Large animal models of atherosclerosis--new tools for persistent problems in cardiovascular medicine.

Coronary heart disease and ischaemic stroke caused by atherosclerosis are leading causes of illness and death worldwide. Small animal models have provided insight into the fundamental mechanisms driving early atherosclerosis, but it is increasingly clear that new strategies and research tools are needed to translate these discoveries into improved prevention and treatment of symptomatic atherosclerosis in humans. Key challenges include better understanding of processes in late atherosclerosis, factors affecting atherosclerosis in the coronary bed, and the development of reliable imaging biomarker tools for risk stratification and monitoring of drug effects in humans. Efficient large animal models of atherosclerosis may help tackle these problems. Recent years have seen tremendous advances in gene-editing tools for large animals. This has made it possible to create gene-modified minipigs that develop atherosclerosis with many similarities to humans in terms of predilection for lesion sites and histopathology. Together with existing porcine models of atherosclerosis that are based on spontaneous mutations or severe diabetes, such models open new avenues for translational research in atherosclerosis. In this review, we discuss the merits of different animal models of atherosclerosis and give examples of important research problems where porcine models could prove pivotal for progress.

Demonstration of the presence of independent pre-osteoblastic and pre-adipocytic cell populations in bone marrow-derived mesenchymal stem cells.

Mesenchymal stem cells (MSC) are defined as plastic-adherent, clonal cells that are common progenitors for osteoblasts and adipocytes. An inverse relationship between bone and fat has been observed in several clinical conditions and has been suggested to be caused by re-directing MSC differentiation into one particular lineage. However, this inverse relationship between bone and fat is not consistent and under certain in vivo conditions, bone and fat can change independently suggesting separate precursor cell populations. In order to test for this hypothesis, we extensively characterized two plastic-adherent clonal MSC lines (mMSC1 and mMSC2) derived from murine bone marrow. The two cell lines grew readily in culture and have undergone more than 100 population doublings with no apparent differences in their growth rates. Both cell lines were positive for the murine MSC marker Sca-1 and mMSC1 was also positive for CD13. Both cell lines were exposed to in vitro culture induction of osteogenesis and adipogenesis. mMSC1 and not mMSC2 were only able to differentiate to adipocytes evidenced by the expression of adipocyte markers (aP2, adiponectin, adipsin, PPARgamma2 and C/EBPa) and the presence of mature adipocytes visualized by Oil Red O staining. On the other hand, mMSC2 and not mMSC1 differentiated to osteoblast lineage as demonstrated by up-regulation of osteoblastic makers (CBFA1/RUNX2, Osterix, alkaline phosphatase, bone sialoprotein and osteopontin) and formation of alizarin red stained mineralized matrix in vitro. Consistent with the in vitro results, mMSC2 and not mMSC1, were able to form bone in vivo after subcutaneous implantation in immune-deficient (NOD/SCID) mice. Our data suggest that contrary to the current belief, bone marrow contains clonal subpopulations of cells that are committed to either osteoblast or adipocyte lineage. These cell populations may undergo independent changes during aging and in bone diseases and thus represent important targets for therapy.

From vulnerable plaque to atherothrombosis.

Plaque rupture precipitates approximately 75% of all fatal coronary thrombi. Therefore, the plaque prone to rupture is the primary focus of this review. The lipid-rich core and fibrous cap are pivotal in the understanding of plaque rupture. Plaque rupture is a localized process within the plaque caused by degradation of a tiny fibrous cap rather than by diffuse inflammation of the plaque. Atherosclerosis is a multifocal disease, but plaques prone to rupture seem to be oligofocal at most.

Tissue distribution and engraftment of human mesenchymal stem cells immortalized by human telomerase reverse transcriptase gene.

Engraftment of mesenchymal stem cells (MSC) in peripheral tissues for replenishing of local stem cell function has been proposed as a therapeutic approach to degenerative diseases. We have previously reported the development of an immortalized human telomerase reverse transcriptase transduced MSC line (hMSC-TERT). In the present study, we co-transduced hMSC-TERT with enhanced green fluorescent protein gene, and studied tissue distribution, engraftment, and cell survival after intracardiac and intravenous injections in immunodeficient mice. The pattern of organ distribution suggested that infused cells were efficiently arrested in microvasculature during first-pass, but only for a fraction of the infused cells was arrest followed by vascular emigration and tissue engraftment. Few engrafted cells in lungs, heart, and kidney glomeruli remained after 4 weeks. These observations are consistent with several reports on limited systemic transplantability of primary MSC. HMSC-TERT may constitute a valuable tool for mechanistic studies on how to control MSC homing and engraftment.

Dietary supplementation with methionine and homocysteine promotes early atherosclerosis but not plaque rupture in ApoE-deficient mice.

Hyperhomocysteinemia is an independent risk factor for atherothrombosis. However, causality is unproven, and it remains unknown whether hyperhomocysteinemia promotes atherosclerosis, plaque rupture, and/or thrombosis. We evaluated the short- and long-term effects of hyperhomocysteinemia on plaque size and structure in 99 atherosclerosis-prone apolipoprotein E-deficient mice. Hyperhomocysteinemia was induced by methionine (Met) or homocysteine (HcyH) supplementation: low Met (+11 g Met/kg food), high Met (+33 g Met/kg food), low HcyH (0.9 g HcyH/L drinking water), and high HcyH (1.8 g HcyH/L drinking water). Met and HcyH supplementation significantly raised plasma total homocysteine levels by 4- to 16-fold above those observed in mice fed a control diet (up to 146.1 micromol/L). Compared with controls, aortic root plaque size was significantly larger in supplemented groups after 3 months (56% and 173% larger in high-Met and high-HcyH, respectively) but not after 12 months. Hyperhomocysteinemia was associated with an increase in the amount of collagen in plaques after both 3 and 12 months. Mechanical testing of the tail tendons revealed no weakening of collagen after 12 months of hyperhomocysteinemia. Many plaques in both control and supplemented mice appeared rupture prone morphologically, but all aortic root plaques and all but 1 coronary plaque had an intact surface without rupture or thrombosis. Thus, diet-induced hyperhomocysteinemia promotes early atherosclerosis and plaque fibrosis but does not, even in the long term, weaken collagen or induce plaque rupture.

Red wine does not reduce mature atherosclerosis in apolipoprotein E-deficient mice.

BACKGROUND: Red wine polyphenols and ethanol reduce fatty streak formation (early atherosclerosis) in various animal models. These experimental results support the observation that alcoholic beverages protect against myocardial infarction in humans. However, fatty streaks may not reflect the pathology of mature and clinically relevant atherosclerosis. The present study examined the effects of red wine polyphenols and ethanol on mature atherosclerosis in apolipoprotein E-deficient mice. METHODS AND RESULTS: Eighty-four 7-week-old mice were randomized to receive water, red wine (diluted to 6% ethanol v/v), 6% ethanol v/v, or red wine powder in water. All mice were fed a normal chow diet. At 26 weeks of age, the mice were killed. HDL cholesterol was raised 12.0% (95% CI, 4.0% to 20.0%) and 9.2% (95% CI, 1.5% to 16.9%) by red wine and ethanol, respectively. At the end of study, all mice exhibited advanced atherosclerosis in the aortic bulb, whereas less mature atherosclerosis predominated in the brachiocephalic trunk. The amount of atherosclerosis in the aortic bulb and the brachiocephalic trunk were similar in all groups (P:=0.92 and P:=0.14, respectively). To evaluate whether ethanol or red wine polyphenols were protective by stabilizing atherosclerotic plaques rather than reducing their size, we measured the percentage of collagen-poor areas in left coronary sinus plaques as a morphological criterion of plaque stability. The percentage of collagen-poor areas did not differ between groups (P:=0.71). CONCLUSIONS: Neither ethanol nor red wine polyphenols reduced mature atherosclerosis or changed the content of collagen in plaques in apolipoprotein E-deficient mice.