Dystroglycan in the molecular diagnosis of the podocytopathies

Protein N-glycans in Healthy and Sclerotic Glomeruli in Diabetic Kidney Disease

BACKGROUND

Diabetes is expected to directly impact renal glycosylation, yet to date, there has not been a comprehensive evaluation of alterations in N-glycan composition in the glomeruli of patients with diabetic kidney disease (DKD).

METHODS

We used untargeted mass spectrometry imaging to identify N-glycan structures in healthy and sclerotic glomeruli in FFPE sections from needle biopsies of five patients with DKD and three healthy kidney samples. Regional proteomics was performed on glomeruli from additional biopsies from the same patients to compare the abundances of enzymes involved in glycosylation. Secondary analysis of single nuclei transcriptomics (snRNAseq) data was used to inform on transcript levels of glycosylation machinery in different cell types and states.

RESULTS

We detected 120 N-glycans, and among them identified twelve of these protein post-translated modifications that were significantly increased in glomeruli. All glomeruli-specific N-glycans contained an N-acetyllactosamine (LacNAc) epitope. Five N-glycan structures were highly discriminant between sclerotic and healthy glomeruli. Sclerotic glomeruli had an additional set of glycans lacking fucose linked to their core, and they did not show tetra-antennary structures that are common in healthy glomeruli. Orthogonal omics analyses revealed lower protein abundance and lower gene expression involved in synthesizing fucosylated and branched N-glycans in sclerotic podocytes. In snRNAseq and regional proteomics analyses, we observed that genes and/or proteins involved in sialylation and LacNAc synthesis were also downregulated in DKD glomeruli, but this alteration remained undetectable by our spatial N-glycomics assay.

CONCLUSIONS

Integrative spatial glycomics, proteomics, and transcriptomics revealed protein N-glycosylation characteristic of sclerotic glomeruli in DKD.

Disinfectant dodecyl dimethyl benzyl ammonium chloride (DDBAC) disrupts gut microbiota, phospholipids, and calcium signaling in honeybees (Apis mellifera) at an environmentally relevant level

One of the impacts of the Coronavirus disease 2019 (COVID-19) pandemic has been a profound increase in the application amounts of disinfectants. Dodecyl dimethyl benzyl ammonium chloride (DDBAC) is a widely used disinfectant, yet its hazards to non-target species remain largely unknown. We are unaware of any studies assessing DDBAC's impacts on honeybee, a pollinator species that is a useful indicator of environmental pollution essential for many forms of agricultural production. Here, we assessed the potentially negative effects of DDBAC on honeybees. After conducting a formal toxicity evaluation of DDBAC on honeybee mortality, we detected an accumulation of DDBAC in the honeybee midgut. We subsequently studied the midgut tissues of honeybees exposed to sub-lethal concentrations of DDBAC: histopathological examination revealed damage to midgut tissue upon DDBAC exposure, microbiome analysis showed a decreased abundance of beneficial midgut microbiota, lipidomics analysis revealed a significant reduction in cell membrane phospholipids with known functions in signal transduction, and a transcriptome analysis detected altered expression of genes involved in calcium signaling pathways (that variously function in calcium absorption, muscle contraction, and neurotransmission). Thus, our study establishes that DDBAC impacts honeybee midgut functions at multiple levels. Our study represents an early warning about the hazards of DDBAC and appeals for the proper stewardship of DDBAC to ensure the protection of our ecological environment.

Glycosylation in health and disease

The glycome describes the complete repertoire of glycoconjugates composed of carbohydrate chains, or glycans, that are covalently linked to lipid or protein molecules. Glycoconjugates are formed through a process called glycosylation and can differ in their glycan sequences, the connections between them and their length. Glycoconjugate synthesis is a dynamic process that depends on the local milieu of enzymes, sugar precursors and organelle structures as well as the cell types involved and cellular signals. Studies of rare genetic disorders that affect glycosylation first highlighted the biological importance of the glycome, and technological advances have improved our understanding of its heterogeneity and complexity. Researchers can now routinely assess how the secreted and cell-surface glycomes reflect overall cellular status in health and disease. In fact, changes in glycosylation can modulate inflammatory responses, enable viral immune escape, promote cancer cell metastasis or regulate apoptosis; the composition of the glycome also affects kidney function in health and disease. New insights into the structure and function of the glycome can now be applied to therapy development and could improve our ability to fine-tune immunological responses and inflammation, optimize the performance of therapeutic antibodies and boost immune responses to cancer. These examples illustrate the potential of the emerging field of 'glycomedicine'.

Extracellular Matrix in Kidney Fibrosis: More Than Just a Scaffold

Kidney fibrosis is the common histological end-point of progressive, chronic kidney diseases (CKDs) regardless of the underlying etiology. The hallmark of renal fibrosis, similar to all other organs, is pathological deposition of extracellular matrix (ECM). Renal ECM is a complex network of collagens, elastin, and several glycoproteins and proteoglycans forming basal membranes and interstitial space. Several ECM functions beyond providing a scaffold and organ stability are being increasingly recognized, for example, in inflammation. ECM composition is determined by the function of each of the histological compartments of the kidney, that is, glomeruli, tubulo-interstitium, and vessels. Renal ECM is a dynamic structure undergoing remodeling, particularly during fibrosis. From a clinical perspective, ECM proteins are directly involved in several rare renal diseases and indirectly in CKD progression during renal fibrosis. ECM proteins could serve as specific non-invasive biomarkers of fibrosis and scaffolds in regenerative medicine. The gold standard and currently only specific means to measure renal fibrosis is renal biopsy, but new diagnostic approaches are appearing. Here, we discuss the localization, function, and remodeling of major renal ECM components in healthy and diseased, fibrotic kidneys and the potential use of ECM in diagnostics of renal fibrosis and in tissue engineering.

Understanding podocytopathy and its relevance to clinical nephrology

Podocytopathies are the most common group of glomerular disorder leading to proteinuria. On the basis of pathophysiology, light microscopic and ultrastructural evaluation, the podocytopathies include minimal change disease, diffuse mesangial sclerosis, focal segmental glomerulosclerosis and collapsing glomerulopathy. The present review summarizes the basic etiopathogenesis of podocytopthies, highlights the common genetic and acquired factors in its causation, puts forth various diagnostic modalities and discusses the role of emerging agents or treatment.

Focal and segmental glomerulosclerosis: multiple pathways are involved

Focal segmental glomerulosclerosis (FSGS) is not a disease but a clinicopathologic entity. The term FSGS itself is a misnomer because its lesions are not always focal, segmental, or sclerotic. Its clinical expression also widely varies and is nonspecific. Confronted with such diversity, one cannot but translate the title of this contribution into a unifying version focusing on the podocyte, initial culprit, or victim of multiple processes leading to FSGS. Some have been identified in human glomerulopathies and/or in animal or cell culture models, and are classified as secondary. Genetic forms, nonsyndromic or syndromic, have adduced a wealth of knowledge on the slit diaphragm architecture and explain the reason for their steroid resistance. Others, mostly expressed by a nephrotic syndrome, will be considered as idiopathic until the offending factor(s) that affect the molecular array of the slit diaphragm filtration barrier are identified and counteracted. Recent research has lead to suggesting that FSGS is not a T-cell-driven autoimmune glomerulopathy. Thus, treatments considered as etiologic, including glucocorticoids and calcineurin inhibitors, are in fact endowed with a mode of action on podocytes that suggests that drugs used such as immunosuppressors also might be considered as antiproteinuric agents.

Genetics of focal segmental glomerulosclerosis and human immunodeficiency virus-associated collapsing glomerulopathy: the role of MYH9 genetic variation

Until recently, knowledge of genetic causes of glomerular disease was limited to certain rare or uncommon inherited diseases, and to genes, either rare or with small effect, identified in candidate gene studies. These genetic factors accounted for only a very small fraction of kidney disease. However, the striking differences in frequency of many forms of kidney disease between African Americans and European Americans, which could not be explained completely by cultural or economic factors, pointed to a large unidentified genetic influence. Because focal segmental glomerulosclerosis (FSGS) and human immunodeficiency virus-associated collapsing glomerulopathy have striking racial disparities, we performed an admixture mapping study to identify contributing genetic factors. Admixture mapping identified genetic variants in the nonmuscle myosin heavy chain 9 gene (MYH9) as having a major influence on both FSGS and human immunodeficiency virus-associated collapsing glomerulopathy, with odds ratios from 4 to 8 and attributable fractions of 70% to 100%. Previously identified, rare, inherited MYH9 disorders point to a mechanism by which MYH9 variation disrupts the actin-myosin filaments responsible for maintaining the structure of podocytes, the cells that provide one of three filtration barriers in the glomeruli. MYH9 variation has a smaller but still highly significant effect on nondiabetic kidney disease, and a weaker but significant effect on diabetic kidney disease; it is unclear whether underlying cryptic FSGS is responsible for the MYH9 association with these diseases. The strong predicted power of MYH9 variation for disease indicates a clear role for genetic testing for these variants in personalized medicine, for assessment of genetic risk, and potentially for diagnosis.