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In a trial involving patients with later-stage ADPKD, the V 2 -receptor antagonist tolvaptan resulted in a slower decline than placebo in the estimated GFR over a 1-year period, which may slow the onset of end-stage kidney disease.

Autosomal dominant polycystic kidney disease is the most common inherited kidney disease and accounts for 7–10% of all patients on renal replacement therapy worldwide. Although first reported 500 years ago, this disorder is still regarded as untreatable and its pathogenesis is poorly understood despite much study. During the past 40 years, however, remarkable advances have transformed our understanding of how the disease develops and have led to rapid changes in diagnosis, prognosis, and treatment, especially during the past decade. This Review will summarise the key findings, highlight recent developments, and look ahead to the changes in clinical practice that will likely arise from the adoption of a new management framework for this major kidney disease.

In the past decade, kidney disease diagnosed with objective measures of kidney damage and function has been recognised as a major public health burden. The population prevalence of chronic kidney disease exceeds 10%, and is more than 50% in high-risk subpopulations. Independent of age, sex, ethnic group, and comorbidity, strong, graded, and consistent associations exist between clinical prognosis and two hallmarks of chronic kidney disease: reduced glomerular filtration rate and increased urinary albumin excretion. Furthermore, an acute reduction in glomerular filtration rate is a risk factor for adverse clinical outcomes and the development and progression of chronic kidney disease. An increasing amount of evidence suggests that the kidneys are not only target organs of many diseases but also can strikingly aggravate or start systemic pathophysiological processes through their complex functions and effects on body homoeostasis. Risk of kidney disease has a notable genetic component, and identified genes have provided new insights into relevant abnormalities in renal structure and function and essential homoeostatic processes. Collaboration across general and specialised health-care professionals is needed to fully address the challenge of prevention of acute and chronic kidney disease and improve outcomes.

Peritoneal dialysis involves diffusive and convective transports and osmosis through the highly vascularized peritoneal membrane. The capillary endothelium offers the rate-limiting hindrance for solute and water transport. It can be functionally described in terms of a three-pore model including transcellular, ultrasmall pores responsible for free-water transport during crystalloid osmosis. Several lines of evidence have demonstrated that the water channel aquaporin-1 (AQP1) corresponds to the ultrasmall pore located in endothelial cells. Studies in Aqp1 mice have shown that deletion of AQP1 is reflected by a 50% decrease in ultrafiltration and a disappearance of the sodium sieving. Haploinsufficiency in AQP1 is also reflected by a significant attenuation of water transport. Conversely, studies in a rat model and in PD patients have shown that the induction of AQP1 in peritoneal capillaries by corticosteroids is reflected by increased water transport and ultrafiltration, without affecting the osmotic gradient and small-solute transport. Recent data have demonstrated that a novel agonist of AQP1, predicted to stabilize the open-state conformation of the channel, modulates water transport and improves ultrafiltration. Whether increasing the expression of AQP1 or gating the already existing channels would be clinically useful in PD patients remains to be investigated.

Little is known about the molecular changes that take place in the kidney during the aging process. In order to better understand these changes, we measured mRNA and protein levels in genetically diverse mice at different ages. We observed distinctive change in mRNA and protein levels as a function of age. Changes in both mRNA and protein are associated with increased immune infiltration and decreases in mitochondrial function. Proteins show a greater extent of change and reveal changes in a wide array of biological processes including unique, organ-specific features of aging in kidney. Most importantly, we observed functionally important age-related changes in protein that occur in the absence of corresponding changes in mRNA. Our findings suggest that mRNA profiling alone provides an incomplete picture of molecular aging in the kidney and that examination of changes in proteins is essential to understand aging processes that are not transcriptionally regulated.

Deregulation of mitochondrial network in terminally differentiated cells contributes to a broad spectrum of disorders. Methylmalonic acidemia (MMA) is one of the most common inherited metabolic disorders, due to deficiency of the mitochondrial methylmalonyl-coenzyme A mutase (MMUT). How MMUT deficiency triggers cell damage remains unknown, preventing the development of disease–modifying therapies. Here we combine genetic and pharmacological approaches to demonstrate that MMUT deficiency induces metabolic and mitochondrial alterations that are exacerbated by anomalies in PINK1/Parkin–mediated mitophagy, causing the accumulation of dysfunctional mitochondria that trigger epithelial stress and ultimately cell damage. Using drug–disease network perturbation modelling, we predict targetable pathways, whose modulation repairs mitochondrial dysfunctions in patient–derived cells and alleviate phenotype changes in mmut –deficient zebrafish. These results suggest a link between primary MMUT deficiency, diseased mitochondria, mitophagy dysfunction and epithelial stress, and provide potential therapeutic perspectives for MMA. Methylmalonic acidemia is an inherited metabolic disease caused by loss or mutation of the enzyme MMUT. Here the authors use cell and animal models to show that MMUT mutations lead to defective mitophagy and stress in kidney cells, contributing to the pathogenesis in methylmalonic acidemia patients.

Key Points OCRL mutations cause Lowe syndrome, an X-linked disease characterized by congenital cataracts, central nervous system involvement and renal Fanconi syndrome; the only available treatments are surgery for cataracts and symptomatic care for renal dysfunction OCRL encodes a 5-phosphatase that acts preferentially on phosphatidylinositol 4,5-bisphosphate (PI(4,5)P 2 ), a phosphoinositide with a pivotal role in intracellular trafficking; disease-causing mutations occur throughout the OCRL gene, but mainly in exons 9–15, which encode the catalytic domain Mutations in OCRL also cause Dent disease 2, a milder condition that results in renal Fanconi syndrome similar to that of Dent disease 1, caused by mutations in the gene that encodes the endosomal chloride channel ClC-5 OCRL localizes mainly in endolysosomal compartments; its dysfunction causes an accumulation of PI(4,5)P 2 resulting in delayed recycling of receptors required for protein reabsorption and impairment of the lysosomal–autophagic pathway Mouse and zebrafish animal models of Lowe syndrome are available, but these do not fully recapitulate the manifestations of Lowe syndrome Areas for future research include the mechanisms underlying the tissue selective manifestations of Lowe syndrome and Dent disease 2 as well as the identification of effective therapeutic strategies Dysfunction of endolysosomal pathways can lead to generalized dysfunction of the proximal tubule. Here, De Matteis and colleagues describe the role of the inositol polyphosphate 5-phosphatase, OCRL, in the endolysosomal pathway and how mutations in the encoding gene lead to the clinical manifestations of Lowe syndrome and Dent disease 2. Lowe syndrome is an X-linked disease that is characterized by congenital cataracts, central hypotonia, intellectual disability and renal Fanconi syndrome. The disease is caused by mutations in OCRL , which encodes an inositol polyphosphate 5-phosphatase (OCRL) that acts on phosphoinositides — quantitatively minor constituents of cell membranes that are nonetheless pivotal regulators of intracellular trafficking. In this Review we summarize the considerable progress made over the past decade in understanding the cellular roles of OCRL in regulating phosphoinositide balance along the endolysosomal pathway, a fundamental system for the reabsorption of proteins and solutes by proximal tubular cells. We discuss how studies of OCRL have led to important discoveries about the basic mechanisms of membrane trafficking and describe the key features and limitations of the currently available animal models of Lowe syndrome. Mutations in OCRL can also give rise to a milder pathology, Dent disease 2, which is characterized by renal Fanconi syndrome in the absence of extrarenal pathologies. Understanding how mutations in OCRL give rise to two clinical entities with differing extrarenal manifestations represents an opportunity to identify molecular pathways that could be targeted to develop treatments for these conditions.

Uromodulin (Tamm–Horsfall protein) is the most abundant protein excreted in the urine under physiological conditions. It is exclusively produced in the kidney and secreted into the urine via proteolytic cleavage. Its biological function is still not fully understood. Uromodulin has been linked to water/electrolyte balance and to kidney innate immunity. Also, studies in knockout mice demonstrated that it has a protective role against urinary tract infections and renal stone formation. Mutations in the gene encoding uromodulin lead to rare autosomal dominant diseases, collectively referred to as uromodulin-associated kidney diseases. They are characterized by progressive tubulointerstitial damage, impaired urinary concentrating ability, hyperuricemia, renal cysts, and progressive renal failure. Novel in vivo studies point at intracellular accumulation of mutant uromodulin as a key primary event in the disease pathogenesis. Recently, genome-wide association studies identified uromodulin as a risk factor for chronic kidney disease (CKD) and hypertension, and suggested that the level of uromodulin in the urine could represent a useful biomarker for the development of CKD. In this review, we summarize these recent investigations, ranging from invalidation studies in mouse to Mendelian disorders and genome-wide associations, which led to a rediscovery of uromodulin and boosted the scientific and clinical interest for this long discovered molecule.

At least 10% of adults and nearly all children who receive renal-replacement therapy have an inherited kidney disease. These patients rarely die when their disease progresses and can remain alive for many years because of advances in organ-replacement therapy. However, these disorders substantially decrease their quality of life and have a large effect on health-care systems. Since the kidneys regulate essential homoeostatic processes, inherited kidney disorders have multisystem complications, which add to the usual challenges for rare disorders. In this review, we discuss the nature of rare inherited kidney diseases, the challenges they pose, and opportunities from technological advances, which are well suited to target the kidney. Mechanistic insights from rare disorders are relevant for common disorders such as hypertension, kidney stones, cardiovascular disease, and progression of chronic kidney disease.

Rare autosomal dominant tubulointerstitial kidney disease is caused by mutations in the genes encoding uromodulin (UMOD), hepatocyte nuclear factor-1β (HNF1B), renin (REN), and mucin-1 (MUC1). Multiple names have been proposed for these disorders, including ‘Medullary Cystic Kidney Disease (MCKD) type 2’, ‘Familial Juvenile Hyperuricemic Nephropathy (FJHN)’, or ‘Uromodulin-Associated Kidney Disease (UAKD)’ for UMOD-related diseases and ‘MCKD type 1’ for the disease caused by MUC1 mutations. The multiplicity of these terms, and the fact that cysts are not pathognomonic, creates confusion. Kidney Disease: Improving Global Outcomes (KDIGO) proposes adoption of a new terminology for this group of diseases using the term ‘Autosomal Dominant Tubulointerstitial Kidney Disease’ (ADTKD) appended by a gene-based subclassification, and suggests diagnostic criteria. Implementation of these recommendations is anticipated to facilitate recognition and characterization of these monogenic diseases. A better understanding of these rare disorders may be relevant for the tubulointerstitial fibrosis component in many forms of chronic kidney disease.