| Popis: |
The misfolding and aggregation of proteins is the pathological hallmark of amyloid diseases including Alzheimer's disease (AD), familial amyloid polyneuropathy, and type 2 diabetes mellitus (T2DM). Insofar as the misfolding process results in the formation of pathogenic species, inhibition of misfolding is thought to be a promising approach to the prevention of the aforementioned diseases. Mitochondrial dysfunction has been implicated in many amyloid diseases suggesting an important mitochondrial role. Humanin and its derivatives are a novel class of mitochondrially-derived peptides with insulin sensitizing activity and various cytoprotective effects in AD and other disease model systems. Here we tested whether humanin can promote health in misfolding diseases by acting as a molecular chaperone that prevents amyloid misfolding. We tested whether islet amyloid polypeptide (IAPP), a peptide that misfolds and causes toxicity in T2DM, would be responsive to humanin. Using thioflavin T fluorescence we found that substoichiometric concentrations of the humanin-S14G analogue (HNG) potently inhibit the misfolding of hIAPP. As assessed by circular dichroism, HNG prevents misfolding by maintaining hIAPP in a predominantly random coil structure in solution. Unexpectedly, site-directed spin labeling of HNG in concert with electron paramagnetic resonance (EPR) revealed that HNG is capable of forming higher order complexes. Ongoing investigation into the potency of these higher order structures will test whether they participate in the inhibition of IAPP misfolding. Finally HNG appears to have biological effects including a partial attenuation of IAPP-mediated cytotoxicity and a reversal of the increase in oxygen consumption seen when INS832/13 cells, a rodent insulinoma cell line, are challenged with IAPP. In summary our studies suggest the possibility that humanin, and perhaps other mitochondrially-derived peptides, have chaperone-like properties that could reverse the pathological processes involved in the development of T2DM. |
