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The mitochondria-targeted peptide SS-31 binds lipid bilayers and modulates surface electrostatics as a key component of its mechanism of action.

ABSTRACT: Mitochondrial dysfunction underlies many heritable diseases, acquired pathologies, and aging-related declines in health. Szeto-Schiller (SS) peptides comprise a class of amphipathic tetrapeptides that are efficacious toward a wide array of mitochondrial disorders and are believed to target mitochondrial membranes because they are enriched in the anionic phospholipid cardiolipin (CL). However, little is known regarding how SS peptides interact with or alter the physical properties of lipid bilayers. In this study, using biophysical and computational approaches, we have analyzed the interactions of the lead compound SS-31 (elamipretide) with model and mitochondrial membranes. Our results show that this polybasic peptide partitions into the membrane interfacial region with an affinity and a lipid binding density that are directly related to surface charge. We found that SS-31 binding does not destabilize lamellar bilayers even at the highest binding concentrations; however, it did cause saturable alterations in lipid packing. Most notably, SS-31 modulated the surface electrostatics of both model and mitochondrial membranes. We propose nonexclusive mechanisms by which the tuning of surface charge could underpin the mitoprotective properties of SS-31, including alteration of the distribution of ions and basic proteins at the interface, and/or modulation of bilayer physical properties. As a proof of concept, we show that SS-31 alters divalent cation (calcium) distribution within the interfacial region and reduces the energetic burden of calcium stress in mitochondria. The mechanistic details of SS-31 revealed in this study will help inform the development of future compound variants with enhanced efficacy and bioavailability.

SUBMITTER: Mitchell W

PROVIDER: S-EPMC7247319 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Functional decline and structural alterations of the brain microvasculature are associated with cognitive impairment and development of dementias such as Alzheimer’s disease during aging. Although mechanisms of leading to microvascular changes during aging are not clear, the loss of mitochondria and reduced efficiency of remaining mitochondria appear to play a major role. While pharmacological agents which target mitochondria such as SS-31 have been shown to be effective in beneficial during aging and diseases, the full extent on mitochondrial- and non-mitochondrial proteins in the brain microvasculature has not been examined. We tested the hypothesis that attenuation of aging-associated changes in the brain microvascular proteome via targeting mitochondria represents a therapeutic option in the aging brain. We used male, aged (>18 months) C57Bl6/J mice treated with a mitochondria-targeted tetrapeptide, SS-31 or vehicle saline. Baseline cerebral blood flow (CBF) was determined using laser speckle imaging during the two-week treatment period. Then, isolated cortical microvessels (MVs), composed of end arterioles, capillaries, and venules, were used for Orbitrap Eclipse Tribrid mass spectrometry. Baseline CBF was similar between the groups, whereas bioinformatic analysis revealed substantial differences in protein abundance of cortical MVs between SS-31 and vehicle groups. Specifically, we identified 6,266 proteins in our data set from which 12% were mitochondrial or mitochondria associated. 107 of these proteins were significantly differentially expressed between the treatment and vehicle groups, and were associated with the oxidative phosphorylation, metabolism, antioxidant defense system, or mitochondrial dynamics. Administration of SS-31 also affected many non-mitochondrial proteins. Our findings suggest that mitochondria in the microvasculature represent a therapeutic target in the aging brain, and widespread changes in the proteome may underlie the mechanisms of rejuvenating actions of SS-31 in the aging phenotype.

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The mitochondria-targeted peptide SS-31 binds lipid bilayers and modulates surface electrostatics as a key component of its mechanism of action.

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