Exploring the role of IL-32 in premature age-related cardiovascular diseases in HIV-infected individuals

Abstract Despite the introduction of combined antiretroviral therapy (cART), HIV infection continues to accelerate non-infectious comorbidities such as premature-age associated cardiovascular disease (CVD). However, only a subpopulation of HIV-infected and treated patients is prone to these complications. Therefore, it is important to understand the pathogenesis of these accelerated disorders and to identify predictive markers of premature CVD that can be used for early diagnosis and prevention strategies. In the current study, we investigated the potential use of the pro-inflammatory cytokine IL-32 as a biomarker for CVD. Human IL-32 is a key polyfunctional cytokine. Previous studies have attributed both intracellular anti-viral functions against HIV-1 but also immunosuppressive properties to this novel cytokine due to the induction of type I and type III interferons and through the creation of an environment conducive to HIV-1 replication, respectively. IL-32 is involved in several infectious and non-infectious pathologies with increased expression in various inflammatory autoimmune diseases, certain cancers, pulmonary diseases, and viral infections. It can induce other inflammatory cytokines such as IL-6, IL-8 and TNF-α. It is expressed in both immune and non-immune cells. However, IL-32 cell surface receptors have yet to be identified.  IL-32 expression can be induced by mitogens, bacteria and viruses.  IL-32 is encoded by a single gene that produce several isoforms by multiple splicing. These isoforms were recently described to exhibit distinct immune-regulatory potential: pro-inflammatory (α & γ), anti-inflammatory (β & θ), and regulatory (δ). Of note, IL-32δ is known to bind IL-32β and inhibits its anti-inflammatory functions. The contribution of these isoforms to infectious and inflammatory disease is poorly understood. Our group has previously shown that IL-32 is upregulated during HIV-1 infection and that it correlates with persistent inflammation and disease progression. Given that chronic inflammation is associated with CVD, a condition with increased prevalence in the HIV-infected population, we sought to characterize the role IL-32 in CVD progression.  Our results showed significantly high levels of total IL-32 (pool of all isoforms) in the plasma of HIV+ (cART-treated) individuals compared to non-infected controls. We were the first to show that there is a differential expression of IL-32 levels depending on sex and age in HIV infected individuals.  Infected women were found to have higher levels of IL-32 in their plasma, when compared to men. Furthermore, women under the age of 50 had significantly higher levels of IL-32 compared to women over 50, whereas the opposite was observed in men (although age-associated difference in this group did not reach statistical significance). At the transcriptional level, all IL-32 isoforms were highly expressed in HIV+ individuals compared to non-infected controls. By comparing IL-32 isoforms from treated subjects with cardiovascular imaging, we show that the ratio between certain IL-32 isoforms, particularly the D and beta isoforms (D/β ratio), positively and significantly correlates with the total atherosclerotic plaque volume of the coronary artery. Given the role of IL-32β in the induction of the anti-inflammatory cytokine IL-10, our data suggests a protective role for IL-32β against CVD but a deleterious role for IL-32D. Furthermore, our data showed that HIV infection selectively upregulates IL-32D early post-infection. Overall, the results of this study are the first to show that the ratio IL-32D/β can be used as a predictive biomarker for coronary artery plaque formation and CVD in HIV+ ART-treated subjects.  Keywords: HIV-1, Interleukin-32, CVD

Keyphrases: IL-32, HIV, Cardiovasular disease, Premature aging, cytokine, CVD, Interleukin-32