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Elevated protein carbonylation, and misfolding in sciatic nerve from db/db and Sod1(-/-) mice: plausible link between oxidative stress and demyelination.

Hamilton RT, Bhattacharya A, Walsh ME, Shi Y, Wei R, Zhang Y, Rodriguez KA, Buffenstein R, Chaudhuri AR, Van Remmen H - PLoS ONE (2013)

Bottom Line: Since peripheral myelin protein 22 (PMP22) is a key component of myelin sheath and has been found mutated and aggregated in several peripheral neuropathies, we predicted that an increase in carbonylation and aggregation of PMP22 may be associated with demyelination in dbdb mice.Indeed, PMP22 was found to be carbonylated and aggregated in sciatic nerves of dbdb mice.Sequence-driven hydropathy plot analysis and in vitro oxidation-induced aggregation of purified PMP22 protein supported the premise for oxidation-dependent aggregation of PMP22 in dbdb mice.

View Article: PubMed Central - PubMed

Affiliation: Department of Cellular and Structural Biology, University of Texas Health Science Center, San Antonio, Texas, USA.

ABSTRACT
Diabetic peripheral polyneuropathy is associated with decrements in motor/sensory neuron myelination, nerve conduction and muscle function; however, the mechanisms of reduced myelination in diabetes are poorly understood. Chronic elevation of oxidative stress may be one of the potential determinants for demyelination as lipids and proteins are important structural constituents of myelin and highly susceptible to oxidation. The goal of the current study was to determine whether there is a link between protein oxidation/misfolding and demyelination. We chose two distinct models to test our hypothesis: 1) the leptin receptor deficient mouse (dbdb) model of diabetic polyneuropathy and 2) superoxide dismutase 1 knockout (Sod1(-/-) ) mouse model of in vivo oxidative stress. Both experimental models displayed a significant decrement in nerve conduction, increase in tail distal motor latency as well as reduced myelin thickness and fiber/axon diameter. Further biochemical studies demonstrated that oxidative stress is likely to be a potential key player in the demyelination process as both models exhibited significant elevation in protein carbonylation and alterations in protein conformation. Since peripheral myelin protein 22 (PMP22) is a key component of myelin sheath and has been found mutated and aggregated in several peripheral neuropathies, we predicted that an increase in carbonylation and aggregation of PMP22 may be associated with demyelination in dbdb mice. Indeed, PMP22 was found to be carbonylated and aggregated in sciatic nerves of dbdb mice. Sequence-driven hydropathy plot analysis and in vitro oxidation-induced aggregation of purified PMP22 protein supported the premise for oxidation-dependent aggregation of PMP22 in dbdb mice. Collectively, these data strongly suggest for the first time that oxidation-mediated protein misfolding and aggregation of key myelin proteins may be linked to demyelination and reduced nerve conduction in peripheral neuropathies.

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In vitro assessment of oxidative stress-induced aggregation of PMP22 protein.Purified PMP22 protein was subjected to in vitro oxidation with increasing concentrations of tert-butyl hydroperoxide. SDS-PAGE was performed on oxidized PMP22 protein from both the soluble and detergent-soluble protein fractions. Results are expressed as mean ± SEM (n = 6; *p<0.05 by two-tailed t-test).
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pone-0065725-g006: In vitro assessment of oxidative stress-induced aggregation of PMP22 protein.Purified PMP22 protein was subjected to in vitro oxidation with increasing concentrations of tert-butyl hydroperoxide. SDS-PAGE was performed on oxidized PMP22 protein from both the soluble and detergent-soluble protein fractions. Results are expressed as mean ± SEM (n = 6; *p<0.05 by two-tailed t-test).

Mentions: Based on these intriguing in vivo observations, we predicted that the oxidative environment is likely to induce aggregation of PMP22 protein which has been found as aggregates in multiple PMP22 aggregation-dependent neuropathies. Therefore, we exposed purified PMP22 to different concentrations of tBHP (which generates hydroxyl radical and forms protein carbonyls) and then followed the structural consequences of PMP22. The results of Figure 6 shows a dose-dependent increase in insoluble to soluble ratio of PMP22, which confirms our in vivo finding that oxidative stress indeed increases the sensitivity of PMP22 to undergo aggregation.


Elevated protein carbonylation, and misfolding in sciatic nerve from db/db and Sod1(-/-) mice: plausible link between oxidative stress and demyelination.

Hamilton RT, Bhattacharya A, Walsh ME, Shi Y, Wei R, Zhang Y, Rodriguez KA, Buffenstein R, Chaudhuri AR, Van Remmen H - PLoS ONE (2013)

In vitro assessment of oxidative stress-induced aggregation of PMP22 protein.Purified PMP22 protein was subjected to in vitro oxidation with increasing concentrations of tert-butyl hydroperoxide. SDS-PAGE was performed on oxidized PMP22 protein from both the soluble and detergent-soluble protein fractions. Results are expressed as mean ± SEM (n = 6; *p<0.05 by two-tailed t-test).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3672154&req=5

pone-0065725-g006: In vitro assessment of oxidative stress-induced aggregation of PMP22 protein.Purified PMP22 protein was subjected to in vitro oxidation with increasing concentrations of tert-butyl hydroperoxide. SDS-PAGE was performed on oxidized PMP22 protein from both the soluble and detergent-soluble protein fractions. Results are expressed as mean ± SEM (n = 6; *p<0.05 by two-tailed t-test).
Mentions: Based on these intriguing in vivo observations, we predicted that the oxidative environment is likely to induce aggregation of PMP22 protein which has been found as aggregates in multiple PMP22 aggregation-dependent neuropathies. Therefore, we exposed purified PMP22 to different concentrations of tBHP (which generates hydroxyl radical and forms protein carbonyls) and then followed the structural consequences of PMP22. The results of Figure 6 shows a dose-dependent increase in insoluble to soluble ratio of PMP22, which confirms our in vivo finding that oxidative stress indeed increases the sensitivity of PMP22 to undergo aggregation.

Bottom Line: Since peripheral myelin protein 22 (PMP22) is a key component of myelin sheath and has been found mutated and aggregated in several peripheral neuropathies, we predicted that an increase in carbonylation and aggregation of PMP22 may be associated with demyelination in dbdb mice.Indeed, PMP22 was found to be carbonylated and aggregated in sciatic nerves of dbdb mice.Sequence-driven hydropathy plot analysis and in vitro oxidation-induced aggregation of purified PMP22 protein supported the premise for oxidation-dependent aggregation of PMP22 in dbdb mice.

View Article: PubMed Central - PubMed

Affiliation: Department of Cellular and Structural Biology, University of Texas Health Science Center, San Antonio, Texas, USA.

ABSTRACT
Diabetic peripheral polyneuropathy is associated with decrements in motor/sensory neuron myelination, nerve conduction and muscle function; however, the mechanisms of reduced myelination in diabetes are poorly understood. Chronic elevation of oxidative stress may be one of the potential determinants for demyelination as lipids and proteins are important structural constituents of myelin and highly susceptible to oxidation. The goal of the current study was to determine whether there is a link between protein oxidation/misfolding and demyelination. We chose two distinct models to test our hypothesis: 1) the leptin receptor deficient mouse (dbdb) model of diabetic polyneuropathy and 2) superoxide dismutase 1 knockout (Sod1(-/-) ) mouse model of in vivo oxidative stress. Both experimental models displayed a significant decrement in nerve conduction, increase in tail distal motor latency as well as reduced myelin thickness and fiber/axon diameter. Further biochemical studies demonstrated that oxidative stress is likely to be a potential key player in the demyelination process as both models exhibited significant elevation in protein carbonylation and alterations in protein conformation. Since peripheral myelin protein 22 (PMP22) is a key component of myelin sheath and has been found mutated and aggregated in several peripheral neuropathies, we predicted that an increase in carbonylation and aggregation of PMP22 may be associated with demyelination in dbdb mice. Indeed, PMP22 was found to be carbonylated and aggregated in sciatic nerves of dbdb mice. Sequence-driven hydropathy plot analysis and in vitro oxidation-induced aggregation of purified PMP22 protein supported the premise for oxidation-dependent aggregation of PMP22 in dbdb mice. Collectively, these data strongly suggest for the first time that oxidation-mediated protein misfolding and aggregation of key myelin proteins may be linked to demyelination and reduced nerve conduction in peripheral neuropathies.

Show MeSH
Related in: MedlinePlus