NF B Promotes Inflammation, Coagulation, and Fibrosis in the Aging Glomerulus

The peak prevalence of ESRD from glomerulosclerosis occurs at 70 to 79 years. To understand why old glomeruli are prone to failure, we analyzed the Fischer 344 rat model of aging under ad libitum-fed (rapid aging) and calorie-restricted (slowed aging) conditions. All glomerular cells contained genes whose expression changed “linearly” during adult life from 2 to 24 months: mesangial cells (e.g., MMP9), endothelial cells (e.g., ICAM and VCAM), parietal epithelial cells (e.g., ceruloplasmin), and podocytes (e.g., nephrin and prepronociceptin). Patterns of aging glomerular gene expression closely resembled atherosclerosis, including activation of endothelial cells, epithelial cells, and macrophages, as well as proinflammatory pathways related to cell adhesion, chemotaxis, blood coagulation, oxidoreductases, matrix metalloproteinases, and TGFactivation. We used a nonbiased data-mining approach to identify NF B as the likely transcriptional regulator of these events. We confirmed NF B activation by two independent methods: translocation of NF B p50 to glomerular nuclei and ChIP assays demonstrating NF B p50 binding to the B motif of target genes in old versus young glomeruli. These data suggest that old glomeruli exhibit NF B-associated up-regulation of a proinflammatory, procoagulable, and profibrotic phenotype compared with young glomeruli; these distinctions could explain their enhanced susceptibility to failure. Furthermore, these results provide a potential mechanistic explanation for the close relationship between ESRD and atherosclerotic organ failure as two parallel arms of age-associated NF B-driven processes. J Am Soc Nephrol 21: 587–597, 2010. doi: 10.1681/ASN.2009060663 The peak prevalence for treated end-stage kidney disease (ESKD) is 70 to 79 years of age.1 The major pathologic phenotype of ESKD of old age is glomerulosclerosis, and autopsy studies show an increasing proportion of sclerotic glomeruli after age 40 years in otherwise normal humans.2,3 Because ESKD is frequently associated with other common diseases of older age, such as diabetes and hypertension, it is often causally attributed to these conditions. However, it is likely that the aging process itself contributes to ESKD in ways that are not well understood. Rat models of aging clearly demonstrate progressive glomerulosclerosis as an age-related phenomenon independent of diabetes and hypertension and accelerated by a high-calorie diet.4 –10 The Fischer 344 rat, in which diabetes and hypertension are not features, is a well-established model system for aging.11,12 We defined changes in structure, function, and gene expression in the glomerulus in the Fischer 344 rat during aging, and compared rats that were fed an ad libitum diet (to promote ageReceived June 24, 2009. Accepted November 25, 2009. Published online ahead of print. Publication date available at www.jasn.org. J.E.W. and S.R.P. contributed equally to this work. Correspondence: Dr. Jocelyn E. Wiggins, 1560A MSRB2, 1150 West Medicine Center Drive, Ann Arbor, MI 48109-0676. Phone: 734-615-4460; Fax: 734-763-0982; E-mail: wiggi@umich.edu Copyright 2010 by the American Society of Nephrology BASIC RESEARCH www.jasn.org J Am Soc Nephrol 21: 587–597, 2010 ISSN : 1046-6673/2104-587 587 related changes) to those that were calorie-restricted (to slow the rate of aging and onset of glomerulosclerosis).10 We found podocyte stress and depletion associated with age-associated glomerulosclerosis as in other forms of glomerulosclerosis.10,13 Aging is a genetically regulated process that can be modified by environmental factors. Mutations in genes controlling the insulin/IGF pathway alter life span throughout species ranging from yeast through worms and flies to mammals.14 –16 Similarly, the Sir2 family of NAD -dependent lysine deacetylases has a role in aging.17,18 Physiologic interventions, including calorie restriction and exercise, delay onset of the aging phenotype in the broad range of species.18 –20 The NF B pathway has previously been identified as a candidate activator of age-related transcriptional changes in human and mouse tissues.21–24 Genetic blockade of NF B in mouse skin reversed the normal age-associated pattern of gene expression and the aging phenotype, thereby demonstrating that disruption of this single gene was sufficient to reverse features of aging, even in late life.22,24 In the nonactivated state, NF B proteins are held in the cytoplasm by binding to I B proteins. Stress states cause degradation of I B, thereby releasing NF B to translocate to the nucleus and bind to the consensus B DNA motif in promoter and enhancer regions of genes involved in innate/adaptive immunity, cell adhesion, inflammation, cell stress responses, and apoptosis.24 –26 To understand the molecular events associated with the aging process in the rat glomerulus, we used a statistical approach to identify genes whose expression changed “linearly” (incrementally in the same direction) over time from young adulthood to old age. An unbiased data-mining method identified NF B as a common transcription factor that could drive changes in aging-associated glomerular gene expression. We then confirmed NF B activation in old versus young glomeruli by demonstrating immunofluorescent translocation of NF B to the nucleus as well as localization of NF B protein on the regulatory regions of key genes by chromatin immunoprecipitation (ChIP) analysis. These data are consistent with the concept that the old glomerulus is different from the young glomerulus, and is in a proinflammatory, procoagulant, and profibrotic state that sets it up for failure.