PIK3CA inhibition in models of proliferative glomerulonephritis and lupus nephritis

Cell cycle disorders in podocytes: an emerging and increasingly recognized phenomenon

Proteinuria is observed in various kidney diseases and is frequently associated with a compromised glomerular filtration barrier. Podocytes, as a crucial component of this barrier, play an essential role in preserving the kidney's normal filtration function. Podocytes are terminally differentiated cells that typically do not proliferate. However, certain harmful stimuli can trigger podocytes to re-enter the cell cycle. Due to its unique cytoskeletal structure, podocytes are unable to maintain the structure of the foot process and complete cell division at the same time, eventually form binucleated or multinucleated podocytes. Studies have found that podocytes re-entering the cell cycle are more susceptible to injury, and are prone to detachment from the basement membrane or apoptosis, which are accompanied by the widening of foot processes. This eventually leads to podocyte mitotic catastrophe and the development of proteinuria. Podocyte cell cycle disorders have previously been found mainly in focal segmental glomerulosclerosis and IgA nephropathy. In recent years, this phenomenon has been frequently identified in diabetic kidney disease and lupus nephritis. An expanding body of research has begun to investigate the mechanisms underlying podocyte cell cycle disorders, including cell cycle re-entry, cell cycle arrest, and mitotic catastrophe. This review consolidates the existing literature on podocyte cell cycle disorders in renal diseases and summarizes the molecules that trigger podocyte re-entry into the cell cycle, thereby providing new drug targets for mitigating podocyte damage. This is essential for alleviating podocyte injury, reducing proteinuria, and delaying the progression of kidney diseases.

Spatial transcriptomics in autoimmune rheumatic disease: potential clinical applications and perspectives

Spatial transcriptomics is a cutting-edge technology that analyzes gene expression at the cellular level within tissues while integrating spatial location information. This concept, which combines high-plex RNA sequencing with spatial data, emerged in the early 2010s. Spatial transcriptomics has rapidly expanded with the development of technologies such as in situ hybridization, in situ sequencing, in situ spatial barcoding, and microdissection-based methods. Each technique offers advanced mapping resolution and precise spatial assessments at the single-cell level. Over the past decade, the use of spatial transcriptomics on clinical samples has enabled researchers to identify gene expressions in specific diseased foci, significantly enhancing our understanding of cellular interactions and disease processes. In the field of rheumatology, the complex and elusive pathophysiology of diseases such as rheumatoid arthritis, systemic lupus erythematosus, and Sjögren's syndrome remains a challenge for personalized treatment. Spatial transcriptomics provides insights into how different cell populations interact within disease foci, such as the synovial tissue, kidneys, and salivary glands. This review summarizes the development of spatial transcriptomics and current insights into the pathophysiology of autoimmune rheumatic diseases, focusing on immune cell distribution and cellular interactions within tissues. We also explore the potential of spatial transcriptomics from a clinical perspective and discuss the possibilities for translating this technology to the bedside.

The Role of Podocytes in Lupus Pathology

PURPOSE OF REVIEW

Kidney injury due to lupus nephritis (LN) is a severe and sometimes life-threatening sequela of systemic lupus erythematosus. Autoimmune injury to podocytes has been increasingly demonstrated to be a key driver of LN-related kidney injury because these cells play key roles in glomerular filtration barrier homeostasis. Irreparable podocyte injury impairs these processes and can lead to proteinuria, which is an indicator of poor prognosis in LN. This review highlights recent advances in our understanding of the involvement of podocytes in the pathogenesis of LN and discusses new podocyte-targeted therapeutic strategies.

RECENT FINDINGS

Podocytes play a key role in glomerular filtration barrier homeostasis, both by helping to secrete and organize the glomerular basement membrane and by the formation of a glomerular slit diaphragm between adjacent cells. Recent studies revealed the involvement of abnormal calcium signaling, dysregulation of actin-related proteins, and mitotic catastrophe in LN progression. In addition, podocytes express many molecules related to the innate and adaptive immune responses. IgG from patients with LN induces direct injury of podocytes, inflammasome, and interactions with immune cells which have been shown to promote the development of LN. Our understanding of the role of podocytes in the pathogenesis of LN has been improved. Recent studies have shed light on potential therapeutic strategies targeting podocytes to control kidney injury.

Cluster of differentiation-44 as a novel biomarker of lupus nephritis and its role in kidney inflammation and fibrosis

Introduction

CD44 is a transmembrane glycoprotein implicated in tissue inflammation and fibrosis. We investigated its role in kidney inflammation and fibrosis in a murine model of lupus nephritis (LN), and the clinico-pathological association of serum CD44 level in patients with biopsy-proven Class III/IV ± V LN.

Methods

NZB/W F1 mice were treated with control IgG or anti-CD44 monoclonal antibody for 4 weeks and disease parameters assessed. Serum CD44 level in LN patients was determined by ELISA. Control groups included healthy subjects and patients with non-renal SLE or non-lupus renal disease.

Results

CD44 expression was absent in the normal kidney, but it was expressed in proximal and distal tubular epithelial cells and infiltrating cells in renal biopsies from patients with active proliferative LN. ScRNA-Seq datasets confirmed that CD44 was predominantly expressed in tubular cells and all immune cells identified in LN patients including tissue resident, inflammatory and phagocytic macrophages, Treg cells, effector and central memory CD4+ T cells, resident memory CD8+ T cells and naïve and activated B cells. Treatment of NZB/W F1 mice with anti-CD44 antibody preserved kidney histology and reduced proteinuria, tubulo-interstitial infiltration of CD3+, CD4+ and CD19+ immune cells, and mediators of kidney fibrosis compared to Control mice. Longitudinal studies showed that serum CD44 level increased prior to clinical renal flare by 4.5 months and the level decreased after treatment. ROC curve analysis showed that CD44 level distinguished patients with active LN from healthy subjects and patients with quiescent LN, active non-renal lupus, and non-lupus CKD (ROC AUC of 0.99, 0.96, 0.99 and 0.99 respectively). CD44 level correlated with leukocyte infiltration and interstitial inflammation scores in active LN kidney biopsies.

Discussion

Our findings suggest that CD44 plays a pathogenic role in renal parenchymal inflammation and fibrosis in active LN and monitoring CD44 may facilitate early diagnosis of flare.

Genetic insights into the mechanisms of proliferative glomerulonephritis

Glomerular visceral epithelial cells (i.e., podocytes) are an essential component of the tripartite glomerular filtration barrier. Healthy podocytes are terminally differentiated cells with limited replicative capacity; however, inappropriate cell cycle reentry can be induced in podocytes by various injurious stimuli. In this issue of the JCI, Yamaguchi et al. report on a somatic mosaic gain-of-function mutation in the phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic α subunit (p110α, encoded by PIK3CA). The study reveals that activating mutations of p110α can drive podocyte proliferation in PIK3CA-related overgrowth syndrome (PROS). They also showed that selective, small-molecule inhibitors of p110 may be useful for the treatment of proliferative glomerulonephritis.