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.

An Updated Review and Meta Analysis of Lipoprotein Glomerulopathy

More than 200 cases of lipoprotein glomerulopathy (LPG) have been reported since it was first discovered 30 years ago. Although relatively rare, LPG is clinically an important cause of nephrotic syndrome and end-stage renal disease. Mutations in the APOE gene are the leading cause of LPG. APOE mutations are an important determinant of lipid profiles and cardiovascular health in the population and can precipitate dysbetalipoproteinemia and glomerulopathy. Apolipoprotein E-related glomerular disorders include APOE2 homozygote glomerulopathy and LPG with heterozygous APOE mutations. In recent years, there has been a rapid increase in the number of LPG case reports and some progress in research into the mechanism and animal models of LPG. We consequently need to update recent epidemiological studies and the molecular mechanisms of LPG. This endeavor may help us not only to diagnose and treat LPG in a more personized manner but also to better understand the potential relationship between lipids and the kidney.

Lipoprotein Glomerulopathy-Like Lesions in Atherosclerotic Mice Defected With HDL Receptor SR-B1

High-density lipoprotein (HDL) homeostasis is important in maintaining both cardiovascular and renal health. Scavenger receptor class B type 1 (SR-B1), the major HDL receptor in mammals, plays a crucial role in reverse cholesterol transport and HDL metabolism. Evidence from mouse study has well demonstrated that HDL disorders caused by Srb1 inactivation accelerate atherosclerosis and even induce lethal cardiovascular diseases. However, the renal consequences of Srb1 dysfunction are still unknown. Here we explored this issue in both Srb1 knockout (Srb1-/-) mice and atherosclerotic low-density lipoprotein receptor knockout (Ldlr-/-) mice with Srb1 deletion. Our data showed that no apparent renal damage was observed in 5-month-old Srb1-/- mice fed on standard rodent chow diet as well as Srb1-/- mice fed on a high-fat diet (HFD) for 12 weeks. However, 5-month-old Srb1/Ldlr-/- mice fed on rodent chow had increased urinary albumin excretion and developed spontaneous intraglomerular Oil-red O (ORO)-positive lipoprotein deposition that is similar to lesions observed in human lipoprotein glomerulopathy (LPG). HFD feeding accelerated LPG-like lesions in Srb1/Ldlr-/- mice, inducing severe proteinuria and significantly promoting intraglomerular ORO-positive lipoprotein deposition. Interestingly, probucol reversed HFD-induced HDL disorders and almost fully abrogated LPG-like lesions in Srb1/Ldlr-/- mice. In conclusion, the present study demonstrates that SR-B1 dysfunction leads to LPG-like lesions in atherosclerotic mice, which could be rescued by probucol. SR-B1 loss-of-function mutant carriers therefore might be susceptible to developing metabolic nephropathy in addition to cardiovascular diseases, and probucol might be a potential therapeutics.

The Vicious Cycle of Renal Lipotoxicity and Mitochondrial Dysfunction

The kidney is one of the most energy-demanding organs that require abundant and healthy mitochondria to maintain proper function. Increasing evidence suggests a strong association between mitochondrial dysfunction and chronic kidney diseases (CKDs). Lipids are not only important sources of energy but also essential components of mitochondrial membrane structures. Dysregulation of mitochondrial oxidative metabolism and increased reactive oxygen species (ROS) production lead to compromised mitochondrial lipid utilization, resulting in lipid accumulation and renal lipotoxicity. However, lipotoxicity can be either the cause or the consequence of mitochondrial dysfunction. Imbalanced lipid metabolism, in turn, can hamper mitochondrial dynamics, contributing to the alteration of mitochondrial lipids and reduction in mitochondrial function. In this review, we summarize the interplay between renal lipotoxicity and mitochondrial dysfunction, with a focus on glomerular diseases.

Intravascular cardiac lipoproteinosis: extrarenal manifestation of lipoprotein glomerulopathy

Intracapillary lipoprotein thrombi are a distinct histopathologic finding described in the setting of lipoprotein glomerulopathy. The disease is associated with mutations in the apolipoprotein E gene and responds well to lipid-lowering treatments. Lipoprotein glomerulopathy is thought to primarily affect the kidneys, and lipoprotein thrombi have never been described in any other organ. Herein we present the first recognized case with extrarenal manifestations in the form of intravascular cardiac lipoprotein deposition.

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.

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.

Thermodynamic destabilization and aggregation propensity as the mechanism behind the association of apoE3 mutants and lipoprotein glomerulopathy

Lipoprotein glomerulopathy (LPG) is a rare renal disease, characterized by lipoprotein thrombi in glomerular capillaries. A series of apoE mutations have been associated with LPG development. We previously showed that three mutants based on apoE3 sequence, in which an arginine was substituted by proline, are thermodynamically destabilized and aggregation-prone. To examine whether other LPG-associated apoE3 mutations induce similar effects, we characterized three nonproline LPG-associated apoE3 mutations, namely, R25C (apoEKyoto), R114C (apoETsukuba), and A152D (apoELasVegas). All three apoE3 variants are found to have significantly reduced helical content and to be thermodynamically destabilized, both in lipid-free and lipoprotein-associated form, and to expose a larger portion of hydrophobic surface to the solvent compared with WT apoE3. Furthermore, all three apoE3 variants are aggregation-prone, as shown by dynamic light-scattering measurements and by their enhanced capacity to bind the amyloid probe thioflavin T. Overall, our data suggest that the LPG-associated apoE3 mutations R25C, R114C, and A152D induce protein misfolding, which may contribute to protein aggregation in glomerular capillaries. The similar effects of both LPG-associated proline and nonproline mutations on apoE3 structure suggest that the thermodynamic destabilization and enhanced aggregation of apoE3 may constitute a common underlying mechanism behind the pathogenesis of LPG.

Glomerular Lesions in Proteinuric Miniature Schnauzer Dogs

Miniature Schnauzer dogs are predisposed to idiopathic hypertriglyerceridemia, which increases risk for diseases such as pancreatitis and gallbladder mucocele. Recently, elevated triglyceride concentrations have been associated with proteinuria in this breed, although it is difficult to determine which abnormality is primary. Retrospective review of renal tissue from 27 proteinuric Miniature Schnauzers revealed that 20 dogs had ultrastructural evidence of osmophilic globules consistent with lipid in glomerular tufts. Seven of these dogs had lipid thromboemboli in glomerular capillary loops that distorted their shape and compressed circulating erythrocytes. Triglyceride concentrations were reported in 6 of these 7 dogs, and all were hypertriglyceridemic. In addition, glomerular lipidosis (defined as accumulation of foam cells within peripheral capillary loops) was identified in a single dog. The remaining 12 dogs had smaller amounts of lipid that could only be identified ultrastructurally. Neither signalment data nor clinicopathologic parameters (serum albumin, serum creatinine, urine protein-to-creatinine ratio, and blood pressure) differed among the various types of lipid lesions. During the time course of this study, all dogs diagnosed with glomerular lipid thromboemboli were Miniature Schnauzers, underscoring the importance of recognizing these clear spaces within capillary loops as lipid.

Genetic analysis of intracapillary glomerular lipoprotein deposits in aging mice

BACKGROUND

Renal aging is characterized by functional and structural changes like decreased glomerular filtration rate, and glomerular, tubular and interstitial damage. To gain insight in pathways involved in renal aging, we studied aged mouse strains and used genetic analysis to identify genes associated with aging phenotypes.

METHODS

Upon morphological screening in kidneys from 20-month-old mice from 26 inbred strains we noted intracapillary PAS-positive deposits. The severity of these deposits was quantified by scoring of a total of 50 glomeruli per section (grade 0-4). Electron microscopy and immunohistochemical staining for apoE, apoB, apoA-IV and perilipin-2 was performed to further characterize the lesions. To identify loci associated with these PAS-positive intracapillary glomerular deposits, we performed haplotype association mapping.

RESULTS

Six out of 26 mouse strains showed glomerular PAS-positive deposits. The severity of these deposits varied: NOD(0.97), NZW(0.41), NON(0.30), B10(0.21), C3 H(0.9) and C57BR(0.7). The intracapillary deposits were strongly positive for apoE and weakly positive for apoB and apoA-IV. Haplotype association mapping showed a strong association with a 30-Kb haplotype block on Chr 1 within the Esrrg gene. We investigated 1 Mb on each site of this region, which includes the genes Spata17, Gpatch2, Esrrg, Ush2a and Kctd3.

CONCLUSIONS

By analyzing 26 aged mouse strains we found that some strains developed an intracapillary PAS and apoE-positive lesion and identified a small haplotype block on Chr 1 within the Esrrg gene to be associated with these lipoprotein deposits. The region spanning this haplotype block contains the genes Spata17, Gpatch2, Esrrg, Ush2a and Kctd3, which are all highly expressed in the kidney. Esrrg might be involved in the evolvement of these glomerular deposits by influencing lipid metabolism and possibly immune reponses.

Apolipoprotein e mutation and double filtration plasmapheresis therapy on a new Chinese patient with lipoprotein glomerulopathy

BACKGROUND/AIMS

Lipoprotein glomerulopathy (LPG) is a rare hereditary disease. In this study, we investigated the apoE mutation and the role of double filtration plasmapheresis therapy (DFPP) on a new Chinese patient with LPG.

METHODS

Renal biopsy was performed on this patient to allow a definitive diagnosis. The mutations in the coding sequence of apoE and the hereditary pedigree of this patient were investigated by DNA sequencing. The patient was treated with DFPP, and clinical parameters before and after DFPP were compared.

RESULTS

Two missense mutations were found in this patient: Cys112Arg and Arg25Cys. Arg25Cys was previously designated as APOE Kyoto. Family genotyping showed that Cys112Arg and Arg25Cys mutation were transmitted through his father and his mother, respectively. The patient's parents are healthy so far to date. Possibly there was a dose effect on apoE mutation induced LPG. Furthermore, DFPP treatment was first used on this patient and led to dramatic changes: Proteinuria and apo E values declined, and hemoglobin level increased significantly.

CONCLUSION

APOE Kyoto mutation was found in a new Chinese patient with LPG, accompanied by Cys112Arg. More cases and further functional experiments are needed to investigate the role of these two mutations together in LPG. DFPP is an effective therapeutic modality for improving NS in patients with LPG.

Macrophage-derived apoESendai suppresses atherosclerosis while causing lipoprotein glomerulopathy in hyperlipidemic mice

Lipoprotein glomerulopathy (LPG) is a renal disease often accompanied by dyslipidemia and increased serum apoE levels. apoESendai (Arg145Pro), a rare mutant based on the apoE3 sequence carrying an apoE2 charge, causes LPG in humans and transgenic mice, but its effects on the artery wall are unknown. Macrophage expression of apoESendai may also directly influence renal and arterial homeostasis. We investigated the effects of macrophage-expressed apoESendai in apoE(-/-) mice with or without LDL receptor (LDLR). Murine bone marrow transduced to express apoE2, apoE3, or apoESendai was transplanted into lethally irradiated mice. Macrophage apoESendai expression reduced aortic lesion size and inflammation by 32 and 28%, respectively, compared with apoE2 in apoE(-/-) recipients. No differences in lesion size or inflammation were found between apoESendai and apoE3 in apoE(-/-) recipients. Macrophage apoESendai expression also reduced aortic lesion size by 18% and inflammation by 29% compared with apoE2 in apoE(-/-)/LDLR(-/-) recipients. Glomerular lesions compatible with LPG with increased mesangial matrix, extracellular lipid accumulation, and focal mesangiolysis were only observed in apoE(-/-)/LDLR(-/-) mice expressing apoESendai. Thus, macrophage expression of apoESendai protects against atherosclerosis while causing lipoprotein glomerulopathy. This is the first demonstration of an apoprotein variant having opposing effects on vascular and renal homeostasis.

Lipoprotein glomerulopathy associated with a mutation in apolipoprotein e

Lipoprotein glomerulopathy is a pathological condition characterized by lipid accumulation in the glomerular capillaries that has been associated with the presence of rare mutants of apolipoprotein E (ApoE). We describe a 51-year-old Italian patient presenting Type III hyperlipidemia and proteinuria in whom renal biopsy showed capillary ectasia and intraluminal lipid deposits, suggesting the diagnosis of lipoprotein glomerulopathy. The patient, who had elevated plasma ApoE level, was found to be heterozygous for a mutation in ApoE (Arg150Cys), designated apoE_MODENA. This mutation induces the formation of ApoE dimers that are detectable under non-reducing conditions. Treatment with hypolipidemic drugs did not result in a complete remission of the proteinuria and was accompanied by a slow but progressive worsening of renal function with the persistence of intracapillary lipid thrombi. The introduction of low-density lipoprotein aphaeresis combined with a more aggressive lipid lowering and antihypertensive therapy resulted in the remission of proteinuria and a substantial improvement of renal function. Switching from low-density lipoprotein aphaeresis to plasma filtration did not result in an equivalent control of renal damage. The patient died of intracranial hemorrhage during an acute episode of malignant hypertension.

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.

Thermodynamic and structural destabilization of apoE3 by hereditary mutations associated with the development of lipoprotein glomerulopathy

Lipoprotein glomerulopathy (LPG) is a dominant inherited kidney disorder characterized by lipoprotein thrombi in glomerular capillaries. Single-amino-acid mutations in apoE have been associated with the development of the disease, although the mechanism is unknown. In an effort to gain mechanistic insight linking the presence of such mutations and the development of LPG, we evaluated the effects of three of the most common apoE3 variants associated with this disease, namely R145P(Sendai), R147P(Chicago), and R158P(Osaka or Kurashiki), on the structural and conformational integrity of the protein. All three variants were found to have significantly reduced helical content, to expose a larger portion of hydrophobic surface to the solvent, and to be significantly thermodynamically destabilized, often lacking functionally relevant unfolding intermediates. Furthermore, all variants were aggregation prone and had enhanced sensitivity to protease digestion. Finally, although the variants were able to form discoidal lipoprotein particles, discrete subpopulations of poorly formed or aberrant particles were evident. Furthermore, these lipoprotein particles were thermodynamically destabilized and aggregation prone. Overall, our data suggest that these mutations induce a generalized unfolding of the N-terminal domain of apoE3 toward a molten-globule-like structure. ApoE3 N-terminal domain unfolding due to mutation may constitute a common mechanism underlying the protein's association with the pathogenesis of LPG.