Monocytes and their mitochondria in Alzheimer's disease

Mitochondrial ultra structure appears abnormal in human neurons in end stage Alzheimer's disease (AD). Alterations in cristae structure and fragmented mitochondria have been reported. We observe a similar loss of mitochondrial cristae structure in a blood cell model induced by diazoxide (Dz), a known K-ATP channel activator.;In the blood cell model, Dz altered mitochondrial structure and also protected the cells from a potent inducer of apoptosis. The apoptotic protection of Dz extended to a neuronal cell model in their un-differentiated state with no Dz protection afforded after the neuronal cells differentiated. Whether or not Dz altered mitochondrial structure in the neuronal model was not determined.;The dual effects of Dz, on mitochondrial structure and on apoptotic protection, appear to occur on different time-scales and it was not clear if the Dz effect on mitochondrial structure was related to Dz apoptotic protection.;Primary blood cells were examined to investigate both effects of Dz. Monocytes could be protected from apoptosis with Dz pre-treatment and monocyte mitochondrial structure was altered in a dose dependent manner within the Dz one-hour pretreatment period. The Dz dose required to confer apoptotic protection produced slight alterations in mitochondrial structure but a higher dose produced mitochondrial structure like mitochondrial structure previously reported in neurons of AD patients.;Since mitochondrial structure in primary blood cells could be induced to appear identical to mitochondria in AD neurons and blood cells are affected in AD, our goal became to determine if morphological variation would be evident in AD blood cells and/or their mitochondria. The hypothesis that structural anomalies exist in tissue outside the brain in AD was tested by close examination of blood cells, specifically monocytes, from human donors.;Whole blood was donated and peripheral blood mononuclear cells (PBMCs) were isolated. An aliquot of PBMCs was fixed immediately for transmission electron microscopy (TEM) and then viewed to identify and count monocytes. ImageJ, image analysis software, was used for all measurements in TEM pictures including the number of native monocytes per grid space, the primary monocyte size, and the mitochondrial number/size/circularity per cell.;Macrophages were selected from the remaining PBMCs by plating and in vitro differentiated for seven days. These monocyte-derived macrophages (MDMs) were counted for each donor sample.;All samples were collected and analyzed blind, without any specific knowledge of the donors. After case identification, the AD data was compared to aged control (no-clinical sign of AD) or "NC" data.;The AD donors display a two-fold increase in native monocytes over NC donors. The AD native monocytes were on average 70% larger with 50% more individual mitochondria per cell than those isolated from NC donors. The AD monocyte mitochondria were smaller and more circular in the majority of the AD cells, indicative of fragmented mitochondria.;Even though the number of AD native monocytes was consistently twice that of NC native monocytes in our TEM space grid count, when plated in vitro the number of MDMs was 25% less in AD compared to NC. In addition, the number of AD MDMs shows a significant positive correlation with the donor's mini mental-state examine (MMSE) score, a measure of cognitive ability.;These data support the hypothesis that structural abnormalities exist in tissue outside the brain in AD monocytes and their mitochondria. These structural clues combined with emergent research involving monocyte/macrophage function in neurodegeneration may prove useful as a non-invasive tool in following AD progression.