Abdominal aortic aneurysm (AAA) is an asymptomatic disease of high mortality rate (65% to 85%) if rupture occurs. Surgical repair is the only effective treatment, but limited to eligible patients (about 10% of total). No effective pharmacological approach has been identified to limit AAA progression and rupture. Male sex is an important risk factor for AAA, with about 4-6:1 male to female prevalence ratio. The reasons for this sex disparity are unknown, but the delayed onset of AAA in women suggests that estrogen and its receptors (ERs) may play a role in reducing the prevalence of AAA. Administration of estrogen has protective effects in AAA animal models through reduction of pro-inflammatory mediators and the proteolytic pathway. However, long- term estrogen therapy cannot be widely applied to treat AAA patients due to undesirable side-effects. Human genetic studies uncovered that Kruppel-like factor 14 (KLF14) is robustly associated with chronic metabolic diseases with a sex difference. We previously reported the biological function of KLF14 and its activator, perhexiline, clinically used to treat angina and heart failure, in lipid metabolism and demonstrate the strong anti-inflammatory effect of KLF14. Our preliminary data described herein established that macrophage- selective Klf14 knockout mice showed significantly increased AAA incidence rates in females, comparable to those in males, suggesting impaired protective effects of estrogen/ER?/? pathway. Besides the inhibitory effects of KLF14 on the inflammatory response and MMP-9 activity, we further found that estrogen upregulates the expression of KLF14 while KLF14, in turn, is a critical transcription factor upregulating the expression of ER?/? in macrophages, uncovering a feedforward loop that may contribute to the observed sex disparity. Perhexiline increased the levels of ER?/? in a KLF14-dependent manner. A cholesterol metabolite, 24- hydroxycholesterol (24HC), functioned as an endogenous ER?/? agonistic molecule and enhanced the anti- inflammatory effect of perhexiline in macrophages. Most importantly, administration of perhexiline significantly reduced AAA dissection/rupture and increased survival rate in male mice. Based on our preliminary findings, the proposed project will test the central hypothesis that KLF14 protects against AAA development/dissection /rupture by suppressing inflammation and enhancing ER?/?-dependent protective roles in macrophages.
The specific aims will 1) define that macrophage KLF14 is an important regulator of sex differences in AAA mouse models; 2) determine how KLF14 regulates the estrogen/ERs pathway which contributes to sex-dimorphic protective effects on AAA; and 3) determine that activation of KLF14 inhibits development/dissection/rupture in AAA mouse models. Based on the sex-specific functions of KLF14 in AAA, this mechanistic research will establish KLF14 as a novel therapeutic target and will set a solid foundation towards clinical utilization of KLF14 activators, like perhexiline, as a viable drug therapy for AAA, with the potential to change current treatment paradigms for AAA.
Abdominal aortic aneurysm (AAA) is a life-threatening condition in adults, especially in male individuals, because estrogen and estrogen receptors have protective roles against AAA in females. A new mechanism was identified by which a factor, KLF14, inhibits inflammation and increases estrogen receptors in macrophages. The information generated from this study will promote the development of more effective drug therapies for the prevention of rupture or to promote reversion of AAA, which currently are not available.
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