Differences in Cell-Type–Specific Responses to Angiotensin II Explain Cardiac Remodeling Differences in C57BL/6 Mouse Substrains

Abstract

T he highly used C57BL/6 mouse inbred strain is the preferred choice for mouse transgenic and knockout studies 1 and was the first strain whose genome was fully sequenced. 2 However, several C57BL6 substrains have emerged over the years, each showing genomic differences because of genetic drift and displaying various phenotypic differences. 1,3 One example is the difference between the C57BL/6J and C57BL/6N substrains. The C57BL/6 strain was initially developed at The Jackson Laboratory, and mice from that colony are identified as C57BL/6J. In 1951, some mice were separated from the original colony to initiate a new colony at the National Institutes of Health, the latter being identified as C57BL/6N. 1 Despite the recognition that genetic drift between mouse strains may compromise the reproducibility of experimental data over time and place, 4 there are still many publications where the substrain of origin of C57BL/6 mice is not mentioned. However, a recent study reported that the cardiac output of C57BL/6N male mice is higher than that of their C57BL/6J counterparts.5 Likewise, the effects of transverse aortic constriction on survival and the remodeling of left ventricles (LV) are much greater in C57BL/6N than in C57BL/6J mice. 6 Thus, evidence indicates that genetic drift can significantly alter cardiac phenotypes in the established C57BL/6 inbred strain.Despite indications that hearts from the C57BL/6N and C57BL/6J mouse substrains differ in terms of their contractility, as well as their responses to stress-induced overload (including survival rate, maintenance of cardiac function, and development of hypertrophy), no information is available about the underlying molecular and cellular mechanisms. We compared the effects of either subacute (48 hours) and chronic (14 days) infusions of angiotensin II (Ang II) on LV remodeling in both substrains. As we observed substrainspecific differences in expression for some genes known to be specific for particular cell-types, we further confirmed Abstract-Despite indications that hearts from the C57BL/6N and C57BL/6J mouse substrains differ in terms of their contractility and their responses to stress-induced overload, no information is available about the underlying molecular and cellular mechanisms. We tested whether subacute (48 hours) and chronic (14 days) administration of angiotensin II (500 ng/kg per day) had different effects on the left ventricles of male C57BL/6J and C57BL/6N mice. Despite higher blood pressure in C57BL/6J mice, chronic angiotensin II induced fibrosis and increased the left ventricular weight/body weight ratio and cardiac expression of markers of left ventricular hypertrophy to a greater extent in C57BL/6N mice. Subacute angiotensin II affected a greater number of cardiac genes in C57BL/6N than in C57BL/6J mice. Some of the most prominent differences were observed for markers of (1) macrophage activation and M2 polarization, including 2 genes (osteopontin and galectin-3) whose inactivation was reported as sufficient to prevent angiotensin...

Dissecting the role of myeloid and mesenchymal fibroblasts in age-dependent cardiac fibrosis

“…4A), suggesting that Nnt may play a protective role in a slowly-progressing aging heart. This is in contrast to observations that, with injury, the young B6N heart responds more severely to stress than age-matching B6J hearts [4, 37]. Although Nnt is considered an antioxidative enzyme, in pathophysiological conditions such as pressure overload (and perhaps in others) Nnt reverses its action and instead of generating NADPH, it depletes it to support NADH and ATP production.…”

Assessing Cardiac Metabolism

“…Although rodent strain selection has always been part of any study design, the increased availability and use of genetically modified rodents, particularly mice, as model systems for human diseases has revolutionized the way we conduct research in general while increasing awareness about the influence of genetic background on the resulting phenotype, which encompasses the cardiac phenotype. For example, many studies have reported mouse strain variations for cardiac function, 38,39 response to β-adrenergic stimulation 40 and angiotensin II, 41 and capacity for calcium handling, 42,43 but also for susceptibility to specific pathophysiological states, such as myocardial hypertrophy 44,45 or heart failure. 46 In terms of cardiac metabolism, only a few studies have made a systematic comparison among commonly used control mouse strains.…”

Mylk3null C57BL/6N mice develop cardiomyopathy, whereasNntnull C57BL/6J mice do not

“…Surprisingly, research from the Maack Lab showed the NNT-null B6J mouse is protected from oxidative stress and heart failure in comparison with the B6N mouse, possibly because of a "reverse activity" of NNT in the B6N mouse (14). Furthermore, the NNT-replete B6N mice show increased fibrosis in response to chronic angiotensin II treatment, along with increased expression of cardiac remodelling genes; however, the authors demonstrate these changes are not due to NNT status (15). B6N mice are more susceptible to transaortic constriction than B6J with B6N having lower survival rates and cardiac function (17).…”

“…Subsequently, a further 19 families have been reported, with a single, highly consanguineous patient developing hypertrophic CM with a homozygous NNT mutation and three monoallelic variants have been linked to left ventricular non-compaction (10). A number of publications have linked NNT expression levels to cardiovascular traits, including remodelling differences, hypertension, and heart growth in mice and zebra fish (12,13,14,15,16). Surprisingly, research from the Maack Lab showed the NNT-null B6J mouse is protected from oxidative stress and heart failure in comparison with the B6N mouse, possibly because of a "reverse activity" of NNT in the B6N mouse (14).…”