Upregulation of Nucleotide-Binding Oligomerization Domain-, LRR- and Pyrin Domain-Containing Protein 3 in Motoneurons Following Peripheral Nerve Injury in Mice

Abstract

Neuronal injuries are accompanied by release and accumulation of damage-associated molecules, which in turn may contribute to activation of the immune system. Since a wide range of danger signals (including endogenous ones) are detected by the nucleotide-binding oligomerization domain-, LRR- and pyrin domain-containing protein 3 (NLRP3) pattern recognition receptor, we hypothesized that NLRP3 may become activated in response to motor neuron injury. Here we show that peripheral injury of the oculomotor and the hypoglossal nerves results in upregulation of NLRP3 in corresponding motor nuclei in the brainstem of mice. Although basal expression of NLRP3 was observed in microglia, astroglia and neurons as well, its upregulation and co-localization with apoptosis-associated speck-like protein containing a caspase activation and recruitment domain, suggesting inflammasome activation, was only detected in neurons. Consequently, increased production of active pro-inflammatory cytokines interleukin-1β and interleukin-18 were detected after hypoglossal nerve axotomy. Injury-sensitive hypoglossal neurons responded with a more pronounced NLRP3 upregulation than injury-resistant motor neurons of the oculomotor nucleus. We further demonstrated that the mitochondrial protector diazoxide was able to reduce NLRP3 upregulation in a post-operative treatment paradigm. Our results indicate that NLRP3 is activated in motoneurons following acute nerve injury. Blockade of NLRP3 activation might contribute to the previously observed anti-inflammatory and neuroprotective effects of diazoxide.

Motoneuronal inflammasome activation triggers excessive neuroinflammation and impedes regeneration after sciatic nerve injury

“…Although not primarily involved in immune reactions, neurons can express inflammasome receptors, including NLRP1, NLRC4 and AIM2 in response to different pathological conditions [ 44 ], but the role of NLRP3 in neurons has been less well investigated so far. However, besides our present findings and earlier studies [ 18 ], other results also suggest that neuronal NLRP3 can be involved in different pathologies, such as ischemic stroke [ 45 ], neurodegeneration [ 17 , 46 ], epilepsy [ 47 ], trauma and sterile inflammation [ 48 , 49 ]. Therefore, although microglia and astrocytes are considered the main resident cells of inflammasome activation in the CNS [ 50 ], there is increasing evidence suggesting that neurons are not only innocent bystanders in inflammatory processes and NLRP3 inflammasomes can be activated in these cells as well.…”

“…The quantification method was previously used and described by our laboratory [ 18 , 22 ], based on an interactive macro for the Image-Pro Plus image analysis software (RRID:SCR_016879, Media Cybernetics, Rockville, MD, USA). Briefly, 8 spinal cord sections for each groups were stained for Iba1 and glial fibrillary acidic protein (GFAP) with DAB-based IHC from each animal ( N = 4 animals/group).…”

“…Although NLRP3 activation has been described in different neurodegenerative conditions [ 12 , 13 ] and observed in various cell types of the central nervous system (CNS), including astrocytes, microglia and neurons [ 14 – 17 ], our understanding on the exact mechanism of action and the possibilities for therapeutical interventions is still limited. Previously, we described the motoneuron-specific upregulation of NLRP3 in the brainstem following hypoglossal nerve axotomy, accompanied by increased levels of mature IL-1β [ 18 ]. Here, we aimed at understanding the role of NLRP3 inflammasome activation in sciatic nerve injury.…”

Focus on the role of mitochondria in NLRP3 inflammasome activation: A prospective target for the treatment of ischemic stroke (Review)

“…Indeed, mitochondrial dysfunction plays a pivotal role in the initiation and activation of the NLRP3 inflammasome ( 210 ). Diazoxide prohibits NLRP3 inflammasome activation to prevent inflammation ( 211 ). In addition, diazoxide improves mitochondrial dysfunction following ORG/R in primary microglia BV2 cell by preventing mitochondrial depolarization and the opening of MPTP to inhibit NLRP3 inflammasome activation ( 212 ).…”

Cerebral Pericytes and Endothelial Cells Communicate through Inflammasome-Dependent Signals

“…Besides infiltrating cells of the innate and adaptive immune systems, resident cells of the brain also participate in the initiation and propagation of inflammatory reactions. Under inflammatory conditions, all cells of the NVU may become activated, including CECs, pericytes, glial cells (microglia and astrocytes) [ 25 ], and even neurons [ 27 ]. Notably, implication of cerebral vessels has two main aspects: BBB opening and cytokine secretion.…”