In geriatrics, chronic kidney disease and cardiovascular disease are common, closely related comorbidities, as one increases the risk for the other. For example, in the first year of dialysis the risk for a cardiovascular event increases 50% in patients with renal failure. Cardiovascular disease is still the major cause of death in the U.S., and the number of people with chronic kidney disease is rising dramatically.
We use mouse models to study the complex genetics of both cardiovascular and renal diseases to identify the risk factors and learn how we can reduce them. We do this through several different approaches, using both the natural genetic variation between the different inbred strains (linkage analysis and genome-wide association studies) and by inducing mutations both randomly (ENU-mutagenesis) and specifically (gene knockout). Once candidate genes are identified, we closely collaborate with the Mount Desert Island Biological Laboratory to further study candidate genes in zebrafish and C. elegans (http://www.mdibl.org/faculty/Ron_Korstanje/368/). With this multi-species strategy, we are streamlining the process of narrowing candidate gene lists and focusing our powerful mouse genetic resources on only the most likely candidate genes. This strategy will speed mammalian gene identification and the development of clinical treatments, and it will also serve as a template for identification of genes related to other diseases.
Genes that are involved in cardiovascular disease
For many years our lab has performed quantitative trait locus analysis in crosses between inbred strains to determine the loci that are responsible for the differences in HDL cholesterol levels between the strains. We have used many strain combinations and identified several major effect genes through this strategy. To increase the success of this approach and identify genes with smaller effects, we re-analyzed and combined the data from 22 crosses (several datasets were donated by other investigators). This has lead to the identification of several novel candidate genes that we are currently testing for their involvement in cardiovascular disease.
Interaction with vitamin D
Studies in humans show a correlation between vitamin D levels and HDL cholesterol levels. We recently found that increasing vitamin D in the diet results in an increase in HDL cholesterol levels only in certain strains. Furthermore, analyzing reciprocal crosses shows that to get a beneficial effect in the offspring, it matters whether the vitamin D sensitive strain is the mother or the father, suggesting that epigenetics plays a role. We are now trying to identify the genes causing the effect and study the mechanisms.
In addition to identifying HDL genes through natural occurring variation in the mouse we also induce genetic variation through ENU-mutagenesis. We identified 15 B6 mutants with lower or higher HDL levels compared to wildtype B6 mice and are mapping the mutated genes. We already have several novel genes for which we currently do not understand their role in the regulation of HDL cholesterol levels. Characterizing these mutations and the effect on cardiovascular disease is ongoing.
Genes that are involved in aging related kidney disease
Genetic mapping in aging populations
The presence of albumin in the urine (albuminuria) is an important marker for renal damage. We measured albuminuria in 28 inbred strains at 6, 12, 18, and 24 months of age and used this data for association with genetic loci. We identified 16 loci, of which 4 were confirmed in human, by association studies in populations with renal disease. In addition to measuring albuminuria, we now use the kidneys from the aged mice to look at histological changes. For example, mesangial matrix expansion (MME) is a characteristic in chronic kidney disease and we identified the strains that show MME in the males at 20 months of age. We found that the strains with MME have a 9bp sequence in the promoter of a gene called Far2 in common and that their Far2 expression is two-fold higher compared to the strains without MME. Preliminary studies in cell cultures show that the 9bp sequence is responsible for the expression difference and that overexpression of the gene causes MME.
Testing candidate genes in zebrafish and C. elegans
A common strategy to test whether candidate genes found in the above studies are causing cardiovascular, renal, and/or longevity phenotypes is by studying mice in which the gene is knocked out. However, this is a long and expensive process and the large number of candidate genes makes it problematic. In collaboration with the Mount Desert Island Biological Laboratory, we knocked down gene expression in zebrafish to look at renal phenotypes, and in C. elegans to look at longevity. For example, Gorasp is a gene that we identified in our aging study to be associated with albuminuria. Knockdown of this gene in zebrafish leads to proteinuria, while knockdown in C. elegans leads to an increase in lifespan of 15%. These results seem to contradict and suggest that the gene is involved in different processes with different effects on disease and aging.
Principal Investigator: Ron Korstanje, Ph.D.
Postdoctoral Fellow: George Sutphin, Ph.D.
Predoctoral Associate: Seungbum Choi, B.S., M.S.
Research Laboratory Manager: Susan Sheehan, B.A., M.S.
Research Assistant II: Aleksandra Aljakna, B.A., Ken Walsh, B.S.
Research Assistant I: Shannon Bean, B.S., Christy Fitzpatrick, B.S.
Biomedical Technologist I: Holly Savage
Laboratory Technician IV: Rachel Gott, Beverly Macy
Scientific Writer: Joanne Currer
Research Administrative Assistant: Patricia Cherry
Aljakna A, Choi S, Savage H, Hageman Blair R, Gu T, Svenson KL, Churchill GA, Hibbs M, Korstanje R. 2012. Pla2g12b and Hpn are genes identified by mouse ENU mutagenesis that affect HDL cholesterol . PLoS One 7(8):e43139. PMCID: PMC3422231
Korstanje R, Zhang W, Thaisz J, Staedtler F, Harttman N, Xu L, Feng M, Yanas L, Valdar W, Churchill GA, DiPetrillo K. 2012. Genome-wide association mapping of quantitative traits in outbred mice. G3 (Bethesda) 2(2):167-174. PMCID: PMC328432
Srivastava U, Paigen BJ, Korstanje R. 2012. Differences in health status affect susceptibility and mapping of genetic loci for atherosclerosis (fatty streak) in inbred mice . Arterioscler Thromb Vasc Biol 32(10):2380-2386. PMCID: PMC3563286
Leduc MS, Lyons M, Darvishi K, Walsh K, Sheehan S, Amend S, Cox A, Orho-Melander M, Kathiresan S, Paigen B, Korstanje R. 2011. The Mouse QTL Map Helps Interpret Human Genome-Wide Association Studies for HDL Cholesterol. Journal of Lipid Research 52(6):1139-1149.
Hageman RS, Leduc MS, Korstanje R, Paigen B, Churchill GA. 2011. A Bayesian framework for inference of the genotype-phenotype map for segregating populations. Genetics 187(4):1163-1170.
Sinke A, Caputo C, Tsaih S, Yuan R, Ren D, Deen P, Korstanje R. 2011. Genetic analysis of plasma sodium concentration in mice and identification of Nalcn, a novel player in osmoregulation. Physiological Genomics 43(5):265-270.
Hageman RS, Leduc MS, Caputo C, Tsaih SW, Churchill GA, Korstanje R. 2011. Uncovering Genes and Regulatory Pathways Related to Urinary Albumin Excretion in Mice. Journal of the American Society of Nephrology 22(1):73-81.
Cox A, Sheehan S, Kloting I, Paigen B, Korstanje R. 2010. Combining QTL Data for HDL Cholesterol Levels from Two Different Species Leads to Smaller Confidence Intervals. Heredity 105(5):426-432.
Garret M, Pezzolesi M, Korstanje R. 2010. Integrating human, rat, and mouse data to identify the genetic factors involved in chronic kidney disease. Journal of the American Society of Nephrology 21(3):398-405.
Tsaih S, Pezzolesi M, Yuan R, Warram JH, Krolewski A, Korstanje R. 2010. Genetic analysis of albuminuria in the aging mouse. Kidney International 77(3):201-210.
Xing S, Yuan R, Svenson K, Jorgenson L, So M, Paigen B, Korstanje R. 2009. Genetic influence on electrocardiogram time intervals and heart rate in aging mice. AJP Heart and Circulatory Physiology 296(6):H1907-1913.
Kamilic J, Lely AT, van Goor H, Buikema H, Tent H, Navis GJ, Korstanje R. 2009. Differential ACE expression among tissues in allele-specific Wistar rat lines. Mammalian Genome 20(3):170-179.
Tsaih S & Korstanje R. 2009. Haplotype Association Mapping in mice. Methods in Molecular Biology 573:213-222.
Doorenbos C, Tsaih S, Sheehan S, Ishimori N, Navis G, Churchill G, DiPetrillo K, Korstanje R. 2008. Quantitative Trait Loci for urinary albumin in crosses between C57BL/6J and A/J inbred mice in the presence and absence of Apoe. Genetics 179:693-699.
Matteson PG, Desai J, Korstanje R, Lazar G, Borsuk TE, Rollins J, Kadambi S, Joseph J, Rahman T, Wink J, Benayed R, Paigen B, Millonig JH. 2008. The orphan G protein coupled receptor, Gpr161, encodes the vacuolated lens locus and controls neurulation and lens development. PNAS 105(6):2088-2093.