To our knowledge, this is the first study that assessed mitochondrial RNA expression along with mtDNA levels in the fat tissue of HIV infected subjects with lipoatrophy and which included an ART naïve group as well as an HIV negative control group. Few prior studies have assessed the effects of ART on mtRNAs (11
), and only one (11
) was performed on HIV-infected subjects. In this report, we show that both mtRNA and mtDNA are significantly decreased in HIV infected adults with lipoatrophy when compared to either HIV-infected ART naïve group or an uninfected control group. Interestingly no differences were found between HIV+ ART-naïve group and HIV-negative controls, suggesting that these mitochondrial disturbances are the result of ART and not to HIV infection itself. Earlier reports have suggested that HIV infection itself might cause mtDNA decline in ART-naïve subjects, but this was shown mostly in peripheral blood mononuclear cells, and not in adipose tissue (15
). In this study, the different groups were closely matched by age. This matching is crucial for the success of any such trial aimed at studying the effect of HIV and/or treatment on mitochondrial indices in HIV infected adults since increasing age may be associated with more mitochondrial abnormalities (17
) which may significantly confound the study results in the absence of careful matching. Also, our HIV negative group had significantly higher BMI, which makes our results even stronger since obesity has been linked to mitochondrial abnormalities (18
), and therefore the higher BMI in our population may have attenuated the observed differences in mitochondrial abnormalities between the studied groups.
Mitochondrial DNA depletion in HIV infected treated subjects with lipoatrophy has been consistently described (1
). However, mitochondrial dysfunction is not always associated with mtDNA depletion (20
), and severe mtDNA depletion has been reported in asymptomatic subjects (22
). Thus, additional mechanisms for mitochondrial alterations in HIV beyond only mtDNA depletion are likely, as recently suggested (20
). To our knowledge only one prior small study assessed mtRNA levels in adipose tissue of 11 HIV+ patients with lipoatrophy and 7 HIV uninfected controls (11
). The mtRNA levels in that study were also reduced in HIV+ when compared to HIV negative controls, but no HIV+ group without lipoatrophy was included, making it impossible to differentiate between the effects of HIV infection versus those of ART. The importance of mtRNA alterations, independently of mtDNA depletion, has been suggested by prior cell culture work. Galluzzi et al have previously shown that NRTIs can induce a significant decrease in mtRNA levels in cell lines, even before any noticeable mtDNA depletion (12
). Similarly, d’Amati et al have shown a significant disruption of mitochondrial cristae and alteration of mtRNA, but no change in mtDNA levels after 4 weeks of AZT treatment of mouse muscle cells (13
). In our study, the lack of correlation between mtRNA alteration and mtDNA levels suggest that the alteration in transcription is not secondary to changes in mtDNA but is rather a primary effect of therapy. Interestingly, only the mitochondrial heavy chain transcripts, ND1 and CYTB, were decreased in HIV-infected treated subjects with lipoatrophy and not the light chain transcript ND6. This suggests that mitochondrial heavy strand transcription is affected but not light chain transcription. In addition, the fact that limb fat/BMI correlated with mtRNA but not mtDNA also suggests that mtRNA alteration may indeed be the primary mitochondrial alteration that only at times coexists with mtDNA depletion. The study reported by Mallon et al support this hypothesis (14
). In that study, Mallon reported a significant decrease in mtRNA production after 2 weeks of NRTI in healthy HIV uninfected adults (14
). This occurred before any changes in mtDNA levels of fat mass.
On regression analysis, only limb fat and limb fat adjusted to BMI (limb fat/BMI) correlated with all three mtRNA measurements while HIV disease factors like CD4 cell count and duration of HIV infection did not. This again supports our observation that the mtRNA alterations in HIV infected with lipoatrophy are linked to the use of antiretroviral therapy. The duration of thymidine NRTIs correlated with fat mtDNA levels although PI duration was also independently correlated. Limb fat/BMI did not correlate with mtDNA levels.
As expected, HIV-infected treated subjects with lipoatrophy had higher fasting triglycerides, cholesterol, HOMA-IR when compared to ART naïve. Additionally, correlation analysis showed that HDL cholesterol correlated with all three mitochondrial transcripts. Mitochondrial function is sensitive to fat (25
), insulin, and glucose levels (26
). The mitochondria maybe uncoupled due to the increased fat and this is corresponding with decreased transcription. Insulin resistance is associated with decreased ATP production. Thus, there maybe multiple etiologies for the mitochondrial dysfunction
One limitation of our study is the lack of HIV-infected treated control group without lipoatrophy. We have recently learned that it is difficult to fully exclude lipoatrophy by clinical assessment alone in HIV patients. Indeed, studies have shown that despite the lack of clinical diagnosis of lipoatrophy, HIV infected women and men have lower amount of peripheral fat when compared to gender- and age-matched HIV negative subjects (27
), suggesting that clinical lipoatrophy may only be the extreme form of peripheral fat loss in HIV patients and that the subclinical form may be more common than previously thought. Thus a group of HIV treated without lipoatrophy is challenging to enroll but would need to be explored in future studies. In addition, incorporating detailed mitochondrial indices in future ART-switch studies of subjects with lipoatrophy would be helpful in dissecting the effect of ART in general from that of lipoatrophy.
In summary, a significant decrease in mtDNA levels and in mtRNAs were found in HIV infected subjects on ART with lipoatrophy, but not in ART-naïve subjects. This strongly support that ART, and not HIV infection, play the major role in the generation of mitochondrial disturbances in HIV lipoatrophy. The correlation found between limb fat/BMI and mtRNA and not mtDNA, support the fact that mtRNA alteration, and not mtDNA depletion, may be the primary mitochondrial disturbance in HIV lipoatrophy.