In vivo imaging of brown adipose tissue vasculature reactivity during adrenergic stimulation of non-shivering thermogenesis in mice

Abstract

Brown adipose tissue (BAT) is a fat tissue specialized in heat production (non-shivering thermogenesis) and used by mammals to defend core body temperature when exposed to cold. Several studies have shown that during non-shivering thermogenesis the increase in BAT oxygen demand is met by a local and specific increase in tissue’s blood flow. While the vasculature of BAT has been extensively studied postmortem in rodents using histology, optical and CT imaging techniques, vasculature changes during stimulation of non-shivering thermogenesis have never been directly detected in vivo. Here, by using computed tomography (CT) angiography with gold nanoparticles we investigate, non-invasively, changes in BAT vasculature during adrenergic stimulation of non-shivering thermogenesis by norepinephrine, a vasoconstrictor known to mediate brown fat heat production, and by CL 316,243, a specific β3-adrenergic agonist also known to elicit BAT thermogenesis in rodents. We found that while CL 316,243 causes local vasodilation in BAT, with little impact on the rest of the vasculature throughout the body, norepinephrine leads to local vasodilation in addition to peripheral vasoconstriction. As a result, a significantly greater relative increase in BAT perfusion is observed following the injection of NE compared to CL. This study demonstrates the use of in vivo CT angiography as an effective tool in assessing vascular reactivity in BAT both qualitatively and quantitatively in preclinical studies.

In-vivo detection of white adipose tissue browning: a multimodality imaging approach

“…The small increase in tissue radiodensity seen in non-enhanced CT scans after norepinephrine injection is essentially amplified in xenon-enhanced CT scans as the increase in tissue blood flow is expected to reduce xenon wash-in time and increase xenon tissue uptake. As previously shown, increase in blood flow after norepinephrine injection is, although not indicative of BAT thermogenesis 35 , a hallmark of brown adipose tissue, both in rodents 13 , 36 and in humans 37 . Interestingly, this increase occurred not just after browning induction, but also before browning induction, indicating that inguinal fat is different than other white fat depots, even before browning occurs.…”

“…The UCP1 protein is activated by long chain fatty acids, which also represent the major substrate for heat production in BAT 9,10 . Unlike WAT, BAT is highly vascularized and, during stimulation of BAT thermogenesis, blood flow to BAT increases by several folds to efficiently redistribute the heat produced to other tissues [11][12][13] . While BAT activation is known to regulate blood glucose and fatty acids and to be associated with a healthier metabolic profile in humans, recent studies in mice have shown that browning of white adipose tissue, which leads to beige fat, either by gene editing of preadipocytes or autologous fat transplants, also improves glucose and lipid homeostasis [14][15][16] .Compared to brown adipocytes, beige adipocytes are morphologically more like white adipocytes than brown adipocytes.…”

Apigenin Self-Assembled Collagen Biomatrix for Reprogramming the Obese Wound Microenvironment for Its Management and Repair

“…After washing with DMEM, 1 mm 2 -sized pieces were placed on collagen and Apg self-assembled collagen biomatrix coated 24-well plate. DMEM­(HG) was added slowly without disturbing the adipose tissue and cultured for 7 days . The images were captured by using a Leica phase-contrast microscope.…”

“…DMEM(HG) was added slowly without disturbing the adipose tissue and cultured for 7 days. 31 The images were captured by using a Leica phase-contrast microscope. The sprouting area was calculated using Angio Tool64 version 0.6a software.…”

Table_1.docx

“…Unlocking the therapeutic potential of brown and beige AT requires technological advancements that account for the great variety of hormonal and cellular factors influencing the cellular composition and vascularization of the AT niche (31). The vasculature of BAT is pivotal in non-shivering thermogenesis, making BAT one of the most highly vascularized tissues, with an extensive network of microvessels (19,32). Recent developments in bioengineered in vitro models of AT facilitate important cell-cell and cell-ECM interactions, making them superior at recapitulating the native in vivo milieu compared to standard 2D cultures of SVFderived in vitro differentiated adipocytes (30).…”