Chakrabarti Sumita, Madia Priyanka A, Gintzler Alan R
Department of Obstetrics and Gynecology, State University of New York, Brooklyn, New York, USA.
J Neurochem. 2016 Mar;136(6):1119-1130. doi: 10.1111/jnc.13519. Epub 2016 Jan 20.
We recently reported (Verzillo, et al. J. Neurochem: 130, 790-796, 2014) that chronic systemic morphine selectively up-regulates mRNA encoding two C-terminal μ-opioid receptor (MOR) splice variants, MOR-1C1 and MOR-1B2 (MOR-1B2/-1C1). Given the known disconnects between changes in levels of mRNA and corresponding protein, it is essential to directly demonstrate that chronic opioid treatment elevates functional MOR-1B2/-1C1 protein prior to inferring relevance of these MOR variants to spinal opioid tolerance mechanisms. Accordingly, we investigated the ability of chronic opioid exposure to up-regulate MOR protein in Chinese hamster ovary cells stably transfected with rat MOR variants MOR-1B2, MOR-1C1, or MOR-1 (considered to be the predominant MOR). Findings revealed that chronic treatment with the clinically relevant opioids morphine, oxycodone and hydrocodone substantially up-regulated membrane MOR-1B2/-1C1 protein. This up-regulation was abolished by the protein synthesis inhibitor cycloheximide, eliminating contributions from receptor redistribution. The increment in MOR-1B2/-1C1 protein was paralleled by a significant increment in opioid agonist-stimulated GTPγS-binding (reflective of increased aggregate MOR G protein coupling) indicating that up-regulated MOR-1B2/-1C1 represented functional receptors. Strikingly, these tolerance-associated adaptations of MOR-1B2/-1C1 differed considerably from those of MOR-1. Antithetical regulation of MOR-1B2/-1C1 and MOR-1 by chronic opioids has significant implications for the design of new therapeutic agents to counteract opioid analgesic tolerance and accompanying addiction. Since chronic opioids induce MOR-1B2/-1C1 up-regulation in spinal cord of males, but not females, elucidating cellular compartments and intracellular pathways mediating MOR-1B2/-1C1 up-regulation and defining their unique signaling attributes would enable a precision medicinal approach to pain management and addiction therapy. In the spinal cord of males, but not females, chronic morphine up-regulates mRNA encoding two mu-opioid receptor (MOR) variants, MOR-1B2 and MOR-1C1 (MOR-1B2/-1C1). We now demonstrate that chronic treatment with the clinically relevant opioids morphine, hydrocodone or oxycodone up-regulates MOR-1B2/-1C1 functional protein, which is dependent on de novo protein synthesis. Findings underscore the importance of unique signaling attributes of MOR variants to sexually dimorphic tolerance mechanisms.
我们最近报道（韦尔齐洛等人，《神经化学杂志》：130，790 - 796，2014年），慢性全身性吗啡选择性地上调编码两种C末端μ-阿片受体（MOR）剪接变体MOR-1C1和MOR-1B2（MOR-1B2/-1C1）的mRNA。鉴于已知mRNA水平变化与相应蛋白质之间的脱节，在推断这些MOR变体与脊髓阿片类药物耐受机制的相关性之前，直接证明慢性阿片类药物治疗能提高功能性MOR-1B2/-1C1蛋白至关重要。因此，我们研究了慢性阿片类药物暴露对稳定转染大鼠MOR变体MOR-1B2、MOR-1C1或MOR-1（被认为是主要的MOR）的中国仓鼠卵巢细胞中MOR蛋白上调的能力。研究结果表明，临床相关阿片类药物吗啡、羟考酮和氢可酮的慢性治疗显著上调了膜MOR-1B2/-1C1蛋白。这种上调被蛋白质合成抑制剂环己酰亚胺消除，排除了受体重新分布的影响。MOR-1B2/-1C1蛋白的增加与阿片类激动剂刺激的GTPγS结合的显著增加平行（反映总的MOR G蛋白偶联增加），表明上调的MOR-1B2/-1C1代表功能性受体。令人惊讶的是，MOR-1B2/-1C1这些与耐受相关的适应性变化与MOR-1的变化有很大不同。慢性阿片类药物对MOR-1B2/-1C1和MOR-1的相反调节对设计新的治疗药物以对抗阿片类镇痛耐受及伴随的成瘾有重要意义。由于慢性阿片类药物在雄性而非雌性的脊髓中诱导MOR-1B2/-1C1上调，阐明介导MOR-1B2/-1C1上调的细胞区室和细胞内途径并确定其独特的信号特性，将有助于采用精准医学方法进行疼痛管理和成瘾治疗。在雄性而非雌性的脊髓中，慢性吗啡上调编码两种μ-阿片受体（MOR）变体MOR-1B2和MOR-1C1（MOR-1B2/-1C1）的mRNA。我们现在证明，临床相关阿片类药物吗啡、氢可酮或羟考酮的慢性治疗上调了MOR-1B2/-1C1功能性蛋白，这依赖于从头合成蛋白质。研究结果强调了MOR变体独特的信号特性对性别二态性耐受机制的重要性。
