Abstract
Neuronal active Caspase-6 (Casp6) is associated with Alzheimer disease (AD), cognitive impairment, and axonal degeneration. Caspase-1 (Casp1) can activate Casp6 but the expression and functionality of Casp1-activating inflammasomes has not been well-defined in human neurons. Here, we show that primary cultures of human CNS neurons expressed functional Nod-like receptor protein 1 (NLRP1), absent in melanoma 2, and ICE protease activating factor, but not the NLRP3, inflammasome receptor components. NLRP1 neutralizing antibodies in a cell-free system, and NLRP1 siRNAs in neurons hampered stress-induced Casp1 activation. NLRP1 and Casp1 siRNAs also abolished stress-induced Casp6 activation in neurons. The functionality of the NLRP1 inflammasome in serum-deprived neurons was also demonstrated by NLRP1 siRNA-mediated inhibition of speck formation of the apoptosis-associated speck-like protein containing a caspase recruitment domain conjugated to green fluorescent protein. These results indicated a novel stress-induced intraneuronal NLRP1/Casp1/Casp6 pathway. Lipopolysaccharide induced Casp1 and Casp6 activation in wild-type mice brain cortex, but not in that of Nlrp1−/− and Casp1−/− mice. NLRP1 immunopositive neurons were increased 25- to 30-fold in AD brains compared with non-AD brains. NLRP1 immunoreactivity in these neurons co-localized with Casp6 activity. Furthermore, the NLRP1/Casp1/Casp6 pathway increased amyloid beta peptide 42 ratio in serum-deprived neurons. Therefore, CNS human neurons express functional NLRP1 inflammasomes, which activate Casp1 and subsequently Casp6, thus revealing a fundamental mechanism linking intraneuronal inflammasome activation to Casp1-generated interleukin-1-β-mediated neuroinflammation and Casp6-mediated axonal degeneration.
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Abbreviations
- Aβ:
-
amyloid beta peptide
- AD:
-
Alzheimer disease
- AIM2:
-
absent in melanoma 2
- ASC:
-
apoptosis speck-like protein containing a caspase recruitment domain
- BzATP:
-
benzylated ATP
- BBG:
-
Brilliant Blue G
- CA1:
-
Cornus ammonis region 1
- Casp1:
-
Caspase-1
- Casp6:
-
Caspase-6
- CD68:
-
cluster of differentiation 68
- DAMP:
-
danger-associated molecular patterns
- FDU:
-
fluorodeoxyuridine
- GFAP:
-
glial fibrillary acidic protein
- IL-1β:
-
Interleukin-1-beta
- IPAF-1:
-
ICE protease activating factor
- MAP2:
-
microtubule-associated protein 2
- MDP:
-
muramyl dipeptide
- NLRP1:
-
Nod-like receptor protein 1
- NLRP3:
-
Nod-like receptor protein 3
- NSAID:
-
non-steroidal anti-inflammatory drugs
- PAMP:
-
pathogen-associated molecular patterns
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Acknowledgements
We thank Marc-André Déry for generating the ASC-GFP construct. The Canadian Foundation of Innovation, Canadian Institutes of Health Research (CIHR) MOP-243413-BCA-CGAG-45097, and the JGH Foundation (ALB), and NIH Grant P30 AG010133 (BG) supported this work. Dr. Vikas Kaushal was a recipient of McGill’s CIHR Neuroinflammation Training Program award (2010-2012); Prateep Pakavathkumar is the recipient of a Fonds de recherche Québec-Santé scholarship (2011–2013) and the FRSQ-Alzheimer Society of Canada doctoral award (2014–2016).
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Kaushal, V., Dye, R., Pakavathkumar, P. et al. Neuronal NLRP1 inflammasome activation of Caspase-1 coordinately regulates inflammatory interleukin-1-beta production and axonal degeneration-associated Caspase-6 activation. Cell Death Differ 22, 1676–1686 (2015). https://doi.org/10.1038/cdd.2015.16
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DOI: https://doi.org/10.1038/cdd.2015.16
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