Molecular Imaging of neuroHIv using animals models of disease

使用转基因大鼠的研究摘要： 1.在以往文献研究的基础上，我们曾期望在HIV转基因大鼠的脑内发现显著的小胶质细胞激活，并且这种激活会随着年龄的增长而增加。为了开发一种成像生物标记物，我们决定在三个不同的年龄组：青年、中年和老年(3、9和16个月大)进行18F-DPA714 PET成像。我们在每个年龄段将TG与年龄匹配的对照组进行比较。我们使用喹啉酸动物模型作为阳性对照。与我们的预期相反，我们只观察到TG大鼠的平均SUVc(经体重校正的SUV)值比年龄匹配的WT大鼠略高，这在任何地区或年龄组都没有达到统计学意义。同样，与年龄匹配的对照组相比，不同年龄的TG大鼠大脑中Iba1的免疫荧光染色没有显著差异。我们通过测量TG和年龄匹配的对照组脑裂解物中的细胞因子水平进一步证实了我们的发现，并发现它们是相似的。 2.我们进一步对不同年龄的TG大鼠脑进行了详细的免疫组织化学评价，并与年龄匹配的WT大鼠脑进行了比较。TG大鼠脑内最显著的发现是GFAP染色进行性消失，提示星形胶质细胞功能障碍/损伤，纹状体和穹隆体随年龄的增长而显著恶化。除星形细胞胞体明显减少外，TG大鼠星形胶质细胞突起也有一定程度的丢失/减弱。相比之下，小胶质细胞似乎在早期(1-3月龄)略有激活，但随着动物年龄的增长，这种激活程度有所下降。 3.尽管与WT大鼠相比，TG大鼠存在运动和行为障碍，但18F-FDG-PET的纵向和横断面差异在两组大鼠之间没有达到显著差异。在最后一次FDG成像后，在相同的动物身上进行的14C-DG放射自显影测量的葡萄糖代谢没有显著差异，进一步证实了这些结果。然而，我们使用18F-FolyPride PET成像观察到，与年龄匹配的对照组相比，成年TG大鼠脑中背侧纹状体(DS)和腹侧纹状体(VS)的D2/3受体显著减少。在较年轻的动物中，D2/3受体的减少仅在DS中显著，这表明存在神经/多巴胺能损伤的持续趋势，并随着年龄的增长而恶化。我们在免疫荧光上看到的TH减少(多巴胺合成的早期步骤)和在PET上看到的突触后受体密度降低(D2/3)相结合，支持在这个动物模型中多巴胺能神经元功能障碍/丢失的概念。我们的结论是，18F-FolyPride可以检测到TG大鼠的多巴胺能系统功能障碍，并可能成为评价神经保护措施的一个合理的成像生物标志物。 4.我们正在评估氧化应激在TG大鼠神经病理中的作用。 使用受SIV感染的猴子的研究摘要： 1.我们假设在SIV感染的急性期(相对于接种前扫描)，11C-DASB结合会减少，并可能在ART治疗后逆转。我们使用的是感染了神经毒力SIV毒株SIVsm804E的恒河猴。我们用11C-DASB在猴体内进行了免疫前后的靶向SERT的PET成像，以检测SIV感染下的5-羟色胺能系统状态。当我们将最后一次时间点成像(11C-DASB PET)与接种前的扫描进行比较时，我们发现大多数感染SIV的动物(7只动物中有6只)5-羟色胺转运体(SERT)水平/表达增加。目前，我们正在研究病毒对SERT表达的潜在表观遗传效应。 2.我们还在以外周病毒血症和疾病控制(模拟最佳治疗的HIV+患者)为协变量，研究SIV感染猴子的神经炎性变化的演变。为了实现这一目标，我们正在使用18F-DPA-714作为体内感染SIV的猴子体内小胶质细胞激活(神经炎症)的PET成像生物标志物。我们正在对接种前和接种后、治疗前后进行成像。与我们预期的不同，我们没有发现18F-DPA714 PET成像在猴子体内的转位蛋白表达增加(5/5在接种后显示结合减少而不是增加)。我们认为这与脑脊液病毒载量测量的中枢神经系统受累的严重程度有关。在治疗和中断治疗后，我们现在继续进行影像研究。

Summary of studies using the transgenic rats: 1. Based on previous studies in the literature we had expected to find significant microglial activation in the brains of the HIV transgenic rats which would increase with age. In order to develop an imaging biomarker we decided to use 18F-DPA714 PET imaging at three different age groups: young, middle aged and old (3, 9 and 16 month-old). We compared Tg to age matched controls at each of those ages. We used the quinolinic acid animal model as a positive control. Contrary to our expectations, we observed only slightly higher mean SUVc (SUV corrected for weight) values in the Tg rats compared to age-matched WT rats, which did not reach statistical significance in any region or age group. Similarly, immunofluorescent staining for Iba1 in the Tg rat brains at different ages showed no significant differences when compared to age matched controls. We further confirmed our findings by measuring cytokine levels in the brain lysates of Tg and age-matched controls and found them to be similar. 2. We further performed a detailed immunohistochemical evaluation of the Tg rat brains at different ages, and compared to age-matched WT rat brains. The most significant finding in the Tg rat brains was progressive loss of GFAP staining, suggesting astrocytic dysfunction/damage, significantly worsening with age in the striatum and corpus callosum. Besides decreased conspicuity of the astrocytic cell bodies, there was definite loss/attenuation of astroctytic processes in the Tg rats. In comparison, the microglia appeared to be slightly activated early-on (1-3 months of age), but this decreased as the animals got older. 3. Despite the motor and behavioral deficits we saw in the Tg rat compared to WT rats, the longitudinal and cross-sectional differences by 18F-FDG -PET did not reach significance between the two cohorts. These results were further confirmed by the lack of significant difference in glucose metabolism as measured by 14C-DG-autoradiography performed on the same animals after the last FDG imaging sessions. We observed however significantly decreased D2/3 receptors in the adult Tg rat brains compared to age-matched controls, in both the dorsal striatum (DS) and ventral striatum (VS), using 18F-fallypride PET imaging. In younger animals, the decrease in D2/3 receptors was only significant in the DS, suggesting that there was a continuous trend of neurological/dopaminergic damage that worsens with age. The combination of decreased TH that we saw on immunofluorescence (early step in dopamine synthesis) and decreased post synaptic receptor density (D2/3) seen on PET supports the notion of dopaminergic neuronal dysfunction/loss in this animal model. We concluded that 18F-fallypride can detect dopaminergic system dysfunction in the Tg rats and may be a reasonable imaging biomarker to evaluate neuroprotective approaches. 4. We are now evaluating the role of oxidative stress in the neuropathology of the tg rat. Summary of studies using the SIV infected monkeys: 1. We hypothesized that 11C-DASB binding will decrease in the acute phase of SIV infection (with respect to pre-inoculation scans) and will potentially reverse with ART treatment. We are using rhesus macaques infected with the neurovirulent SIV strain, SIVsm804E. We are performing PET imaging targeting SERT using 11C-DASB in monkeys before and after inoculation, in order to detect serotonergic system status under the effect of SIV infection. We found that the serotonin transporter (SERT) levels/expression increased in most animals (6 out of 7) who were infected with SIV when we compared the last time point imaging (11C-DASB PET) to the preinoculation scans. We are investigating a potential epigenetic effect of the virus on SERT expression at this point. 2. We are also investigating the evolution of neuroinflammatory changes in the SIV-infected monkeys using peripheral viremia and disease control (simulating optimally treated HIV+ patients) as covariants. Towards this goal, we are using 18F-DPA-714 as PET imaging biomarker of microglial activation (neuroinflammation), in vivo, in the SIV-infected monkeys. We are imaging pre-inoculation as well as post-inoculation, before and after treatment. Unlike what we expected, we did not find increased translocator protein expression using 18F-DPA714 PET imaging in the monkeys (5 out 5 showing decreased binding after inoculation rather than increased binding). We believe this correlates to the severity of CNS involvement as measured by CSF viral load. We are now continuing the imaging study after treatment and interruption of treatment.