Deficiency of TNFalpha converting enzyme (TACE/ADAM17) causes a lean, hypermetabolic phenotype in mice

Abstract

Energy homeostasis involves central nervous system integration of afferent inputs that coordinately regulate food intake and energy expenditure. Here, we report that adult homozygous TNFalpha converting enzyme (TACE)-deficient mice exhibit one of the most dramatic examples of hypermetabolism yet reported in a rodent system. Because this effect is not matched by increased food intake, mice lacking TACE exhibit a lean phenotype. In the hypothalamus of these mice, neurons in the arcuate nucleus exhibit intact responses to reduced fat mass and low circulating leptin levels, suggesting that defects in other components of the energy homeostasis system explain the phenotype of Tace(DeltaZn/DeltaZn) mice. Elevated levels of uncoupling protein-1 in brown adipose tissue from Tace(DeltaZn/DeltaZn) mice when compared with weight-matched controls suggest that deficient TACE activity is linked to increased sympathetic outflow. These findings collectively identify a novel and potentially important role for TACE in energy homeostasis.

Figure 1

Tace^ΔZn/ΔZn mice have reduced fat mass despite normal food intake. QMR measurements were performed on 12- to 14-wk-old male Tace^ΔZn/ΔZn, WT, and WT-CR mice. A, Body weight (***, WT vs. Tace^ΔZn/ΔZn, P < 0.001; **, WT vs. WT-CR; #, Tace^ΔZn/ΔZn vs. WT-CR, P < 0.01). B, Leptin plasma levels (*, WT vs. Tace^ΔZn/ΔZn, P < 0.05). C, Fat mass (***, WT vs. Tace^ΔZn/ΔZn, P < 0.001; *, WT vs. WT-CR, P < 0.05). D, Lean mass (***, WT vs. Tace^ΔZn/ΔZn, P < 0.001; *, WT vs. WT-CR, P < 0.05). E, Fat mass as a percentage of total body weight (*, WT vs. Tace^ΔZn/ΔZn, P < 0.05). F, Lean mass as a percentage of total body weight. G, Food intake was measured as described in experimental procedures. In panels, data are presented as mean ± sem. For A, C, D, E, and F, n = 10–14; B, n = 4–10; G, n = 4–5.

Figure 2

MEFs from Tace^ΔZn/ΔZn mice are not defective in adipocyte differentiation. Primary MEFs derived from wild-type (A) and Tace^ΔZn/ΔZn (B) 14.5-d-old embryos were treated with differentiation mixture (DM) as described under experimental procedures. At d 8 after induction, cells were stained for lipid droplets with Oil Red O. C, Quantification of neutral lipid (Oil Red O) accumulation during adipocyte differentiation from wild-type and Tace^ΔZn/ΔZn MEFs treated at d 8 after induction with or without DM. Data are presented as mean ± sem from triplicate cultures. Scale, 40 μm.

Figure 3

WAT from Tace^ΔZn/ΔZn mice exhibits a multilocular appearance and increased cellularity. Paraffin-embedded sections of gonadal WAT from wild-type (A) and Tace^ΔZn/ΔZn (B) littermates stained with H&E. WAT from Tace^ΔZn/ΔZn mice showed a multilocular appearance with increased eosin staining. C, Quantitation of the number of adipocytes and nuclei within WAT H&E sections. At least three fields were evaluated per fat pad. Data are presented as mean ± sem (n = 5). Differences between WT and Tace^ΔZn/ΔZn mice were evaluated with Student’s t test. **, P < 0.001. Scale, 10 μm.

Figure 4

Tace^ΔZn/ΔZn mice have dramatically increased energy expenditure. A, VO₂ in WT, Tace^ΔZn/ΔZn, and WT-CR mice. Arrows indicate when WT-CR mice were given access to food as described in experimental procedures. B, Mean VO² consumption during dark and light cycles (***, WT vs. Tace^ΔZn/ΔZn; ###, Tace^ΔZn/ΔZn vs. WT-CR; **, WT vs. WT-CR, P < 0.001). C, Mean RER during dark and light cycles (*, WT vs. WT-CR and Tace^ΔZn/ΔZn vs. WT-CR, P < 0.05). D, Mean ambulatory activity during dark and light cycles (**, WT vs. Tace^ΔZn/ΔZn and WT vs. WT-CR, P < 0.01). E, Mean VO₂ consumption at thermoneutrality in the dark cycle (***, WT vs. Tace^ΔZn/ΔZn, P < 0.001). F, Mean VO₂ consumption at thermoneutrality in the light cycle (***, WT vs. Tace^ΔZn/ΔZn, P < 0.001). All values are given as mean ± sem (n = 4–10/group).

Figure 5

BAT from Tace^ΔZn/ΔZn mice exhibits increased cellularity and UCP-1 protein levels. Paraffin-embedded sections of BAT from WT (A) and Tace^ΔZn/ΔZn (B) littermates stained with H&E. BAT from Tace^ΔZn/ΔZn mice showed increased eosin staining. C, Calculation of the number of adipocyte nuclei within BAT H&E sections. At least three fields were evaluated per fat pad. Data are presented as mean ± sem (n = 4–5). Differences between WT and Tace^ΔZn/ΔZn mice were evaluated with Student’s t test (**, P < 0.05). Scale, 10 μm. D, A representative example of Western blot analysis for UCP-1 expression in protein extracts of BAT obtained from Tace^ΔZn/ΔZn and sex-matched WT control mice. β-Actin was used a protein loading control.

Figure 6

Tace^ΔZn/ΔZn mice display appropriate neuropeptide expression within the ARC of the hypothalamus. Neuropeptide gene expression in the ARC from WT, Tace^ΔZn/ΔZn and WT-CR littermates was examined by real-time PCR. A, NPY mRNA levels (**, WT vs. Tace^ΔZn/ΔZn, P < 0.001; *, WT vs. WT-CR; #, Tace^ΔZn/ΔZn vs. WT-CR, P < 0.05). B, Agouti-related peptide (AgRP) mRNA levels (**, WT vs. Tace^ΔZn/ΔZn, P < 0.001; *, WT vs. WT-CR; #, Tace^ΔZn/ΔZn vs. WT-CR, P < 0.05). C, Proopiomelanocortin (POMC) mRNA levels (**, WT vs. Tace^ΔZn/ΔZn and WT vs. WT-CR, P < 0.01). All values are given as mean ± sem (n = 5–7/group).