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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 significant difference between ghrelin‐O‐acyltransferase (GOAT) WT and KO mice after MPTP exposure. (a and b) Plasma analysis of acyl and des‐acyl ghrelin show an elevation in des‐acyl ghrelin with negligible acylated ghrelin in GOAT KO mice. Both acylated and des‐acylated ghrelin are present in GOAT WT 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 no effect of genotype in response to MPTP. (f) Overall cell volume showed a significant reduction with MPTP regardless of genotype. Stereological quantification of ionized calcium binding adaptor molecule 1 (IBA1) (g) and GFAP (h) shows elevated levels following MPTP, independent of genotype. (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 was not different between genotypes. (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 post‐MPTP administration with no significant effect of genotype. (o and p) MPTP significantly reduced both dopamine and DOPAC with no effect of genotype. (q) MPTP treatment significantly elevated the DOPAC:dopamine ratio regardless of genotype. (r) Plasma corticosterone levels are significantly elevated in response to MPTP and also in saline‐treated GOAT KO mice. a, significant compared to GOAT WT saline‐treated mice and b, significant compared to GOAT WT MPTP‐treated mice. Data are represented as mean ± SEM (n = 6–7, two‐way anova). Scale bar = 100 μm.
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jnc13576-fig-0003: No significant difference between ghrelin‐O‐acyltransferase (GOAT) WT and KO mice after MPTP exposure. (a and b) Plasma analysis of acyl and des‐acyl ghrelin show an elevation in des‐acyl ghrelin with negligible acylated ghrelin in GOAT KO mice. Both acylated and des‐acylated ghrelin are present in GOAT WT 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 no effect of genotype in response to MPTP. (f) Overall cell volume showed a significant reduction with MPTP regardless of genotype. Stereological quantification of ionized calcium binding adaptor molecule 1 (IBA1) (g) and GFAP (h) shows elevated levels following MPTP, independent of genotype. (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 was not different between genotypes. (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 post‐MPTP administration with no significant effect of genotype. (o and p) MPTP significantly reduced both dopamine and DOPAC with no effect of genotype. (q) MPTP treatment significantly elevated the DOPAC:dopamine ratio regardless of genotype. (r) Plasma corticosterone levels are significantly elevated in response to MPTP and also in saline‐treated GOAT KO mice. a, significant compared to GOAT WT saline‐treated mice and b, significant compared to GOAT WT MPTP‐treated mice. Data are represented as mean ± SEM (n = 6–7, two‐way anova). Scale bar = 100 μm.

Mentions: As shown above des‐acylated ghrelin did not attenuate SN TH cell number or cell volume loss in a mouse model of PD. To strengthen these observations, we employed a genetic mouse model that exhibits increased endogenous des‐acyl ghrelin and no acylated ghrelin throughout the animal's entire lifespan. Mice lacking the enzyme GOAT have high levels of des‐acyl ghrelin and negligible acylated ghrelin (Fig. 3a and b) and thereby provide an ideal model to test the role of endogenously high des‐acyl ghrelin. We also analysed various metabolic markers in the plasma and found elevated NEFA (Fig. 3c) and Triglycerides (Fig. 3d) with no change in blood glucose (Figure S1f) in response to MPTP. MPTP administration significantly reduced the number and size of TH neurons (Fig. 3e, f and k) concurrent with elevated GFAP and IBA1 cells in both GOAT WT and KO mice, with no overall effect of genotype (Fig 3g and h). These results were mirrored in the analysis of TH protein levels in both the SN and Striatum (Fig. 3l–n). HPLC analysis of dopamine and DOPAC revealed a significant reduction with MPTP administration with no effect of genotype (Fig. 3o and p). Genotype did not alter the DOPAC:DA ratio (Fig. 3q). Interestingly, corticosterone levels were elevated in GOAT KO mice and with MPTP indicating a stress response to the elevated levels of des‐acyl ghrelin (Fig 3r).


Acylated but not des ‐ acyl ghrelin is neuroprotective in an MPTP mouse model of Parkinson's disease
No significant difference between ghrelin‐O‐acyltransferase (GOAT) WT and KO mice after MPTP exposure. (a and b) Plasma analysis of acyl and des‐acyl ghrelin show an elevation in des‐acyl ghrelin with negligible acylated ghrelin in GOAT KO mice. Both acylated and des‐acylated ghrelin are present in GOAT WT 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 no effect of genotype in response to MPTP. (f) Overall cell volume showed a significant reduction with MPTP regardless of genotype. Stereological quantification of ionized calcium binding adaptor molecule 1 (IBA1) (g) and GFAP (h) shows elevated levels following MPTP, independent of genotype. (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 was not different between genotypes. (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 post‐MPTP administration with no significant effect of genotype. (o and p) MPTP significantly reduced both dopamine and DOPAC with no effect of genotype. (q) MPTP treatment significantly elevated the DOPAC:dopamine ratio regardless of genotype. (r) Plasma corticosterone levels are significantly elevated in response to MPTP and also in saline‐treated GOAT KO mice. a, significant compared to GOAT WT saline‐treated mice and b, significant compared to GOAT WT MPTP‐treated mice. Data are represented as mean ± SEM (n = 6–7, two‐way anova). Scale bar = 100 μm.
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jnc13576-fig-0003: No significant difference between ghrelin‐O‐acyltransferase (GOAT) WT and KO mice after MPTP exposure. (a and b) Plasma analysis of acyl and des‐acyl ghrelin show an elevation in des‐acyl ghrelin with negligible acylated ghrelin in GOAT KO mice. Both acylated and des‐acylated ghrelin are present in GOAT WT 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 no effect of genotype in response to MPTP. (f) Overall cell volume showed a significant reduction with MPTP regardless of genotype. Stereological quantification of ionized calcium binding adaptor molecule 1 (IBA1) (g) and GFAP (h) shows elevated levels following MPTP, independent of genotype. (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 was not different between genotypes. (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 post‐MPTP administration with no significant effect of genotype. (o and p) MPTP significantly reduced both dopamine and DOPAC with no effect of genotype. (q) MPTP treatment significantly elevated the DOPAC:dopamine ratio regardless of genotype. (r) Plasma corticosterone levels are significantly elevated in response to MPTP and also in saline‐treated GOAT KO mice. a, significant compared to GOAT WT saline‐treated mice and b, significant compared to GOAT WT MPTP‐treated mice. Data are represented as mean ± SEM (n = 6–7, two‐way anova). Scale bar = 100 μm.
Mentions: As shown above des‐acylated ghrelin did not attenuate SN TH cell number or cell volume loss in a mouse model of PD. To strengthen these observations, we employed a genetic mouse model that exhibits increased endogenous des‐acyl ghrelin and no acylated ghrelin throughout the animal's entire lifespan. Mice lacking the enzyme GOAT have high levels of des‐acyl ghrelin and negligible acylated ghrelin (Fig. 3a and b) and thereby provide an ideal model to test the role of endogenously high des‐acyl ghrelin. We also analysed various metabolic markers in the plasma and found elevated NEFA (Fig. 3c) and Triglycerides (Fig. 3d) with no change in blood glucose (Figure S1f) in response to MPTP. MPTP administration significantly reduced the number and size of TH neurons (Fig. 3e, f and k) concurrent with elevated GFAP and IBA1 cells in both GOAT WT and KO mice, with no overall effect of genotype (Fig 3g and h). These results were mirrored in the analysis of TH protein levels in both the SN and Striatum (Fig. 3l–n). HPLC analysis of dopamine and DOPAC revealed a significant reduction with MPTP administration with no effect of genotype (Fig. 3o and p). Genotype did not alter the DOPAC:DA ratio (Fig. 3q). Interestingly, corticosterone levels were elevated in GOAT KO mice and with MPTP indicating a stress response to the elevated levels of des‐acyl ghrelin (Fig 3r).

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