Granzyme K - A novel marker to identify the presence and rupture of abdominal aortic aneurysm

Highlights

• Increased GZMK expression in human AAA serum and tissues was observed.

• GZMK expression was positively related to AAA diameter or circulating CRP.

• Serum GZMK could be a novel biomarker in identifying the presence and rupture of AAA.

Abstract

Background

Immune inflammatory dysfunction is a hallmark of abdominal aortic aneurysm (AAA). Granzyme K (GZMK) is involved in the regulation of inflammation. However, the correlation between GZMK expression and AAA risk remains unknown.

Methods

This case-control study included 112 AAA patients and 112 controls. Serum GZMK levels were determined by enzyme-linked immunosorbent assay and immunohistochemistry was utilized to determine GZMK expression in aortic tissues.

Results

Compared with controls, AAA patients had higher levels of serum GZMK, and GZMK expression in AAA tissues was increased and positively associated with its serum levels (r = 0.688, P = 0.019). A positive association of serum GZMK levels with CRP or AAA diameter was confirmed, while there was a relationship between tissue GZMK expression and AAA diameter. The AUC of serum GZMK for AAA diagnosis was 0.78 with the sensitivity and specificity of 62.5% and 81.2%, whereas AUC for rupture detection was 0.76 with a sensitivity of 90.0% and specificity of 51.3%. A combination of clinically used inflammatory parameters with serum GZMK could enhance the accuracy of WBC or CRP alone in detecting AAA or rupture type. Multiple logistic analyses revealed an association of per unit increase of serum GZMK with AAA presence (OR = 1.046, P < 0.001) and its rupture risk (OR = 1.015, P = 0.048) after adjusting for confounding factors.

Conclusions

Our study provides proof that elevated GZMK expression both in serum and tissues is correlated with the presence of AAA, and serum GZMK may be a useful non-invasive marker that helps to identify AAA and its rupture risk in clinical practice.

Introduction

Abdominal aortic aneurysm (AAA) is a complicated vascular disease featured by localized and progressive dilation of abdominal aorta with life-threatening implications [1]. Important risk factors for AAA include old age, male gender, smoking, hypertension and dyslipidemia [2,3]. Patients with AAA are at high risk to develop aortic rupture, which carries 80–90% mortality [4,5]. Accumulating evidence have supported a major role of inflammation accompanied by immune cell infiltration in AAA formation and rupture, which contributes to medial degeneration of the aorta as well as aortic wall remodeling and weakness [[6], [7], [8], [9]]. Thus, it is an urgent need to explore immune-inflammatory targets for early disease detection, risk stratification and appropriate intervention, which can attenuate adverse clinical outcomes of AAA.

Granzyme K (GZMK), a proinflammatory member of granzyme family, was first discovered in human lymphokine-activated killer cells, and mainly expressed by cytotoxic lymphocytes and monocyte/macrophage cells [[10], [11], [12], [13]]. GZMK can serve as an accelerator of inflammatory processes that directly induce proinflammatory cytokine release, reactive oxygen species generation, endothelial dysfunction and subsequent immune cell recruitment [14,15]. As a secreted molecule, GZMK can also be found in the extracellular milieu where they will exert similar regulating functions [16,17]. In healthy individuals, serum GZMK levels were low or undetectable, whereas levels of soluble GZMK were notably elevated in the circulation under some inflammatory conditions [[18], [19], [20]]. A compelling body of work have shown that GZMK may play unique and influential parts in cardiovascular injury and tissue remodeling, and increased GZMK expression in myocardial tissue of myocardial I/R injury mouse model has been observed [21,22]. Although some granzymes, such as granzyme B, have been recognized to play a pathological role in AAA progression, little is yet known about the value of GZMK expression in the diagnosis and rupture detection of AAA [3].

Given these into account, we conducted this pilot study with the aim to define the expression pattern of GZMK in serum as well as tissue samples of patients diagnosed with AAA and correlate them with the concentration of classical AAA-related circulating biomarkers and aneurysm size. Then, we evaluated the importance of GZMK as a diagnostic biomarker in detecting AAA and its rupture. Our study might help understand the underlying pathogenesis of AAA, and advance the progress of early diagnosis and novel noninvasive therapeutic strategy.