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A Method to Study the Impact of Chemically-induced Ovarian Failure on Exercise Capacity and Cardiac Adaptation in Mice

The risk of cardiovascular disease (CVD) increases in post-menopausal women, yet, the role of exercise, as a preventative measure for CVD risk in ...

University of Arizona

In vitro exposure of Postnatal Day 4 (PND4) rat ovaries to the occupational chemical 4-vinylcyclohexene diepoxide (VCD) destroys specifically primordial and primary follicles via acceleration of atresia. Because oocyte-expressed c-kit (KIT) plays a critical role in follicle survival and activation, a direct interaction of VCD with KIT as its mechanism of ovotoxicity was investigated. PND4 rat ovaries were cultured with and without VCD (30 μM) for 2 days. When assessed by Western analysis or mobility shift detection, phosphorylated KIT (pKIT) was decreased (P < 0.05) by VCD exposure, while total KIT protein was unaffected. Anti-mouse KIT2 (ACK2) antibody binds KIT and blocks its signaling pathways, whereas anti-mouse KIT 4 (ACK4) antibody binds KIT but does not block its activity. PND4 rat ovaries were incubated for 2 days with and without VCD with and without ACK2 (80 μg/ml) or ACK4 (80 μg/ml). ACK2 decreased pKIT; however, ACK4 had no effect. Conversely, ACK2 did not affect a VCD-induced decrease in pKIT, whereas ACK4 further reduced it. Because ACK2 and ACK4 (known to directly bind KIT) affect VCD responses, these results support the fact that VCD interacts directly with KIT. The effect of these antibodies on VCD-induced follicle loss was measured after 8 days of incubation. ACK2 further reduced (P < 0.05) VCD-induced follicle loss, whereas ACK4 did not affect it. These findings demonstrate that VCD induces ovotoxicity by direct inhibition of KIT autophosphorylation of the oocyte. The data also further support the vital function of KIT and its signaling pathway in primordial follicle survival and activation, as well as its role in VCD-induced ovotoxicity.

Inhibition of ovarian KIT phosphorylation by the ovotoxicant 4-vinylcyclohexene diepoxide in rats.

Recently, MicroRNAs (miR) and AMP-kinase (AMPK) have emerged as prominent players in the development of cardiac hypertrophy and heart failure. We hypothesized that components of the adenosine monophosphate-activated kinase (AMPK) pathway are targeted by miRs and alter AMPK signaling during pathological cardiac stress.

Micro-RNA-195 and -451 regulate the LKB1/AMPK signaling axis by targeting MO25.

The pathological progression of hypertrophic cardiomyopathy (HCM) is sexually dimorphic such that male HCM mice develop phenotypic indicators of cardiac disease well before female HCM mice. Here, we hypothesized that alterations in myofilament function underlies, in part, this sex dimorphism in HCM disease development. Firstly, 10-12month female HCM (harboring a mutant [R403Q] myosin heavy chain) mice presented with proportionately larger hearts than male HCM mice. Next, we determined Ca(2+)-sensitive tension development in demembranated cardiac trabeculae excised from 10-12month female and male HCM mice. Whereas HCM did not impact Ca(2+)-sensitive tension development in male trabeculae, female HCM trabeculae were more sensitive to Ca(2+) than wild-type (WT) counterparts and both WT and HCM males. We hypothesized that the underlying cause of this sex difference in Ca(2+)-sensitive tension development was due to changes in Ca(2+) handling and sarcomeric proteins, including expression of SR Ca(2+) ATPase (2a) (SERCA2a), β-myosin heavy chain (β-MyHC) and post-translational modifications of myofilament proteins. Female HCM hearts showed an elevation of SERCA2a and β-MyHC protein whereas male HCM hearts showed a similar elevation of β-MyHC protein but a reduced level of cardiac troponin T (cTnT) phosphorylation. We also measured the distribution of cardiac troponin I (cTnI) phosphospecies using phosphate-affinity SDS-PAGE. The distribution of cTnI phosphospecies depended on sex and HCM. In conclusion, female and male HCM mice display sex dimorphic myofilament function that is accompanied by a sex- and HCM-dependent distribution of sarcomeric proteins and cTnI phosphospecies.

Sexually dimorphic myofilament function and cardiac troponin I phosphospecies distribution in hypertrophic cardiomyopathy mice.

Although familial hypertrophic cardiomyopathy (FHC) is characterized as cardiac disease in the absence of overt stressors, disease penetrance, and pathological progression largely depend on modifying factors. Accordingly, pressure overload by transverse aortic constriction (TAC) was induced in 2-month-old, male mice with and without a FHC (R403Q) mutation in α-myosin heavy chain. A significantly greater number of FHC mice (n = 8) than wild-type (WT) mice (n = 5) died during the 9-week study period. TAC induced a significant increase in cardiac mass whether measured at 2 or 9 weeks post-TAC in both WT and FHC mice, albeit to a different extent. However, the temporal and morphological trajectory of ventricular remodeling was impacted by the FHC transgene. Both WT and FHC hearts responded to TAC with an early (2 weeks post-TAC) and significant augmentation of the relative wall thickness (RWT) indicative of concentric hypertrophy. By 9 weeks post-TAC, RWT decreased in WT hearts (eccentric hypertrophy) but remained elevated in FHC hearts. WT hearts following TAC demonstrated enhanced cardiac function as measured by the end-systolic pressure-volume relationship, pre-load recruitable stroke work (PRSW), and myocardial relaxation indicative of compensatory hypertrophy. Similarly, TAC induced differential histological and cellular remodeling; TAC reduced expression of the sarcoplasmic reticulum Ca(2+)-ATPase (2a) (SERCA2a; 2 and 9 weeks) and phospholamban (PLN; 2 weeks) but increased PLN phosphorylation (2 weeks) and β-myosin heavy chain (β-MyHC; 9 weeks) in WT hearts. FHC-TAC hearts showed increased β-MyHC (2 and 9 weeks) and a late (9 weeks) decrease in PLN expression concomitant with a significant increase in PLN phosphorylation. We conclude that FHC hearts respond to TAC induced pressure overload with increased premature death, severe concentric hypertrophy, and a differential ability to undergo morphological, functional, or cellular remodeling compared to WT hearts.

Article	Year
Inhibition of ovarian KIT phosphorylation by the ovotoxicant 4-vinylcyclohexene diepoxide in rats. Biology of reproduction\| PubMed ID: 21677306	2011
Micro-RNA-195 and -451 regulate the LKB1/AMPK signaling axis by targeting MO25. PloS one\| PubMed ID: 22844503	2012
Sexually dimorphic myofilament function and cardiac troponin I phosphospecies distribution in hypertrophic cardiomyopathy mice. Archives of biochemistry and biophysics\| PubMed ID: 23352598	2013
Temporal and morphological impact of pressure overload in transgenic FHC mice. Frontiers in physiology\| PubMed ID: 23986715	2013

Laurel McKee

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