Focal segmental glomerulosclerosis with heterozygous apolipoprotein E5 (Glu3Lys)

Proteomics of Plasma and Plasma-Treated Podocytes: Application to Focal and Segmental Glomerulosclerosis

Focal and segmental glomerulosclerosis (FSGS) is a severe form of idiopathic nephrotic syndrome (INS), a glomerulopathy of presumably immune origin that is attributed to extrarenal pathogenic circulating factors. The recurrence of FSGS (rFSGS) after transplant occurs in 30% to 50% of cases. The direct analysis of patient plasma proteome has scarcely been addressed to date, mainly due to the methodological difficulties associated with plasma complexity and dynamic range. In this study, first, we compared different methods of plasma preparation, second, we compared the plasma proteomes of rFSGS and controls using two preparation methods, and third, we analyzed the early proximal signaling events in podocytes subjected to patient plasma, through a combination of phosphoproteomics and lipid-raft proteomics (raftomics). By combining immunodepletion and high pH fractionation, we performed a differential proteomic analysis of soluble plasma proteins and of extracellular vesicles (EV) obtained from healthy controls, non-INS patient controls, and rFSGS patients (n = 4). In both the soluble- and the EV-protein sets from the rFSGS patients, we found a statistically significant increase in a cluster of proteins involved in neutrophil degranulation. A group of lipid-binding proteins, generally associated with lipoproteins, was found to be decreased in the soluble set from the rFSGS patients. In addition, three amino acid transporters involved in mTORC1 activation were found to be significantly increased in the EV from the rFSGS. Next, we incubated human podocytes for 30 min with 10% plasma from both groups of patients. The phosphoproteomics and raftomics of the podocytes revealed profound differences in the proteins involved in the mTOR pathway, in autophagy, and in cytoskeleton organization. We analyzed the correlation between the abundance of plasma and plasma-regulated podocyte proteins. The observed changes highlight some of the mechanisms involved in FSGS recurrence and could be used as specific early markers of circulating-factor activity in podocytes.

From degenerative disease to malignant tumors: Insight to the function of ApoE

Apolipoprotein E (ApoE) is a multifunctional protein involved in lipid transport and lipoprotein metabolism, mediating lipid distribution/redistribution in tissues and cells. It can also regulate inflammation and immune function, maintain cytoskeleton stability, and improve neural tissue Function. Due to genetic polymorphisms of ApoE (ε2, ε3, and ε4), its three common structural isoforms (ApoE2, ApoE3, ApoE4) are also associated with the risk of many diseases, especially degenerative diseases, such as vascular degenerative diseases including atherosclerosis (AS), coronary heart disease (CHD), and neurodegenerative disease like Alzheimer's disease (AD). The frequency of the ε4 allele and APOE variants were significantly higher than that of the ε2 and ε3 alleles in the patients with CHD or AD. In recent years, ApoE has frequently appeared in tumor research and become a tumor biomarker gradually. It has been found that ApoE is highly expressed in most solid tumor tissues, such as glioblastoma, gastric cancer, pancreatic ductal cell carcinoma, etc. Studies illustrated that ApoE could regulate the polarization changes of macrophages, participate in the construction of tumor immune microenvironment, regulate tumor inflammation and immune response and play a role in tumor progression, invasion, and metastasis. Of course, many functions of ApoE and its relationship with diseases are still under research. By reviewing the structure and function of ApoE from degeneration diseases to tumor neoplasms, we hope to better understand such a biomarker and further explore the value of ApoE in later studies.

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.

Apolipoprotein E and Atherosclerosis

PURPOSE OF REVIEW

The functions, genetic variations and impact of apolipoprotein E on lipoprotein metabolism in general are placed in the context of clinical practice dealing with moderate dyslipidaemia as well as dysbetalipoproteinemia, a highly atherogenic disorder and lipoprotein glomerulopathy.

RECENT FINDINGS

Additional variants of apolipoprotein E and participation of apolipoprotein E in inflammation are of interest. The mostly favourable effects of apolipoprotein E2 as well as the atherogenic nature of apolipoproteinE4, which has an association with cognitive impairment, are confirmed. The contribution of remnant lipoproteins of triglyceride-rich lipoproteins, of which dysbetalipoproteinemia represents an extreme, is explored in atherosclerosis. Mimetic peptides may present new therapeutic approaches. Apolipoprotein E is an important determinant of the lipid profile and cardiovascular health in the population at large and can precipitate dysbetalipoproteinemia and glomerulopathy. Awareness of apolipoprotein E polymorphisms should improve medical care.

Dyslipidemia in Kidney Disorders: Perspectives on Mitochondria Homeostasis and Therapeutic Opportunities

To excrete body nitrogen waste and regulate electrolyte and fluid balance, the kidney has developed into an energy factory with only second to the heart in mitochondrial content in the body to meet the high-energy demand and regulate homeostasis. Energy supply from the renal mitochondria majorly depends on lipid metabolism, with programed enzyme systems in fatty acid β-oxidation and Krebs cycle. Renal mitochondria integrate several metabolic pathways, including AMPK/PGC-1α, PPARs, and CD36 signaling to maintain energy homeostasis for dynamic and static requirements. The pathobiology of several kidney disorders, including diabetic nephropathy, acute and chronic kidney injuries, has been primarily linked to impaired mitochondrial bioenergetics. Such homeostatic disruption in turn stimulates a pathological adaptation, with mitochondrial enzyme system reprograming possibly leading to dyslipidemia. However, this alteration, while rescuing oncotic pressure deficit secondary to albuminuria and dissipating edematous disorder, also imposes an ominous lipotoxic consequence. Reprograming of lipid metabolism in kidney injury is essential to preserve the integrity of kidney mitochondria, thereby preventing massive collateral damage including excessive autophagy and chronic inflammation. Here, we review dyslipidemia in kidney disorders and the most recent advances on targeting mitochondrial energy metabolism as a therapeutic strategy to restrict renal lipotoxicity, achieve salutary anti-edematous effects, and restore mitochondrial homeostasis.

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.

Mechanisms of Scarring in Focal Segmental Glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) presents with scar in parts of some glomeruli and often progresses to global and diffuse glomerulosclerosis. Podocyte injury is the initial target in primary FSGS, induced by a circulating factor. Several gene variants, for example, APOL1, are associated with increased susceptibility to FSGS. Primary FSGS may be due to genetic mutation in key podocyte genes. Increased work stress after loss of nephrons, epigenetic mechanisms, and various profibrotic pathways can contribute to progressive sclerosis, regardless of the initial injury. The progression of FSGS lesions also involves crosstalk between podocytes and other kidney cells, such as parietal epithelial cells, glomerular endothelial cells, and even tubular epithelial cells. New insights related to these mechanisms could potentially lead to new therapeutic strategies to prevent progression of FSGS.