Seeding of visceral adipose tissue with perinatally generated regulatory T cells shapes the metabolic tenor in mice

The Foxp3+CD4+ regulatory T cells (Tregs) generated around birth are phenotypically and functionally distinct from those engendered during adulthood. That perinatally produced Tregs persist for a protracted period in peripheral lymphoid organs has been well documented, as has their superior ability to protect the organism from many autoimmune diseases. However, their contribution to pools of nonlymphoid-tissue Tregs and their homeostatic functions therein have been little studied. We show that perinatal Tregs preferentially derive from a CD25+Foxp3- thymocyte progenitor; that they seed and persist to varying degrees in every nonlymphoid tissue examined; and that transient depletion of perinatally generated Tregs in adults, but not in neonates, is followed by poor reconstitution of Treg numbers and phenotypes in epidydimal (e) VAT, the skin and the meninges but not in several lymphoid and other nonlymphoid tissues. Potential clinical implications of such a deficiency are highlighted by findings on mice subjected to weight cycling: imposing a low-fat – high-fat – low-fat diet regimen results in an impoverished eVAT, but not spleen, Treg compartment, accompanied by normal weight gain and glucose tolerance but profound insulin resistance. These findings point to a layered immune system, the different layers exerting specialized, non-redundant functions. Overall design: Regulatory T cell (Treg) differentiation in the thymus was examined by flow-cytometrically purifying Treg progenitors from male C57B6.Foxp3.GFP perinatal moue thymus based on surface CD25 and FoxP3-GFP expression at day 5, day 12, and day 49 post birth (P1 = CD4+CD8-CD25+FoxP3- progenitors, P2= CD4+CD8-CD25-FoxP3+ progenitors). To explore why perinatally generated Tregs variably repopulate tissues, 12 week old C57B6.Foxp3.eGFP.DTR+ and DTR- male littermates were i.p. injected with diptheria toxin for three consecutive days to deplete existing Tregs. Mice were rested for 8-9 weeks before analyzing a panel of tissues (Spleen, Lung, Liver, Ear Skin, and Visceral Adipose Tissue). Treg populations in each tissue were digested with a tissue specific protocol and cytometrically purified based on CD4+Foxp3GFP+ expression. Each replicate consists of 500-1000 double sorted cells following the standard Immgen (www.immgen.org) protocol.