Several
studies have shown that liver fibrosis progresses more rapidly in HIV-HCV
coinfected people compared to those with hepatitis
C alone, though some research suggests this is less of a concern for patients
with well-controlled HIV disease and well-preserved CD4
cell counts.
At the 15th Conference on Retroviruses
and Opportunistic Infections this week in Boston, researchers from Mt Sinai
School of Medicine in New York City presented data that shed further light on
possible mechanisms underlying this phenomenon.
"Fibrosis
progression correlates with HIV viremia suggesting a direct role of HIV in liver
fibrogenesis," they noted as background. "CCR5 and CXCR4, the 2 major
co-receptors required for HIV entry into cells, are expressed on hepatic stellate
cells, the cell central to the fibrotic process."
The
investigators concluded a laboratory study to examine whether HIV enters hepatic
stellate cells and actively replicates, and to characterize the effect of HIV
overall and the HIV envelope gp120 on stellate cell biology.
They first
assessed the capacity of 2 strains of HIV - CXCR4-tropic HIV IIIB and CCR5-tropic
HIV Bal -- to infect stellate cells using an enzyme-linked immunosorbent assay
(ELISA) for supernatant p24 (an indicator of active HIV replication). LX2 cells,
a human hepatic stellate cell line, were then infected with these HIV strains
and washed to remove unbound virus. Significant concentrations of p24 (>2 ng/mL)
were detected on all days through day 7.
Since CXCR4-tropic HIV strains
predominate later in the course of HIV disease -- coincident with chronic liver
disease in HIV-HCV coinfected patients - the researchers next examined whether
HIV IIIB infects primary human hepatic stellate cells (passage #3) and replicates,
using the p24 assay and qRT-PCR for unspliced and multiply-spliced HIV-1 RNA.
The
detection of p24 (>8 ng/mL) associated with intracellular unspliced and multi-spliced
HIV suggests active replication (confirmed by sequencing MS HIV-1). The ability
of HIV to infect hepatic stellate cells was confirmed by challenging the cells
with a recombinant HIV expressing GFP in place of the early gene nef. The finding
of GFP-positive cells indicates HIV entry and early gene expression. Because HIV
infection may be either CD4-dependent or -independent, CD4 expression by hepatic
stellate cells was documented by immunofluorescence.
Results
•
CD4-blocking experiments revealed that HIV
IIIB entry into hepatic stellate cells was CD4-independent.
•
HIV infection promoted hepatic stellate cell
activation, since qRT-PCR demonstrated a 1.6-fold increase in collagen I (P <
0.0001) and a 1.5-fold increase in alpha-SMA mRNA (P < 0.0001).
•
Incubation with either monomeric gp120 (X4)
or AT-2 treated X4 (oligomeric gp120) for 1 to 24 hours resulted in 2.1-fold (P
< 0.007) and 1.4-fold (P < 0.004) increases in collagen I mRNA levels, respectively.
Conclusion
"HIV
enters and actively replicates within hepatic stellate cells independent of CD4,"
the investigators concluded. "Both viral entry as well as exposure of cells
to viral envelope glycoproteins can promote activation and collagen induction
in hepatic stellate cells." They added that, "These results suggest
that direct infection or env-mediated activation of hepatic stellate cells may
contribute to rapid development of fibrosis in patients coinfected with HIV/HCV."
Mt
Sinai School of Medicine, New York, NY.
2/5/08
Reference A
Tuyama, F Hong, A Mosoian, and others. HIV Entry and Replication in Stellate Cells
Promotes Cellular Activation and Fibrogenesis: Implications for Hepatic Fibrosis
in HIV/HCV Co-infection. CROI 2008. Boston, MA. February 3-6, 2008. Abstract 57.
HIV
Entry into Hepatic Stellate Cells Promotes Liver Fibrosis Progression
