Leptin modulates the effects of acyl CoA:diacylglycerol acyltransferase deficiency on murine fur and sebaceous glands

Abstract

Acyl CoA:diacylglycerol acyltransferase (DGAT) is a ubiquitously expressed enzyme that catalyzes the final reaction in the major pathways of triglyceride synthesis. Mice lacking DGAT1 (Dgat(-/-)) demonstrate significant changes in lipid metabolism in several tissues, including the skin. Here we report the effects of DGAT1 deficiency on fur and sebaceous glands. Adult Dgat(-/-) mice had dry fur and hair loss, which were associated with atrophic sebaceous glands and fur lipid abnormalities. As a result, Dgat(-/-) mice had impaired water repulsion and defective thermoregulation after water immersion. These phenotypes were mostly absent in Dgat(-/-) mice with leptin deficiency, indicating an unexpected role for leptin in modulating the skin phenotype. Our findings indicate that DGAT1 plays an important role in normal fur and sebaceous gland physiology and provide evidence that leptin modulates these processes in the skin.

Figure 1

Effects of DGAT1 deficiency on fur appearance, water repulsion, and thermoregulation in mice. (a) Dry fur and hair loss in a 16-week-old male Dgat^–/– mouse. (b) Male Dgat^+/+ and Dgat^–/– mice 5 minutes after water immersion. (c and d) Impaired water repulsion and thermoregulation in Dgat^–/– mice after water immersion. Dgat^–/– mice retained more water in their fur than did Dgat^+/+ mice, as reflected by a greater increase in mean relative body weight (c). Dgat^–/– mice also developed hypothermia (d). n = 4 per genotype. *P < 0.05.

Figure 2

Abnormalities of water repulsion and thermoregulation in DGAT1-deficient A^Y/a but not ob/ob mice. (a and b) Effect of DGAT1 deficiency on water repulsion (a) and thermoregulation (b) of A^Y/a mice after water immersion. (c–h) Effect of DGAT1 deficiency on water repulsion and thermoregulation of ob/ob mice after water immersion. (c and d) No leptin infusion. (e and f) After 2 weeks of subcutaneous leptin infusion (+ Peripheral leptin). (g and h) Two weeks after the leptin infusion was stopped (After leptin). For each experiment, n = 4 per genotype. *P < 0.05.

Figure 3

DGAT1 mRNA expression in skin. An antisense probe detected DGAT1 mRNA expression in sebaceous glands (arrows, left panel) of skin from wild-type mice. Specific hybridization was not detected by the control sense probe (right panel).

Figure 4

Age modulates the effect of DGAT1 deficiency on sebaceous gland morphology. (a and b) In 6-week-old male mice, the sebaceous glands (SG) and hair follicles (HF) appeared to be normal, regardless of Dgat genotype. (c and d) In 3-month-old male mice, DGAT1 deficiency was associated with atrophic sebaceous glands; for most hair follicles, sebaceous glands were not identifiable. Bar, 30 μm.

Figure 5

Sebaceous gland abnormalities in DGAT1-deficient A^Y/a but not ob/ob mice. (a and b) Skin section from Dgat^+/+A^Y/a mice (a) and Dgat^–/–A^Y/a mice (b). (c–j) Skin sections from Dgat^+/+ob/ob and Dgat^–/–ob/ob mice. (c and d) No leptin infusion. (e and f) After 2 weeks of subcutaneous leptin infusion (+ Peripheral leptin). (g and h) After 2 weeks of intracerebroventricular leptin infusion (+ Central leptin). (i and j) Two weeks after the leptin infusion was stopped (After leptin). Representative samples from male mice are shown. SG, sebaceous gland. Bar, 30 μm.

Figure 6

Abnormal fur lipid content in Dgat^–/– mice. (a) Absence of specific lipids in the fur of Dgat^–/– mice (white and gray arrows). (b) Effects of leptin on fur lipid content. The putative type II wax diester is indicated with a white arrow. Lipids were analyzed by TLC with hexane/ethyl ether/acetic acid (a) and hexane/benzene (b). Experiments were performed 3–4 times. Representative results are shown.

Figure 7

Effects of androgens on fur lipids in Dgat^–/– mice. The putative type II wax diester is indicated with an open arrow. Lipids were analyzed by TLC with hexane/benzene. For lanes 3 and 4, testosterone propionate was injected subcutaneously for 2 weeks. For lanes 5 and 6, fur lipids were extracted 2 weeks after castration. Experiments were performed twice. Representative results are shown.

Figure 8

Upregulation of DGAT2 in the skin of ob/ob mice. (a) mRNA expression of DGAT2. n = 3 per genotype. *P < 0.05 vs. Dgat^+/+. (b) Increased upregulation of DGAT2 mRNA expression in ob/ob mice with DGAT1 deficiency. n = 3 per genotype. *P < 0.05.

Figure 9

A model of how DGAT enzymes, leptin, and androgens modulate sebaceous gland biology. Our data suggest the existence of at least two pathways involved in maintaining normal morphology and functioning of sebaceous glands. (a) One of these pathways (presumably the major pathway) requires DGAT1, whereas the other pathway (the alternative pathway) may require DGAT2. Androgens stimulate the activity of both pathways, whereas leptin downregulates the activity of the alternative pathway. (b) In DGAT1 deficiency, only the alternative pathway is functional, resulting in sebaceous gland atrophy and decreased production of wax diesters. (c) With leptin deficiency, the activity of the alternative pathway is upregulated to levels comparable to those of the major pathway, leading to sebaceous gland hypertrophy and increased fur lipid production. (d) This upregulation of the alternative pathway can compensate for the loss of DGAT1, thereby accounting for the relatively normal sebaceous gland and fur lipid findings in Dgat^–/–ob/ob mice.