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Acylated but not des ‐ acyl ghrelin is neuroprotective in an MPTP mouse model of Parkinson's disease

View Article: PubMed Central - PubMed

ABSTRACT

The gut hormone ghrelin is widely beneficial in many disease states. However, ghrelin exists in two distinctive isoforms, each with its own metabolic profile. In Parkinson's Disease (PD) acylated ghrelin administration is neuroprotective, however, the role of des‐acylated ghrelin remains unknown. In this study, we wanted to identify the relative contribution each isoform plays using the MPTP model of PD. Chronic administration of acylated ghrelin in mice lacking both isoforms of ghrelin (Ghrelin KO) attenuated the MPTP‐induced loss on tyrosine hydroxylase (TH) neuronal number and volume and TH protein expression in the nigrostriatal pathway. Moreover, acylated ghrelin reduced the increase in glial fibrillary acidic protein and Ionized calcium binding adaptor molecule 1 microglia in the substantia nigra. However, injection of acylated ghrelin also elevated plasma des‐acylated ghrelin, indicating in vivo deacetylation. Next, we chronically administered des‐acylated ghrelin to Ghrelin KO mice and observed no neuroprotective effects in terms of TH cell number, TH protein expression, glial fibrillary acidic protein and ionized calcium binding adaptor molecule 1 cell number. The lack of a protective effect was mirrored in ghrelin‐O‐acyltransferase KO mice, which lack the ability to acylate ghrelin and consequently these mice have chronically increased plasma des‐acyl ghrelin. Plasma corticosterone was elevated in ghrelin‐O‐acyltransferase KO mice and with des‐acylated ghrelin administration. Overall, our studies suggest that acylated ghrelin is the isoform responsible for in vivo neuroprotection and that pharmacological approaches preventing plasma conversion from acyl ghrelin to des‐acyl ghrelin may have clinical efficacy to help slow or prevent the debilitating effects of PD.

Ghrelin exists in the plasma as acyl and des‐acyl ghrelin. We determined the form responsible for in vivo neuroprotection in a mouse model of Parkinson's disease. Although exogenous acyl ghrelin is deacylated in situ to des‐acyl, only acyl ghrelin was neuroprotective by attenuating dopamine cell loss and glial activation. Acyl ghrelin is a therapeutic option to reduce Parkinson's Disease progression.

Cover image: for this issue: doi: 10.1111/jnc.13316.

No MeSH data available.


Related in: MedlinePlus

No neuroprotective action in Ghrelin KO mice re‐instated with des‐acyl ghrelin. (a and b) Plasma analysis of acyl and des‐acyl ghrelin show an elevation in des‐acyl ghrelin after injection and no change in acylated ghrelin levels. The red dotted line indicates average circulating levels of acyl and des‐acyl ghrelin in wild‐type mice. (c and d) Plasma non‐esterified fatty acid and Triglyceride levels are elevated post‐MPTP administration. (e) Stereological quantification of tyrosine hydroxylase (TH) neurons in the SN showing a significant reduction after MPTP administration but no effect with chronic des‐acyl ghrelin. (f) Overall cell volume showed a significant reduction with MPTP regardless of injection. Stereological quantification of ionized calcium binding adaptor molecule 1 (IBA1) (g) and GFAP (h) shows elevated levels following MPTP, with no difference between chronic saline and chronic des‐acyl ghrelin. (i + j) Representative images showing MPTP induced (i) microglial and (j) astrocyte activation in the SN (green = TH and red = (I) IBA1 or (j) GFAP). (k) TH cell distribution shows no difference comparing MPTP saline and MPTP des‐acyl ghrelin. (l) Representative western blot images of TH and beta actin in the SN and Striatum. Quantification of TH levels in the SN (m) and Striatum (n) reveals a significant loss of TH in MPTP‐treated mice with no effect of des‐acyl ghrelin. (o and p) MPTP significantly reduced both dopamine and DOPAC with no effect of des‐ acyl ghrelin. (q) MPTP treatment significantly elevated the DOPAC:dopamine ratio regardless of treatment. (r) Plasma corticosterone levels are significantly elevated in response to both des‐acylated ghrelin and MPTP with a cumulative effect when co‐administered. a, significant compared to Saline/saline‐treated mice and b, significant compared to Saline/MPTP‐treated mice. *p < 0.05, ****p < 0.0001 significant compared to Saline/Saline. Data are represented as mean ± SEM (n = 6, two‐way anova). Scale bar = 100 μm.
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jnc13576-fig-0002: No neuroprotective action in Ghrelin KO mice re‐instated with des‐acyl ghrelin. (a and b) Plasma analysis of acyl and des‐acyl ghrelin show an elevation in des‐acyl ghrelin after injection and no change in acylated ghrelin levels. The red dotted line indicates average circulating levels of acyl and des‐acyl ghrelin in wild‐type mice. (c and d) Plasma non‐esterified fatty acid and Triglyceride levels are elevated post‐MPTP administration. (e) Stereological quantification of tyrosine hydroxylase (TH) neurons in the SN showing a significant reduction after MPTP administration but no effect with chronic des‐acyl ghrelin. (f) Overall cell volume showed a significant reduction with MPTP regardless of injection. Stereological quantification of ionized calcium binding adaptor molecule 1 (IBA1) (g) and GFAP (h) shows elevated levels following MPTP, with no difference between chronic saline and chronic des‐acyl ghrelin. (i + j) Representative images showing MPTP induced (i) microglial and (j) astrocyte activation in the SN (green = TH and red = (I) IBA1 or (j) GFAP). (k) TH cell distribution shows no difference comparing MPTP saline and MPTP des‐acyl ghrelin. (l) Representative western blot images of TH and beta actin in the SN and Striatum. Quantification of TH levels in the SN (m) and Striatum (n) reveals a significant loss of TH in MPTP‐treated mice with no effect of des‐acyl ghrelin. (o and p) MPTP significantly reduced both dopamine and DOPAC with no effect of des‐ acyl ghrelin. (q) MPTP treatment significantly elevated the DOPAC:dopamine ratio regardless of treatment. (r) Plasma corticosterone levels are significantly elevated in response to both des‐acylated ghrelin and MPTP with a cumulative effect when co‐administered. a, significant compared to Saline/saline‐treated mice and b, significant compared to Saline/MPTP‐treated mice. *p < 0.05, ****p < 0.0001 significant compared to Saline/Saline. Data are represented as mean ± SEM (n = 6, two‐way anova). Scale bar = 100 μm.

Mentions: To determine the relative neuroprotective potential of des‐acyl ghrelin in vivo, we chronically administered Ghrelin KO mice (lacking both acylated and des‐acylated ghrelin) with des‐acyl ghrelin. The use of Ghrelin KO mice allowed us to directly assess the impact of the exogenously administered des‐acyl ghrelin without confounding changes in the acyl to des‐acyl ghrelin ratio. Plasma analysis shows negligible acylated ghrelin levels and a higher than average circulating plasma des‐acyl concentration (Fig. 2a and b). This indicates that des‐acyl ghrelin cannot be converted back to its acylated counterpart and that any observed effects are solely because of elevated des‐acyl ghrelin. We analysed various metabolic markers in the plasma and found elevated NEFA (Fig. 2c) and Triglycerides (Fig. 2d) with no change in blood glucose (Figure S1d) in response to MPTP.


Acylated but not des ‐ acyl ghrelin is neuroprotective in an MPTP mouse model of Parkinson's disease
No neuroprotective action in Ghrelin KO mice re‐instated with des‐acyl ghrelin. (a and b) Plasma analysis of acyl and des‐acyl ghrelin show an elevation in des‐acyl ghrelin after injection and no change in acylated ghrelin levels. The red dotted line indicates average circulating levels of acyl and des‐acyl ghrelin in wild‐type mice. (c and d) Plasma non‐esterified fatty acid and Triglyceride levels are elevated post‐MPTP administration. (e) Stereological quantification of tyrosine hydroxylase (TH) neurons in the SN showing a significant reduction after MPTP administration but no effect with chronic des‐acyl ghrelin. (f) Overall cell volume showed a significant reduction with MPTP regardless of injection. Stereological quantification of ionized calcium binding adaptor molecule 1 (IBA1) (g) and GFAP (h) shows elevated levels following MPTP, with no difference between chronic saline and chronic des‐acyl ghrelin. (i + j) Representative images showing MPTP induced (i) microglial and (j) astrocyte activation in the SN (green = TH and red = (I) IBA1 or (j) GFAP). (k) TH cell distribution shows no difference comparing MPTP saline and MPTP des‐acyl ghrelin. (l) Representative western blot images of TH and beta actin in the SN and Striatum. Quantification of TH levels in the SN (m) and Striatum (n) reveals a significant loss of TH in MPTP‐treated mice with no effect of des‐acyl ghrelin. (o and p) MPTP significantly reduced both dopamine and DOPAC with no effect of des‐ acyl ghrelin. (q) MPTP treatment significantly elevated the DOPAC:dopamine ratio regardless of treatment. (r) Plasma corticosterone levels are significantly elevated in response to both des‐acylated ghrelin and MPTP with a cumulative effect when co‐administered. a, significant compared to Saline/saline‐treated mice and b, significant compared to Saline/MPTP‐treated mice. *p < 0.05, ****p < 0.0001 significant compared to Saline/Saline. Data are represented as mean ± SEM (n = 6, two‐way anova). Scale bar = 100 μm.
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jnc13576-fig-0002: No neuroprotective action in Ghrelin KO mice re‐instated with des‐acyl ghrelin. (a and b) Plasma analysis of acyl and des‐acyl ghrelin show an elevation in des‐acyl ghrelin after injection and no change in acylated ghrelin levels. The red dotted line indicates average circulating levels of acyl and des‐acyl ghrelin in wild‐type mice. (c and d) Plasma non‐esterified fatty acid and Triglyceride levels are elevated post‐MPTP administration. (e) Stereological quantification of tyrosine hydroxylase (TH) neurons in the SN showing a significant reduction after MPTP administration but no effect with chronic des‐acyl ghrelin. (f) Overall cell volume showed a significant reduction with MPTP regardless of injection. Stereological quantification of ionized calcium binding adaptor molecule 1 (IBA1) (g) and GFAP (h) shows elevated levels following MPTP, with no difference between chronic saline and chronic des‐acyl ghrelin. (i + j) Representative images showing MPTP induced (i) microglial and (j) astrocyte activation in the SN (green = TH and red = (I) IBA1 or (j) GFAP). (k) TH cell distribution shows no difference comparing MPTP saline and MPTP des‐acyl ghrelin. (l) Representative western blot images of TH and beta actin in the SN and Striatum. Quantification of TH levels in the SN (m) and Striatum (n) reveals a significant loss of TH in MPTP‐treated mice with no effect of des‐acyl ghrelin. (o and p) MPTP significantly reduced both dopamine and DOPAC with no effect of des‐ acyl ghrelin. (q) MPTP treatment significantly elevated the DOPAC:dopamine ratio regardless of treatment. (r) Plasma corticosterone levels are significantly elevated in response to both des‐acylated ghrelin and MPTP with a cumulative effect when co‐administered. a, significant compared to Saline/saline‐treated mice and b, significant compared to Saline/MPTP‐treated mice. *p < 0.05, ****p < 0.0001 significant compared to Saline/Saline. Data are represented as mean ± SEM (n = 6, two‐way anova). Scale bar = 100 μm.
Mentions: To determine the relative neuroprotective potential of des‐acyl ghrelin in vivo, we chronically administered Ghrelin KO mice (lacking both acylated and des‐acylated ghrelin) with des‐acyl ghrelin. The use of Ghrelin KO mice allowed us to directly assess the impact of the exogenously administered des‐acyl ghrelin without confounding changes in the acyl to des‐acyl ghrelin ratio. Plasma analysis shows negligible acylated ghrelin levels and a higher than average circulating plasma des‐acyl concentration (Fig. 2a and b). This indicates that des‐acyl ghrelin cannot be converted back to its acylated counterpart and that any observed effects are solely because of elevated des‐acyl ghrelin. We analysed various metabolic markers in the plasma and found elevated NEFA (Fig. 2c) and Triglycerides (Fig. 2d) with no change in blood glucose (Figure S1d) in response to MPTP.

View Article: PubMed Central - PubMed

ABSTRACT

The gut hormone ghrelin is widely beneficial in many disease states. However, ghrelin exists in two distinctive isoforms, each with its own metabolic profile. In Parkinson's Disease (PD) acylated ghrelin administration is neuroprotective, however, the role of des&#8208;acylated ghrelin remains unknown. In this study, we wanted to identify the relative contribution each isoform plays using the MPTP model of PD. Chronic administration of acylated ghrelin in mice lacking both isoforms of ghrelin (Ghrelin KO) attenuated the MPTP&#8208;induced loss on tyrosine hydroxylase (TH) neuronal number and volume and TH protein expression in the nigrostriatal pathway. Moreover, acylated ghrelin reduced the increase in glial fibrillary acidic protein and Ionized calcium binding adaptor molecule 1 microglia in the substantia nigra. However, injection of acylated ghrelin also elevated plasma des&#8208;acylated ghrelin, indicating in&nbsp;vivo deacetylation. Next, we chronically administered des&#8208;acylated ghrelin to Ghrelin KO mice and observed no neuroprotective effects in terms of TH cell number, TH protein expression, glial fibrillary acidic protein and ionized calcium binding adaptor molecule 1 cell number. The lack of a protective effect was mirrored in ghrelin&#8208;O&#8208;acyltransferase KO mice, which lack the ability to acylate ghrelin and consequently these mice have chronically increased plasma des&#8208;acyl ghrelin. Plasma corticosterone was elevated in ghrelin&#8208;O&#8208;acyltransferase KO mice and with des&#8208;acylated ghrelin administration. Overall, our studies suggest that acylated ghrelin is the isoform responsible for in&nbsp;vivo neuroprotection and that pharmacological approaches preventing plasma conversion from acyl ghrelin to des&#8208;acyl ghrelin may have clinical efficacy to help slow or prevent the debilitating effects of PD.

Ghrelin exists in the plasma as acyl and des&#8208;acyl ghrelin. We determined the form responsible for in&nbsp;vivo neuroprotection in a mouse model of Parkinson's disease. Although exogenous acyl ghrelin is deacylated in&nbsp;situ to des&#8208;acyl, only acyl ghrelin was neuroprotective by attenuating dopamine cell loss and glial activation. Acyl ghrelin is a therapeutic option to reduce Parkinson's Disease progression.

Cover image: for this issue: doi: 10.1111/jnc.13316.

No MeSH data available.


Related in: MedlinePlus