Sexually Dimorphic Relationships Among Saa3 (Serum Amyloid A3) Inflammation, and Cholesterol Metabolism Modulate Atherosclerosis in Mice

Objective: Expression of the extrahepatic acute-phase protein Saa3 (serum amyloid A3) increases in response to acute and chronic inflammatory stimuli and is elevated in adipose tissue and macrophages in obese mice. A recent report suggested that Saa3 is proatherogenic in male ApoE −/− mice. Because of our previous observation that female but not male Saa3-deficient mice are protected from obesity, adipose inflammation, and hyperlipidemia, we sought to determine whether Saa3 differentially modulates atherosclerosis in mice of both sexes. Approach and Results: To promote atherosclerosis, Saa3 +/+ and Saa3 −/− male and female mice were crossed with Ldlr −/− mice. All mice consumed a diet high in saturated fat and sucrose with 0.15% added cholesterol for 16 weeks. Plasma lipids and atherosclerosis levels were assessed. Female Saa3 −/− Ldlr − /− mice exhibited elevated cholesterol levels relative to Saa3 +/+ Ldlr −/− controls and exhibited increased atherosclerosis, while male Saa3 −/− Ldlr −/− mice were protected from atherosclerosis. Data from the hybrid mouse diversity panel revealed that Saa3 associates strongly with inflammatory, Trem2-associated, and tissue remodeling genes and pathways in males but not females, an effect confirmed in liver tissue, atherosclerotic lesions, and cultured macrophages. Macrophages isolated from male and female mice showed differential inflammatory effects of Saa3 deficiency, an effect linked with sex steroid signaling. Cholesterol efflux capacity was increased in Saa3 −/− males only. Conclusions: Saa3 is proatherogenic in male but atheroprotective in female mice, effects that may be related to sex-specific relationships between Saa3, cholesterol metabolism, inflammatory genes, and Trem2 macrophages.

Extreme Phenotypic Diversity in Operant Responding for an Intravenous Cocaine or Saline Infusion in the Hybrid Mouse Diversity Panel

ABSTRACTCocaine self-administration is complexly determined trait, and a substantial proportion of individual differences in cocaine use is determined by genetic variation. Cocaine intravenous self-administration (IVSA) procedures in laboratory animals provide opportunities to prospectively investigate neurogenetic influences on the acquisition of voluntary cocaine use. Large and genetically diverse mouse populations, including the Hybrid Mouse Diversity Panel (HMDP), have been developed for forward genetic approaches that can reveal genetic variants that influence traits like cocaine IVSA. This population enables high resolution and well-powered genome wide association studies, as well as the discovery of genetic correlations. Here, we provide information on cocaine (or saline - as a control) IVSA in 65 strains of the HMDP. We found cocaine IVSA to be substantially heritable in this population, with strain-level intake ranging for near zero to >25 mg/kg/session. Though saline IVSA was also found to be heritable, a very modest genetic correlation between cocaine and saline IVSA indicates that operant responding for the cocaine reinforcer was influenced by a substantial proportion of unique genetic variants. These data indicate that the HMDP is suitable for forward genetic approaches for the analysis of cocaine IVSA, and this project has also led to the discovery of reference strains with extreme cocaine IVSA phenotypes, revealing them as polygenic models of risk and resilience to cocaine reinforcement. This is part of an ongoing effort to characterize genetic and genomic variation that moderates cocaine IVSA, which may, in turn, provide a more comprehensive understanding of cocaine risk genetics and neurobiology.

Estrogen receptor α controls metabolism in white and brown adipocytes by regulating Polg1 and mitochondrial remodeling

Obesity is heightened during aging, and although the estrogen receptor α (ERα) has been implicated in the prevention of obesity, its molecular actions in adipocytes remain inadequately understood. Here, we show that adipose tissue ESR1/Esr1 expression inversely associated with adiposity and positively associated with genes involved in mitochondrial metabolism and markers of metabolic health in 700 Finnish men and 100 strains of inbred mice from the UCLA Hybrid Mouse Diversity Panel. To determine the anti-obesity actions of ERα in fat, we selectively deleted Esr1 from white and brown adipocytes in mice. In white adipose tissue, Esr1 controlled oxidative metabolism by restraining the targeted elimination of mitochondria via the E3 ubiquitin ligase parkin. mtDNA content was elevated, and adipose tissue mass was reduced in adipose-selective parkin knockout mice. In brown fat centrally involved in body temperature maintenance, Esr1 was requisite for both mitochondrial remodeling by dynamin-related protein 1 (Drp1) and uncoupled respiration thermogenesis by uncoupled protein 1 (Ucp1). In both white and brown fat of female mice and adipocytes in culture, mitochondrial dysfunction in the context of Esr1 deletion was paralleled by a reduction in the expression of the mtDNA polymerase γ subunit Polg1. We identified Polg1 as an ERα target gene by showing that ERα binds the Polg1 promoter to control its expression in 3T3L1 adipocytes. These findings support strategies leveraging ERα action on mitochondrial function in adipocytes to combat obesity and metabolic dysfunction.

The Ca2+ transient as a feedback sensor controlling cardiomyocyte ionic conductances in mouse populations

Conductances of ion channels and transporters controlling cardiac excitation may vary in a population of subjects with different cardiac gene expression patterns. However, the amount of variability and its origin are not quantitatively known. We propose a new conceptual approach to predict this variability that consists of finding combinations of conductances generating a normal intracellular Ca2+ transient without any constraint on the action potential. Furthermore, we validate experimentally its predictions using the Hybrid Mouse Diversity Panel, a model system of genetically diverse mouse strains that allows us to quantify inter-subject versus intra-subject variability. The method predicts that conductances of inward Ca2+ and outward K+ currents compensate each other to generate a normal Ca2+ transient in good quantitative agreement with current measurements in ventricular myocytes from hearts of different isogenic strains. Our results suggest that a feedback mechanism sensing the aggregate Ca2+ transient of the heart suffices to regulate ionic conductances.

Genetic control of the HDL proteome

High-density lipoproteins (HDL) are nanoparticles with >80 associated proteins, phospholipids, cholesterol and cholesteryl esters. A comprehensive genetic analysis of the regulation of proteome of HDL isolated from a panel of 100 diverse inbred strains of mice, Hybrid Mouse Diversity Panel (HMDP), revealed widely varied HDL protein levels across the strains. Some of this variation was explained by local, cis-acting regulation, termed cis-protein quantitative trait loci. Variations in apolipoprotein A-II and apolipoprotein C-3 affected the abundance of multiple HDL proteins indicating a coordinated regulation. We identified modules of co-varying proteins and define a protein-protein interaction network describing the protein composition of the naturally occurring subspecies of HDL in mice. Sterol efflux capacity varied up to 3-fold across the strains and HDL proteins displayed distinct correlation patterns with macrophage and ABCA1 specific cholesterol efflux capacity and cholesterol exchange, suggesting that subspecies of HDL participate in discrete functions. The baseline and stimulated sterol efflux capacity phenotypes associated with distinct QTLs with smaller effect size suggesting a multi genetic regulation. Our results highlight the complexity of HDL particles by revealing high degree of heterogeneity and intercorrelation, some of which is associated with functional variation, supporting the concept that HDL-cholesterol alone is not an accurate measure of HDL’s properties such as protection against CAD.

Genome-wide Association Study for Noise-induced Cochlear Synaptopathy

Article SummaryIn order to elucidate the genetic architecture of the auditory hair cell synapse and the susceptibility to noise-induced cochlear synaptopathy, we are providing the first genome-wide association study with 111 strains (n=695) of the Hybrid Mouse Diversity Panel based upon the strain variation of the wave 1 P1-N1 amplitude of the auditory brainstem responses both before and after noise exposure. Based on this association analysis and our cochlear gene expression data, we identified several novel loci and prioritized positional candidate genes related to cochlear synaptopathy, especially after exposure to noise.AbstractThis is the first genome-wide association study (GWAS) with the Hybrid Mouse Diversity Panel (HMDP) to define the genetic landscape of the auditory hair cell synapse and the susceptibility to noise-induced cochlear synaptopathy. We tested 5-week old female mice (n=695) from 111 HMDP strains (n= 6-7/strain) at baseline and post noise exposure using ABR wave 1 suprathreshold amplitudes (P1-N1 at 80 dB SPL) at 8, 12, 16, 24 and 32 kHz tone burst stimuli. Mice were exposed for 2 hours to 10 kHz octave band noise (OBN) at 108 dB SPL. A broad range of suprathreshold ABR wave 1 amplitude were detected across the HMDP strains. At the genome-wide significance threshold (-logP = 5.39), associations on Chr. 3 and Chr. 16 were identified at baseline. Also, association peaks on Chr. 2 and Chr. 13 were determined post noise exposure. In order to prioritize candidate genes, we generated gene expression microarray profiles using RNA isolated from cochleae in 64 HMDP strains (n =3 arrays per strain). We then used EMMA to perform an association analysis between all SNPs and array probes mapping within each region. A total of 17 genes (2 within Chr. 3 association, 6 within Chr. 2 association and 9 within Chr. 13 association) of these 3 loci were identified with at least 1 probe whose expression was regulated by a significant cis eQTL in the cochlea. Also, the genetic architecture of noise induced cochlear synaptopathy is distinct from that of baseline auditory nerve/synapse integrity. In summary, from this GWAS and our eQTL data, we identified 4 novel loci and prioritized positional candidate genes related to cochlear synaptopathy at baseline and after exposure to noise.

Variability and compensation of cardiomycoyte ionic conductances at the population level

Conductances of ion channels and transporters controlling cardiac excitation may vary in a population of subjects with different cardiac gene expression patterns. However, the amount of variability and its origin are not quantitatively known. We propose a new computational method to predict this variability that consists of finding combinations of conductances generating a normal intracellular Ca2+ transient without any constraint on the action potential. Furthermore, we validate experimentally its predictions using the Hybrid Mouse Diversity Panel, a model system of genetically diverse mouse strains that allows us to quantify inter-subject versus intra-subject variability. The method predicts that conductances of inward Ca2+ and outward K+ currents compensate each other to generate a normal Ca2+ transient in good quantitative agreement with current measurements in ventricular myocytes from hearts of different isogenic strains. Our results suggest that a feedback mechanism sensing the aggregate Ca2+ transient of the heart suffices to regulate ionic conductances.