Adiponectin: Some excellent reviews 

Adiponectin exists in normal peripheral circulation at a concentration of 2-30ug/ml with levels within the brain being estimated at 1000x lower, and as might be expected for such a complex player, adiponectin has multiple forms  in circulation from trimers and multi-oligomers, to cleavage fragments, all of which seemingly have physiological roles depending upon the tissue examined.

Adiponectin in cardiovascular inflammation and obesity. Aprahamian T.R. and Sam F. Int J Inflam. 2011;2011:376909 

Adiponectin Receptor Signalling in the Brain. Thundyil J., Pavlovski D., Sobey C.G., Arumugam T.V.  Br J Pharmacol. 2011 Jun 30.

Adiponectin and metabolic syndrome. Matsuzawa Y., Funahashi T., Kihara S., Shimomura I.  Arterioscler Thromb Vasc Biol. 2004 Jan;24(1):29-33. 

The roles of APPL1 and APPL2 in adiponectin signalling 

The proteins APPL1 and APPL2  are the critical partners in transmitting cell signals from the AdipoRs to downstream kinases such as AMPK, AKT, and p38 for instance. Interestingly APPL1 and APPL2 appear to interact with discrete sets of internal proteins and also appear to oppositely regulate adiponectin's signaling functions within various cells types, governing as Wang put it "the Yin-Yang regulator of adiponectin signaling". 

APPL1 binds to adiponectin receptors and mediates adiponectin signalling and function.  Mao X. et al Nat Cell Biol. 2006 May;8(5):516-23

Western Blot showing APPL1 expression in mammalian cells using rabbit polyclonal antibody to human APPL1 (R-1331-100). Image courtesy of Mao X. et al (2006) 

Yin-Yang regulation of adiponectin signaling by APPL isoforms in muscle cells.  Wang C. et al J Biol Chem. 2009 Nov 13;284(46):31608-15.

Adiponectin receptors AdipoR1 and AdipoR2  

Adiponection's pleiotrophic influences appear to be mediated by two primary cell receptors AdipoR1 and AdipoR2 with a newly discovered T-cadherin possibly playing some sort of a mediating or binding role still to come.  Adiponectin's receptors are expressed in a variety of tissues from muscle to bone to brain and vary in the abilities to bind the many forms of adiponectin as well.  Moreover the receptors are a special class of G-protein coupled receptors that among other things have a reversed internal N-termini and extra-cellular COOH termini and thus have quite different downstream signaling mechanisms than traditional G-protein coupled receptors.      

Cloning of adiponectin receptors that mediate antidiabetic metabolic effects. Yamauchi T. et al Nature. 2003 Jun 12;423(6941):762-9  

Biosensis is proud to offer a suite of products for continued research into adiponectin, its receptors and intracellular mediators, as well as assays to monitor their collective effects.