. Insulin degrading enzyme activity selectively decreases in the hippocampal formation of cases at high risk to develop Alzheimer's disease. Neurobiol Aging. 2007 Jun;28(6):824-30. PubMed.

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  1. The authors demonstrate a potential role of IDE, direct or indirect, in Abeta metabolism. It is however hard to understand why other proteases involved in Abeta metabolism such as BACE-1, neprilysin, or ECE was not quantified using the same samples. I also recommend Zhao et al. eximine the quantity of AICD because AICD is a far better substrate for IDE than any other protein thus far reported.

  2. I really like this paper and think it is quite important. However, some caution should be given to the interpretation of "membrane-associated" IDE. In our experience, most membrane purification protocols actually end up purifying largely mitochondrial IDE, a pool that is generated from alternative translation initiation (Leissring et al., 2004). In fact, rigorous washing with bicarbonate and sonication removes all of the IDE in the "membrane fraction," suggesting that the IDE is actually in the inner matrix of the mitochondrion (see Farris et al., 2005).

    Nonetheless, this finding may be of high significance itself, if mitochondrial IDE actually plays some protective role in AD, a hypothesis we are currently investigating. Also, it is very likely that the levels of mitochondrial IDE track with cytosolic and other pools of IDE.

    References:

    . Alternative splicing of human insulin-degrading enzyme yields a novel isoform with a decreased ability to degrade insulin and amyloid beta-protein. Biochemistry. 2005 May 3;44(17):6513-25. PubMed.

    . Alternative translation initiation generates a novel isoform of insulin-degrading enzyme targeted to mitochondria. Biochem J. 2004 Nov 1;383(Pt. 3):439-46. PubMed.

    View all comments by Malcolm Leissring
  3. This elegant voxel-based morphometric study demonstrates white matter degeneration of the anteromedial parahippocampal gyrus. The authors have attributed these changes, at least in part, to degeneration of the perforant pathway connecting the entorhinal cortex to the CA1 and dentate gyrus of the hippocampus. Consistent with these findings, our group recently demonstrated preferential atrophy of the CA1 in amnestic mild cognitive impairment patients who progress to Alzheimer disease.

    References:

    . Conversion of mild cognitive impairment to Alzheimer disease predicted by hippocampal atrophy maps. Arch Neurol. 2006 May;63(5):693-9. PubMed.

    View all comments by Liana Apostolova
  4. Neuronal Loss Specific to Hippocampus in AD
    Regional specificity of neuronal loss in Alzheimer disease was a long observed but unexplained topic, wherein many explanations have been put forward in the recent past. The recent report of Zhao et al., 2006, is an excellent attempt to explain why there is a hippocampal-specific neurodegeneration-related change (e.g., the B to Z transition in the DNA conformation) in the hippocampus of moderately and severely affected Alzheimer disease patients. Earlier, Sugaya et al., 1997, reported the topographic association between DNA fragmentation in the hippocampus and Alzheimer disease neuropathology. Zhao et al., 2006, seem to prove that decreased IDE level in hippocampus is related to progressive clinical dementia, but how neuronal abnormalities specific to the hippocampus lead to detectable alteration in IDE is still not clear.

    References:

    . First evidence to show the topological change of DNA from B-dNA to Z-DNA conformation in the hippocampus of Alzheimer's brain. Neuromolecular Med. 2002;2(3):289-97. PubMed.

    . Topographic associations between DNA fragmentation and Alzheimer's disease neuropathology in the hippocampus. Neurochem Int. 1997 Aug;31(2):275-81. PubMed.

    View all comments by K.S. Jagannatha Rao

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  1. MCI—Hippocampal IDE, Parahippocampal White Matter in Decline