Sympathetic innervation of inguinal white adipose tissue in the mouse

Abstract

Adipose tissue plays an important role in metabolic homeostasis and its prominent role as endocrine organ is now well recognized. Adipose tissue is controlled via the sympathetic nervous system (SNS). New viral, molecular-genetic tools will soon allow a more detailed study of adipose tissue innervation in metabolic function, yet, the precise anatomical extent of preganglionic and postganglionic inputs to the inguinal white adipose tissue (iWAT) is limited. Furthermore, several viral, molecular-genetic tools will require the use of cre/loxP mouse models, while the available studies on sympathetic iWAT innervation were established in larger species. In this study, we generated a detailed map for the sympathetic innervation of iWAT in male and female mice. We adapted iDISCO tissue clearing to process large, whole-body specimens for an unprecedented view of the natural abdominal SNS. Combined with pseudorabies virus retrograde tracing from the iWAT, we defined the preganglionic and postganglionic sympathetic input to iWAT. We used fluorescence-guided anatomical dissections of sympathetic nerves in reporter mice to further clarify that postganglionic axons connect to iWAT via lateral cutaneous rami (dorsolumbar iWAT portion) and the lumbar plexus (inguinal iWAT portion). Importantly, these rami carry axons that branch to iWAT, as well as axons that travel further to innervate the skin and vasculature, and their functional impact will require consideration in denervation studies. Our study may serve as a comprehensive map for future experiments that employ virally driven neuromodulation techniques to predict anatomy-based viral labeling. K E Y W O R D S iDISCO, imaging, pseudorabies virus, sympathetic chain ganglia, tissue clearing, transsynaptic retrograde tracing 1 | INTRODUCTION Historically, white adipose tissue (WAT) was largely considered a storage depot for excess energy (Steiner & Cahill, 1964). However, given the increasing number of obese individuals plagued with metabolic syndrome, and the associated risk for life-threatening comorbidities like Type 2 diabetes, cancer, and cardiovascular disease (Eyre et al., 2004), intense research over the last decades has highlighted a

Visualization and analysis of whole depot adipose tissue neural innervation

“…This has allowed us to further our understanding of scWAT in mice by characterizing the innervation that exists within this tissue with greater scrutiny, demonstrating neurovascular interactions, parenchymal innervation, neuroimmune interactions, and neuro-adipose connections. It has been demonstrated previously that the neurites innervating scWAT branch from the same NBs that lead to the skin (Huesing et al, 2021), but we and others have clearly demonstrated that axon endings do terminate inside the parenchyma of scWAT. For the first time, we reveal a terminal junction of axons in scWAT, which we call the neuro-adipose nexus.…”

“…White adipose tissue (WAT) is typically associated with energy storage, but is a dynamic and plastic tissue capable of undergoing transformation during the “browning” process (stimulated by negative energy balance states like exercise or cold), which leads to increased presence of brown adipocytes and increased sympathetic neurite outgrowth. WAT is now appreciated to be highly innervated by both sympathetic ( Foster et al., 1982 ; Foster and Bartness, 2006 ; Huesing et al., 2021 ) and sensory nerves ( Fishman and Dark, 1987 ; Bartness et al., 2010 ), but not parasympathetic nerves ( Giordano et al., 2006 ).…”

Organization of sympathetic innervation of interscapular brown adipose tissue in the mouse

“…For iDISCO immunohistochemical staining and tissue clearing, UCP1cre reporter mice were perfused with saline and paraformaldehyde as described earlier (Francois et al, 2019;Huesing et al, 2021) and interscapular BAT was dissected as an entire tissue block keeping core BAT and surrounding WAT intact to maintain the tissue context (n = 5, 5 males). We followed the iDISCO method with modification from (Renier et al 2014) for TH-protein (1:1000, rabbit anti-TH, Millipore, Cat# AB152, RRID:AB_390204) (Meurers et al, 2009), the endothelial marker CD31 (1:300, rabbit anti-CD31, Novus Biologicals, Cat#AF3628, RRID:AB_2161028) (Huesing et al, 2021), and/or GFP reporter (1:400, chicken anti-GFP, Abcam, Cat#ab13970, RRID:AB_300798) (Zhang et al, 2011) as published at protocol.io (dx.doi.org/10.17504/protocols.io.wzuff6w).…”

Early postnatal interactions between beige adipocytes and sympathetic neurites regulate innervation of subcutaneous fat

“…Sympathetic innervation plays an important role in regulating two key aspects of adipose tissue function: lipolysis and thermogenesis. Dense sympathetic parenchymal innervation is observed in both iBAT and the inguinal region of iWAT, where beige adipocytes are primarily located; however, sparse innervation is found in eWAT and the dorsolateral region of iWAT, an area of the tissue that is devoid of beige adipocytes even under long term cold stimulation (Chi et al, 2018b;Dichamp et al, 2019;Huesing et al, 2020;Murano et al, 2009;Zeng et al, 2019). The strong association between thermogenic adipocytes and dense sympathetic neurites as well as the association between white adipocytes and sparse innervation suggests that adipocyte type may determine the density of sympathetic parenchymal innervation.…”