Intrathecal Noggin administration in rats temporally ameliorates mechanical allodynia induced by a chronic constriction injury

Neurotropin® ameliorates chronic pain associated with scar formation in a mouse model: A gene expression analysis of the inflammatory response

Background: Scar formation after trauma and surgery involves an inflammatory response and can lead to the development of chronic pain. Neurotropin® (NTP) is a nonprotein extract of inflamed skin of rabbits inoculated with vaccinia virus. It has been widely used for the treatment of chronic pain. However, the in vivo effects of NTP on painful scar formation have not been determined. To investigate the molecular mechanisms underlying the effects of NTP on the inflammatory response, we evaluated gene expression in the scar tissues and dorsal root ganglions (DRGs) of mice administered NTP and control mice. Methods and results: Mice injected with saline or NTP were used as controls; other mice were subjected to surgery on the left hind paw to induce painful scar formation, and then injected with saline or NTP. Hind paw pain was evaluated by measuring the threshold for mechanical stimulation using the von Frey test. The paw withdrawal threshold gradually returned to pre-operative levels over 4 weeks post-operation; NTP-treated mice showed a significantly shortened recovery time of approximately 3 weeks, suggesting that NTP exerted an analgesic effect in this mouse model. Total RNA was extracted from the scarred hind paw tissues and DRGs were collected 1 week post-operation for a microarray analysis. Gene set enrichment analysis revealed that the expression of some gene sets related to inflammatory responses was activated or inhibited following surgery and NTP administration. Quantitative real-time reverse transcription-polymerase chain reaction analysis results for several genes were consistent with the microarray results. Conclusion: The administration of NTP to the hind paws of mice with painful scar formation following surgery diminished nociceptive pain and reduced the inflammatory response. NTP inhibited the expression of some genes involved in the response to surgery-induced inflammation. Therefore, NTP is a potential therapeutic option for painful scar associated with chronic pain.

The Role of Bone Morphogenetic Protein 4 in Microglial Polarization in the Process of Neuropathic Pain

Background

Neuropathic pain (NP) is known to be highly correlated with microglial polarization, of which the regulatory mechanism remains to be elucidated. Here, the aim of this study is to further investigate the relationship between bone morphogenetic protein 4 (BMP4) and microglial polarization in the process of NP.

Methods

Firstly, normal adult rats received intrathecal BMP4 administration to assess BMP4ʹs effect on microglial polarization. Secondly, a BMP4 antagonist – Noggin – was applied to a rat NP model achieved by L5 spinal nerve ligation (SNL) to investigate whether antagonizing BMP4 signaling could alleviate allodynia by reversing the imbalance of the M1/M2 polarization ratio. In both experiments, Von-Frey filaments were used to test the changes in the paw withdrawal threshold (PWT), and Western blotting, immuno-fluorescence, PCR and flow cytometry were further performed to investigate microglial activity and the expression patterns of M1 and M2 markers, respectively.

Results

Firstly, BMP4 administration induced a significant PWT decrease and microglial activation in normal rats; Western blotting, PCR and flow cytometry further revealed that M1 markers including CD16, MHCII, and TNF-α showed a marked elevation after BMP4 application; while M2 markers, such as Arg-1, CD204 and IL-4, peaked at an early stage (P1 or P4) and then fell to the Sham level on P7, leading to a persistent imbalance of the M1/M2 ratio throughout the 1st week. Secondly, Noggin treatment significantly relieved allodynia and microglial activation in SNL rats. Moreover, Noggin persistently downregulated the M1 marker levels and simultaneously induced a late-stage elevation of M2 markers expressions, thereby reversing the imbalance of the M1/M2 polarization ratio.

Conclusion

Our results indicate that BMP4 has the ability to induce microglial polarization. Antagonizing BMP4 signaling can relieve pain behavior via mitigating microglial activation and reversing the imbalance of the M1/M2 polarization ratio in the process of NP.

Effect of intrathecal administration of exogenous noggin on neuropathic pain

OBJECTIVES

To explore the effect of intrathecal administration of exogenous noggin (NOG) on the pain behavior in the neuropathic pain (NP) rats through L5 spinal nerve ligation (SNL), and to examine the regulative role of NOG in astrocyte activation, inflammatory cytokines and downstream signals.

METHODS

A total of 40 adult male Sprague Dawley (SD) rats were randomly divided into 3 groups: a control group (n=10), a SNL group (SNL+intrathecal injection of artificial cerebrospinal fluid, n=15), and a SNL+NOG group (SNL+intrathecal injection of recombinant NOG protein, n=15). Von-Frey filaments were used to test the changes of paw withdrawal threshold (PWT) at Day 1 before operation, and Day 1, Day 4, Day 7 and Day 14 after operation in each group. Immunofluorescence was used to observe the activation of astrocyte located in the dorsal horn of spinal cord in the 3 groups. Western blotting was conducted to detect the expression levels of glial fibrillary acidic protein (GFAP), interleukin-6 (IL-6), signal transducer and activator of transcription (STAT3) and phosphorylation STAT3 (p-STAT3).

RESULTS

Compared with the control group, the PWT in the SNL group was markedly decreased at each time point, together with the increase in GFAP, IL-6 and the ratio of p-STAT3/STAT3 (all P<0.05). Meanwhile, compared with the SNL group, the PWT in the lumbar swelling of spinal cord in the SNL+NOG group was elevated at Day 4 and lasted to Day 14 (P<0.05), accompanied by the decrease in GFAP, IL-6 and the ratio of p-STAT3/STAT3 (all P<0.05).

CONCLUSIONS

The intrathecal administration of NOG may alleviate NP in the SNL rats through inhibiting astrocyte activation and down-regulating the STAT3 signal pathway.

Noggin Inhibits IL-1β and BMP-2 Expression, and Attenuates Cartilage Degeneration and Subchondral Bone Destruction in Experimental Osteoarthritis

Osteoarthritis (OA) is a chronic inflammatory and progressive joint disease that results in cartilage degradation and subchondral bone remodeling. The proinflammatory cytokine interleukin 1 beta (IL-1β) is abundantly expressed in OA and plays a crucial role in cartilage remodeling, although its role in the activity of chondrocytes in cartilage and subchondral remodeling remains unclear. In this study, stimulating chondrogenic ATDC5 cells with IL-1β increased the levels of bone morphogenetic protein 2 (BMP-2), promoted articular cartilage degradation, and enhanced structural remodeling. Immunohistochemistry staining and microcomputed tomography imaging of the subchondral trabecular bone region in the experimental OA rat model revealed that the OA disease promotes levels of IL-1β, BMP-2, and matrix metalloproteinase 13 (MMP-13) expression in the articular cartilage and enhances subchondral bone remodeling. The intra-articular injection of Noggin protein (a BMP-2 inhibitor) attenuated subchondral bone remodeling and disease progression in OA rats. We also found that IL-1β increased BMP-2 expression by activating the mitogen-activated protein kinase (MEK), extracellular signal-regulated kinase (ERK), and specificity protein 1 (Sp1) signaling pathways. We conclude that IL-1β promotes BMP-2 expression in chondrocytes via the MEK/ERK/Sp1 signaling pathways. The administration of Noggin protein reduces the expression of IL-1β and BMP-2, which prevents cartilage degeneration and OA development.

Role of bone morphogenetic protein-2/4 in astrocyte activation in neuropathic pain

Background

Bone morphogenetic protein-2/4 (BMP2/4) has been recognized as promoters of astrocyte activity. Substantial evidence suggests that BMP2/4 may be elevated and plays a critical role in astrocyte activation upon spinal cord injury. Although neuropathic pain is similarly associated with astrocyte activation, the participation of BMP2/4 in this regard still remains unclear.

Methods

A rat model of neuropathic pain achieved by spinal nerve ligation at L5 was used to evaluate the expression of glial fibrillary acidic protein and BMP2/4 in the spinal cord in days 1, 4, 7, 10, and 14. Next, normal rats received intrathecal exogenous BMP2/4 and the antagonist Noggin to assess the effect of BMP2/4 on astrocyte activation. In both experiments, von Frey filaments were used to evaluate the changes in paw withdrawal threshold. In addition, Western blotting and immunofluorescence were performed to assess the expression of glial fibrillary acidic protein, BMP2/4, p-Smad 1/5/8, and phospho-signal transducer and activator of transcription-3 (p-STAT3) in the spinal cord.

Results

Firstly, spinal nerve ligation caused a significant increase in the expression of BMP4, while BMP2 levels remained unchanged. Secondly, exogenous BMP4 but not BMP2 induced a significant decrease in paw withdrawal threshold, along with the upregulation of glial fibrillary acidic protein. Moreover, exogenous BMP4 stimulated both p-Smad 1/5/8 and p-STAT3, while BMP2 only upregulated p-Smad 1/5/8. Finally, exogenous Noggin alleviated the decrease in paw withdrawal threshold induced by BMP4 and reduced astrocyte activation, as well as p-STAT3 upregulation.

Conclusions

Our results indicate only BMP4—and not BMP2—intervened in allodynia in rats by eliciting glial activation probably through both p-Smad 1/5/8 and p-STAT3 signaling.