Current development of patient-specific induced pluripotent stem cells harbouring mitochondrial gene mutations and their applications in the treatment of sensorineural hearing loss.

Of all the human body's sensory systems, the auditory system is perhaps its most intricate. Hearing loss can result from even modest damage or cell death in the inner ear, and is the most common form of sensory loss. Human hearing is made possible by the sensory epithelium, the lateral wall, and auditory nerves. The most prominent functional cells in the sensory epithelium are outer hair cells (OHCs), inner hair cells (IHCs), and supporting cells. Different sound frequencies are processed by OHCs and IHCs in different cochlear regions, with those in the apex responsible for low frequencies and those in the basal region responsible for high frequencies. Hair cells can be damaged or destroyed by loud noise, aging process, genetic mutations, ototoxicity, infection, and illness. As such, they are a primary target for treating sensorineural hearing loss. Other areas known to affect hearing include spiral ganglion neurons (SGNs) in the auditory nerve. Age-related degradation of HCs and SGNs can also cause hearing loss. The aim of this review is to introduce the roles of mitochondria in human auditory system and the inner ear's main cell types and cellular functions, before going on to detail the likely health benefits of iPSC technology. We posit that patient-specific iPSCs with mitochondrial gene mutations will be an important aspect of regenerative medicine and will lead to significant progress in the treatment of SNHL.

Pretreatment with intrathecal amitriptyline potentiates anti-hyperalgesic effects of post-injury intra-peritoneal amitriptyline following spinal nerve ligation.

BACKGROUND: Amitriptyline, a tricyclic antidepressant and potent use-dependent blocker of sodium channels, has been shown to attenuate acute and chronic pain in several preclinical modes. The purpose of this study was to investigate whether intrathecal pretreatment with amitriptyline combined with post-injury intra-peritoneal amitriptyline is more effective than post-injury treatment alone on L5 spinal nerve ligation (SNL)-induced neuropathic pain. METHODS: 96 adult male Sprague-Dawley rats were allocated into 4 groups: group S, Sham; group L, L5 spinal nerve Ligation with vehicle treatment; group A, SNL and post-injury intra-peritoneal (Abdominal) amitriptyline twice daily × 3 days; group P, intrathecal Pretreatment with amitriptyline, SNL and intra-peritoneal amitriptyline twice daily × 3 days. Responses to thermal and mechanical stimuli, as well as sodium channel expression in injured dorsal root ganglion (DRG) and activated glial cells in spinal dorsal horn (SDH) were measured pre-operatively and on post-operative day (POD) 4, 7, 14, 21 and 28. RESULTS: SNL-evoked hyper-sensitivity responses to thermal and mechanical stimuli, up-regulated Nav1.3 and down-regulated Nav1.8 expression in DRG, and activated microglia and astrocytes in SDH. In group A, intra-peritoneal amitriptyline alone alleviated thermal hypersensitivity on POD7, reversed Nav1.8 and reduced activated microglia on POD14. In group P, intrathecal pretreatment with amitriptyline not only potentiated the effect of intra-peritoneal amitriptyline on thermal hypersensitivity and Nav1.8, but attenuated mechanical hypersensitivity on POD7 and reduced up-regulated Nav1.3 on POD14. Furthermore, this treatment regimen reduced astrocyte activation on POD14. CONCLUSIONS: Concomitant intrathecal pretreatment and post-injury intra-peritoneal amitriptyline was more effective than post-injury treatment alone on attenuation of behavioral hypersensitivity, decrease of activated microglia and astrocytes and dysregulated Nav1.3 and 1.8.

miRNA Expression Change in Dorsal Root Ganglia After Peripheral Nerve Injury.

The role of microRNAs (miRNAs) in the regulation of nerve injury-induced neuropathic pain is unclear. The aims of this study were to assess and compare miRNA expression profiles in dorsal root ganglia (DRG) following three different kinds of peripheral nerve injury, including spinal nerve ligation (SNL), dorsal root transection (DRT), and ventral root transection (VRT), in Sprague-Dawley rats. Responses to thermal and mechanical stimuli were measured preoperatively and on postoperative days (PODs) 1, 4, and 7. A miRNA microarray analysis was used to detect the miRNA expression profiles in injured L5 DRG from SNL, DRT, and VRT on POD 7. Validation of miRNA expression was performed by qPCR and in situ hybridization. Rats receiving SNL displayed significantly higher mechanical hypersensitivity, but those receiving DRT developed higher thermal hypersensitivity. The number of miRNAs that were significantly upregulated in L5 DRG was 49 (7.2%), 25 (3.7%), and 146 (21.5%) following SNL, DRT, and VRT, respectively. On the other hand, 35 (5.1%) miRNAs were significantly downregulated in the SNL group, 21 (3.1%) miRNAs in the DRT group, and 41 (6.0%) miRNAs in the VRT group. Of the four miRNAs that were mutually aberrant in all three models, two were significantly upregulated (twofold), miR-21 and miR-31, and two were significantly downregulated, miR-668 and miR-672. Using in situ hybridization, miRNA-21, miRNA-31, miRNA-668, and miRNA-672 were found to localize to neurons in the DRG. Collectively, the mutual abnormal miRNA expression of miR-21, miR-31, miR-668, and miR-677 implied that these miRNAs may be therapeutic targets for alleviating multiple forms of neuropathic pain.

Intrathecal CGS-26303 Pretreatment Attenuates Spinal Nerve Ligation-Induced Neuropathic Pain in the Spinal Cord.

BACKGROUND: Matrix metalloproteinase (MMPs) and endothelin-1 may prove to be important in the generation of pain induced by inflammation and nerve lesion. This study aimed to investigate the relationship between endothelin receptors and MMPs. METHODS: Male Sprague-Dawley rats (250-300 g) were divided into 5 groups: a normal (control) group; an L5 spinal nerve ligation (SNL) group; a CGS-26303 IT + L5 SNL group; a BQ-123 IT + L5 SNL group; and a BQ-788 IT + L5 SNL group. The expression of glial fibrillary acidic protein, endothelin-A receptor (ETAR), endothelin-B receptor, MMP-2, and MMP-9 in the ipsilateral L5 dorsal root ganglion (DRG) and the activation of microglia and astrocytes in the L5 spinal dorsal horn (SDH) were quantified by immunofluorescence and Western blotting. RESULTS: Intrathecal pretreatment with CGS-26303 significantly attenuated the hyperalgesic and mechanical responses induced by SNL for 4 days, whereas BQ-123 administration alleviated the hyperalgesia only for 3 hours and mechanical allodynia for only 1 hour. Pretreatment with CGS-26303 significantly down-regulated the glial fibrillary acidic protein, ET-A, MMP-2, and MMP-9 expressions in DRG and their effect lasted for 6 hours, 1 day, 7 days, and 1 day, respectively. By immunofluorescence and Western blotting, there was colocalization of ETAR and MMP-9 in the DRG neurons, whereas MMP-2 was expressed in DRG satellite cells. Furthermore, CGS-26303 treatment also reduced SNL-induced microglia and astrocyte activation on the SDH for 7 days. CONCLUSIONS: In this study, CGS-26303 can attenuate SNL-induced neuropathic pain by down-regulating MMP-9, MMP-2, and ETAR expressions in the DRG and by glia cell activation in the SDH.

Sciatic Nerve Intrafascicular Lidocaine Injection-induced Peripheral Neuropathic Pain: Alleviation by Systemic Minocycline Administration.

OBJECTIVE: Peripheral nerve block guidance with a nerve stimulator or echo may not prevent intrafascicular injury. This study investigated whether intrafascicular lidocaine induces peripheral neuropathic pain and whether this pain can be alleviated by minocycline administration. METHODS: A total of 168 male Sprague-Dawley rats were included. In experiment 1, 2% lidocaine (0.1 mL) was injected into the left sciatic nerve. Hindpaw responses to thermal and mechanical stimuli, and sodium channel and activating transcription factor (ATF-3) expression in dorsal root ganglion (DRG) and glial cells in the spinal dorsal horn (SDH), were measured on days 4, 7, 14, 21, and 28. On the basis of the results in experiment 1, rats in experiment 2 were divided into sham, extraneural, intrafascicular, peri-injury minocycline, and postinjury minocycline groups. Behavioral responses, macrophage recruitment, expression changes of myelin basic protein and Schwann cells in the sciatic nerve, dysregulated expression of ATF-3 in the DRG, and activated glial cells in L5 SDH were assessed on days 7 and 14. RESULTS: Intrafascicular lidocaine induced mechanical allodynia, downregulated Nav1.8, increased ATF-3 expression in the DRG, and activated glial cells in the SDH. Increased expression of macrophages, Schwann cells, and myelin basic protein was found in the sciatic nerve. Minocycline attenuated intrafascicular lidocaine-induced neuropathic pain and nerve damage significantly. Peri-injury minocycline was better than postinjury minocycline administration in alleviating mechanical behaviors, mitigating macrophage recruitment into the sciatic nerve, and suppressing activated microglial cells in the spinal cord. DISCUSSION: Systemic minocycline administration alleviates intrafascicular lidocaine injection-induced peripheral nerve damage.