, retroendocytosis), storage, or execution of intracellular functions, are largely unknown.

SPONTANEOUS LIPOPROTEIN GLOMERULOPATHY-LIKE NEPHROPATHY IN A SQUIRREL (SCIURUS VULGARIS)

Lipoprotein glomerulopathy (LPG) is a rare human glomerular disease caused by abnormal lipid metabolism. Naturally occurring LPG has not been reported in animals. We describe the histopathological characterization of spontaneous LPG-like nephropathy in a captive squirrel ( Sciurus vulgaris ). Macroscopically, swollen glomeruli were distinctively identified as fine white granules in the renal cortex. Histologically, most glomeruli were markedly enlarged with distended capillaries containing faintly eosinophilic and amorphous materials. The amorphous material was negative using the periodic acid-Schiff reaction, periodic acid-methenamine silver stain, or Masson's trichrome stain. Sudan III staining revealed lipid in the materials, and immunohistochemistry demonstrated that the material additionally contained apolipoprotein E. Electron microscopy showed numerous lipid granules and vacuoles of various sizes in the capillary lumina associated with foot process effacement of podocytes. These pathological characteristics bear some resemblance to those of human LPG.

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.

Lipoprotein glomerulopathy in China

Lipoprotein glomerulopathy (LPG), a rare renal disease, is mainly reported in Japan and China. Chinese cases of LPG showed similar clinical and pathological features as reports from other countries. Three types of APOE mutation have been detected in those patients: APOE Maebashi (142Arg-144Leu-0) and APOE Kyoto (Arg25-Cys) were initially reported, and APOE Guangzhou (Arg150-Pro) is a novel mutation in Chinese patients with LPG. Asymptomatic carriers of all three mutations exist in families, but serum lipid and apolipoprotein E (apoE) levels are markedly elevated. In most of Chinese patients with LPG, long-term treatment with statins or bezafibrates appears to decrease proteinuria. LPG provides a disease model by which to explore pathogenic roles of apoE in common diseases.

A possible structural basis behind the pathogenic role of apolipoprotein E hereditary mutations associated with lipoprotein glomerulopathy

Single amino acid mutations in apolipoprotein E (apoE) have been associated with the development of the rare kidney disease lipoprotein glomerulopathy (LPG). Although the genetic linkage to disease development is well established, the mechanism of pathogenesis is largely unknown, limiting therapeutic insight. Here, we summarize current knowledge in the field and focus on the possible effects of LPG-associated mutations on the structure of apoE. Recent findings have suggested that mutation-induced folding perturbations in apoE lead to structural destabilization and aggregation, effects that may underlie lipoprotein thrombi accumulation in the glomerulus, a hallmark of LPG. The recognition that structural destabilization may underlie the association between apoE mutations and LPG can be key for development of new innovative treatments for this rare disease.

A founder haplotype of APOE-Sendai mutation associated with lipoprotein glomerulopathy

Lipoprotein glomerulopathy (LPG) is a hereditary disease characterized by lipoprotein thrombi in the glomerulus, hyperlipoproteinemia, and a marked increase in serum apolipoprotein E (APOE). More than 12 APOE mutations have been identified as causes of LPG, and APOE-Sendai (Arg145Pro) mutation was frequently detected in patients from the eastern part of Japan including Yamagata prefecture. Recently, effective therapy with intensive lipid-lowering agents was established, and epidemiologic data are required for early diagnosis. We determined the haplotype structure of APOE-Sendai in 13 patients from 9 unrelated families with LPG, and found that the haplotype of all APOE-Sendai mutations was identical, suggesting that APOE-Sendai mutation is common in Japanese patients probably through a founder effect. We also studied the gene frequency of APOE-Sendai in 2023 control subjects and 418 patients receiving hemodialysis in Yamagata prefecture using the TaqMan method, but did not identify any subjects carrying the mutation, indicating that it is very rare in the general population even in the eastern part of Japan. In addition to APOE mutation, other genetic and/or epigenetic factors are considered to be involved in the pathogenesis of LPG because of its low penetrance. The patients did not have a common haplotype of the counterpart APOE allele, and some patients had the same haplotype of the counterpart APOE allele as the asymptomatic carriers. These results suggest that the counterpart APOE allele is not likely associated with the onset of LPG. Further study is required to clarify the pathogenesis of LPG.

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.

Scavenger receptor expressions in the kidneys of mice with lipoprotein glomerulopathy

BACKGROUND

To clarify whether dysfunction of the scavenger receptor (SR) participates in the development of lipoprotein glomerulopathy (LPG) in immunoglobulin F(c) receptor γ chain (F(c)Rγ)-deficient mice [F(c)Rγ knock-out (KO) mice] with induced chronic graft-versus-host disease (cGVHD).

METHOD

In wild-type (WT) and F(c)Rγ KO C57BL/6 mice, cGVHD was induced by injection of lymphoid cells from donor Bm12 mice. At 6 months after injection, the mice were sacrificed and histologically examined. Total RNA was extracted from the kidneys and cytokine, chemokine, and SR transcript expressions were evaluated by reverse transcription-polymerase chain reaction.

RESULTS

Three of 4 female cGVHD(+)/F(c)Rγ KO mice presented LPG in >60% of glomeruli. cGVHD(-) and cGVHD(+)/WT mice did not show LPG. The SRs CD36, CD68, and CXCL16 showed a significant difference in the values of their transcripts between cGVHD(+)/WT and cGVHD(+)/F(c)Rγ KO mice. Among them, only CD36 showed a drastic decline of mRNA expressions in cGVHD(+)/F(c)Rγ KO mice.

CONCLUSION

CD36 may play a crucial role in the development of LPG in F(c)Rγ KO mice with cGVHD. In addition to the apolipoprotein E mutation, dysfunction of lipid clearance in the kidney might be one of the factors for the development of LPG.

Lipoprotein glomerulopathy

PURPOSE OF REVIEW

Lipoprotein glomerulopathy is a rare disorder characterized by proteinuria, renal insufficiency and disturbances in lipoprotein metabolism closely related to those observed in type III hyperlipidemia. Rare mutations in apolipoprotein E (apoE) gene may contribute to the pathogenesis of the disease. This article reviews the clinical and laboratory features of lipoprotein glomerulopathy, discusses the mechanisms that may be implicated in its pathogenesis and summarizes the currently available therapeutic options.

RECENT FINDINGS

During the past years two new apoE gene mutations were described in Caucasian patients, apoE Modena (Arg150→Cys) and apoE Las Vegas (Ala152→Asp), a finding indicating that the disease may be more common in white populations than initially thought. Results from case studies suggest that fibrates improve renal pathology and may result in the complete clinical remission of the disease. LDL-apheresis or immunoadsorption onto staphylococcal protein A may also have a role in refractory cases.

SUMMARY

Lipid glomerulopathy is a rare, poorly understood disorder with potentially detrimental consequences. The determination of the effects of apoE mutations on the structural and functional characteristics of the mature protein may provide new insights in the pathogenesis of the disease. Meanwhile, intensive lipid-lowering may reduce proteinuria and preserve renal function in this patient group.

Successful treatment of lipoprotein glomerulopathy in a daughter and a mother using niceritrol

We report two patients, a daughter and a mother, with lipoprotein glomerulopathy (LPG) who were successfully treated with niceritrol. Both patients carried a mutation in the apolipoprotein E (apoE) gene known as ApoE Tokyo/Maebashi. The daughter was found to have proteinuria at the age of 4 years. Four years later, she was diagnosed as having LPG based on a renal biopsy. She was treated with several medications including pravastatin, ethyl icosapentate, enalapril, warfarin and cyclophosphamide, all of which failed to reduce her proteinuria. At the age of 17 years, she exhibited an increase in proteinuria and a decline in renal function, despite ongoing treatment with pravastatin and enalapril. After switching from pravastatin to niceritrol, a marked reduction in the proteinuria and an improvement in renal function were observed. Her mother was found to have proteinuria at the age of 57 years and was diagnosed as having LPG based on a renal biopsy. She was also treated with niceritrol, resulting in an improvement in her proteinuria and renal function. These cases suggest that niceritrol might be a useful therapeutic option for LPG.

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.

Disappearance of intraglomerular lipoprotein thrombi and marked improvement of nephrotic syndrome by bezafibrate treatment in a patient with lipoprotein glomerulopathy

Lipoprotein glomerulopathy (LPG) is a hereditary disorder characterized by intraglomerular lipoprotein thrombi and increased serum apolipoprotein (apo) E. Patients with LPG usually manifest with nephrotic syndrome, and some progress to renal failure; however, no effective therapeutic regimen has been established for this disease. We experienced a patient with LPG for whom bezafibrate treatment was very effective. This 30-year-old Japanese woman had nephrotic syndrome and type III hyperlipoproteinemia. Renal biopsy showed markedly dilated capillary lumina containing massive lipoprotein thrombi. Plasma apo E concentration was elevated to twice that of normal controls. She was proved to be a heterozygote of apo E2 Kyoto (Arg25Cys). After 2 years treatment with bezafibrate (400 mg/day), her plasma albumin gradually increased from 2.1 to 4.0 mg/dl, and intraglomerular lipoprotein thrombi disappeared almost completely. Bezafibrate decreased plasma apo E and dramatically increased high density lipoprotein (HDL)-cholesterol. The decrease in apo E was observed mainly in the pre-beta-fraction, not in the alpha fraction. Lipidological analyses of our patient suggest that the origin her lipoprotein thrombi may be mainly from pre-beta-lipoproteins and that HDL might be involved in resolving lipoprotein thrombi. Our case suggests that administration of fibrates such as bezafibrate may be a novel therapeutic strategy for resolving intraglomerular thrombi and improving nephrotic syndrome in patients with LPG.

A patient with apolipoprotein E2 variant (Q187E) without lipoprotein glomerulopathy

Four apolipoprotein (apo) E variants have been reported to be associated with lipoprotein glomerulopathy (LPG), which is characterized by type III hyperlipoproteinemia (type III HLP) and proteinuria and frequently leads to nephrotic syndrome. We report the histologic findings in the kidneys of a type III HLP patient with an apo E variant, apo E Toranomon, in which the glutamine at residue 187 in apo E is substituted by glutamic acid (Q187E). The patient also had type 2 diabetes mellitus. No evidence of lipoprotein thrombi suggestive of LPG was detected, however, and the histologic diagnosis was diabetic nephrosclerosis. This unique case illustrates that not all apo E variants result in LPG, and the location of mutations in the apo E protein is one of the important determinants for the development of LPG.

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.

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.

Virus-mediated transduction of apolipoprotein E (ApoE)-sendai develops lipoprotein glomerulopathy in ApoE-deficient mice

Lipoprotein glomerulopathy (LPG) is a unique renal disease characterized by thrombus-like substances in markedly dilated glomerular capillaries, dysbetalipoproteinemia, and elevated plasma concentrations of apoE. Recent studies identified several apoE mutations in patients with LPG, including apoE2(R145P) Sendai (apoE-Sendai). Virus-mediated transduction of apoE-Sendai in apoE-deficient hypercholesterolemic mice resulted in insufficient correction of hypercholesterolemia and a marked and temporal induction of plasma triglyceride levels. In vitro binding studies showed that apoE-Sendai has a reduced affinity for the low density lipoprotein receptor, suggesting that dysbetalipoproteinemia in LPG is caused by the apoE mutation. Furthermore, histological examination revealed marked intraglomerular depositions of apoE-containing lipoproteins in mice injected with apoE-Sendai virus. These LPG-like depositions were detected 6 days after virus injection and were sustained for at least 60 days. Our results demonstrated that apoE-Sendai is an etiological cause of LPG.