BMT decreases HFD-induced weight gain associated with decreased preadipocyte number and insulin secretion

Abstract

Experimental bone marrow transplantation (BMT) in mice is commonly used to assess the role of immune cell-specific genes in various pathophysiological settings. The application of BMT in obesity research is hampered by the significant reduction in high-fat diet (HFD)-induced obesity. We set out to characterize metabolic tissues that may be affected by the BMT procedure and impair the HFD-induced response. Male C57BL/6 mice underwent syngeneic BMT using lethal irradiation. After a recovery period of 8 weeks they were fed a low-fat diet (LFD) or HFD for 16 weeks. HFD-induced obesity was reduced in mice after BMT as compared to HFD-fed control mice, characterized by both a reduced fat (-33%; p<0.01) and lean (-11%; p<0.01) mass, while food intake and energy expenditure were unaffected. As compared to control mice, BMT-treated mice had a reduced mature adipocyte volume (approx. -45%; p<0.05) and reduced numbers of preadipocytes (-38%; p<0.05) and macrophages (-62%; p<0.05) in subcutaneous, gonadal and visceral white adipose tissue. In BMT-treated mice, pancreas weight (-46%; p<0.01) was disproportionally decreased. This was associated with reduced plasma insulin (-68%; p<0.05) and C-peptide (-37%; p<0.01) levels and a delayed glucose clearance in BMT-treated mice on HFD as compared to control mice. In conclusion, the reduction in HFD-induced obesity after BMT in mice is at least partly due to alterations in the adipose tissue cell pool composition as well as to a decreased pancreatic secretion of the anabolic hormone insulin. These effects should be considered when interpreting results of experimental BMT in metabolic studies.

Fig 1. BMT decreased diet-induced obesity.

(A) Male C57BL/6 mice underwent BMT at time point 0 weeks. From 0 weeks until week 8, mice were fed a chow diet and from time point 8 weeks, mice were fed either a 10% LFD. (B) Body weight gain of BMT-treated mice, over a period of 16 weeks LFD, was reduced compared to control mice. Values are means ± SD; n = 7–12; * p<0.05,** p<0.01, *** p<0.001.

Fig 2. BMT has long term effects on white adipose tissue.

(A) Weight of sWAT and vWAT pads was decreased in BMT-treated mice as compared to control mice. (B) The volume of mature adipocytes was lower in BMT-treated mice than control mice. (C) The number of mature adipocytes was not affected in the three WAT pads, (D) but the number of preadipocytes in all three WAT pads was lower in BMT-treated mice than control mice. (E) Macrophage number per fad pad was lower in the three fat pads of BMT-treated mice vs. control mice. (F) Linear regression analysis of macrophage number per fat pad and gWAT pad weight showed decreased macrophage numbers in gWAT in BMT-treated mice compared to control mice. Values are means ± SD; n = 7–12; * p<0.05, ** p<0.01, *** p<0.001.

Fig 3. BMT decreased weight of different organs.

(A) BMT decreased the weight of liver, thymus, spleen and the pancreas both on LFD and HFD. (B) Linear regression analysis of pancreas weight and body weight showed a lower pancreas weight in the BMT-treated mice, independently of body weight. Values are means ± SD; n = 7–12; * p<0.05, ** p<0.01, *** p<0.001.

Fig 4. BMT did not affect pancreatic beta cell area and beta cell mass.

(A) Beta cell area and (B) beta cell mass were not different in the BMT-treated mice. Values are means ± SD; n = 5.

Fig 5. BMT mice had lower plasma insulin levels and glucose tolerance on a HFD.

(A) Fasting plasma glucose of BMT-treated and control mice did not differ on LFD or HFD. (B) BMT-treated mice tended to have higher fasting plasma glucose concentrations for similar body weights. (C) BMT-treated mice had lowered fasting plasma insulin levels only on HFD. (D) BMT-treated mice had lowered plasma C-peptide concentrations on HFD. (E) There is a linear relation between pancreas weight and fasting plasma C-peptide concentrations. (F) IVGTT revealed that BMT-treated mice have a higher plasma glucose clearance half-life, only on HFD. Values are means ± SD; n = 7–12; * p<0.05, ** p<0.01.