| 摘要: | 阻抗素(resistin)是一種與胰島素抗性和能量平衡有關的脂肪素。研究指出， isoproterenol (ISO，一種β adrenergic receptor agonist)可降低3T3-L1脂肪細胞內resistin mRNA的表現量，但目前對於ISO是否會調控resistin的釋放以及其活化cAMP訊息傳導的機制仍不明瞭。本研究利用ELISA方法分析不同藥劑處理3T3-L1脂肪細胞或小鼠腹腔脂肪細胞對resistin釋放之影響。結果顯示ISO或forskolin皆可抑制兩種脂肪細胞對resistin的釋放，且ISO對resistin釋放的抑制作用可完全被PKA抑制劑Rp-8-CPT-cAMPS回復。進一步使用dibutyryl-cAMP (dbcAMP)處理3T3-L1脂肪細胞或小鼠腹腔脂肪細胞，結果顯示僅小鼠脂肪細胞的resistin釋放有明顯抑制作用。第三型環狀核苷酸磷酸二酯酶(PDE3)是脂肪細胞內降解cAMP的酵素，負責調節細胞內cAMP濃度及其訊息傳遞路徑。將cAMP類似物dbcAMP與PDE3抑制劑cilostazol共同處理3T3-L1脂肪細胞，可使resistin的釋放量明顯下降，PKA抑制劑能將此抑制作用完全回復。此外，我們發現利用PKA活化劑6-Bnz-cAMP處理兩種脂肪細胞可抑制resistin的釋放，而Epac活化劑8-pCPT-2'-O-Me-cAMP則無此作用。這些結果顯示，在脂肪細胞中cAMP抑制resistin釋放是經由活化PKA而非Epac路徑所致。本研究亦發現，TNF-alpha與PI3K抑制劑LY294002均可降低resistin的釋放，但其抑制作用不會被PKA抑制劑回復，顯示TNF-alpha與PI3K抑制劑的抑制作用不是經由活化PKA訊息傳導所致。再者，本研究利用胰島素刺激3T3-L1脂肪細胞以活化PI3K，結果顯示其對resistin的釋放無顯著影響，然而胰島素會阻斷LY294002對resistin的抑制作用，使resistin釋放回升，由此我們推測當PI3K被抑制時，胰島素可經由活化其他路徑以增加resistin的釋放。我們也發現，AMPK促進劑AICAR與AMPK抑制劑Compound C皆會抑制脂肪細胞釋放resistin，此不相容結果之原因仍不甚明瞭。綜合本研究結果，脂肪細胞釋放resistin可被多種訊息傳遞路徑及分子所調控，包括cAMP/PDE3/PKA、PI3K、TNF-alpha?receptor及AMPK等。Resistin is an adipokine which is implicated in adipogenesis, insulin resistance, and inflammation. Its mRNA expression in mouse adipocytes is demonstated to be down-regulated by the cAMP-elevating agent isoproterenol (ISO), a β-adrenergic receptor agonist, but the mechanism underlying this cAMP signaling remains undefined. In this study, treatment of mouse primary and 3T3-L1 adipocytes with ISO, revealed that the resistin release was significantly reduced. Additionally, this response was reversed by the PKA inhibitor Rp-8-CPT-cAMPS. This decrease in the resistin release was mimicked by the treatment of the cells with the PKA activator 6-Bnz-cAMP, whereas the Epac activator 8-pCPT-2'-O-Me-cAMP did not alter the resistin release. These results indicated that the PKA activation mediates the ISO/cAMP-induced reduction of resistin release. The resistin release was also significantly suppressed when 3T3-L1 adipocytes were incubated with a combination of the cAMP-specific phosphodiestrase PDE3 inhibitor cilostazol and dibutyryl-cAMP (dbcAMP). Like the ISO-induced signaling, this decrease was also reversed by the PKA inhibitor, indicating that the decrease of resistin release by dbcAMP and PDE3 inhibitor is also mediated by PKA activation. Treatment of adipocytes with TNF-alpha and PI3K inhibitor LY294002 also showed a significant decrease in resistn release, but such effect was not reversed by the PKA inhibitor, suggesting that signal pathways other than cAMP signaling are involved in resistin production. Moreover, insulin alone was found no effect on resistin release in 3T3-L1 adipocytes, but it could block the inhibitory effect of PI3K inhibitor, suggesting that a PI3K-independent pathway may mediate the insulin action. Taken together, these results demonstrated that in mouse adipocytes the resistin release is regulated by distinct signal pathways including cAMP/PDE3/PKA, TNF-alpha?receptor, and PI3K signaling. |
