PKCδ null mutations in a mouse model of osteoarthritis alter osteoarthritic pain independently of joint pathology by augmenting NGF/TrkA-induced axonal outgrowth.

OBJECTIVES: A key clinical paradox in osteoarthritis (OA), a prevalent age-related joint disorder characterised by cartilage degeneration and debilitating pain, is that the severity of joint pain does not strictly correlate with radiographic and histological defects in joint tissues. Here, we determined whether protein kinase Cδ (PKCδ), a key mediator of cartilage degeneration, is critical to the mechanism by which OA develops from an asymptomatic joint-degenerative condition to a painful disease. METHODS: OA was induced in 10-week-old PKCδ null (PKCδ-/-) and wild-type mice by destabilisation of the medial meniscus (DMM) followed by comprehensive examination of the histology, molecular pathways and knee-pain-related-behaviours in mice, and comparisons with human biopsies. RESULTS: In the DMM model, the loss of PKCδ expression prevented cartilage degeneration but exacerbated OA-associated hyperalgesia. Cartilage preservation corresponded with reduced levels of inflammatory cytokines and of cartilage-degrading enzymes in the joints of PKCδ-deficient DMM mice. Hyperalgesia was associated with stimulation of nerve growth factor (NGF) by fibroblast-like synovial cells and with increased synovial angiogenesis. Results from tissue specimens of patients with symptomatic OA strikingly resembled our findings from the OA animal model. In PKCδ null mice, increases in sensory neuron distribution in knee OA synovium and activation of the NGF-tropomyosin receptor kinase (TrkA) axis in innervating dorsal root ganglia were highly correlated with knee OA hyperalgesia. CONCLUSIONS: Increased distribution of synovial sensory neurons in the joints, and augmentation of NGF/TrkA signalling, causes OA hyperalgesia independently of cartilage preservation.

Two tarantula venom peptides as potent and differential Na(V) channels blockers.

Voltage dependent sodium (Na(V)) channels are large membrane spanning proteins which lie in the basis of action potential generation and propagation in excitable cells and hence are essential mediators of neuronal signaling. Inhibition of Na(V) channel activity is one of the core mechanisms to treat conditions related to neuronal hyperexcitability, such as epilepsy in the clinic. Na(V) channel blockers are also extensively used to locally inhibit action potential generation and related pain perceptions in the form of local anesthetics. Here we describe the isolation, biochemical characterization, synthesis and in vitro characterization of two potent Na(V) channel blockers from the venom of the Paraphysa scrofa (Phrixotrichus auratus) tarantula spider. Both Voltage sensor toxin 3 (VSTx-3, κ-theraphotoxin-Gr4a) and GTx1-15 (Toxin Gtx1-15), were originally isolated from the venom of the related tarantula Grammostola rosea and described as K(V) and Ca(V) channel blockers, respectively. In our hands, GTx1-15 was shown to be a potent inhibitor of tetrodotoxin (TTX)-sensitive channels (IC50 0.007 µM for hNa(V)1.7 and 0.12 µM for hNa(V)1.3 channels), with very little effect on TTX-resistant (Na(V)1.5 and NaV1.8) channels. VSTx-3 was demonstrated to be a potent, TTX-sensitive sodium channel blocker and especially, potent blocker of Na(V)1.8 channels (IC50 0.19 µM for hNa(V)1.3, 0.43 µM for hNa(V)1.7 and 0.77 µM for hNa(V)1.8 channels). Such potent inhibitors with differential selectivity among Na(V) channel isoforms may be used as tools to study the roles of the different channels in processes related to hyperexcitability and as lead compounds to treat pathological pain conditions.