Quantification of Bone Fatty Acid Metabolism and Its Regulation by Adipocyte Lipoprotein Lipase

Figures

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  Figure 1. The skeleton is an adipose organ: (A) Total lipid content in metabolically active tissues (highlighted in black) and parts of the skeleton (highlighted in red) from 12-week-old female C57BL6/J mice. Mean ± SEM, n = 5; (B) Environmental scanning electron microscopy of a distal tibial specimen from 12-week-old female C57BL6/J mice revealing both cortical bone as well as adipocyte-containing bone marrow (red box indicates area in the tibia, scale bar: 0.1 mm).

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  Figure 2. Tibia but not femoral bone marrow resembles adipose fatty acid profiles. Relative fatty acid composition determined by gas chromatography from: (A) epididymal white adipose tissue (EpiWAT); (B) brown adipose tissue (BAT); (C) Liver; (D) Heart; (E) Muscle; (F) femoral bone marrow (Femur BM); (G) tibial bone marrow (Tibia BM); (H) cortical bone from femur (Femur cort.); and (I) cortical bone from tibia (Tibia cort.) from 12-week-old female C57BL6/J mice. Mean, n = 7.

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  Figure 3. The skeleton significantly contributes to nutrient handling: (A) 12-week-old male C57BL6/J mice received an oral fat load mixed with radioactive polyunsaturated acids (3H-PUFAs) as well as for saturated fatty acids (14C-SFA) tracers; Organ uptake was determined by scintillation counting in isolated tissues. Mean ± SEM, n = 7; (B) PUFA-to-SFA ratio for metabolically active tissues (highlighted in black) and parts of the skeleton (highlighted in red) calculated from A; (C) total organ uptake for metabolically active tissues and the skeleton for SFAs; and (D) PUFAs; and (E) total organ uptake after an oral glucose tolerance test with tracer amounts of 14C-deoxyglucose in 12-week-old male C57BL6/J. Mean ± SEM; n = 6 per group. EpiWAT: Epididymal white adipose tissue, BAT: brown adipose tissue, BM: bone marrow.

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  Figure 4. Nutrient handling in aLKO mice: (A) Quantitative real-time PCR analysis of Lpl expression in metabolically active tissues (highlighted in black) and parts of the skeleton (highlighted in red) in 12-week-old female C57BL6/J mice; and (B) adipocyte-specific Lpl knock-out (aLKO) mice compared to wild-type controls; (C) Total tissue lipids in aLKO mice and controls. Mean ± SEM; n = 5 per group; (D) Organ uptake of: 3H-SFA tracers; and (E) 14C-deoxyglucose after a combined oral tolerance test. Mean ± SEM; n = 6 per group. (* p < 0.05, # p < 0.01). BAT: brown adipose tissue, BM: bone marrow.

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  Figure 5. Role of LPL for bone fatty acid composition. Change in relative fatty acid composition determined by gas chromatography from: (A) Femur BM; (B) Tibia BM; (C) Femur cort.; and (D) Tibia cort. isolated from 12-week-old female aLKO mice and wild-type controls. Mean ± SEM; n = 5 per group. LPL: lipoprotein lipase; BM: bone marrow; aLKO: adipocyte-specific lipoprotein lipase knock-out (* p < 0.05).