Mimecan, a Hormone Abundantly Expressed in Adipose Tissue, Reduced Food Intake Independently of Leptin Signaling

Abstract

Adipokines such as leptin play important roles in the regulation of energy metabolism, particularly in the control of appetite. Here, we describe a hormone, mimecan, which is abundantly expressed in adipose tissue. Mimecan was observed to inhibit food intake and reduce body weight in mice. Intraperitoneal injection of a mimecan-maltose binding protein (-MBP) complex inhibited food intake in C57BL/6J mice, which was attenuated by pretreatment with polyclonal antibody against mimecan. Notably, mimecan-MBP also induced anorexia in A(y)/a and db/db mice. Furthermore, the expression of interleukin (IL)-1β and IL-6 was up-regulated in the hypothalamus by mimecan-MBP, as well as in N9 microglia cells by recombinant mouse mimecan. Taken together, the results suggest that mimecan is a satiety hormone in adipose tissue, and that mimecan inhibits food intake independently of leptin signaling by inducing IL-1β and IL-6 expression in the hypothalamus.

Keywords: Anorexia; IL-1β; IL-6; Leptin; Mimecan.

Fig. 1

Mimecan expressed in various mouse tissues and secreted into the blood. (a) Mimecan mRNA expression in various tissues from C57BL/6J mice determined by northern blot analysis. (b) Mimecan corresponding to 25 kDa and 12 kDa was detected in human serum by western blot analysis using monoclonal antibody against mimecan. H1–H4 represents four healthy individuals. M: molecular weight markers. Body mass index (BMI) of the individuals: H1, 21.8; H2, 21.5; H3, 19.5; H4, 25.7. (c) Northern blot analysis of mimecan mRNA expression in adipose tissue from C57BL/6J mice fasting for 0, 24, and 48 h (n = 4 for each time point). The right histogram is the gray scale of mimecan mRNA expression. Data are expressed as means ± SEM. *P < 0.05 vs 0 h. Statistical analysis was performed by one-way ANOVA.

Fig. 2

Intraperitoneal (i.p.) and intracerebroventricular (i.c.v.) injections of mimecan induced a reduction in food intake and the anorexic effect of mimecan was attenuated by pretreatment with polyclonal antibody or by heat-inactivated mimecan. (a) Cumulative food intake of C57BL/6J mice responding to i.p. injection of different doses of mimecan-MBP (Mim-MBP) at indicated time points after 12 h of fasting (8:00 p.m.–8:00 a.m., n = 8). (b) Suppression of food intake in C57BL/6J mice with ad libitum access to food when responding to i.p. injection of Mim-MBP (0.05 μmol/kg) (n = 5), compared to phosphate-buffered saline (PBS) or maltose binding protein (MBP). (c) Suppression of food intake in Spraque–Dawley (SD) rats responding to i.c.v. injection of mimecan-MBP (Mim-MBP) (2 nmol/kg) (n = 8). (d) Cumulative food intake of C57BL/6J mice after i.p. injection with active or inactive Mim-MBP (n = 5). (e) Antibody neutralization test in C57BL/6J mice. Mice were pretreated with polyclonal antibody against mimecan or rabbit preimmune IgG by i.p. injection (n = 12). (f) Suppression of food intake of C57BL/6J mice responding to i.p. injection of mimecan-His (Mim-His) (0.05 μmol/kg) (n = 6). *P < 0.05; **P < 0.01 vs. PBS at the indicated time points in (a) and (b). *P < 0.05; **P < 0.01 vs. Mim-MBP inactivated at time points in (d). Data are expressed as means ± SEM. *P < 0.05; **P < 0.01. Statistical analysis was performed by one-way ANOVA.

Fig. 3

The anorexic effect of mimecan was independent of leptin and melanocortin signaling. (a, b) Effect of mimecan on daily food intake (a) and body weight increment (b) in db/db mice with ad libitum access to food (0.05 μmol/kg; i.p. injection, n = 9–10). (b) Daily body weight change (g) = body weight on the indicated day — body weight on day 0. The solid circles and squares represent the changes of body weight during mimecan-MBP or MBP treatment, respectively. The empty circles and squares represent the changes of body weight after stopping injections of mimecan-MBP or MBP, respectively. (c) Cumulative food intake of A^y/a mice treated with Mim-MBP (0.05 μmol/kg) after fasting for 6 h (i.p. injection, n = 4–5). Data are expressed as means ± SEM. *P < 0.05; **P < 0.01. Statistical analysis was performed by one-way ANOVA.

Fig. 4

Effect of mimecan on IL-1β, IL-6, and SOCS3 expression and features of mimecan knockout mice. (a) The mRNA expression of IL-1β, IL-6, and SOCS3 in the hypothalamus from C57BL/6J mice (n = 10) with ad libitum access to food, treated with active or inactive Mim-MBP (0.05 μmol/kg) by i.p. injection for 4 h. The reference gene was actin. (b) Effect of recombinant mouse mimecan (rm Mim) (100 nM for 4 h) on the expression of IL-1β, SOCS3, and IL-6 in N9 microglia cells. The reference gene was actin. (c, d) The body weight (c) and daily food intake (d) in Min^−/− (knockout) mice and wild type (WT) littermates with ad libitum access to food (n = 25). (e) Leptin mRNA expression in adipose tissue from Min^−/− mice and WT littermates (n = 4). (f) Levels of leptin in serum from Mim^−/− mice and WT littermates (n = 12). Data are expressed as means ± SEM. *P < 0.05; **P < 0.01. Statistical analysis was performed by one-way ANOVA.