Non-neuronal cholinergic signaling, mediated by acetylcholine, plays important roles in physiological processes including inflammation and immunity. Our group first discovered evidence of non-neuronal cholinergic circuitry in adipose tissue, whereby immune cells secrete acetylcholine to activate beige adipocytes during adaptive thermogenesis. Here, we reveal that macrophages are the cellular protagonists responsible for secreting acetylcholine to regulate thermogenic activation in subcutaneous fat, and we term these cells cholinergic adipose macrophages (ChAMs). An adaptive increase in ChAM abundance is evident following acute cold exposure, and macrophage-specific deletion of choline acetyltransferase (ChAT), the enzyme for acetylcholine biosynthesis, impairs the cold-induced thermogenic capacity of mice. Further, using pharmacological and genetic approaches, we show that ChAMs are regulated via adrenergic signaling, specifically through the b 2 adrenergic receptor. These findings demonstrate that macrophages are an essential adipose tissue source of acetylcholine for the regulation of adaptive thermogenesis, and may be useful for therapeutic targeting in metabolic diseases.

No abstract

Adipose tissues communicate with the central nervous system to maintain whole-body energy homeostasis. The mainstream view is that circulating hormones secreted by the fat convey the metabolic state to the brain, which integrates peripheral information and regulates adipocyte function through noradrenergic sympathetic output1. Moreover, somatosensory neurons of the dorsal root ganglia innervate adipose tissue2. However, the lack of genetic tools to selectively target these neurons has limited understanding of their physiological importance. Here we developed viral, genetic and imaging strategies to manipulate sensory nerves in an organ-specific manner in mice. This enabled us to visualize the entire axonal projection of dorsal root ganglia from the soma to subcutaneous adipocytes, establishing the anatomical underpinnings of adipose sensory innervation. Functionally, selective sensory ablation in adipose tissue enhanced the lipogenic and thermogenetic transcriptional programs, resulting in an enlarged fat pad, enrichment of beige adipocytes and elevated body temperature under thermoneutral conditions. The sensory-ablation-induced phenotypes required intact sympathetic function. We postulate that beige-fat-innervating sensory neurons modulate adipocyte function by acting as a brake on the sympathetic system. These results reveal an important role of the innervation by dorsal root ganglia of adipose tissues, and could enable future studies to examine the role of sensory innervation of disparate interoceptive systems.

Bipolar disorder (BD) is characterized by recurrent mood episodes, and circadian rhythm disturbances. Past studies have identified calcium channel genes as risk loci for BD. CACNA1C encodes an L-type calcium channel (LTCC) involved in the entrainment of circadian rhythms to light. Another calcium channel, i.e., the ryanodine receptor (RYR), is involved in ­circadian phase delays. It is unknown whether variants in CACNA1C or other calcium channels contribute to the circadian phenotype in BD. We hypothesized that, by using temperature cycles, we could model circadian entrainment in fibroblasts from BD patients and controls to interrogate the circadian functions of LTCCs. Using Per2-luc, a bioluminescent reporter, we verified that cells entrain to temperature rhythms in vitro. Under constant temperature conditions, the LTCC antagonist verapamil shortened the circadian period, and the RYR antagonist dantrolene lengthened the period. However, neither drug affected temperature entrainment. Fibroblasts from BD patients and controls also entrained to temperature. In cells from BD patients, the rhythm amplitude was lower under entrained, but not constant, conditions. Temperature entrainment was otherwise similar between BD and control cells. However, the CACNA1C genotype among BD cells predicted the degree to which cells entrained. We conclude that assessment of rhythms under entrained conditions reveals additional rhythm abnormalities in BD that are not observable under constant temperature conditions.