Accelerated postnatal growth increases lipogenic gene expression and adipocyte size in low-birth weight mice

Abstract

Objective: To characterize the hormonal milieu and adipose gene expression in response to catch-up growth (CUG), a growth pattern associated with obesity and diabetes risk, in a mouse model of low birth weight (LBW).

Research design and methods: ICR mice were food restricted by 50% from gestational days 12.5-18.5, reducing offspring birth weight by 25%. During the suckling period, dams were either fed ad libitum, permitting CUG in offspring, or food restricted, preventing CUG. Offspring were killed at age 3 weeks, and gonadal fat was removed for RNA extraction, array analysis, RT-PCR, and evaluation of cell size and number. Serum insulin, thyroxine (T4), corticosterone, and adipokines were measured.

Results: At age 3 weeks, LBW mice with CUG (designated U-C) had body weight comparable with controls (designated C-C); weight was reduced by 49% in LBW mice without CUG (designated U-U). Adiposity was altered by postnatal nutrition, with gonadal fat increased by 50% in U-C and decreased by 58% in U-U mice (P < 0.05 vs. C-C mice). Adipose expression of the lipogenic genes Fasn, AccI, Lpin1, and Srebf1 was significantly increased in U-C compared with both C-C and U-U mice (P < 0.05). Mitochondrial DNA copy number was reduced by >50% in U-C versus U-U mice (P = 0.014). Although cell numbers did not differ, mean adipocyte diameter was increased in U-C and reduced in U-U mice (P < 0.01).

Conclusions: CUG results in increased adipose tissue lipogenic gene expression and adipocyte diameter but not increased cellularity, suggesting that catch-up fat is primarily associated with lipogenesis rather than adipogenesis in this murine model.

FIG. 1.

A: Experimental schema. B: White adipose tissue mass (WAT mass represents sum of epididymal, perirenal, and flank subcutaneous fad pads), age 3 weeks. * and † denote P < 0.05 vs. C-C; groups with different symbols have statistically significant differences (P < 0.05). C: Daily food intake in 4-week-old animals expressed as grams of food per grams of body weight per 24 h. *Denote P < 0.05 vs. C-C. D: Agouti-related peptide staining in the periventricular nucleus of the hypothalamus of 6-month-old animals. Note the increase in signal intensity in the C-U and U-U panels. E: Agouti-related peptide fiber density, quantitated by image analysis. *Denote P < 0.05 vs. C-C. (A high-quality digital representation of this figure is available in the online issue.)

FIG. 2.

A: Expression of genes related to adipocyte differentiation by RT-PCR. B: Expression of genes related to retinol signaling by RT-PCR. *P < 0.05 vs. C-C; comparisons of U-C vs. U-U also reached P < 0.05 for Rxr-α and Rar-β2. ‡Data are normalized to expression of cyclophilin or TBP. Gene expression in the C-C group is set as 1; □, C-U group; ■, U-C group; ▨, U-U group.

FIG. 3.

A: Gonadal fat expression of genes related to mitochondrial biogenesis and thermogenesis by RT-PCR. *P < 0.05 vs. CC. mRNA abundance is normalized to expression of the housekeeping gene cyclophilin. Gene expression in the C-C group is set as 1. B: Abundance of the mitochondrial-encoded gene Cox-2 relative to the nuclear-encoded gene β-globin in gonadal fat pads. The relative proportion of Cox-2 to β-globin is proportional to the amount of mitochondrial DNA per cell. *P < 0.05. C: Abundance of the mitochondrial-encoded gene ND-1 relative to the nuclear-encoded gene β-globin in gonadal fat pads. The relative proportion of ND-1 to β-globin is proportional to the amount of mitochondrial DNA per cell. , C-U; ■, U-C; ▨, U-U.

FIG. 4.

A: Gonadal fat expression of genes related to lipogenesis by RT-PCR. B: Gonadal fat expression of genes regulating lipogenesis by RT-PCR. *P < 0.05 vs. C-C; comparisons of U-C vs. U-U also reached P < 0.05 for AccI, Acss2, Fasn, Hmgcs1, Insig1, Insig2, and Lpin1α. ‡mRNA abundance is normalized to expression of cyclophilin or TBP. Gene expression in the C-C group is set as 1. □, C-U; ■, U-C; ▨, U-U.

FIG. 5.

A: Quantitation of osmium-fixed adipocytes per gonadal fat depot. *P < 0.05 vs. C-C. B: Distribution of adipocyte diameter (microns) in gonadal fat depots; data obtained by image analysis of histologic sections. C: Histologic sections of formalin-fixed gonadal adipose tissue, hematoxilin and eosin stained, shown at ×600 magnification. Note the small, multiloculated adipocytes in C-U and the increased adipocyte diameter in U-C. (A high-quality digital representation of this figure is available in the online issue.)