Elucidating mechanisms of HIV-1 intron-containing RNA-induced inflammatory response
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Abstract
Human Immunodeficiency Virus type 1 (HIV-1) is the causative agent of AIDS in humans. While antiretroviral therapy (ART) has been successful in reducing viremia to undetectable levels and significantly extending the lifespan of people living with HIV (PWH), these individuals continue to experience chronic inflammation and immune activation, referred to as ‘inflammaging,’ leading to the development of age-associated co-morbidities such as cardiovascular disease, neurodegenerative disorders, and certain types of cancers. These disorders are increasingly observed in older PWH, compared to age-matched uninfected individuals. Chronic immune activation and inflammation are highly predictive of these age-associated co-morbidities and increased risk of mortality, thus necessitating studies to identify novel therapeutic targets to alleviate this ‘inflammaging” phenotype. HIV-1 infection of long-lived cells, such as memory CD4+ T cells and tissue-resident macrophages, facilitates virus persistence, primarily due to the ability of the virus to integrate its genetic material within the human chromosomal DNA. Furthermore, even in the absence of viral replication, persistence of transcriptionally competent HIV-1 reservoirs and expression of HIV-1 RNA are hypothesized to be important mediators of persistent, low grade innate immune activation, that compounds the inflammaging phenotype in older PWH, though mechanisms remain unclear.This dissertation aims to identify mechanisms of HIV-1 RNA sensing in macrophages and CD4+ T cells and their contribution to chronic inflammation in older PWH. Previous work from our group has demonstrated that de novo transcribed HIV-1 intron containing RNA (icRNA) results in the secretion of pro-inflammatory cytokines and type I interferon (IFN) in a mitochondrial antiviral signaling (MAVS) dependent manner. In this study, I demonstrate an essential role of melanoma differentiation-associated protein 5 (MDA5) in sensing HIV-1 icRNA and promoting MAVS-dependent interferon regulatory factor 5 (IRF5) activation in macrophages. Suppression of MDA5, but not Retinoic acid-inducible gene (RIG-I) expression nor disruption of endosomal toll-like receptor (TLR) pathway, abrogated HIV-1 icRNA-induced type I IFN responses and interferon gamma-induced protein 10 (IP-10) expression in macrophages. Furthermore, induction of IP-10 in macrophages upon HIV-1 icRNA sensing by MDA5 was uniquely dependent on IRF5. Additionally, monocytes and monocyte-derived macrophages (MDMs) from older (>50 years) individuals exhibit constitutively higher levels of IRF5 expression compared to younger (<35 years) individuals, and HIV-1 icRNA induced IP-10 expression was significantly enhanced in older MDMs, which was attenuated upon ablation of IRF5 expression. These findings suggest that IRF5 functions as a major mediator of pro-inflammatory response downstream of MDA5-dependent HIV-1 icRNA sensing in MDMs and that IRF5 dysregulation in aged individuals might contribute to the inflammaging phenotype.
Interestingly, the mechanism for icRNA sensing appears to be different in CD4+ T cells. My preliminary findings indicate that while cytoplasmic HIV-1 icRNA expression induces IRF5-dependent IFN secretion in virus-infected T cells, surprisingly MDA5 was not required, suggesting presence of an alternate cytoplasmic RNA sensing mechanism that mediates HIV-1 icRNA-induced innate response in T cells. These findings suggest that IRF5 is an important regulator of the innate immune response to HIV-1 icRNA expression in HIV-infected macrophages and T cells, and represents a promising target for novel therapeutics to alleviate the ‘inflammaging’ phenotype increasingly observed in older PWH.
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2025