Nesfatin-1 stimulates fatty-acid oxidation by activating AMP-activated protein kinase in STZ-induced type 2 diabetic mice

Abstract

Nesfatin-1 is an anorexigenic peptide involved in energy homeostasis. Recently, nesfatin-1 was reported to decrease blood glucose level and improve insulin sensitivity in high-fat diet-fed rats. However, little information is known about the influence of nesfatin-1 on lipid metabolism either in physiological or diabetic condition. This study undertook whether nesfatin-1 was involved in the pathophysiology in Streptozotocin-induced type 2 diabetic mice (T2DM), which was induced by a combination of high-calorie diet and two low-doses Streptozotocin. We observed that plasma nesfatin-1 was significantly increased while expression of nesfatin-1 neurons were decreased in hypothalamus in diabetes group compared to only high-calorie diet control group; intravenous injection of nesfatin-1 decreased 0-1h, 0-2h, 0-3h cumulative food intake in T2DM, but 0-24h total food intake had no difference between groups. Body weight and plasma FFA were normalized after nesfatin-1(10 µg/Kg) administration for 6 days. These results suggested that nesfatin-1 improved lipid disorder in T2DM. It was found that blood glucose and insulin resistance coefficient decreased with treatment of nesfatin-1 (both in 1 µg/Kg and 10 µg/Kg doses) in diabetes mice. For further understanding the role of nesfatin-1 on lipid metabolism, we detected p-AMPK and p-ACC of skeletal muscle in T2DM using western blotting. The expression of p-AMPK and p-ACC increased when nesfatin-1 was given with doses 1 µg/Kg but not in doses 10 µg/Kg. Taken together, nesfatin-1 participated in the development of T2DM and stimulated free fatty acid utilization via AMPK-ACC pathway in skeletal muscle in T2DM.

Figure 1. Concentration and distribution of nesfatin-1 in plasma, PVN, SON and gastric mucosa.

(A) Concentrations of plasma nesfatin-1 2h after i.v. nesfatin-1 or NS injection. Nesfatin-1 expression in (B) PVN, (D) SON and (F) gastric mucosa in HFDN control mice. Nesfatin-1 expression in (C) PVN, (E) SON and (G) gastric mucosa in T2DM mice. The intensity of nesfatin-1 positive neurons in (H) PVN and (I) SON.The arrow points to nesfatin-1 positive cells. Scale bar in B, D and F = 200 µm for B-C, D-E, F-G respectively. Data were presented as means± S.E.M. *p<0.05, **p<0.01(compared with HFDN group), ^##p<0.01(compared with DMN group).

Figure 2. Effects of nesfatin-1 on blood glucose, plasma insulin and IR coefficient.

(A) The blood glucose changes pre- and post -i.v. injection. (B) The plasma insulin levels. (C) The insulin-resistance coefficient. HOMA IR = fasting plasma insulin (µU/ml)×fasting plasma glucose (mmol/l)/22.5. All data were expressed as the mean ± S.E.M of 4–8 mice/group. *p<0.05, **p<0.01 (compared with the HFDN group). ^#p<0.05, ^##p<0.01 (compared with DMN group), ⁺p<0.05 (compared with DML group)

Figure 3. Effects of nesfatin-1 on cumulative food intake, body weight changes and FFA levels.

(A) Cumulative food intake levels of 0–1h, 0–2h, 0–24h. (B) The body weight changes pre- and post- the 6-day long i.v. injection. (C) The plasma FFA levels after 6-day i.v. injection of nesfatin-1 or NS. All data were expressed as the mean ± S.E.M of 4–8 mice/group. *p<0.05, **p<0.01 (compared with the HFDN group) ^#p<0.05, ^##p<0.01(compared with DMN group)

Figure 4. Nesfatin-1 effects on the activation of AMPK and ACC in skeletal muscle.

P-AMPK relative to t-AMPK in (A) red gastroenemius, (C) soleus and (E) white gastroenemius. P-ACC relative to total t-ACC in (B) red gastroenemius (D) soleus and (F) white gastroenemius. All data were expressed as the mean ± S.E.M of 4–8 mice/group. *p<0.05, **p<0.01 (compared with the HFDN group) ^#p<0.05 (compared with the DMN group)

Figure 5. Effect of nesfatin-1(both endogenous and exogenous) on fat metabolism in the muscle in STZ-treated mice.

The pathway of endogenous nesfatin-1 effect is showed by the white arrow and that of the exogenous nesfatin-1 is showed by the red arrow. The dashed arrow shows the possible pathway of exogenous nesfatin-1 affecting food intake.