Historical aspects of proteinuria

Emerging Technologies to Study the Glomerular Filtration Barrier

Kidney disease is characterized by loss of glomerular function with clinical manifestation of proteinuria. Identifying the cellular and molecular changes that lead to loss of protein in the urine is challenging due to the complexity of the filtration barrier, constituted by podocytes, glomerular endothelial cells, and glomerular basement membrane. In this review, we will discuss how technologies like single cell RNA sequencing and bioinformatics-based spatial transcriptomics, as well as in vitro systems like kidney organoids and the glomerulus-on-a-chip, have contributed to our understanding of glomerular pathophysiology. Knowledge gained from these studies will contribute toward the development of personalized therapeutic approaches for patients affected by proteinuric diseases.

From Proteinuria to Fibrosis: An Update on Pathophysiology and Treatment Options

BACKGROUND

Proteinuria is a key biomarker in nephrology. It is central to diagnosis and risk assessment and the primary target of many important therapies. Etiologies resulting in pathological proteinuria include congenital and acquired disorders, as well as both glomerular (immune/non-immune mediated) and tubular defects.

SUMMARY

Untreated proteinuria is strongly linked to progressive loss of kidney function and kidney failure. Excess protein reaching the renal tubules is ordinarily resorbed by the tubular epithelium. However, when these mechanisms are overwhelmed, a variety of inflammatory and fibrotic pathways are activated, causing both interstitial fibrosis and glomerulosclerosis. Nevertheless, the specific mechanisms underlying this are complex and remain incompletely understood. Recently, a number of treatments, in addition to angiotensin system blockade, have been shown to effectively slow the progression of proteinuric chronic kidney disease. However, additional therapies are clearly needed. Key message: This review provides an update on the pathophysiology of proteinuria, the pathways leading to fibrosis, and an overview of current and emerging therapies.

A narrative review of proteinuria and albuminuria as clinical biomarkers in children

Proteinuria is an important biomarker commonly used to detect and manage kidney disease in children. There are now a variety of methods available to measure urinary protein loss, and physicians are faced with several contrasting strategies: 24-h or timed collection versus spot samples (first-morning or random), measurement of total urinary protein versus selective measurement of urinary albumin, unadjusted urine protein concentration versus protein-to-creatinine ratio and the use of dipstick versus laboratory-based methods. In this review, we will discuss the advantages and disadvantages of these different approaches. We will then summarise the evidence base for proteinuria as a clinical biomarker in different settings, including discussion of the current and potential role of measuring low-level albuminuria. Finally, we will highlight gaps in the literature and opportunities for further research into proteinuria among children.

Membranous nephropathy: thinking through the therapeutic options

Idiopathic membranous nephropathy (IMN) remains the most common cause of the nephrotic syndrome in adults and one of the leading identifiable causes of end-stage kidney disease. Prior to considering the best approach to treatment, three important components need to be considered. First, the natural history of the typical membranous patient today; second, the importance of identifying the causative factors; and third, the integration of the current data on the known autoantibody/antigen systems involved in IMN into the diagnosis and management of the patient. Combining this with information on the known indicators associated with a poor prognosis plus new data on surrogate markers that provide important clues that the treatment plan is correct has provided us with a more secure platform for choosing the right treatment for each patient. This already provides a more rational and precise approach to the use of our current therapeutic options. Even today, we can slow disease progression and in the future new approaches and new therapies are likely to lead to prevention of progression or even reversal of the injury in IMN, thereby leading to improved quality of life of our patients.

Membranous nephropathy: integrating basic science into improved clinical management

Idiopathic membranous nephropathy (INM) remains a common cause of the nephrotic syndrome in adults. The autoimmune nature of IMN was clearly delineated in 2009 with the identification of the glomerular-deposited IgG to be a podocyte receptor, phospholipase A2 receptor (PLA2R) in 70% to 75% of cases. This anti-PLA2R autoantibody, predominantly the IgG4 subclass, has been quantitated in serum using an enzyme-linked immunosorbent assay and has been used to aid diagnosis and monitor response to immunosuppressive therapy. In 2014, a second autoantigen, thrombospondin type 1 domain-containing 7A (THSD7A), was identified. Immunostaining of biopsy specimens has further detected either PLA2R or THSD7A antigen in the deposited immune complexes in 5% to 10% of cases autoantibody seronegative at the time of biopsy. Therefore, the term IMN should now be superseded by the term primary or autoimmune MN (AMN) (anti-PLA2R or anti-THSD7A positive) classifying ∼80% to 90% of cases previously designated IMN. Cases of secondary MN associated with other diseases show much lower association with these autoantibodies, but their true incidence in secondary cases still needs to be defined. How knowledge of the autoimmune mechanism and the sequential measurement of these autoantibodies is likely to change the clinical management and trajectory of AMN by more precisely defining its diagnosis, prognosis, and treatment is discussed. Their application early in the disease course to new and old therapies will provide additional precision to AMN management. We also review innovative therapeutic approaches on the horizon that are expected to lead to our ultimate goal of improved patient care in A(I)MN.