We have shown for the first time that mesenchymal stem cells (MSCs) and isolates from the stromal vascular fraction (SVF) of subcutaneous fat tissue can be turned into brown/brite fat cells without gene transfer, solely under the influence of macromolecular crowding (Lee et al., under review). The cells we generate express high levels of UCP-1 mRNA (and protein), and exhibit uncoupled respiration. UCP1 interrupts the flow of protons through ATP synthase by providing an alternative channel to dissipate the proton gradient, thus shorting the circuit. To maintain the proton gradient, mitochondrial respiration is increased, more oxygen is consumed and with it, glucose and free fatty acids. Less ATP is produced, and heat is generated. This is a unique property of brown adipocytes (BA).
It therefore follows that a natural or synthetic substance that could activate Brown Adipose Tissue (BAT) in a consumer would increase their metabolic rate and would help to lose weight and to burn off excess glucose. This would be the dream product of a nutraceutical and food supplement company, both as a lifestyle supplement and as a clinically highly valuable auxiliary compound to treat metabolic syndrome.
The availability of human BA progenitor cells has been very limited along with the number of cells that can be harvested. Only three human tissue sources with appreciable UCP1 mRNA induction (>20-fold) without genetic manipulation and reprogramming have thus far been published: Prepubic subcutaneous fat from infants (Pisani et al., 2011), and supraclavicular (Lee et al., 2011) and mediastinal (Silva et al., 2014) fat deposits in adults. All sources require either parental consent, image-guided biopsies in the neck region, or open chest surgery. There are efforts to generate BA from induced pluripotent cells, but yields are notoriously low. With MSCs and SVF, we added two human progenitor sources from an easily approachable and sustainable source. These two human BAT models are IP-protected (Patent pending; Lee M, Sheppard A, Raghunath M, "Generation of Brown Adipose Tissue (BAT) from Mesenchymal Cells", WO2013137826 A1). Importantly, we have optimized the efficacy of the differentiation protocol with a current differentiation time of 13 days which represents a time range hitherto known only for mouse work (in preparation).
We are currently developing a human BAT discovery platform to study thermogenic and browning agents for the pharmaceutical and nutraceutical industry. In collaboration with researchers from A*STAR and Waseda University, we have developed a heat-sensing dye that will be crucial in detecting uncoupled respiration in functional BAT (soon to be published). Our group is spearheading the generation of human BAT from bone-marrow derived MSCs and subcutaneous fat SVF and therefore has the key to two sustainable human progenitor sources for human BAT worldwide.
From the basic science point of view, we have developed a particular interest in transient receptor potential channels (TRPs), currently emerging as mechanoreceptors on BAT. An expansive sweep revealed the presence of various TRPs expressed in BAs differentiated from bone-marrow derived MSCs in our system. Excitingly, macromolecular crowding seems to influence expression and markedly upregulates expression of these receptors. This is intriguing and gives inroads into models of non-adrenergic activation of BAT via selective stimulation of TRPs. A potential target TRP currently under investigation is TRPM8, the cold-and-menthol receptor.