抵抗素(resistin)是體內糖類代謝的重要調控者，與肥胖引起的胰島素阻抗有關。文獻報導isoproterenol (ISO)與TNF-?可抑制3T3-L1脂肪細胞表現resistin mRNA。然而resistin的釋出是否受cAMP訊息傳遞調控目前仍不清楚。環狀核苷酸磷酸雙酯酶(PDE)是細胞內分解cAMP與cGMP的酵素，對調節環狀核苷酸的濃度及其訊息傳導扮演著重要的角色。因此本研究主要目的在探討cAMP-PDE在脂肪細胞內對resistin表現之影響，主要利用ELISA方法測量藥物處理3T3-L1與小鼠脂肪細胞釋放resistin之改變。結果顯示ISO可抑制兩種脂肪細胞釋放resistin量，且cilostazol與rolipram均可增強ISO的抑制作用，然而ISO的抑制作用不會被PKA抑制劑H89回復。以dibutyryl-cAMP (dbcAMP)處理小鼠或3T3-L1脂肪細胞，我們發現僅小鼠脂肪細胞之resistin釋放有顯著下降，至於3T3-L1脂肪細胞，dbcAMP與PDE3抑制劑cilostazol共同處理可明顯抑制resistin釋放，但rolipram則無此協同效果，再者，cilostazol與dbcAMP的抑制作用可被H89完全回復，顯示此抑制作用是藉由抑制PDE3活性進而活化PKA訊息傳導所致。TNF-?亦可降低resistin釋放，但此抑制作用不受cilostazol或cAMP訊息傳導所調控。文獻報導TNF-?抑制resistin表現是由於活化iNOS-NO (nitric oxide)，雖然NO可活化guanylyl cyclase (GC)使cGMP濃度增加，但8-bromo-cGMP對resistin釋放並無影響，表示TNF-?的抑制作用不是藉由增加細胞內cGMP的濃度所致。本研究也利用PKC活化劑phorbol myristate acetate (PMA)與鈣離子增升劑ionomycin處理3T3-L1脂肪細胞，結果顯示PMA或ionomycin單獨或共同處理細胞均可抑制resistin釋放。我們也發現，PI3K抑制劑LY294002與GSK3抑制劑LiCl均可抑制3T3-L1脂肪細胞釋放resistin，綜合以上結果得知，脂肪細胞分泌resistin會被多種訊息傳遞分子調控，包括cAMP/PDE3/PKA、Ca+2/PKC與PI3k等 The adipocyte-secreted hormone resistin has been implicated in regulation of glucose homeostasis, adipogenesis and inflammation, and is linked to obesity-related insulin resistance. Evidence indicates that isoproterenol (ISO) and tumor necrosis factor-? (TNF-?? are pivotal negative mediators in resistin gene expression, but mechanisms underlying these effects remain largely unknown. Cyclic AMP signaling is known to be critical in regulation of lipid and glucose metabolism, and intracellular cAMP concentrations can be regulated by cAMP-hydrolyzing phosphodiesterases (cAMP-PDEs). In this study, we investigated the effects of cAMP-PDE on resistin release in mouse primary and 3T3-L1 adipocytes. By ELISA analysis, we observed that resistin release was significantly reduced in the cells following ISO treatment. The release was further decreased by co-stimulation of the cells with the PDE3 inhibitor cilostazol or PDE4 inhibitor rolipram. Howover, this inhibition was not reversed by the PKA inhibitor H89, indicating that ISO/cAMP-regulated resistin release is not mediated by PKA activity. We have also found that treatment of cells with dibutyryl-cAMP (dbcAMP) in combination with cilostazol, but not rolipram, leads to a marked decrease in resistin release in the adipocytes and this decrease was fully reversed by H89, indicating that the suppression of resistin release by dbcAMP and cilostazol requires PKA activation. The resistin release in the adipocytes was also blocked by TNF-? treatment. However, this effect was not regulated by cilostazol or dbcAMP. We further observed that the resistin release in 3T3-L1 adipcytes was inhibited by the PKC activator phorbol myristate (PMA) as well as the Ca+2 ionophore ionomycin. The PI3K inhibitor LY294002 and the GSK3 inhibitor LiCl also exhibited inhibitory effects on the resistin release in these cells. Taken together, these findings indicate that the resistin release in mouse adipocytes is regulated by several signaling molecules, including cAMP/PDE3/PKA, Ca+2/PKC, PI3K and GSK3.
