Zhao Chunnian, Lai Justin S, Warsh Jerry J, Li Peter P
Laboratory of Cellular and Molecular Pathophysiology, Centre for Addiction and Mental Health, Toronto, Ontario, Canada.
J Neurosci Res. 2006 Aug 1;84(2):389-97. doi: 10.1002/jnr.20875.
Disturbances in Galpha(s-L) levels and function have been implicated in the pathophysiology of bipolar disorder, but the role of these changes in the development of the illness is not clear. In view of the critical role of Galpha(s)-mediated cAMP signaling in regulating cell survival, we investigated the potential role of Galpha(s-L) in modulating susceptibility to cellular stressors in human SH-SY5Y neuroblastoma cells. Overexpression of Galpha(s-L) to a level twice that of the vector-transfected cells did not directly affect cell viability but significantly increased the sensitivity to induction of cell death by serum deprivation and other apoptotic stimuli, including staurosporine, H(2)O(2), and tunicamycin. This enhanced sensitivity was associated with increased caspase-3 activation and appearance of fragmented nuclei (Hoechst 33342 staining). The broad-spectrum caspase inhibitor z-VAD-fmk completely suppressed cell death evoked by these apoptotic insults in both vector-transfected and Galpha(s-L)-overexpressing cells. The increased vulnerability conferred by increased Galpha(s-L) expression was neither mimicked by cAMP analogs 8-Br-cAMP, 8-CPT-cAMP, and 8-CPT-2Me-cAMP nor attenuated by PKA inhibitors Rp-cAMPS and KT5720. These data indicate that Galpha(s-L) may modulate apoptotic processes in a caspase-dependent manner through a signaling cascade that is independent of the cAMP/PKA or cAMP/Epac pathway. These results suggest that enhanced Galpha(s-L) expression, as was observed in post-mortem brain of bipolar patients, may impair cellular resilience in response to intracellular stress signals resulting from mitochondrial and/or endoplasmic reticulum dysfunction implicated in this disorder.
Gα(s-L)水平和功能的紊乱与双相情感障碍的病理生理学有关，但这些变化在疾病发展中的作用尚不清楚。鉴于Gα(s)介导的cAMP信号在调节细胞存活中的关键作用，我们研究了Gα(s-L)在调节人SH-SY5Y神经母细胞瘤细胞对细胞应激源易感性方面的潜在作用。将Gα(s-L)过表达至载体转染细胞水平的两倍，并未直接影响细胞活力，但显著增加了血清剥夺和其他凋亡刺激（包括星形孢菌素、H₂O₂和衣霉素）诱导细胞死亡的敏感性。这种增强的敏感性与caspase-3激活增加和细胞核碎片化出现（Hoechst 33342染色）有关。广谱caspase抑制剂z-VAD-fmk完全抑制了载体转染细胞和Gα(s-L)过表达细胞中这些凋亡刺激引起的细胞死亡。cAMP类似物8-Br-cAMP、8-CPT-cAMP和8-CPT-2Me-cAMP均未模拟Gα(s-L)表达增加所带来的易感性增加，PKA抑制剂Rp-cAMPS和KT5720也未减弱这种易感性增加。这些数据表明，Gα(s-L)可能通过一个独立于cAMP/PKA或cAMP/Epac途径的信号级联反应，以caspase依赖的方式调节凋亡过程。这些结果表明，如在双相情感障碍患者的尸检大脑中观察到的那样，Gα(s-L)表达增强可能会损害细胞对该疾病所涉及的线粒体和/或内质网功能障碍引起的细胞内应激信号的恢复能力。
