The acute phase protein α2-macroglobulin induces rat ventricular cardiomyocyte hypertrophy via ERK1,2 and PI3-kinase/Akt pathways☆

Abstract

Objective: α 2 -macroglobulin (α 2 M) is an acute phase protein released to the serum upon challenges such as cardiac hypertrophy and infarction. Here we report on the role of α 2 M in the induction of hypertrophic cell growth, contractile responsiveness of rat ventricular cardiomyocytes, and on the underlying extracellular regulated kinase 1,2 (ERK1,2) and phosphoinositide 3-kinase (PI3-kinase)/Akt pathways. Methods: Cell volume and cross-sectional areas were assessed as parameters of hypertrophic growth, and real time RT-PCR for the analysis of hypertrophy-related genes was performed. Protein synthesis was analyzed by 14 C-phenylalanine incorporation. Activation of ERK1,2, PI3-kinase and Akt was assessed by immunohistochemical analysis of phosphorylated proteins. Contractile responsiveness was investigated by determination of cell shortening following electrical field stimulation. Intracellular calcium concentration [Ca 2+ ] i was determined by fluo-3 microfluorometry. Results: Treatment of ventricular cardiomyocytes for 24 h with α 2 M significantly increased cell volume and protein synthesis as well as expression of hypertrophy-associated genes [brain natriuretic protein (BNP), β-myosin heavy chain (β-MHC), myosin light chain-2 (MLC-2), atrial natriuretic factor (ANF), and skeletal α-actin]. Comparable effects were achieved by treatment of cells with an antibody directed against the α 2 M-receptor LDL receptor-related protein-1 (LRP-1) and counteracted upon coincubation with receptor-associated protein (RAP), suggesting an involvement of α 2 M-LRP-1 signalling. Furthermore, α 2 M treatment increased sarcoplasmic reticulum Ca 2+ -ATPase (SERCA2a) expression, diastolic and systolic [Ca 2+ ] i , and contractile responsiveness after electrical stimulation. Shortly after α 2 M stimulation, activation of ERK1,2, Akt, and PI3-kinase pathways was observed. Consequently, α 2 M-induced protein synthesis was inhibited upon treatment with the ERK1,2 inhibitor UO126 as well as by LY294002 and wortmannin, which inhibit PI3-kinase, and by rapamycin, which inhibits mammalian target of rapamycin (mTOR) downstream of Akt. Conclusions: Our data show that α 2 M induces hypertrophic cell growth in rat ventricular cardiomyocytes via ERK1,2 and PI3-kinase/Akt and improves cardiac cell function.

Role of kallistatin in prevention of cardiac remodeling after chronic myocardial infarction

“…4,21 In addition, ANP, a cardiac hypertrophy marker, is activated in an Akt-dependent manner. 22 However, one study reported that short-term activation of Akt-induced cardiac hypertrophy without ANP gene expression.…”

“…2,3 Elevation of ROS activates a series of hypertrophic signaling kinases and transcription factors to stimulate cardiac hypertrophy. 3,4 Moreover, ROS stimulate fibroblast proliferation and activate the expression of profibrotic factors, including transforming growth factor-b1 (TGF-b1), that facilitate fibrosis and matrix remodeling. [5][6][7] Elevation of vascular oxidative stress and ventricular remodeling contribute to high mortality in chronic heart failure (CHF) patients.…”

The Effects of Interleukin-6 and Cytokine-Induced Neutrophil Chemoattractant-1 on .ALPHA.2-Macroglobulin Production in Rats

“…Introduction α 2 -Macroglobulin (α2M) is a typical acute phase protein in rats [15,16,18,22,27]. Various stimulations of the inflammatory response (e.g., injection of turpentine oil, surgical treatment, and inoculation of microorganisms) result in increased α2M production [13,17,18].…”

“…Serum levels of α2M increase more than one-hundred fold in response to these stimulations [17]. Therefore, α2M is a useful marker of the inflammatory response in rats [17,22]. Jinbo et al measured the changes of many cytokines in rats injected with turpentine oil and found that only interleukin-6 (IL-6) and cytokine-induced neutrophil chemoattractant-1 (CINC-1) increase prior to the elevation of α2M serum levels [17].…”

Molecular Dissection of the Human α2-Macroglobulin Subunit Reveals Domains with Antagonistic Activities in Cell Signaling

“…As a result, ␣ 2 M may inhibit growth factor activity (9,10) or stabilize the growth factor for potential delivery to cell signaling receptors (11). There also is evidence that ␣ 2 M, which is "activated" by reaction with proteases, initiates cell signaling by binding to LRP-1 (12)(13)(14)(15) or other receptors, such as glucose-regulated protein-78 (Grp 78) (16,17). However, in studies with intact ␣ 2 M, the possibility that cell signaling results from growth factors that are carried by ␣ 2 M must be considered (11,18).…”