AMPKα1 knockout enhances nociceptive behaviors and spinal glutamatergic synaptic activities via production of reactive oxygen species in the spinal dorsal horn

Abstract

Emerging studies have shown that pharmacological activation of AMPK produces potent analgesic effects in different animal pain models. Currently, the spinal molecular and synaptic mechanism by which AMPK regulates the pain signaling system remains unclear. To address this issue, we utilized the Cre-LoxP system to conditionally knockout the AMPKα1 gene in the nervous system of mice. We demonstrated that AMPKα1 is imperative for maintaining normal nociception, and mice deficient for AMPKα1 exhibit mechanical allodynia. This is concomitantly associated with increased glutamatergic synaptic activities in neurons located in the superficial spinal dorsal horn, which results from the increased glutamate release from presynaptic terminals and function of ligand-gated glutamate receptors at the postsynaptic neurons. Additionally, AMPKα1 knockout mice have increased activities of extracellular signal-regulated kinases (ERK) and p38 mitogen-activated protein kinases (p38), as well as elevated levels of interleukin-1β (IL-1β), reactive oxygen species (ROS), and heme-oxygenase 1 (HO-1) in the spinal dorsal horn. Systemic administration of a non-specific ROS scavenger (phenyl-N-tert-butylnitrone, PBN) or a HO-1 activator (Cobalt protoporphyrin IX, CoPP) attenuated allodynia in AMPKα1 knockout mice. Bath-perfusion of the ROS scavenger or HO-1 activator effectively attenuated the increased ROS levels and glutamatergic synaptic activities in the spinal dorsal horn. Our findings suggest that ROS are the key down-stream signaling molecules mediating the behavioral hypersensitivity in AMPKα1 knockout mice. Thus, targeting AMPKα1 may represent an effective approach for the treatment of pathological pain conditions associated with neuroinflammation at the spinal dorsal horn.

Differential involvement of reactive oxygen species in a mouse model of capsaicin-induced secondary mechanical hyperalgesia and allodynia

“… 31 – 33 Conversely, conditional knockout of AMPKα1 gene per se increases excitatory synaptic activities in the spinal cord superficial dorsal horn neurons and reduces mechanical threshold in an ROS-dependent manner. 34 Aligned with these reports, the AMPK activator metformin inhibited mechanical allodynia induced by intraplantar capsaicin or intrathecal KO 2 injection in the present study. That only mechanical allodynia development was significantly affected by metformin pretreatment suggests that metformin-sensitive cellular machinery including AMPK is downstream of ROS signaling involved only in central sensitization mechanism for mechanical allodynia, further demonstrating the difference between ROS-induced mechanical hyperalgesia and allodynia in molecular mechanisms.…”

Pharmacological activation of AMPK inhibits incision-evoked mechanical hypersensitivity and the development of hyperalgesic priming in mice

“…Our in vitro experiments on DRG neurons indicate the combination of resveratrol and metformin activate AMPK in at least an additive fashion. These data add to a growing body of evidence that AMPK activation can inhibit the development of acute mechanical hypersensitivity resulting from injury (Melemedjian et al, 2011, Tillu et al, 2012a, Russe et al, 2013, Bullon et al, 2015, Ma et al, 2015, Song et al, 2015, Maixner et al, 2016, Ling et al, 2017), reduce the excitability of nociceptors (Melemedjian et al, 2011, Tillu et al, 2012a, Melemedjian et al, 2013, Asiedu et al, 2017) and prevent the development of hyperalgesic priming (Price and Dussor, 2013, Price et al, 2015, Asiedu et al, 2016, Mejia et al, 2016). We conclude that topical resveratrol and co-treatment of various AMPK activators such as metformin are clinically relevant and could show utility as pain therapeutics in humans.…”

Metformin inhibits spontaneous excitatory postsynaptic currents in spinal dorsal cord neurons from paclitaxel-treated rats

“…Spinal AMPK knockdown by siRNA results in behavioral hypersensitivity (Maixner et al, 2015). Especially, mice lacking AMPKα1 display increased glutamatergic synaptic activity in the spinal dorsal horn and mechanical allodynia (Maixner et al, 2016). These findings provide a clue that metformin may suppress the potentiated spinal synaptic transmission and relieve paclitaxelinduced neuropathic pain by activating spinal AMPK signaling, although it need to examine whether metformin could increase the expression of AMPK in the spinal dorsal horn of rats with the neuropathic pain.…”