C57Bl/6N mice have an attenuated lung inflammatory response to dsRNA compared to C57Bl/6J and BALB/c mice

BACKGROUND

Lower respiratory infections caused by ssRNA viruses are a major health burden globally. Translational mouse models are a valuable tool for medical research, including research on respiratory viral infections. In in vivo mouse models, synthetic dsRNA can be used as a surrogate for ssRNA virus replication. However, studies investigating how genetic background of mice impacts the murine lung inflammatory response to dsRNA is lacking. Hence, we have compared lung immunological responses of BALB/c, C57Bl/6N and C57Bl/6J mice to synthetic dsRNA.

METHODS

dsRNA was administered intranasally to BALB/c, C57Bl/6N and C57Bl/6J mice once/day for three consecutive days. Lactate dehydrogenase (LDH) activity, inflammatory cells, and total protein concentration were analyzed in bronchoalveolar lavage fluid (BALF). Pattern recognition receptors levels (TLR3, MDA5 and RIG-I) were measured in lung homogenates using RT-qPCR and western blot. Gene expression of IFN-β, TNF-α, IL-1β and CXCL1 was assessed in lung homogenates by RT-qPCR. ELISA was used to analyze protein concentrations of CXCL1 and IL-1β in BALF and lung homogenates.

RESULTS

BALB/c and C57Bl/6J mice showed infiltration of neutrophils to the lung, and an increase in total protein concentration and LDH activity in response to dsRNA administration. Only modest increases in these parameters were observed for C57Bl/6N mice. Similarly, dsRNA administration evoked an upregulation of MDA5 and RIG-I gene and protein expression in BALB/c and C57Bl/6J, but not C57Bl/6N, mice. Further, dsRNA provoked an increase in gene expression of TNF-α in BALB/c and C57Bl/6J mice, IL-1β only in C57Bl/6N mice and CXCL1 exclusively in BALB/c mice. BALF levels of CXCL1 and IL-1β were increased in BALB/c and C57Bl/6J mice in response to dsRNA, whereas the response of C57Bl/6N was blunt. Overall, inter-strain comparisons of the lung reactivity to dsRNA revealed that BALB/c, followed by C57Bl/6J, had the most pronounced respiratory inflammatory responses, while the responses of C57Bl/6N mice were attenuated.

CONCLUSIONS

We report clear differences of the lung innate inflammatory response to dsRNA between BALB/c, C57Bl/6J and C57Bl/6N mice. Of particular note, the highlighted differences in the inflammatory response of C57Bl/6J and C57Bl/6N substrains underscore the value of strain selection in mouse models of respiratory viral infections.

The C57Bl/6J mouse strain is more susceptible to angiotensin II-induced aortic aneurysm formation than C57Bl/6N

BACKGROUND AND AIMS

Genetic variations between C57Bl/6 mouse substrains are highly relevant to the investigation of cardiovascular disease. We here assessed whether these variations have an impact on the incidence of abdominal aortic aneurysms (AAA) in C57Bl/6J and 6 N mice.

METHODS

AAA were induced by subcutaneous infusion of 1500 ng/kg*min Angiotensin-II for four weeks in six-month-old male CB57Bl/6J and 6N mice. Aortic smooth muscle cells (VSMC) were isolated from untreated animals for in vitro analysis.

RESULTS

C57Bl/6J mice are more susceptible to AAA formation (76.5% vs. 7.1%, p = 0.0002). C57Bl/6J VSMC expressed more pro-inflammatory molecules such as Nlrp3, Aim2 and NF-κB. Additionally, these cells presented significantly higher levels of NADP/NADPH and oxidative DNA modifications, as indicated by 8-OHdG-staining, compared to C57Bl/6N VSMC.

CONCLUSIONS

In contrast to previous reports, we present evidence that six-month-old C57BL/6J, but not C57BL/6N mice develop AAA. In accordance with the deficiency of nicotinamide-nucleotide-transhydrogenase (Nnt), C57BL/6J VSMC displayed increased oxidative stress, oxidative DNA damage and a stronger inflammatory phenotype than C57BL/6N VSMC.

Genetic background influences expression and function of the cation channel TRPM4 in the mouse heart

Transient receptor potential melastatin 4 (TRPM4) cation channels act in cardiomyocytes as a negative modulator of the L-type Ca²⁺ current. Ubiquitous Trpm4 deletion in mice leads to an increased β-adrenergic inotropy in healthy mice as well as after myocardial infarction. In this study, we set out to investigate cardiac inotropy in mice with cardiomyocyte-specific Trpm4 deletion. The results guided us to investigate the relevance of TRPM4 for catecholamine-evoked Ca²⁺ signaling in cardiomyocytes and inotropy in vivo in TRPM4-deficient mouse models of different genetic background. Cardiac hemodynamics were investigated using pressure-volume analysis. Surprisingly, an increased β-adrenergic inotropy was observed in global TRPM4-deficient mice on a 129SvJ genetic background, but the inotropic response was unaltered in mice with global and cardiomyocyte-specific TRPM4 deletion on the C57Bl/6N background. We found that the expression of TRPM4 proteins is about 78 ± 10% higher in wild-type mice on the 129SvJ versus C57Bl/6N background. In accordance with contractility measurements, our analysis of the intracellular Ca²⁺ transients revealed an increase in ISO-evoked Ca²⁺ rise in Trpm4-deficient cardiomyocytes of the 129SvJ strain, but not of the C57Bl/6N strain. No significant differences were observed between the two mouse strains in the expression of other regulators of cardiomyocyte Ca²⁺ homeostasis. We conclude that the relevance of TRPM4 for cardiac contractility depends on homeostatic TRPM4 expression levels or the genetic endowment in different mouse strains as well as on the health/disease status. Therefore, the concept of inhibiting TRPM4 channels to improve cardiac contractility needs to be carefully explored in specific strains and species and prospectively in different genetically diverse populations of patients.