Nephrology encompasses the study of normal kidney function, kidney disease, and kidney replacement therapy, including kidney transplantation and dialysis. Kidney diseases are a serious public health problem, with nearly 12% of American adults suffering from chronic kidney disease (CKD). Importantly, kidney dysfunction is associated with the increasingly common conditions of obesity, diabetes, and hypertension. Recent technological advances, including genetic and epigenetic screens, metabolic profiling, new model systems, and the use of kidney biopsies for diagnosis and treatment, have created new avenues for the study of kidney pathology. Reviews in this series provide a survey of kidney pathogenesis, including hypertension, diabetic kidney disease, IgA nephropathy, idiopathic membranous nephropathy, acute kidney injury, fibrosis, and mechanisms mediating graft failure after transplantation.
Kidney disease is one of the most prevalent chronic conditions and is a frequent complication of diabetes, cardiovascular disease, and obesity. Recent advances in biomedical research and novel technologies have created opportunities to study kidney disease in a variety of platforms, applied to human populations. The Reviews in this series discuss the kidney in hypertension, diabetes, and monogenic forms of kidney disease, as well as the cellular and molecular mediators of acute kidney injury and fibrosis, IgA nephropathy and idiopathic membranous nephropathy, and kidney transplantation. In this introduction, we briefly review new insights into focal segmental glomerulosclerosis and the role of podocytes in health and disease. Additionally, we discuss how new technologies, therapeutics, and the availability of patient data can help shape the study of kidney disease and ultimately inform policies concerning biomedical research and health care.
John F. O’Toole, John R. Sedor
Fibrosis is a characteristic feature of all forms of chronic kidney disease. Deposition of pathological matrix in the interstitial space and within the walls of glomerular capillaries as well as the cellular processes resulting in this deposition are increasingly recognized as important factors amplifying kidney injury and accelerating nephron demise. Recent insights into the cellular and molecular mechanisms of fibrogenesis herald the promise of new therapies to slow kidney disease progression. This review focuses on new findings that enhance understanding of cellular and molecular mechanisms of fibrosis, the characteristics of myofibroblasts, their progenitors, and molecular pathways regulating both fibrogenesis and its resolution.
Jeremy S. Duffield
As recently as 2002, most cases of primary membranous nephropathy (MN), a relatively common cause of nephrotic syndrome in adults, were considered idiopathic. We now recognize that MN is an organ-specific autoimmune disease in which circulating autoantibodies bind to an intrinsic antigen on glomerular podocytes and form deposits of immune complexes in situ in the glomerular capillary walls. Here we define the clinical and pathological features of MN and describe the experimental models that enabled the discovery of the major target antigen, the M-type phospholipase A2 receptor 1 (PLA2R). We review the pathophysiology of experimental MN and compare and contrast it with the human disease. We discuss the diagnostic value of serological testing for anti-PLA2R and tissue staining for the redistributed antigen, and their utility for differentiating between primary and secondary MN, and between recurrent MN after kidney transplant and de novo MN. We end with consideration of how knowledge of the antigen might direct future therapeutic strategies.
Laurence H. Beck Jr., David J. Salant
Recent advances in defining the genetic mechanisms of disease causation and modification in autosomal dominant polycystic kidney disease (ADPKD) have helped to explain some extreme disease manifestations and other phenotypic variability. Studies of the ADPKD proteins, polycystin-1 and -2, and the development and characterization of animal models that better mimic the human disease, have also helped us to understand pathogenesis and facilitated treatment evaluation. In addition, an improved understanding of aberrant downstream pathways in ADPKD, such as proliferation/secretion-related signaling, energy metabolism, and activated macrophages, in which cAMP and calcium changes may play a role, is leading to the identification of therapeutic targets. Finally, results from recent and ongoing preclinical and clinical trials are greatly improving the prospects for available, effective ADPKD treatments.
Peter C. Harris, Vicente E. Torres
IgA nephropathy (IgAN) represents the leading cause of kidney failure among East Asian populations and the most frequent form of primary glomerulonephritis among Europeans. Patients with IgAN develop characteristic IgA1-containing immune complexes that deposit in the glomerular mesangium, producing progressive kidney injury. Recent studies define IgAN as an autoimmune trait of complex architecture with a strong genetic determination. This Review summarizes new insights into the role of the
Krzysztof Kiryluk, Jan Novak
Diabetic kidney disease (DKD) is the leading cause of kidney failure worldwide and the single strongest predictor of mortality in patients with diabetes. DKD is a prototypical disease of gene and environmental interactions. Tight glucose control significantly decreases DKD incidence, indicating that hyperglycemia-induced metabolic alterations, including changes in energy utilization and mitochondrial dysfunction, play critical roles in disease initiation. Blood pressure control, especially with medications that inhibit the angiotensin system, is the only effective way to slow disease progression. While DKD is considered a microvascular complication of diabetes, growing evidence indicates that podocyte loss and epithelial dysfunction play important roles. Inflammation, cell hypertrophy, and dedifferentiation by the activation of classic pathways of regeneration further contribute to disease progression. Concerted clinical and basic research efforts will be needed to understand DKD pathogenesis and to identify novel drug targets.
Kimberly Reidy, Hyun Mi Kang, Thomas Hostetter, Katalin Susztak
An essential link between the kidney and blood pressure control has long been known. Here, we review evidence supporting the premise that an impaired capacity of the kidney to excrete sodium in response to elevated blood pressure is a major contributor to hypertension, irrespective of the initiating cause. In this regard, recent work suggests that novel pathways controlling key sodium transporters in kidney epithelia have a critical impact on hypertension pathogenesis, supporting a model in which impaired renal sodium excretion is a final common pathway through which vascular, neural, and inflammatory responses raise blood pressure. We also address recent findings calling into question long-standing notions regarding the relationship between sodium intake and changes in body fluid volume. Expanded understanding of the role of the kidney as both a cause and target of hypertension highlights key aspects of pathophysiology and may lead to identification of new strategies for prevention and treatment.
Steven D. Crowley, Thomas M. Coffman
Improvements in clinical care and immunosuppressive medications have positively affected outcomes following kidney transplantation, but graft survival remains suboptimal, with half-lives of approximately 11 years. Late graft loss results from a confluence of processes initiated by ischemia-reperfusion injury and compounded by effector mechanisms of uncontrolled alloreactive T cells and anti-HLA antibodies. When combined with immunosuppressant toxicity, post-transplant diabetes and hypertension, and recurrent disease, among other factors, the result is interstitial fibrosis, tubular atrophy, and graft failure. Emerging evidence over the last decade unexpectedly identified the complement cascade as a common thread in this process. Complement activation and function affects allograft injury at essentially every step. These fundamental new insights, summarized herein, provide the foundation for testing the efficacy of various complement antagonists to improve kidney transplant function and long-term graft survival.
Paolo Cravedi, Peter S. Heeger
Acute kidney injury (AKI) remains a major clinical event with rising incidence, severity, and cost; it now has a morbidity and mortality exceeding acute myocardial infarction. There is also a documented conversion to and acceleration of chronic kidney disease to end-stage renal disease. The multifactorial nature of AKI etiologies and pathophysiology and the lack of diagnostic techniques have hindered translation of preclinical success. An evolving understanding of epithelial, endothelial, and inflammatory cell interactions and individualization of care will result in the eventual development of effective therapeutic strategies. This review focuses on epithelial and endothelial injury mediators, interactions, and targets for therapy.
Bruce A. Molitoris