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Nlrp6 promotes recovery after peripheral nerve injury independently of inflammasomes.

Ydens E, Demon D, Lornet G, De Winter V, Timmerman V, Lamkanfi M, Janssens S - J Neuroinflammation (2015)

Bottom Line: Loss of the inflammasome adaptor apoptosis-associated speck-like protein containing a CARD (ASC) and effector caspase-1 and caspase-11 did not affect sciatic nerve function, suggesting that Nlrp6 contributed to recovery after peripheral nerve injury independently of inflammasomes.However, Nlrp6 deficiency was associated with increased pro-inflammatory extracellular regulated MAP kinase (ERK) signaling, suggesting that hyperinflammation in the absence of Nlrp6 exacerbated peripheral nerve injury.Together, our observations suggest that Nlrp6 contributes to recovery from peripheral nerve injury by dampening inflammatory responses independently of IL-1β and inflammasomes.

View Article: PubMed Central - PubMed

Affiliation: Peripheral Neuropathy Group, Department of Molecular Genetics, VIB and University of Antwerp, Universiteitsplein 1, B-2610, Wilrijk, Antwerpen, Belgium. Elke.ydens@uhasselt.be.

ABSTRACT

Background: NOD-like receptors (Nlrs) are key regulators of immune responses during infection and autoimmunity. A subset of Nlrs assembles inflammasomes, molecular platforms that are activated in response to endogenous danger and microbial ligands and that control release of interleukin (IL)-1β and IL-18. However, their role in response to injury in the nervous system is less understood.

Methods: In this study, we investigated the expression profile of major inflammasome components in the peripheral nervous system (PNS) and explored the physiological role of different Nlrs upon acute nerve injury in mice.

Results: While in basal conditions, predominantly members of NOD-like receptor B (Nlrb) subfamily (NLR family, apoptosis inhibitory proteins (NAIPs)) and Nlrc subfamily (ICE-protease activating factor (IPAF)/NOD) are detected in the sciatic nerve, injury causes a shift towards expression of the Nlrp family. Sterile nerve injury also leads to an increase in expression of the Nlrb subfamily, while bacteria trigger expression of the Nlrc subfamily. Interestingly, loss of Nlrp6 led to strongly impaired nerve function upon nerve crush. Loss of the inflammasome adaptor apoptosis-associated speck-like protein containing a CARD (ASC) and effector caspase-1 and caspase-11 did not affect sciatic nerve function, suggesting that Nlrp6 contributed to recovery after peripheral nerve injury independently of inflammasomes. In line with this, we did not detect release of mature IL-1β upon acute nerve injury despite potent induction of pro-IL-1β and inflammasome components Nlrp3 and Nlrp1. However, Nlrp6 deficiency was associated with increased pro-inflammatory extracellular regulated MAP kinase (ERK) signaling, suggesting that hyperinflammation in the absence of Nlrp6 exacerbated peripheral nerve injury.

Conclusions: Together, our observations suggest that Nlrp6 contributes to recovery from peripheral nerve injury by dampening inflammatory responses independently of IL-1β and inflammasomes.

No MeSH data available.


Related in: MedlinePlus

Induction profile of Nlrs upon acute injury of the sciatic nerve. Expression profile of Nlrb (a), Nlrp (b), and Nlrc (c) subfamily members during acute nerve injury. d Expression profile of several inflammasome components during acute nerve injury. Data is analyzed using the ΔΔCt method, and mRNA expression levels are expressed relative to the basal condition (0-h time point). The graphs show the pooled data of five independent experiments (mean ± SD). e Cell-type-specific expression of Nlrs in steady state and at day 1 post-injury in the peripheral nerve. Schwann cells, resident macrophages, and monocytes were sorted from the peripheral nerve, and expression of several inflammatory markers was determined by RT-qPCR analysis. Mono D1 monocytes at day 1 post-injury, ResMF D1 resident macrophages at day 1 post-injury, ResMF StSt resident macrophages at steady state, SC D1 Schwann cells at day 1 post-injury, SC StSt Schwann cells at steady state, ND not detectable
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Fig3: Induction profile of Nlrs upon acute injury of the sciatic nerve. Expression profile of Nlrb (a), Nlrp (b), and Nlrc (c) subfamily members during acute nerve injury. d Expression profile of several inflammasome components during acute nerve injury. Data is analyzed using the ΔΔCt method, and mRNA expression levels are expressed relative to the basal condition (0-h time point). The graphs show the pooled data of five independent experiments (mean ± SD). e Cell-type-specific expression of Nlrs in steady state and at day 1 post-injury in the peripheral nerve. Schwann cells, resident macrophages, and monocytes were sorted from the peripheral nerve, and expression of several inflammatory markers was determined by RT-qPCR analysis. Mono D1 monocytes at day 1 post-injury, ResMF D1 resident macrophages at day 1 post-injury, ResMF StSt resident macrophages at steady state, SC D1 Schwann cells at day 1 post-injury, SC StSt Schwann cells at steady state, ND not detectable

Mentions: Subsequently, we analyzed the expression profile of the Nlrs in conditions of peripheral nerve injury. Upon acute neurodegeneration, the Nlrb members NAIP1 and NAIP2 were strongly induced 24 h after surgical intervention, while NAIP5 and NAIP6 expression levels remained almost constant (Fig. 3a). Several members of the Nlrp subfamily—Nlrp1, Nlrp3, and Nlrp6—showed increased expression, with Nlrp3 and 6 already showing increased expression from 4 h post-surgery on. Nlrp3 levels remained high until 24 h after injury while Nlrp6 showed a sharper expression peak (Fig. 3b). Nlrp5 and Nlrp9 were borderline detectable over the time course of the experiments. The other Nlrp members did not differ from the contralateral control side (Fig. 3b). NOD2 became slightly induced 24 h upon injury, while NOD1 and IPAF did not increase in expression level (Fig. 3c). In addition, the transcripts of inflammasome-associated genes ASC, caspase-1, and caspase-11 were only moderately induced (ASC) or remained unaffected (caspase-1 and caspase-11) (Fig. 3d). There were no sex differences (data not shown). To find out which cell types contributed to the expression of these different Nlrs in the nerve, we sorted Schwann cells, resident macrophages, and infiltrating monocytes in steady state and at day 1 post-injury from the nerve. The purified cell populations were used for RT-qPCR analysis, and the results are shown in Fig. 3e. NLR molecules are mainly expressed in monocytes and resident macrophages and to a far lesser extent in Schwann cells. It seems that especially monocytes contribute to the observed induction of NAIP1, NAIP2, and Nlrp1 at day 1 after peripheral nerve injury, while resident macrophages induce the expression of NAIP1, Nlrp3, ASC, and MCP-1 1 day after injury. Schwann cells clearly show induction of IL-1β, MCP-1, and Nlrp1 and Nlrp3 upon peripheral nerve injury, but in general, their expression is lower compared to resident macrophages and infiltrating monocytes (Fig. 3e, inserts).Fig. 3


Nlrp6 promotes recovery after peripheral nerve injury independently of inflammasomes.

Ydens E, Demon D, Lornet G, De Winter V, Timmerman V, Lamkanfi M, Janssens S - J Neuroinflammation (2015)

Induction profile of Nlrs upon acute injury of the sciatic nerve. Expression profile of Nlrb (a), Nlrp (b), and Nlrc (c) subfamily members during acute nerve injury. d Expression profile of several inflammasome components during acute nerve injury. Data is analyzed using the ΔΔCt method, and mRNA expression levels are expressed relative to the basal condition (0-h time point). The graphs show the pooled data of five independent experiments (mean ± SD). e Cell-type-specific expression of Nlrs in steady state and at day 1 post-injury in the peripheral nerve. Schwann cells, resident macrophages, and monocytes were sorted from the peripheral nerve, and expression of several inflammatory markers was determined by RT-qPCR analysis. Mono D1 monocytes at day 1 post-injury, ResMF D1 resident macrophages at day 1 post-injury, ResMF StSt resident macrophages at steady state, SC D1 Schwann cells at day 1 post-injury, SC StSt Schwann cells at steady state, ND not detectable
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Fig3: Induction profile of Nlrs upon acute injury of the sciatic nerve. Expression profile of Nlrb (a), Nlrp (b), and Nlrc (c) subfamily members during acute nerve injury. d Expression profile of several inflammasome components during acute nerve injury. Data is analyzed using the ΔΔCt method, and mRNA expression levels are expressed relative to the basal condition (0-h time point). The graphs show the pooled data of five independent experiments (mean ± SD). e Cell-type-specific expression of Nlrs in steady state and at day 1 post-injury in the peripheral nerve. Schwann cells, resident macrophages, and monocytes were sorted from the peripheral nerve, and expression of several inflammatory markers was determined by RT-qPCR analysis. Mono D1 monocytes at day 1 post-injury, ResMF D1 resident macrophages at day 1 post-injury, ResMF StSt resident macrophages at steady state, SC D1 Schwann cells at day 1 post-injury, SC StSt Schwann cells at steady state, ND not detectable
Mentions: Subsequently, we analyzed the expression profile of the Nlrs in conditions of peripheral nerve injury. Upon acute neurodegeneration, the Nlrb members NAIP1 and NAIP2 were strongly induced 24 h after surgical intervention, while NAIP5 and NAIP6 expression levels remained almost constant (Fig. 3a). Several members of the Nlrp subfamily—Nlrp1, Nlrp3, and Nlrp6—showed increased expression, with Nlrp3 and 6 already showing increased expression from 4 h post-surgery on. Nlrp3 levels remained high until 24 h after injury while Nlrp6 showed a sharper expression peak (Fig. 3b). Nlrp5 and Nlrp9 were borderline detectable over the time course of the experiments. The other Nlrp members did not differ from the contralateral control side (Fig. 3b). NOD2 became slightly induced 24 h upon injury, while NOD1 and IPAF did not increase in expression level (Fig. 3c). In addition, the transcripts of inflammasome-associated genes ASC, caspase-1, and caspase-11 were only moderately induced (ASC) or remained unaffected (caspase-1 and caspase-11) (Fig. 3d). There were no sex differences (data not shown). To find out which cell types contributed to the expression of these different Nlrs in the nerve, we sorted Schwann cells, resident macrophages, and infiltrating monocytes in steady state and at day 1 post-injury from the nerve. The purified cell populations were used for RT-qPCR analysis, and the results are shown in Fig. 3e. NLR molecules are mainly expressed in monocytes and resident macrophages and to a far lesser extent in Schwann cells. It seems that especially monocytes contribute to the observed induction of NAIP1, NAIP2, and Nlrp1 at day 1 after peripheral nerve injury, while resident macrophages induce the expression of NAIP1, Nlrp3, ASC, and MCP-1 1 day after injury. Schwann cells clearly show induction of IL-1β, MCP-1, and Nlrp1 and Nlrp3 upon peripheral nerve injury, but in general, their expression is lower compared to resident macrophages and infiltrating monocytes (Fig. 3e, inserts).Fig. 3

Bottom Line: Loss of the inflammasome adaptor apoptosis-associated speck-like protein containing a CARD (ASC) and effector caspase-1 and caspase-11 did not affect sciatic nerve function, suggesting that Nlrp6 contributed to recovery after peripheral nerve injury independently of inflammasomes.However, Nlrp6 deficiency was associated with increased pro-inflammatory extracellular regulated MAP kinase (ERK) signaling, suggesting that hyperinflammation in the absence of Nlrp6 exacerbated peripheral nerve injury.Together, our observations suggest that Nlrp6 contributes to recovery from peripheral nerve injury by dampening inflammatory responses independently of IL-1β and inflammasomes.

View Article: PubMed Central - PubMed

Affiliation: Peripheral Neuropathy Group, Department of Molecular Genetics, VIB and University of Antwerp, Universiteitsplein 1, B-2610, Wilrijk, Antwerpen, Belgium. Elke.ydens@uhasselt.be.

ABSTRACT

Background: NOD-like receptors (Nlrs) are key regulators of immune responses during infection and autoimmunity. A subset of Nlrs assembles inflammasomes, molecular platforms that are activated in response to endogenous danger and microbial ligands and that control release of interleukin (IL)-1β and IL-18. However, their role in response to injury in the nervous system is less understood.

Methods: In this study, we investigated the expression profile of major inflammasome components in the peripheral nervous system (PNS) and explored the physiological role of different Nlrs upon acute nerve injury in mice.

Results: While in basal conditions, predominantly members of NOD-like receptor B (Nlrb) subfamily (NLR family, apoptosis inhibitory proteins (NAIPs)) and Nlrc subfamily (ICE-protease activating factor (IPAF)/NOD) are detected in the sciatic nerve, injury causes a shift towards expression of the Nlrp family. Sterile nerve injury also leads to an increase in expression of the Nlrb subfamily, while bacteria trigger expression of the Nlrc subfamily. Interestingly, loss of Nlrp6 led to strongly impaired nerve function upon nerve crush. Loss of the inflammasome adaptor apoptosis-associated speck-like protein containing a CARD (ASC) and effector caspase-1 and caspase-11 did not affect sciatic nerve function, suggesting that Nlrp6 contributed to recovery after peripheral nerve injury independently of inflammasomes. In line with this, we did not detect release of mature IL-1β upon acute nerve injury despite potent induction of pro-IL-1β and inflammasome components Nlrp3 and Nlrp1. However, Nlrp6 deficiency was associated with increased pro-inflammatory extracellular regulated MAP kinase (ERK) signaling, suggesting that hyperinflammation in the absence of Nlrp6 exacerbated peripheral nerve injury.

Conclusions: Together, our observations suggest that Nlrp6 contributes to recovery from peripheral nerve injury by dampening inflammatory responses independently of IL-1β and inflammasomes.

No MeSH data available.


Related in: MedlinePlus