Thrombospondin 4, a mediator and candidate indicator of pain.

Pain is the most common symptom for which patients seek medical attention. Existing treatments for pain control are largely ineffective due to the lack of an accurate way to objectively measure pain intensity and a poor understanding of the etiology of pain. Thrombospondin 4(TSP4), a member of the thrombospondin gene family, is expressed in neurons and astrocytes and induces pain by interacting with the calcium channel alpha-2-delta-1 subunit (Cavα2δ1). In the present study we show that TSP4 expression level correlates positively with pain intensity, suggesting that TSP4 could be a novel candidate of pain indicator. Using RNAi-lentivirus (RNAi-LV) to knock down TSP4 both in vivo and in vitro, together with electrophysiological experiments involving paired patch-clamp recordings of evoked action potentials and post-synaptic currents in cultured neurons, we found that TSP4 contributes to the development of bone cancer pain, neuropathic pain, and inflammatory pain. This effect is mediated by regulation of neuron excitability via inhibition of synapsin I (Syn I) and modulation of excitatory and inhibitory presynaptic transmission via regulation of vesicular glutamate transporter 2(Vglut2), vesicular GABA transporter (VGAT), and glutamate decarboxylase (GAD) expression. The present study provides a replicable, predictive, valid indicator of pain and demonstrated the underlying molecular and electrophysiological mechanisms by which TSP4 contributes to pain.