ABCC8 adenovirus

Prolonged exposure to Gαi/o receptor agonists, such as opioids, can lead to sensitization of adenylate cyclase (AC), resulting in heterosensitization or cyclic adenosine monophosphate (cAMP) overshoot. Here, researchers show that genetic reduction of AC1 and concurrent upregulation of the ATP-sensitive potassium (KATP) channel subunits SUR1 or Kir6.2 significantly attenuate morphine tolerance and reduce naloxone-induced withdrawal. In vitro models utilized an EPAC2-GFP-cAMP biosensor to study sensitization of adenylate cyclase in SH-SY5Y neuroblastoma cells and HEKΔAC3/6 knockout cells. Acute application of DAMGO significantly reduced the cAMP signal from the EPAC2-GFP-cAMP biosensor, whereas chronic DAMGO administration resulted in enhanced cAMP production following AC stimulation. After establishing AC1-EPAC sensitization in an in vitro model, inhibition of either AC1 or EPAC enhanced potassium channel activity after chronic morphine treatment using a thallium-based assay in SH-SY5Y cells. Similar data were obtained in mouse dorsal root ganglia (DRG) after chronic morphine treatment. This study provides evidence for further investigation of AC1 signaling as a target for opioid tolerance and withdrawal by increasing EPAC activity and affecting potassium channels downstream of opioid receptors.

To determine whether reduction of Adcy1 or upregulation of the neuronal K_ATP channel subunits Abcc8 or Kcnj11 would further influence the development of morphine tolerance or withdrawal, the researchers employed a viral strategy. Upregulation of SUR1 in animals treated with adenovirus (Ad-Abcc8) attenuated morphine tolerance compared with mice treated with control adenovirus (Ad-Null) (Figure 1A). Upregulation of Kir6.2 by adenovirus (Ad-Kcnj11) and Adcy1-shRNA treatment also attenuated morphine tolerance compared with mice treated with control AAV (Scram) and adenovirus (Null) (Figure 1B). Loss of Adcy1 or upregulation of Abcc8/Kcnj11 had less effect on morphine forepaw withdrawal measures (Figure 1C) than on measures after morphine (Figure 1D). After morphine tolerance, mice were subjected to withdrawal by injection of naloxone. The number of recorded jumps was significantly reduced due to Adcy1 deficiency or Abcc8/Kcnj11 upregulation (Figure 1E), but rearing was not affected (Figure 1F). The thresholds pre-vs-post tolerance were shifted at least 1 gram for the control vector-treated mice, but Adcy1-shRNA+Ad-Abcc8 and Adcy1-shRNA+Ad-Kcnj11-treated mice were minimally affected (Figure 1G).

Figure 1. Upregulation of K_ATP channel subunits and downregulation of AC1 reduce morphine tolerance and withdrawal in mice. (Klein A H, et al., 2025)