Depression of Ca²⁺/calmodulin‐dependent protein kinase II in dorsal root ganglion neurons after spinal nerve ligation

Abstract

The enzyme calcium/calmodulin-dependent protein kinase II (CaMKII) is associated with memory and its α isoform is critical for development of activity-induced synaptic changes. Therefore, we hypothesized that CaMKII is involved in altered function of dorsal root ganglion (DRG) neurons after neuronal injury. To test this hypothesis, Sprague–Dawley rats were made hyperalgesic by L5 and L6 spinal nerve ligation (SNL), and changes in total phosphorylated and unphosphorylated CaMKII (tCaMKII) and phosphorylated form of its α isoform (pCaMKIIα) were analyzed using immunochemistry in different subpopulations of DRG. SNL did not induce any changes in tCaMKII between experimental groups, while the overall percentage of pCaMKIIα-positive neurons in injured L5 DRG SNL (24.8%) decreased significantly when compared to control (41.7%). SNL did not change the percentage of pCaMKIIα/N52 colabeled neurons but decreased the percentage of N52-negative nonmyelinated neurons that expressed pCaMKIIα from 27% in control animals to 11% after axotomy. We also observed a significant decrease in the percentage of small nonpeptidergic neurons labeled with IB4 (37.6% in control vs. 4.0% in L5 SNL DRG), as well as a decrease in the percentage of pCaMKIIα/IB4 colabeled neurons in injured L5 DRGs (27% in control vs. 1% in L5 DRG of SNL group). Our results show that reduction in pCaMKIIα levels following peripheral injury is due to the loss of IB4-positive neurons. These results indicate that diminished afferent activity after axotomy may lead to decreased phosphorylation of CaMKIIα.

Regulation of voltage-gated Ca2+ currents by Ca2+/calmodulin-dependent protein kinase II in resting sensory neurons

“…This is consistent with our previous histological observations showing pCaMKII in DRG sensory neurons using a phospho-specific Thr286/287 antibody (Kojundzic et al, 2010). To additionally confirm autonomous CaMKII in resting neurons, we tested CaMKII activity in DRG lysates using the specific peptide substrate AC2.…”

Differential expression of CaMKII isoforms and overall kinase activity in rat dorsal root ganglia after injury

“…Further developmental and subcellular distributions of these two isoforms are seen in the brain (Ouimet et al, 1984, Erondu and Kennedy, 1985, McGuinness et al, 1985, Burgin et al, 1990, Ochiishi et al, 1998) and spinal cord (Terashima et al, 1994), which is compatible with the view that different CaMKII isoforms have particular tissue-specific activities. Although β, γ, and δ isoforms can also be expressed in many tissues, including neurons and support cells in the brain (Ouimet et al, 1984, Tobimatsu and Fujisawa, 1989, Sakagami and Kondo, 1993), prior reports of CaMKII expression in DRGs have shown immunohistochemical colocalization with neuronal markers (Bruggemann et al, 2000, Carlton, 2002, Carlton and Hargett, 2002, Kojundzic et al, 2010), and our present observations indicate that all four (α,β,γ,δ) CaMKII isoforms are expressed in DRGs.…”

“…expression or regulation) is diminished with axotomy. In support of this hypothesis, our immunohistochemical characterization indicated a decrease of autophosphorylated CaMKII (pCaMKII) in sensory neuron somata after SNL (Kojundzic et al, 2010). In the present study we examine the influence of injury upon expression of specific CaMKII isoforms using the SNL model, which has two populations of injured neurons.…”

Crosstalk from cAMP to ERK1/2 emerges during postnatal maturation of nociceptive neurons and is maintained during aging

“…Previous reports demonstrated that CaMKIIα in adult animals is expressed in ∼40% of DRG neurons coexpressing markers for peptidergic and non-peptidergic nociceptors, including TRPV1 (Brüggemann et al, 2000;Carlton and Hargett, 2002;Ichikawa et al, 2004;Isensee et al, 2014b;Kojundzic et al, 2010;Pattinson et al, 2006). CaMKII directly Representative HCS microscopy images of cultured UCHL1-positive sensory neurons isolated from adult rats at 6 weeks of age (W6 group) and labeled with antibodies specific for the classical nociceptive markers TRPV1 and Na v 1.8, the two kinase isoforms PKA-RIIβ (RIIβ) and CaMKIIα, and NF200 as a marker for the mostly non-nociceptive myelinated mechanoreceptive neurons and proprioceptors.…”