CTRP3 is endogenously co-expressed in many tissues with other proteins within the C1q TNF superfamily. However, CTRP3 is unique as it does not form hetero-oligomeric complexes with adiponectin or any other CTRP protein (76). Most CTRP proteins will form hetero-oligomers with adiponectin or at least 1 other CTRP protein when coexpressed (75, 76). However, higher-order oligomers are the primary form by which CTRP3 is found circulating in either human or mouse serum, indicating that CTRP3 high-order oligomeric complexes occur solely between its two splice variants, CTRP3A and CTRP3B (51). While the significance of these posttranslational modifications and higherorder structure formations have yet to be explored, it is likely that these modifications influence the function of CTRP3. Therefore, it is important to differentiate between functional studies and experimental findings gleaned from bacterialproduced compared with other types of recombinant CTRP3 protein. Bacterial-produced recombinant CTRP3 protein does not possess the potentially physiologically relevant posttranslational modifications or multimeric structures, and may explain any observed lack of biological activity (19, 61).
