Adipocyte-Specific Deletion of Lamin A/C Largely Models Human Familial Partial Lipodystrophy Type 2

Abstract

Mechanisms by which autosomal recessive mutations in Lmna cause familial partial lipodystrophy type 2 (FPLD2) are poorly understood. To investigate the function of lamin A/C in adipose tissue, we created mice with an adipocyte-specific loss of Lmna (Lmna ^ADKO). Although Lmna ^ADKO mice develop and maintain adipose tissues in early postnatal life, they show a striking and progressive loss of white and brown adipose tissues as they approach sexual maturity. Lmna ^ADKO mice exhibit surprisingly mild metabolic dysfunction on a chow diet, but on a high-fat diet they share many characteristics of FPLD2 including hyperglycemia, hepatic steatosis, hyperinsulinemia, and almost undetectable circulating adiponectin and leptin. Whereas Lmna ^ADKO mice have reduced regulated and constitutive bone marrow adipose tissue with a concomitant increase in cortical bone, FPLD2 patients have reduced bone mass and bone mineral density compared with controls. In cell culture models of Lmna deficiency, mesenchymal precursors undergo adipogenesis without impairment, whereas fully differentiated adipocytes have increased lipolytic responses to adrenergic stimuli. Lmna ^ADKO mice faithfully reproduce many characteristics of FPLD2 and thus provide a unique animal model to investigate mechanisms underlying Lmna-dependent loss of adipose tissues.

Figure 1

Adipocyte-specific deletion of lamin A/C leads to loss of adipose tissues in mice. A: Representative images of psWAT, gWAT, BAT, and liver from Lmna^FL and Lmna^ADKO male mice 12–14 weeks of age on a normal chow diet. B: Body weight of Lmna^FL and Lmna^ADKO mice 12–14 weeks of age. C: Body composition measured by nuclear magnetic resonance spectroscopy in female Lmna^FL and Lmna^ADKO mice 12 weeks of age. D–G: Tissue weight of Lmna^FL and Lmna^ADKO male and female mice 12–14 weeks of age for psWAT (D), gWAT (E), BAT (F), and liver (G). H: Representative histologic images of the indicated tissues and organs stained with hematoxylin-eosin from Lmna^FL and Lmna^ADKO female mice 12–14 weeks of age. Scale bars 100 μmol/L. *P < 0.05. F, female; M, male.

Figure 2

Lmna^ADKO mice display mild metabolic dysregulation on a normal chow diet. A and B: Glucose tolerance tests for male (A) and female (B) Lmna^FL and Lmna^ADKO mice 14 weeks of age. C and D: Circulating glucose (C) and insulin concentrations (D) in Lmna^FL and Lmna^ADKO mice 12–14 weeks of age with ad libitum feeding or following a 16-h fast. E–G: Circulating adiponectin (E) and concentrations of triacylglycerol (F) and glycerol (G) in serum of Lmna^FL and Lmna^ADKO mice 12–14 weeks of age. H: Insulin tolerance test for female Lmna^FL and Lmna^ADKO mice ∼6 months of age. I: Respiratory exchange ratio (VCO2/VO2) for female Lmna^FL and Lmna^ADKO mice ∼6 months of age; statistical analysis was by ANCOVA with lean body mass as a covariate; data presented as mean ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001. F, female; M, male; ns, not significant.

Figure 3

Adipocyte-specific deletion of Lmna causes loss of regulated and constitutive BMAT and increases cortical bone. A–D: Representative histologic sections stained with hematoxylin-eosin for distal femur (A), proximal tibia (B), distal tibia (C), and caudal vertebra (D) from Lmna^FL and Lmna^ADKO mice 12–14 weeks of age. Scale bar 100 μm. E: Representative μCT scans of the distal tibiae from Lmna^FL and Lmna^ADKO mice 12–14 weeks of age. F and G: Cortical bone area per total bone area (F) and cortical thickness (G) in Lmna^FL and Lmna^ADKO mice 12–14 weeks of age. *P < 0.05. F, female; M, male.

Figure 4

Fat mass, bone mass, and bone mineral density are reduced in patients with R482 mutations in the LMNA gene. A: Fat mass and total mass of arms, legs, trunk, and total body in control and R482 patients. B: Bone mineral density in control (n = 18) and R482 patients (n = 24). C–F: Bone mass in control (n = 18) and R482 patients (n = 24) in the arms (C), legs (D), trunk (E), and total body (F). *P < 0.05, **P < 0.01, ***P < 0.001. BMD, bone mineral density.

Figure 5

HFD challenge exacerbates the lipodystrophic phenotype of Lmna^ADKO mice. A: Body weights of female Lmna^FL and Lmna^ADKO mice over the course of 5 weeks of HFD feeding. B: Weights of psWAT, liver, and spleen in Lmna^FL and Lmna^ADKO mice after 5 weeks of HFD feeding. C: Representative histologic images of psWAT, BAT, liver, and skin of Lmna^FL and Lmna^ADKO mice stained with hematoxylin-eosin. Scale bars 100 μmol/L. D and E: Circulating glucose (D) and insulin concentrations (E) in HFD-fed Lmna^FL and Lmna^ADKO mice fed ad libitum or following an 8-h fast. F: Immunoblot of circulating adiponectin in serum of HFD-fed Lmna^FL and Lmna^ADKO mice. G–I: Circulating leptin (G), triacylglycerol (H), and glycerol (I) concentrations in serum of HFD-fed Lmna^FL and Lmna^ADKO mice. *P < 0.05.

Figure 6

Adipose tissue develops postnatally in Lmna^ADKO mice and is progressively lost with aging. A: Representative images of indicated organs from female Lmna^FL and Lmna^ADKO mice 4 weeks of age. B: psWAT tissue weight at the indicated time points in Lmna^FL and Lmna^ADKO mice. C: Representative histologic images of the indicated organs stained with hematoxylin-eosin from female Lmna^FL and Lmna^ADKO mice 4 weeks of age. Scale bars 100 μmol/L. D: Histomorphometric quantification of adipocyte size in Lmna^FL and Lmna^ADKO mice 4 weeks of age. E: Confocal fluorescent micrographs of the indicated organs in Lmna^FL and Lmna^ADKO mice 6 weeks of age stained for macrophages (Mac2; red), adipocytes (Cav1; green), and cell nuclei (Hoechst; blue). *P < 0.01.

Figure 7

Lmna deletion does not affect adipogenesis of primary precursors. A: Primary Lmna^FL mesenchymal stem cells were treated with adeno-GFP or adeno-Cre prior to differentiation. Representative images at the indicated time points after induction of adipogenesis, with either brightfield microscopy or after staining neutral lipid with Oil Red O. Scale bars 50 μmol/L. B: Immunoblot of indicated proteins in mature adipocytes. C: Glycerol concentrations in conditioned media of mature adipocytes (n = 3) following treatment for 2 h with vehicle (DMSO), forskolin (5 μmol/L), isoproterenol (1 μmol/L), or norepinephrine (1 μmol/L). D: Immunoblot for the indicated proteins in mature adipocytes following 15-min treatment with vehicle (DMSO), forskolin (5 μmol/L), isoproterenol (1 μmol/L), or norepinephrine (1 μmol/L). *P < 0.05. HSL, hormone-sensitive lipase; pHSL, phosphorylated hormone-sensitive lipase.