Background
With long-term survival of people living with HIV (PLH) increased rates of age-related diseases have been observed. Persistent immune activation in PLH and age-related chronic inflammation are hypothesized to be drivers for the development of such diseases. The NLRP3 inflammasome is a multiprotein complex that forms in response to stimulation of pattern recognition receptors by pathogen associated molecular patterns (PAMPs), or by Damage Associated Molecular Patterns (DAMPs). This complex mediates the cleavage of caspase-1, IL-1b and IL-18 to their active forms. Activation of the inflammasome requires a priming step (signal 1) that induces the TLR/NF-kB pathway, and a second step (signal 2), triggered by a PAMP/DAMP and leading to formation of the complex. There is evidence that the development of age-related diseases is related to dysregulated activation of the NLRP3 inflammasome and pathological production of IL-1b. However, significant knowledge gaps in the understanding of human NLRP3 function remain at the interface of HIV and aging.
Methods
We recruited young (21-40) and older (>60 years) HIV-positive and HIV-negative subjects (n=64). Blood was drawn and peripheral blood mononuclear cells were isolated for subsequent experiments.
Results
HIV-positive older subjects have increased inflammasome activation at baseline as demonstrated by higher levels of caspase-1, and higher levels of cleaved IL-1b, and IL-18 (flow cytometry). With LPS stimulation (signal one) we see decreased levels of cleaved IL-1b production via western blot in HIV-positive older adults as compared to HIV-negative older adults and HIV-positive young adults. When LPS stimulation (signal one) is examined via flow cytometry we see increased retention of cleaved IL-1b in the monocytes of HIV-negative young adults compared to HIV-negative and HIV-positive older adults. With signal two we see that HIV-positive older adults have decreased retention of cleaved IL-1b compared to HIV-negative young adults—suggesting differences in Gasdermin signaling. When inflammasome specks are examined (confocal microscopy) we see that HIV-positive older adults have increased number of specks when compared to HIV-negative young adults.
Conclusions
Overall, HIV-positive older adults have increased baseline activation of the inflammasome and subsequently a decreased ability to respond when exposed to PAMPs/DAMPs. The results noted allude to a dysregulation of Gasdermin signaling and inflammasome machinery in HIV-older adults.
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