Selective breeding to develop lines of baboons with high and low blood pressure

Blood pressure and the kidney cortex transcriptome response to high-sodium diet challenge in female nonhuman primates

Blood pressure (BP) is influenced by genetic variation and sodium intake with sex-specific differences; however, studies to identify renal molecular mechanisms underlying the influence of sodium intake on BP in nonhuman primates (NHP) have focused on males. To address the gap in our understanding of molecular mechanisms regulating BP in female primates, we studied sodium-naïve female baboons (n = 7) fed a high-sodium (HS) diet for 6 wk. We hypothesized that in female baboons variation in renal transcriptional networks correlates with variation in BP response to a high-sodium diet. BP was continuously measured for 64-h periods throughout the study by implantable telemetry devices. Sodium intake, blood samples for clinical chemistries, and ultrasound-guided kidney biopsies were collected before and after the HS diet for RNA-Seq and bioinformatic analyses. We found that on the LS diet but not the HS diet, sodium intake and serum 17 β-estradiol concentration correlated with BP. Furthermore, kidney transcriptomes differed by diet-unbiased weighted gene coexpression network analysis revealed modules of genes correlated with BP on the HS diet but not the LS diet. Our results showed variation in BP on the HS diet correlated with variation in novel kidney gene networks regulated by ESR1 and MYC; i.e., these regulators have not been associated with BP regulation in male humans or rodents. Validation of the mechanisms underlying regulation of BP-associated gene networks in female NHP will inform better therapies toward greater precision medicine for women.

Diet-induced early-stage atherosclerosis in baboons: Lipoproteins, atherogenesis, and arterial compliance

BACKGROUND

The purpose of this study was to determine whether dietary manipulation can reliably induce early-stage atherosclerosis and clinically relevant changes in vascular function in an established, well-characterized non-human primate model.

METHODS

We fed 112 baboons a high-cholesterol, high-fat challenge diet for two years. We assayed circulating biomarkers of cardiovascular disease (CVD) risk, at 0, 7, and 104 weeks into the challenge; assessed arterial compliance noninvasively at 104 weeks; and measured atherosclerotic lesions in three major arteries at necropsy.

RESULTS

We observed evidence of atherosclerosis in all but one baboon fed the two-year challenge diet. CVD risk biomarkers, the prevalence, size, and complexity of arterial lesions, plus consequent arterial stiffness, were increased in comparison with dietary control animals.

CONCLUSIONS

Feeding baboons a high-cholesterol, high-fat diet for two years reliably induces atherosclerosis, with risk factor profiles, arterial lesions, and changes in vascular function also seen in humans.

Baboons as a model to study genetics and epigenetics of human disease

A major challenge for understanding susceptibility to common human diseases is determining genetic and environmental factors that influence mechanisms underlying variation in disease-related traits. The most common diseases afflicting the US population are complex diseases that develop as a result of defects in multiple genetically controlled systems in response to environmental challenges. Unraveling the etiology of these diseases is exceedingly difficult because of the many genetic and environmental factors involved. Studies of complex disease genetics in humans are challenging because it is not possible to control pedigree structure and often not practical to control environmental conditions over an extended period of time. Furthermore, access to tissues relevant to many diseases from healthy individuals is quite limited. The baboon is a well-established research model for the study of a wide array of common complex diseases, including dyslipidemia, hypertension, obesity, and osteoporosis. It is possible to acquire tissues from healthy, genetically characterized baboons that have been exposed to defined environmental stimuli. In this review, we describe the genetic and physiologic similarity of baboons with humans, the ability and usefulness of controlling environment and breeding, and current genetic and genomic resources. We discuss studies on genetics of heart disease, obesity, diabetes, metabolic syndrome, hypertension, osteoporosis, osteoarthritis, and intrauterine growth restriction using the baboon as a model for human disease. We also summarize new studies and resources under development, providing examples of potential translational studies for targeted interventions and therapies for human disease.

The baboon kidney transcriptome: analysis of transcript sequence, splice variants, and abundance

The baboon is an invaluable model for the study of human health and disease, including many complex diseases of the kidney. Although scientists have made great progress in developing this animal as a model for numerous areas of biomedical research, genomic resources for the baboon, such as a quality annotated genome, are still lacking. To this end, we characterized the baboon kidney transcriptome using high-throughput cDNA sequencing (RNA-Seq) to identify genes, gene variants, single nucleotide polymorphisms (SNPs), insertion-deletion polymorphisms (InDels), cellular functions, and key pathways in the baboon kidney to provide a genomic resource for the baboon. Analysis of our sequencing data revealed 45,499 high-confidence SNPs and 29,813 InDels comparing baboon cDNA sequences with the human hg18 reference assembly and identified 35,900 cDNAs in the baboon kidney, including 35,150 transcripts representing 15,369 genic genes that are novel for the baboon. Gene ontology analysis of our sequencing dataset also identified numerous biological functions and canonical pathways that were significant in the baboon kidney, including a large number of metabolic pathways that support known functions of the kidney. The results presented in this study catalogues the transcribed mRNAs, noncoding RNAs, and hypothetical proteins in the baboon kidney and establishes a genomic resource for scientists using the baboon as an experimental model.

Selective breeding of primates for use in research: consequences and challenges

Primates are bred in captivity for a number of purposes, from zoo-based captive breeding programmes for conservation to breeding for biomedical research. In each case, breeding animals that are fit for purpose, either as viable candidates for reintroduction or as valid research models, has presented challenges and resulted in steep learning curves. The breeding of animals for biomedical research has become increasingly focused on the production of animals that are less stressed by captive (specifically laboratory) environments. This is because elevated, particularly chronic, stress responses can result in altered physiological, neurological and behavioural states that have the potential to compromise the validity of scientific results. Selective breeding in captivity to, for example, maximise production, select for docile temperament or specific genotypes for biomedical research, is likely to be counter to natural selective pressures for evolutionary fitness. Given that many natural selective pressures active in the wild are absent in captivity, this paper reviews the selective breeding of primates (especially Old World monkeys) in captivity, its potential negative effects, and options that exist for ameliorating these negative effects.

Two loci affect angiotensin I-converting enzyme activity in baboons

Serum LDL cholesterol (LDLC) concentrations and ACE activities are risk factors for the development of cardiovascular disease (CVD). However, the relationship between ACE and CVD susceptibility, and possible mechanisms of action, is controversial. With data on 622 pedigreed baboons, we used statistical genetic methods to determine the mode of inheritance of ACE activities and its relationship to LDLC on different diets. ACE activity was moderately heritable, and quantitative trait linkage analyses detected a quantitative trait locus (QTL) for ACE activity on the baboon homolog of human chromosome 17 (near the ACE structural locus, maximum multipoint lod=7.5, genomic P=0.000003). Bivariate analyses revealed that ACE activity was genetically correlated (rhoG) with LDLC response (LDLCRC) to a high-cholesterol diet (rhoG=0.30+/-0.13, P=0.01) but not to LDLC on a basal diet (rhoG=0.08+/-0.13). Bivariate genetic analyses indicated that a previously detected QTL for LDLCRC had significant (P=0.025) pleiotropic effects on ACE activity levels and accounted for the genetic correlation. Therefore, we have detected 2 putative loci that affect ACE activity in baboons, one of which also affects LDLC dietary response. The existence of at least 2 genes that affect ACE activity, one of which is diet-responsive, may help explain the lack of consistency among studies of the relationship between ACE and CVD.

Sodium-lithium countertransport activity is linked to chromosome 5 in baboons

The genes involved in the regulation of cellular sodium transport characteristics, which are correlated with some forms of essential hypertension, have not yet been identified. We are studying the genes and environmental factors that affect red blood cell sodium-lithium countertransport (SLC) activity and intracellular sodium (ICNa) concentration in 634 baboons that comprise 11 pedigrees of 2 and 3 generations each. To detect and locate possible quantitative trait loci (QTLs) that affect SLC activity and ICNa concentration, we performed a genome screen by using a maximum likelihood-based variance-components linkage analysis program (SOLAR). SLC and ICNa phenotypes as well as genotypes on 281 microsatellite loci were available for all pedigreed animals. Both SLC and ICNa traits were highly heritable (residual heritability 0.593+/-0.083 [P<0.0001] and 0.739+/-0.082 [P<0.0001], respectively). We obtained evidence that a possible QTL for SLC activity is located on the baboon homologue of human chromosome 4 between D4S2456 and D4S2365 with a maximum multipoint lod score of 9.3 (P<10(-)(10)) near D4S1645. This QTL accounts for approximately two thirds of the total additive genetic variation in SLC activity in baboons. Although ICNa concentration was highly heritable, we found no evidence for linkage to a QTL with use of this methodology. Thus, we have evidence that a gene located on the baboon homologue of human chromosome 4 (baboon chromosome 5) affects cell sodium transport in baboons.

Effects of sex, age, weight, and heredity on blood pressure in baboons

Using data on a population of 498 pedigreed baboons, the effects of several covariates, including sex, age, weight, and subspecies, on arterial blood pressures were studied. Females had significantly higher systolic and diastolic arterial blood pressure than males. Both systolic and diastolic arterial blood pressures increased significantly with increasing weight, and for diastolic pressure, the increase was significantly greater in females than in males. Systolic arterial blood pressure significantly decreased with increasing age and the decrease was larger in males. There were significant differences in arterial blood pressures that corresponded with degree of subspecies admixture. © 1995 Wiley-Liss, Inc.