Increase in TGF-β1 Can Lead to HIV Latency in Bronchial Cells
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HIV is a chronic viral disease that incapacitates the host’s immune system, leaving the person immunocompromised, and susceptible to further infection. The development of treatments like Combination antiretroviral therapy (cART) have been able to hinder the virus’ ability to replicate, showing some promise in combatting HIV.
One of the main problems with HIV is that it is extremely stealthy and illusive. Though cART may be successful at preventing HIV from multiplying, it can hide out and become active again down the road. This is called HIV latency, and it can lead to developing other health problems, particularly COPD, and asthma, which could prove to be deadly.
In a study out of Florida International University, a team of researchers sought to determine how HIV latency leads to lung problems on a molecular level, particularly in older HIV patients. They also took into consideration that many HIV positive people may also be smokers, which could further increase their risk for lung diseases.
Led by Dr. Srinivasan Chinnapaiyan, the team focused on a growth factor called TGF-β, and how HIV hijacks its function to create HIV reservoirs. TGF-β is involved in regulating cell growth and development, and is particularly involved in bronchial epithelial cell signaling. It was determined in a previous study that the combination of cigarette smoke and TGF-β lead to an increase in expression of CCR5—a coreceptor that HIV attaches to in order to gain entry to a cell.
They treated normal human bronchial epithelium (NHBE) cells ex-vivo with TGF-β for 16 hours. The cells were then infected with a strain of HIV, and were incubated for another 16 hours. They determined that TGF-β does indeed interfere with HIV transcription in its early stages.
To establish the link between TGF-β and HIV latency, they then performed an identical experiment, but this time the infected cells were treated with a combination of Bryostatin-2 and HMBA, two latency reactivating agents. After an incubation period of 8 days, they found via qRT-PCR that the presence of TGF-β does promote HIV latency through viral suppression.
A) NHBE cultures redifferentiated at the ALI were treated and infected. Culture supernatants were collected on day 8 for post-reactivation p24 analysis using p24 ELISA kit. (B) Total RNA was isolated and HIV transcripts were quantitated by qRT-PCR. TGF-β1 treatment suppresses HIV mRNA and this can be reversed with the combination of LRAs Bryostatin-2 and HMBA. TGF-β1 suppresses viral p24 and this corelates well with mRNA suppression.
The next order of business was to find out if TGF-β had any effect on a known HIV transcriptional repressor called BLIMP-1. This protein has demonstrated its ability to silence transcription by binding directly to the virus, or by recruiting histone deacetylases (HDACs) to tighten chromatin, making it inaccessible to transcriptional machinery.
In the same procedure as stated above, the NHBE cells were treated with TGF-β and infected with HIV. Additionally, on the 6th day of infection, they added Vorinostat—an HDAC inhibitor to some of the infected cells.
After 8 days, the team preformed a ChIP using the ChromaFlash High-Sensitivity ChIP Kit to determine if the direct binding of BLIMP-1 to the HIV had any effect on TGF-β levels. They then performed a qPCR using the EpiQuik Quantitative PCR Fast Kit to analyze the samples.
TGF-β1 mediates HIV suppression via BLIMP-1 and histone deacetylases. NHBE ALI cultures were treated with TGF-β1 or vehicle and infected. (a). NHBE ALI cultures from 4 different lungs; Another set was TGF-β1 treated and infected identically (b). Total RNA was isolated and analyzed for HIV LTR using qRT-PCR (c). TGF-β1 mediated HIV transcriptional suppression can be restored by HDACi suggesting a role of histone deacetylases in TGF-β1 mediated HIV latency. .
They found that treatment with TGF-β significantly increases BLIMP-1 in infected cells, effectively suppressing HIV transcription while simultaneously creating HIV reservoirs. Interestingly, the infected cells treated with Vorinostat but not TGF-β experienced increased HIV growth, suggestingthat HDACs are probably directly involved in the silencing of HIV transcription as well.
The data gathered in this study suggests TGF-β induces HIV latency, but doesn’t totally eradicate it. This can lead to the development of HIV reservoirs, which in turn leaves patients susceptible to further lung disease. Hopefully future research can continue to improve upon existing HIV treatments in the efforts of extending the health and life of people living with HIV.
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