Light-sheet fluorescence images of whole subcutaneous (left) and epididymal (right) fat pads stained with tyrosine hydroxylase. Reproduced with permission from Chi, J. et al. Cell Metab. 27, 226–236.e3 (2018), Elsevier.

Adipo-Clear is a new adipose tissue processing technique for fluorescence microscopy developed by Paul Cohen and colleagues that enables researchers to visualize individual cell types in whole adipose tissues. Using this novel method, the researchers found regional variation in beige adipose biogenesis and were able to characterize the pattern of sympathetic innervation of adipose tissue. The authors also found that the density of sympathetic innervation in adipose tissue is dependent on the expression of PRDM16 in adipocytes.

Traditional histological methods rely on labelling epitopes of interest on thinly sliced fixed tissues by immunohistochemistry or immunofluorescence. In adipose tissues, however, these methods are limited, as the high lipid content makes sectioning difficult and causes light scattering. Adipo-Clear enables the full clearance of lipids in a fat pad, while maintaining tissue integrity. In the present study, Cohen and his team analysed cleared adipose tissues using light-sheet fluorescence microscopy (a technique that can create a 3D visualization of intact tissues).

“We found a striking regional variation in beige adipocyte biogenesis within subcutaneous adipose tissue,” explains Cohen. “We were also able to delineate the pattern of sympathetic innervation of adipose tissue, including large nerve bundles and fine neurite projections, which differ vastly between subcutaneous and visceral depots.” The subcutaneous adipose tissue innervations have a regional pattern, with denser sympathetic innervation corresponding to more beige adipocyte biogenesis. The researchers also found that PRDM16, a protein required for beige adipocyte biogenesis, regulates neurite projections to adipocytes, suggesting that adipocytes could interact with neurons.

“Our aim now is to dissect whether sympathetic innervation of adipose tissue demonstrates plasticity or whether it is established during development,” concludes Cohen.