icon- folder.gif   Conference Reports for NATAP  
  16th CROI
Conference on Retroviruses and Opportunistic Infections Montreal, Canada
February 8-11, 2009
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HIV-1 Induces Apoptosis in primary Osteoblasts: an Alternative Mechanism in the Osteopenia/Osteoporosis Development
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Reported by Jules Levin
CROI 2009 Feb 8-12 Montreal
Marco Borderi*1, Davide Gibellini2, Elisa De Crignis2, Cristina Ponti3, Laura Cimatti2, Carlo Biagetti1, Livia Tampellini1, Maria Carla Re2, and Francesco Chiodo1 Infectious Diseases Inst, Bologna, Italy 1 - Dept of Clin and Experimental Med, Bologna, Italy 2 - and University of Trieste, Trieste, Italy3
This report demonstrated that:
1) HIV-1, heat activated and recombinant gp120 triggered apoptosis in primary osteoblasts.
2) HIV-1 does not infect osteoblasts and HOBIT cells and then the apoptosis induction is related to gp120/cell membrane interaction
3) TNFa is secreted after HIV-1 challenge and neutralizing anti-TNFa antibody tackled the HIV-1 related apoptosis both in osteoblasts and HOBIT cells suggesting a direct role of TNFa in apoptosis induction
Our data showed that HIV-1 significantly induced osteoblasts or HOBIT cells towards apoptosis at 48-96 hours after challenge. Interestingly, in our experimental conditions, programmed cell death was linked to engagement between gp120 and cell membrane. Heat-inactivated HIV-1 or recombinant gp120 elicited apoptosis activation of primary osteoblasts and HOBIT cells as when infectious HIV-1 was employed.
Both HOBIT and primary osteoblasts showed the presence of all three mRNAs, but when membrane protein expressions were analyzed, we observed a weak detection of CD4 and CXCR4 in a small percentage of HOBIT and primary osteoblasts, whereas CCR5 was consistently expressed in the 15% of these cells.
Background: Several HIV-1 infected patients show bone loss and osteopenia/osteoporosis. The mechanisms underlying this degenerative process are unsettled and the interaction between HIV-1 and osteoblasts/osteoclasts cross-talk regulation is still unknown. We analysed whether the primary osteoblasts are permissive to different HIV-1 strains infection and HIV-1 interaction with cell membrane by gp120 to study the mechanisms involved in the bone loss in HIV-1 infection.
Methods: Human hipbone osteoblasts, obtained from commercial sources or isolated from HIV-1 negative subjects (enrolled after giving their informed consent), were challenged by HIV-1 X4 and R5 classical strains. HIV-1 proviral DNA and viral RNA load were determined by PCR and RT- PCR respectively. Flow cytometry procedures were used for apoptosis and membrane markers analysis whereas TNF-_supernatant analysis was performed by commercial kit.
Results: Human osteoblasts, challenged by HIV-1, did not show any positive signal of active (RNA load) or latent (DNA viral load) infection. On the other hand, HIV-1, heat-inactivated HIV-1 and HIV-1 gp120 treatment induced a significant apoptotic activation at 72-96 hours (p<0.01), that is tackled by soluble CD4 treatment, suggesting an interaction between gp120 and cell membrane proteins. CD4, CXCR4 and CCR5 mRNAs were detectable even though CD4 and CXR4 proteins were expressed at very low density and in few cells, whereas CCR5 fig 2B protein was significantly more expressed, suggesting a binding between CD4 and HIV-1 gp120 in absence of HIV entry. As observed in CD34+ hematopoietic cells this phenomenum might be due to a possible lack of functional association between receptor and co-receptor. Further experiments demonstrated that HIV-1, heat-inactivated HIV-1 and HIV-1 gp120 treatment were able to induce TNF-α (a well- known apoptosis-inducer in the osteoblasts) mRNA and a protein increase at 24-96 hours. Moreover, anti-TNF-_pre-treatment tackled the apoptosis induction suggesting a direct role of TNF-αin the HIV-1 activation of apoptotic process.
Conclusions: These results indicate that HIV-1 triggers apoptosis in osteoblasts without infection but through gp120 interaction with cell membrane suggesting a novel mechanism in the HIV-1 related impairment of the bone mass structure homeostasis.