Influence of mitochondrial enzyme deficiency on adult neurogenesis in mouse models of neurodegenerative diseases

Mitochondrial defects including reduction of a key mitochondrial tricarboxylic acid cycle enzyme alpha-ketoglutarate-dehydrogenase complex (KGDHC) are characteristic of many neurodegenerative diseases. KGDHC consists of alpha-ketoglutarate dehydrogenase, dihydrolipoyl succinyltransferase (E2k), and dihydrolipoamide dehydrogenase (Dld) subunits. We investigated whether Dld or E2k deficiency influences adult brain neurogenesis using immunohistochemistry for the immature neuron markers, doublecortin (Dcx) and polysialic acid-neural cell adhesion molecule, as well as a marker for proliferation, proliferating cell nuclear antigen (PCNA). Both Dld- and E2k-deficient mice showed reduced Dcx-positive neuroblasts in the subgranular zone (SGZ) of the hippocampal dentate gyrus compared with wild-type mice. In the E2k knockout mice, increased immunoreactivity for the lipid peroxidation marker, malondialdehyde occurred in the SGZ. These alterations did not occur in the subventricular zone (SVZ). PCNA staining revealed decreased proliferation in the SGZ of E2k-deficient mice. In a transgenic mouse model of Alzheimer's disease, Dcx-positive cells in the SGZ were also reduced compared with wild type, but Dld deficiency did not exacerbate the reduction. In the malonate lesion model of Huntington's disease, Dld deficiency did not alter the lesion-induced increase and migration of Dcx-positive cells from the SVZ into the ipsilateral striatum. Thus, the KGDHC subunit deficiencies associated with elevated lipid peroxidation selectively reduced the number of neuroblasts and proliferating cells in the hippocampal neurogenic zone. However, these mitochondrial defects neither exacerbated certain pathological conditions, such as amyloid precursor protein (APP) mutation-induced reduction of SGZ neuroblasts, nor inhibited malonate-induced migration of SVZ neuroblasts. Our findings support the view that mitochondrial dysfunction can influence the number of neural progenitor cells in the hippocampus of adult mice.

Automated laser-scanning-microbeam fluorescence/Raman image analysis of human lens with multichannel detection: evidence for metabolic production of a green fluorophor

A laser-microprobe fluorescence/Raman spectrometer with a 700-channel detector has been constructed and applied to the collection of data on the distribution of a green fluorophor throughout the exposed area of a human lens sectioned along the visual axis. The area (approximately 6.5 X 9.5 mm) covering the lens section was scanned automatically by the microprobe programmed to measure the fluorescence intensity at 1200 data points. The spectrometer output was accumulated in a microcomputer and displayed as a three-dimensional perspective view showing the fluorescence intensity at each point on the grid. The method permits the precise and detailed mapping at high resolution of the spatial distribution of a fluorophor or Raman-emissive constituent in a plane of the frozen lens to give results not obtainable by any other feasible procedure. The green fluorophor (441.6 nm, excitation wavelength; 520 nm, peak emission wavelength) has a distribution indicating a metabolic rather than a photochemical mode of production. Moreover, the lower level of fluorophor in the anterior segment suggests the existence of mechanisms in the anterior cortex (including the epithelium) that reduce significantly the accumulation of fluorophor. Such distribution studies are invaluable in clarifying metabolic interrelationships among the different zones of the lens, including especially photochemical reactions postulated to involve the effect of daylight on the lens in human subjects.