Systemic Administration of Connexin43 Mimetic Peptide Improves Functional Recovery after Traumatic Spinal Cord Injury in Adult Rats

Abstract

Blocking of Connexin43 hemichannels, the main gap junction protein located on astrocytes in the central nervous system, has been shown to reduce neural injury in a number of models. We demonstrated previously that local administration of a Connexin43 mimetic peptide, Peptide5, reduces secondary tissue damage after spinal cord injury (SCI). Here, we investigated whether acute systemic delivery of Peptide5 is also protective in a model of SCI. Rats were subjected to a mild spinal cord contusion using the Multicentre Animal Spinal Cord Injury Study impactor and were injected intraperitoneally with Peptide5 or a scrambled peptide immediately and at 2 h and 4 h post-injury. Rats were tested for locomotor recovery and pain hypersensitivity and euthanized at 8 h, 24 h, two weeks, or six weeks post-injury. Compared with control rats, Peptide5 treated rats showed significant improvement in hindlimb locomotor function between three and six weeks post-injury and reductions in at-level mechanical allodynia at weeks one and six post-injury. Immunohistochemistry showed that Peptide5 treatment led to a reduction in total Connexin43 and increased phosphorylated Connexin43 at 8 h compared with scrambled peptide. At two and six weeks, lesion size, the astrocytic and the activated macrophage, and/or microglial response were all decreased in the Peptide5 animals. In addition, neuronal cell numbers were higher in the Peptide5 animals compared with the scrambled peptide treated rats at two and six weeks. These results show for the first time that systemic administration of Peptide5 to block the pathological opening of Connexin43 hemichannels is a feasible treatment strategy in this setting, ameliorating the secondary SCI.

Inhibition of glial hemichannels by boldine treatment reduces neuronal suffering in a murine model of Alzheimer's disease

“…Moreover, in acute or chronic pathological situations, sustained activation of HCs can contribute to an excessive release of ATP and/or glutamate with neurotoxic effects that are alleviated by reducing Cx43 expression or function (Bennett et al, ; Schulz et al, ; Takeuchi & Suzumura, ). For instance, following spinal cord injury, the excessive and sustained ATP release was strongly reduced in mice lacking Cx43 in astrocytes with beneficial outcome, smaller lesion area and motor recovery improvement (Huang et al, ), and blocking Cx43 expression with antisense oligonucleotides or Cx43 mimetic peptides applied locally or administered systemically reduced tissue damage and inflammation and improved functional recovery (Cronin, Anderson, Cook, Green, & Becker, ; Mao et al, ; O'Carroll, Alkadhi, Nicholson, & Green, ). Also the increase in glutamate levels observed after perinatal brain ischemia was strongly reduced when Cx43 HCs were inhibited by mimetic peptides (Li et al, ); the consequence of such Cx43 targeting was a reduction of neuronal death and brain infarct size as well as an improved functional recovery (Davidson et al, ; Davidson, Green, Nicholson, Bennet, & Gunn, ; Li et al, ).…”

Tonabersat Prevents Inflammatory Damage in the Central Nervous System by Blocking Connexin43 Hemichannels

“…Instead, tonabersat appears to be acting primarily and directly on connexin hemichannels to reduce channel opening under injury conditions. Tonabersat may offer an orally available approach for various injuries and chronic inflammatory disease indications, including muscular dystrophy [109], amyotrophic lateral sclerosis [110], CNS trauma [43,44], stroke or ischemia [46,47,111,112], glaucoma, diabetic retinopathy and macular degeneration [37,49,50,54,113], as well as Alzheimer's disease [110,114], chronic pain [115], and infectious disease [116] where connexin hemichannels are implicated in injury spread and the perpetuation of inflammatory processes, especially through the inflammasome pathway [40,84,109].…”

“…Peptide5 also reduced inflammation, improved functional outcomes, and retained retinal tissue integrity following bright-light damage used as a model for dry age-related macular degeneration [50]. In other areas of the CNS, Peptide5 improved functional outcomes following spinal cord injury [43,44], and in sheep models of perinatal ischemia and asphyxia by reducing seizures and significantly improving electroencephalographic power [46,47]. Other connexin43 extracellular loopmimicking peptides such as Gap26 [57] and Gap27 [52], and an intracellular acting mimetic peptide, Gap19 [58], have also been reported to limit cell death by reducing connexin43 hemichannel activity following injury.…”

“…Hemichannels also propagate secondary damage signals following spinal cord injury [41][42][43][44], CNS ischemia [35,37,[45][46][47][48], and retinal injuries [49,50], and have been termed Bpathological pores^ [16,51]. Upregulation of the expression of connexin43 following an insult is also reported to exacerbate the extent of secondary damage [37,43,46,[52][53][54][55].…”

Sustained Connexin43 Mimetic Peptide Release From Loaded Nanoparticles Reduces Retinal and Choroidal Photodamage

“…[11][12][13][14][15][16][17] This has been demonstrated in experiments in which connexin channel-blocking mimetic peptides have been used to prevent connexin hemichannel opening and reduce the inflammatory response. 5,[18][19][20][21][22][23][24][25] However, the short half-life of native Cx43 mimetic peptides 26 in solution is potentially an obstacle for long-term therapeutic effects.…”