Limits...
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.

Show MeSH

Related in: MedlinePlus

Reductions in myelin and neuron structure in dbdb and Sod1−/− mice.Thick sections of sciatic nerves were sectioned and visualized at 100x (A) non-diabetic dbm mouse and (B) dbdb mice. (C) Quantification of axon diameter/area, nerve fiber diameter/area, myelin area/thickness and g ratio (axon diameter/fiber diameter) were tabulated from thick sections of dbdb and control mice (n  = 3). Thick sections of (D) 6-mo-old control and (E) 6-mo-old Sod1−/− mice are shown. (F) Quantification was performed similarly to that shown in 2C. Thick sections of (G) 20-mo-old control and (H) 20-mo-old Sod1−/− mice are presented. (I) Quantification was performed similarly to that in 2C and results expressed as mean ± SEM of n = 3 mice/group. Results were analyzed by two-tailed t-test (*p<0.05 by two-tailed t-test).
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3672154&req=5

pone-0065725-g002: Reductions in myelin and neuron structure in dbdb and Sod1−/− mice.Thick sections of sciatic nerves were sectioned and visualized at 100x (A) non-diabetic dbm mouse and (B) dbdb mice. (C) Quantification of axon diameter/area, nerve fiber diameter/area, myelin area/thickness and g ratio (axon diameter/fiber diameter) were tabulated from thick sections of dbdb and control mice (n  = 3). Thick sections of (D) 6-mo-old control and (E) 6-mo-old Sod1−/− mice are shown. (F) Quantification was performed similarly to that shown in 2C. Thick sections of (G) 20-mo-old control and (H) 20-mo-old Sod1−/− mice are presented. (I) Quantification was performed similarly to that in 2C and results expressed as mean ± SEM of n = 3 mice/group. Results were analyzed by two-tailed t-test (*p<0.05 by two-tailed t-test).

Mentions: Since demyelination is closely linked to reduced nerve conduction [2] and oxidative stress is associated with reduced sciatic NCV and increased tdml as shown in Figure 1A–D, we measured axon diameter, nerve fiber diameter and myelin thickness in 5-mo-old dbm and dbdb mice, and 6 and 20 mo-old Sod1−/− mice in toluidine blue stained sciatic nerve thick sections. Dbdb mice exhibited reduced axon, nerve fiber diameter and reduced myelin thickness when compared to comparable sized axons from sections obtained from the sciatic notch in dbm mice (Figure 2 A&B, marked by asterisks). Moreover, a significant reduction in axon diameter/area (p<0.05), fiber diameter/area (p<0.001), myelin thickness/area (p<0.001) and increase in G-ratio (axon diameter/fiber diameter) (p<0.001, Figure 2C) was also observed in these sections. Reductions in axon diameter, fiber diameter and myelin thickness in dbdb mice are consistent with previous studies [2]. In comparison, the Sod1−/− mice exhibited reduced axon and fiber diameters compared to age-matched wild-type mice at 6 months of age (Figure 2D&E), which was confirmed by quantification of axon diameter/area (p<0.001) and fiber diameter/area (p<0.001). The myelin area was reduced but the results did not reach statistical significance (p = 0.16) (Figure 2F). However, 20 month Sod1−/− mice showed reductions in myelin thickness/area and fiber diameter/area (Figure 2G&H). Quantification of nerve morphology demonstrated a significant reduction in fiber diameter/area (p<0.001), and myelin thickness/area (p<0.001) with concomitant increase in G-ratio (p<0.001), by 20 months of age (Figure 2). These results strongly suggest that oxidative stress is closely associated with alterations in peripheral nerve myelin morphology and function.


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)

Reductions in myelin and neuron structure in dbdb and Sod1−/− mice.Thick sections of sciatic nerves were sectioned and visualized at 100x (A) non-diabetic dbm mouse and (B) dbdb mice. (C) Quantification of axon diameter/area, nerve fiber diameter/area, myelin area/thickness and g ratio (axon diameter/fiber diameter) were tabulated from thick sections of dbdb and control mice (n  = 3). Thick sections of (D) 6-mo-old control and (E) 6-mo-old Sod1−/− mice are shown. (F) Quantification was performed similarly to that shown in 2C. Thick sections of (G) 20-mo-old control and (H) 20-mo-old Sod1−/− mice are presented. (I) Quantification was performed similarly to that in 2C and results expressed as mean ± SEM of n = 3 mice/group. Results were analyzed by two-tailed t-test (*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-g002: Reductions in myelin and neuron structure in dbdb and Sod1−/− mice.Thick sections of sciatic nerves were sectioned and visualized at 100x (A) non-diabetic dbm mouse and (B) dbdb mice. (C) Quantification of axon diameter/area, nerve fiber diameter/area, myelin area/thickness and g ratio (axon diameter/fiber diameter) were tabulated from thick sections of dbdb and control mice (n  = 3). Thick sections of (D) 6-mo-old control and (E) 6-mo-old Sod1−/− mice are shown. (F) Quantification was performed similarly to that shown in 2C. Thick sections of (G) 20-mo-old control and (H) 20-mo-old Sod1−/− mice are presented. (I) Quantification was performed similarly to that in 2C and results expressed as mean ± SEM of n = 3 mice/group. Results were analyzed by two-tailed t-test (*p<0.05 by two-tailed t-test).
Mentions: Since demyelination is closely linked to reduced nerve conduction [2] and oxidative stress is associated with reduced sciatic NCV and increased tdml as shown in Figure 1A–D, we measured axon diameter, nerve fiber diameter and myelin thickness in 5-mo-old dbm and dbdb mice, and 6 and 20 mo-old Sod1−/− mice in toluidine blue stained sciatic nerve thick sections. Dbdb mice exhibited reduced axon, nerve fiber diameter and reduced myelin thickness when compared to comparable sized axons from sections obtained from the sciatic notch in dbm mice (Figure 2 A&B, marked by asterisks). Moreover, a significant reduction in axon diameter/area (p<0.05), fiber diameter/area (p<0.001), myelin thickness/area (p<0.001) and increase in G-ratio (axon diameter/fiber diameter) (p<0.001, Figure 2C) was also observed in these sections. Reductions in axon diameter, fiber diameter and myelin thickness in dbdb mice are consistent with previous studies [2]. In comparison, the Sod1−/− mice exhibited reduced axon and fiber diameters compared to age-matched wild-type mice at 6 months of age (Figure 2D&E), which was confirmed by quantification of axon diameter/area (p<0.001) and fiber diameter/area (p<0.001). The myelin area was reduced but the results did not reach statistical significance (p = 0.16) (Figure 2F). However, 20 month Sod1−/− mice showed reductions in myelin thickness/area and fiber diameter/area (Figure 2G&H). Quantification of nerve morphology demonstrated a significant reduction in fiber diameter/area (p<0.001), and myelin thickness/area (p<0.001) with concomitant increase in G-ratio (p<0.001), by 20 months of age (Figure 2). These results strongly suggest that oxidative stress is closely associated with alterations in peripheral nerve myelin morphology and function.

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