Altered macrophage differentiation and leptin expression in visceral white adipose tissue following chronic sleep restriction in mice

Abstract

Chronic sleep restriction (CSR) has been implicated in higher risk of insulin resistance (IR) and immune-metabolic dysfunction. No studies investigated the effect of CSR on macrophage differentiation in vWAT in relation to leptin synthesis and glucose homeostasis. Therefore, this study aimed at assessing blood glucose levels and vWAT expression of leptin, CD38, and CD163 following CSR. Adult male C57BL/6 mice were housed under 12:12 L/D cycle (lights on at 0700 hrs) with free access to food. Following a two-week acclimatization period, animals were divided into 2 groups: 1) control (C, N=8) with normal sleep and 2) experimental/sleep restricted (SR, N=7) subjected to 11 days of sleep restriction. All animals underwent timed weekly measurements of body weight (BW), food consumption, and fasting blood sugar (BS) for the duration of the experiment. They were sacrificed at the end of the study (at 2400 hrs): BW, vWAT weight, and BS were measured; vWAT was processed for leptin, CD38, and CD163 immunocytochemistry. Compared to C, SR mice had a significantly lower BW (21.42±1.72 g vs 19.77±1.14 g, respectively; P=0.006) and vWAT weight (4.25±0.77 % vs 2.35±0.39 %, respectively; P=0.000), and higher BS (105±2 mg/dl vs 150±4 mg/dl, respectively; P=0.000) at the end of the experiment. There was no significant difference in mean food consumption between the 2 groups, even though SR ate more. Qualitative protein analysis of experimental vWAT revealed the presence of CD38-immunoreactive cells, but not leptin or CD163. In contrast, control vWAT showed both leptin- and CD163-, but not CD38-, immunoreactivity. These findings suggest that 1) CSR is associated with a rise in BS, BW loss, absence of leptin synthesis, and expression of M1 (inflammatory) macrophages in vWAT, 2) the elevation in BS and decrease in BW are probably related to disrupted insulin signaling rather than leptin dysregulation, and 3) the possible metabolic dysfunction accompanying CSR is probably related to leptin inhibition and/or inflammation-dependent pathways in vWAT. Although this study could not establish a cause-effect relationship between inflammation and adipoinsular physiology in CSR, its basic findings may lend useful information to prospective studies in this area that may have important medical implications.