Secreted protein acidic and rich in cysteine facilitates age-related cardiac inflammation and macrophage M1 polarization

Abstract

Toba H, de Castro Brás LE, Baicu CF, Zile MR, Lindsey ML, Bradshaw AD. Secreted protein acidic and rich in cysteine facilitates age-related cardiac inflammation and macrophage M1 polarization. Am J Physiol Cell Physiol 308: C972-C982, 2015. First published April 15, 2015; doi:10.1152/ajpcell.00402.2014.-To investigate the role of secreted protein acidic and rich in cysteine (SPARC) in age-related cardiac inflammation, we studied six groups of mice: young (3-5 mo old), middle-aged (10 -12 mo old), and old (18 -29 mo old) C57BL/6 wild-type (WT) and SPARC-null (Null) mice (n ϭ 7-10/group). Cardiac function and structure were determined by echocardiography. The left ventricle was used for cytokine gene array and macrophage quantification by immunohistochemistry. Macrophage infiltration increased with age in WT (n ϭ 5-6/group, P Ͻ 0.05 for young vs. old), but not in Null. Proinflammatory markers (Ccl5, Cx3cl1, Ccr2, and Cxcr3) increased in middle-aged and old WT, whereas they were increased only in old Null compared with respective young (n ϭ 5-6/group, P Ͻ 0.05 for all). These results suggest that SPARC deletion delayed age-related cardiac inflammation. To further assess how SPARC affects inflammation, we stimulated peritoneal macrophages with SPARC (n ϭ 4). SPARC treatment increased expression of proinflammatory macrophage M1 markers and decreased anti-inflammatory M2 markers. Echocardiography (n ϭ 7-10/group) revealed an age-related increase in wall thickness of the left ventricle in WT (0.76 Ϯ 0.02 mm in young vs. 0.91 Ϯ 0.03 mm in old; P Ͻ 0.05) but not in Null (0.78 Ϯ 0.01 mm in young vs. 0.84 Ϯ 0.02 mm in old). In conclusion, SPARC deletion delayed age-related increases in macrophage infiltration and proinflammatory cytokine expression in vivo and in vitro. SPARC acts as an important mediator of age-related cardiac inflammation by increasing the expression of macrophage M1 markers and decreasing M2 markers.

Dissecting the role of myeloid and mesenchymal fibroblasts in age-dependent cardiac fibrosis

“…Indeed, the analysis of fibroblasts derived from aged MCP-1KO and aged B6J hearts demonstrated a 3 fold increased IL-6 mRNA expression (measured by qPCR [8]) in fibroblasts derived from the aged MCP-1KO heart, and although this difference did not reach statistical significance (2.95 ± 1.05 vs 1.00 ± 0.39, P=0.16), it suggests a potential mechanism by which aged MCP-1KO hearts still have a pro-inflammatory environment and partially develop myeloid-dependent fibrosis. An increased macrophage infiltration in the aged B6J mouse heart has been described by others [31, 48], and in these studies the ratio of M1 (classically activated pro-inflammatory macrophage) to M2 alternatively activated macrophage was increased. We have found that both M1 (data not published) and M2a macrophages had an increased presence in the aging heart when compared with young controls.…”

The impact of aging on cardiac extracellular matrix

“…These changes are all blunted by SPARC deletion (Bradshaw et al 2010). Aging SPARC null mice (18–29 month old) also have decreased collagen type III and IV expression and macrophage infiltration compared to aging wild type control mice (de Castro Bras et al 2014; Toba et al 2015). The decrease in collagen III may result in an increased collagen I to collagen III ratio, which would also explain the increase in myocardial diastolic stiffness.…”

“…Secreted protein acidic and rich in cysteine (SPARC) belongs to the matricellular protein family, and SPARC is involved in cross-linked collagen fibril formation (Bradshaw 2009). SPARC is predominantly expressed in cardiac fibroblasts, although cardiomyocytes, endothelial cells, and macrophages also exhibit low SPARC expression (Toba et al 2015). SPARC increases in the LV of 18 to 29 month old mice and has been linked to age-related increases in myocardial diastolic stiffness as well as fibrillar and insoluble collagen content.…”

“…MMP-9 deletion suppresses these phenotypic changes by increasing macrophage mRNA levels of CD206 and Fizz1 and by preventing the age-related shift from of F4/80 + CD206 + M2 cells to F4/80 + CD206 − M1 cells (Ma et al 2015). Macrophage accumulation is also decreased in the LVs of old SPARC-null mice (Toba et al 2015). Isolated peritoneal macrophage stimulated with SPARC recombinant protein showed increased expression of M1 pro-inflammatory polarization markers (Ccl3, Ccl5, TNF-α, and IL-12) and decreased expression of anti-inflammatory M2 polarization markers (Arg1 and Mrc1) (Toba et al 2015).…”

“…Macrophage accumulation is also decreased in the LVs of old SPARC-null mice (Toba et al 2015). Isolated peritoneal macrophage stimulated with SPARC recombinant protein showed increased expression of M1 pro-inflammatory polarization markers (Ccl3, Ccl5, TNF-α, and IL-12) and decreased expression of anti-inflammatory M2 polarization markers (Arg1 and Mrc1) (Toba et al 2015). Therefore, in addition to mediating ECM events in cardiac aging, MMP-9 and SPARC regulate cell physiology and signaling.…”