Pathophysiological Implication of Fetuin-A Glycoprotein in the Development of Metabolic Disorders: A Concise Review - PubMed (original) (raw)

Review

Pathophysiological Implication of Fetuin-A Glycoprotein in the Development of Metabolic Disorders: A Concise Review

Lynda Bourebaba et al. J Clin Med. 2019.

Abstract

: Alpha 2-Heremans-Schmid glycoprotein, also known as fetuin-A (Fet-A), is a multifunctional plasma glycoprotein that has been identified in both animal and human beings. The protein is a hepatokine predominantly synthesized in the liver, which is considered as an important component of diverse normal and pathological processes, including bone metabolism regulation, vascular calcification, insulin resistance, and protease activity control. Epidemiological studies have already consistently demonstrated significant elevated circulating Fet-A in the course of obesity and related complications, such as type 2 diabetes mellitus, metabolic syndrome, and nonalcoholic fatty liver disorder (NAFLD). Moreover, Fet-A has been strongly correlated with many parameters related to metabolic homeostasis dysregulation, such as insulin sensitivity, glucose tolerance, circulating lipid levels (non-esterified free fatty acids and triglycerides), and circulating levels of both pro- and anti-inflammatory factors (C-reactive protein, tumor necrosis factor-α (TNF-α), and interleukin (IL)-6). Metabolic-interfering effects of Fet-A have thus been shown to highly exacerbate insulin resistance (IR) through blocking insulin-stimulated glucose transporter 4 (GLUT-4) translocation and protein kinase B (Akt) activation. Furthermore, the protein appeared to interfere with downstream phosphorylation events in insulin receptor and insulin receptor substrate signaling. The emerging importance of Fet-A for both diagnosis and therapeutics has therefore come to the attention of researchers and the pharmaceutical industry, in the prospect of developing new therapeutic strategies and diagnosis methods for metabolic disorders.

Keywords: biomarker; fetuin-A; hepatokine; insulin resistance; metabolic disorders.

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Conflict of interest statement

There is no conflict of interest.

Figures

Figure 1

Figure 1

Graphical representation of main physiological roles of hepatic-secreted Fetuin-A. Under physiological conditions, Fetuin-A (Fet-A) enhances the absorption and fixation of essential minerals, calcium, and phosphate in the form of hydroxyapatite substituted with a carbonate. Moreover, Fet-A acts as a carrier of insoluble phosphate and calcium, and forms stable mineral complexes, more soluble in the bloodstream, preventing the precipitation of calcium salts through the mediation of their clearance, and the consequent occurrence of vascular calcifications. Fet-A functions as a negative regulator of the innate immune response by inhibiting Lipopolysaccharide (LPS)- or Interferon (IFN)-γ-induced High mobility group box 1 protein (HMGB1) release in macrophages in response to lethal endotoxemia or sepsis.

Figure 2

Figure 2

Pathophysiological implications of Fet-A in the course of metabolic and cardiovascular diseases. Excessive release of Free fatty acids (FFAs) and overaccumulation of glucose in the bloodstream stimulate the biosynthesis of Fetuin-A from hepatocytes through activation of both Nuclear factor kappa B (NF-κB) and ERK 1/2 pathways. Fet-A acts then as an insulin signaling pathway inhibitor by modulating the kinase reaction initiated by insulin on insulin-receptor tyrosine kinase autophosphorylation; insulin-sensitive tissues become less responsive to insulin, triggering insulin resistance. Meanwhile, Fet-A functions as an adaptor between FFA and Toll like receptor 4 (TLR4) signaling in lipid-induced inflammation, and TLR4 signaling leads to the activation of NF-κB and Activator protein 1 (AP-1), which can then upregulate the transcription of inflammatory genes, resulting in the production of inflammatory cytokines that can lead to insulin resistance. On the other hand, decreased Fet-A synthesis is strongly correlated with excessive vascular calcification and general heart failure, as the Fet-A-stabilization effect toward insoluble calcium and phosphate crystals is no longer properly achieved.

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