Animal Studies

Joint pain is composed of both spontaneous and movement-induced pain. In animal models, static bodyweight distribution is a surrogate for spontaneous joint pain. However, there are no commercially-available instruments that measure static bodyweight distribution in normal, pronograde rodents.

In diabetic neuropathy, there is activation of axonal and sensory neuronal degeneration pathways leading to distal axonopathy. The nicotinamide-adenine dinucleotide (NAD+)-dependent deacetylase enzyme, Sirtuin 1 (SIRT1), can prevent activation of these pathways and promote axonal regeneration. In this study, we tested whether increased expression of SIRT1 protein in sensory neurons prevents and reverses experimental diabetic neuropathy induced by a high fat diet (HFD). We generated a transgenic mouse that is inducible and overexpresses SIRT1 protein in neurons (nSIRT1OE Tg). Higher levels of SIRT1 protein were localized to cortical and hippocampal neuronal nuclei in the brain and in nuclei and cytoplasm of small to medium sized neurons in dorsal root ganglia. Wild-type and nSIRT1OE Tg mice were fed with either control diet (6.2% fat) or a HFD (36% fat) for 2 months. HFD-fed wild-type mice developed neuropathy as determined by abnormal motor and sensory nerve conduction velocity, mechanical allodynia, and loss of intraepidermal nerve fibres. In contrast, nSIRT1OE prevented a HFD-induced neuropathy despite the animals remaining hyperglycaemic. To test if nSIRT1OE would reverse HFD-induced neuropathy, nSIRT1OE was activated after mice developed peripheral neuropathy on a HFD. Two months after nSIRT1OE, we observed reversal of neuropathy and an increase in intraepidermal nerve fibre. Cultured adult dorsal root ganglion neurons from nSIRT1OE mice, maintained at high (30 mM) total glucose, showed higher basal and maximal respiratory capacity when compared to adult dorsal root ganglion neurons from wild-type mice. In dorsal root ganglion protein extracts from nSIRT1OE mice, the NAD+-consuming enzyme PARP1 was deactivated and the major deacetylated protein was identified to be an E3 protein ligase, NEDD4-1, a protein required for axonal growth, regeneration and proteostasis in neurodegenerative diseases. Our results indicate that nSIRT1OE prevents and reverses neuropathy. Increased mitochondrial respiratory capacity and NEDD4 activation was associated with increased axonal growth driven by neuronal overexpression of SIRT1. Therapies that regulate NAD+ and thereby target sirtuins may be beneficial in human diabetic sensory polyneuropathy.

Arthritis is often characterized by inflammation and bone destruction. Here we studied the contribution of inflammation and bone destruction to pain.

Trigeminal neuropathic pain is seen as a huge clinical challenge. Although numerous drugs have been developed to treat the condition, some patients have shown intolerance to the drugs and thus continue to suffer. In the present study, a rat model of trigeminal neuropathic pain was established using incorrectly positioned dental implants, which had various manifestations that were similar to human trigeminal neuropathic pain. Using this model, we investigated the differential regulation of JAK2 and PTEN. Firstly, we examined the expression of JAK2 and PTEN in the medullary dorsal horn. After inhibiting JAK2/PTEN, we evaluated nociception-related behavioral alterations. The rat models were established by replacing the left lower second molar with a mini dental implant. Immunoblot assay and immunofluorescence experiments indicated high expression of JAK2 and PTEN in medullary dorsal horn after the nerve injury, which attained plateau levels on post-operative day (POD) 5-10 and 10-20. Administration of adenovirus-shRNA-JAK2 on POD 1 reduced mechanical allodynia and downstream STAT activation. Meanwhile, the administration of adenovirus-shRNA-PTEN on POD 1 attenuated mechanical allodynia while upregulating AKT. In addition to postoperative JAK2 and PTEN activation, dexmedetomidine treatment (10 mg/kg) also modulated the downstream sensors of these signaling molecules. These data suggest that JAK2 and PTEN are pivotal to the development of trigeminal neuropathic pain, and that JAK2 and PTEN suppression alleviates the neuropathic pain.

Neuropathic pain is a common, debilitating clinical issue. Here, the weighted gene co-expression network analysis (WGCNA) was used to identify the specific modules and hub genes that are related to neuropathic pain. The microarray data set of a neuropathic rat model induced by tibial nerve transection (TNT), including dorsal root ganglion (DRG) tissues from TNT model (n = 7) and sham (n = 8) rats, was downloaded from the ArrayExpress database (E-MTAB-2260). The co-expression network modules were identified by the WGCNA package. The protein-protein interaction (PPI) network was constructed, and the node with highest level of connectivity in the network were identified as the hub gene. A total of 1,739 genes and seven modules were identified. The most significant module was the brown module, which contained 215 genes that were primarily associated with the biological process of the defense response and molecular function of calcium ion binding. Furthermore, Ccl2, Fos and Timp1 which were identified as the hub genes in the PPI network and two subnetworks separately. The in vivo studies validated that mRNA and protein levels of Ccl2, Fos and Timp1 were upregulated in DRG and spinal cord tissues after TNT. This study offers novel insights into the molecular mechanisms of neuropathic pain in the context of peripheral nerve injury.

Accidental contact with caterpillar bristles causes local symptoms such as severe pain, intense heat, edema, erythema, and pruritus. However, there is little functional evidence to indicate a potential mechanism. In this study, we analyzed the biological characteristics of the crude venom from the larval stage of living in South-West China. Intraplantar injection of the venom into the hind paws of mice induced severe acute pain behaviors in wild type (WT) mice; the responses were much reduced in TRPV1-deficit (TRPV1 KO) mice. The TRPV1-specific inhibitor, capsazepine, significantly attenuated the pain behaviors. Furthermore, the crude venom evoked strong calcium signals in the dorsal root ganglion (DRG) neurons of WT mice but not those of TRPV1 KO mice. Among the pain-related ion channels we tested, the crude venom only activated the TRPV1 channel. To better understand the venom components, we analyzed the transcriptome of the sebaceous gland region. Our study suggests that TRPV1 serves as a primary nociceptor in caterpillar-induced pain and forms the foundation for elucidating the pain-producing mechanism.