**6. Pathophysiology of Atherosclerosis in TCTP-TG and TCTP+/**<sup>−</sup> **Mice**

*6.1. Exacerbation of Atherosclerosis by TCTP-Induced Hypertension in TCTP-TG/ApoE KO*

Atherosclerosis is a pathological remodeling of arterial walls with the development of atheromatous plaques involving endothelial dysfunction, migration of SMCs, and accumulation of cholesterol in the lesions [79,80]. Arterial hypertension is a key etiological factor in the development of atherosclerosis and, thus, of cardiovascular disorders [79], through the various pathological links including hemodynamic stress [81]. Ang II- and high salt-induced hypertension facilitated the development of atherogenesis in apolipoprotein E-deficient mice (ApoE KO) [82,83] whereas Ang II-induced atherosclerosis was attenuated by enalapril treatment in vivo because of its anti-atherogenic and anti-inflammatory effects [84]. In clinical settings, angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) retard the pathogenic process of atherosclerosis in hypertensive patients [85].

Genetically modified animal models of atherosclerosis include apolipoprotein E knockout mice (ApoE KO), low-density lipoprotein (LDL) receptor knockout mice (LDLR−/−), scavenger receptor class B member 1 knockout mice (SR-BI KO), *db/db* and *ob/ob* mice, Zucker fatty rats, and cholesterol ester transfer protein (CETP) transgenic rats [53]. Among those, the most extensively investigated is the ApoE KO that lacks ApoE, a glycoprotein ligand for receptors that eliminates chylomicron remnants and very low-density lipoproteins (VLDLs), which exhibits spontaneous hypercholesterolemia and the formation of atherosclerotic lesions in vessels [86,87].

Our group investigated whether TCTP overexpression accelerates the process of atherogenesis in animal models [44]. Multiple crossbreeding of TCTP-TG with ApoEnull mice generated nTG/ApoE KO and TCTP-TG/ApoE KO mice having comparable genetic backgrounds (about 97% C57BL/6 and 3% CBA) (Figure 1B). TCTP-TG and nTG mice carrying identical genetic makeup were generated by backcrossing the TCTP-TG C57BL/6×CBA hybrid mice to C57BL/6 mice. The differences in body weight changes and major organ weights were insignificant among the four groups, but the brain, lung, and spleen weights showed an increase in TCTP-TG/ApoE KO compared to TCTP-TG [44]. Following the lipid-enriched western diet of 7-week-old mice for 16 weeks, lipid-laden atherosclerotic plaques were found in the thoracic aorta of ApoE-null mice, but not in that of TCTP-TG [44]. Importantly, the transgenic overexpression of TCTP in ApoE KO showed an exacerbation of atherosclerotic lesions, exhibiting a wider distribution and thicker lesions than that of ApoE KO [44]. The BP elevation of TCTP-TG and TCTP-TG/ApoE KO was comparable [44]. Based on the observation that TCTP-TG shows negligible atherosclerotic lesion formation, hypertension alone was not enough to establish atherosclerotic lesions. Moreover, high-fat diet feeding in TCTP-TG also did not cause atherosclerosis and the animals exhibited normal lipid metabolism [44], suggesting that ApoE genetic malfunction may be a prerequisite for establishing atherosclerosis.

We found that TCTP overexpression in an ApoE KO genetic background did not affect the plasma glucose, albumin, and lipid profiles of ApoE KO mice [44], indicating that atherosclerotic acceleration by TCTP is not mediated by those factors, including increased burden of plasma lipid. Therefore, we speculated that hemodynamic stress or inflammatory responses provoked by high BP [81,88] might be the proatherogenic factors that operate in TCTP-induced atherogenic progression [44]. The potential involvement of ET-1, a potent endothelium-derived vasoactive peptide that is upregulated in atherogenic status to facilitate the proliferation, migration, and contraction of VSMC [89–91], was also proposed. Such a hypothesis can be supported by the findings that Na,K-ATPase inhibition, such as that which results from ouabain treatment, induces ET-1 release from the endothelial cells [92–96] and that TCTP synthesis was upregulated following stimulation of human lung fibroblasts with ET-1 [97], though the interplay between TCTP and ET-1 and its consequences require experimental verification.

Our unpublished data on ligation-induced atherosclerotic mouse model also supports the role of TCTP in the atherogenesis. Two weeks after the ligation operation on the left common carotid artery (LCCA), ligated carotid arteries of TCTP-TG showed a 3.4-fold increase in intimal area compared to that of non-TG, suggesting TCTP-induced exacerbation of atherosclerosis through intimal layer thickening.
