Tamoxifen-independent Cre-activity in SMMHC-CreERT2 mice

L. B. Steffensen*, J. Stubbe, M. Overgaard, J. H. Larsen

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Abstrakt

Background and aims
Recent technological advances have established vascular smooth muscle cells (SMCs) as central players in atherosclerosis. Increasingly complex genetic mouse models have unveiled that 30–70% of cells in experimentally induced atherosclerotic lesions derive from a handful of medial SMCs, and that these can adopt a broad range of plaque cell phenotypes. Most of these models are based on the SMMHC-CreERT2 mouse line as Cre-driver. Importantly, Cre-activation can be controlled in time (by administration of tamoxifen, TAM), which is critical to avoid unwanted effects of premature recombination events. The aim of this study was to scrutinize an unexpected observation of TAM-independent Cre-activity in this mouse line.

Methods
Cre-activity was assessed by PCR in tissues from SMMHC-CreERT2 mice crossed with mice homozygous for loxP-flanked (floxed) exon 4 of Ccn2 (our gene-of-interest), and Ccn2 protein was measured in aortas by targeted mass spectrometry.

Results
We observed spontaneous near-complete excision of floxed Ccn2 in aortas from adult mice that were not treated with TAM. As a result, Ccn2 protein was significantly reduced in aortas from these mice, but not to the same extent as TAM-treated littermates. Remarkably, most of the excision was completed in 4-week-old mice. Excision was Cre-dependent, as knockout bands were negligible in heart and liver (dominated by non-SMCs) of these mice, and undetectable in the aorta in the absence of Cre.

Conclusion
Our observations warrant caution, and we advocate inclusion of appropriate controls (i.e., TAM-untreated mice) in future studies.
OriginalsprogEngelsk
TidsskriftAtherosclerosis Plus
Vol/bind48
Sider (fra-til)8-11
ISSN2667-0909
DOI
StatusUdgivet - apr. 2022

Bibliografisk note

Funding Information:
The study was conducted with financial support from Odense University Hospital and University of Southern Denmark .

Funding Information:
We kindly thank Professor Roel Goldschmeding, UMC Utrecht for providing Ccn2fl/fl mice and Professor Pierre Chambon, GIE-CERBM, France, for generating the Cre-ERT2 construct and Professor Stefan Offermanns, Max-Planck Institute for Heart and Lung Research, Germany for providing us with SMMHC-CreERT2 mice. We thank Gitte Kitlen and Niels Str?mvig Larsen for excellent technical assistance. The study was conducted with financial support from Odense University Hospital and University of Southern Denmark.

Publisher Copyright:
© 2022 The Author(s)

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