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Kasanga EA, Soto I, Centner A, McManus R, Shifflet MK, Navarrete W, Han Y, Lisk J, Ehrhardt T, Wheeler K, Mhatre-Winters I, Richardson JR, Bishop C, Nejtek VA, Salvatore MF. Moderate intensity aerobic exercise alleviates motor deficits in 6-OHDA lesioned rats and reduces serum levels of biomarkers of Parkinson's disease severity without recovery of striatal dopamine or tyrosine hydroxylase. Exp Neurol 2024; 379:114875. [PMID: 38944332 DOI: 10.1016/j.expneurol.2024.114875] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2024] [Revised: 06/11/2024] [Accepted: 06/20/2024] [Indexed: 07/01/2024]
Abstract
Alleviation of motor impairment by aerobic exercise (AE) in Parkinson's disease (PD) patients points to activation of neurobiological mechanisms that may be targetable by therapeutic approaches. However, evidence for AE-related recovery of striatal dopamine (DA) signaling or tyrosine hydroxylase (TH) loss has been inconsistent in rodent studies. This ambiguity may be related to the timing of AE intervention in relation to the status of nigrostriatal neuron loss. Here, we replicated human PD at diagnosis by establishing motor impairment with >80% striatal DA and TH loss prior to initiating AE, and assessed its potential to alleviate motor decline and restore DA and TH loss. We also evaluated if serum levels of neurofilament light (NfL) and glial fibrillary acidic protein (GFAP), biomarkers of human PD severity, changed in response to AE. 6-hydroxydopamine (6-OHDA) was infused unilaterally into rat medial forebrain bundle to induce progressive nigrostriatal neuron loss over 28 days. Moderate intensity AE (3× per week, 40 min/session), began 8-10 days post-lesion following establishment of impaired forelimb use. Striatal tissue DA, TH protein and mRNA, and serum levels of NfL/GFAP were determined 3-wks after AE began. Despite severe striatal DA depletion at AE initiation, forelimb use deficits and hypokinesia onset were alleviated by AE, without recovery of striatal DA or TH protein loss, but reduced NfL and GFAP serum levels. This proof-of-concept study shows AE alleviates motor impairment when initiated with >80% striatal DA loss without obligate recovery of striatal DA or TH protein. Moreover, the AE-related reduction of NfL and GFAP serum levels may serve as objective blood-based biomarkers of AE efficacy.
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Affiliation(s)
- Ella A Kasanga
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX, United States of America
| | - Isabel Soto
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX, United States of America
| | - Ashley Centner
- Department of Psychology, Binghamton University, Binghamton, NY, United States of America
| | - Robert McManus
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX, United States of America
| | - Marla K Shifflet
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX, United States of America
| | - Walter Navarrete
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX, United States of America
| | - Yoonhee Han
- Department of Environmental Health Sciences, Robert Stempel School of Public Health & Social Work, Florida International University, Miami, FL, United States of America; Isakson Center for Neurological Disease Research, College of Veterinary Medicine, University of Georgia, Athens, GA, United States of America
| | - Jerome Lisk
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX, United States of America
| | - Travis Ehrhardt
- Clearcut Ortho Rehab & Diagnostics, Fort Worth, TX, United States of America
| | - Ken Wheeler
- Clearcut Ortho Rehab & Diagnostics, Fort Worth, TX, United States of America
| | - Isha Mhatre-Winters
- Department of Environmental Health Sciences, Robert Stempel School of Public Health & Social Work, Florida International University, Miami, FL, United States of America; Isakson Center for Neurological Disease Research, College of Veterinary Medicine, University of Georgia, Athens, GA, United States of America
| | - Jason R Richardson
- Department of Environmental Health Sciences, Robert Stempel School of Public Health & Social Work, Florida International University, Miami, FL, United States of America; Isakson Center for Neurological Disease Research, College of Veterinary Medicine, University of Georgia, Athens, GA, United States of America
| | - Christopher Bishop
- Department of Psychology, Binghamton University, Binghamton, NY, United States of America
| | - Vicki A Nejtek
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX, United States of America
| | - Michael F Salvatore
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX, United States of America.
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Soto I, McManus R, Navarrete W, Kasanga EA, Doshier K, Nejtek VA, Salvatore MF. Aging accelerates locomotor decline in PINK1 knockout rats in association with decreased nigral, but not striatal, dopamine and tyrosine hydroxylase expression. Exp Neurol 2024; 376:114771. [PMID: 38580154 DOI: 10.1016/j.expneurol.2024.114771] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2024] [Revised: 03/15/2024] [Accepted: 04/02/2024] [Indexed: 04/07/2024]
Abstract
Parkinson's disease (PD) rodent models provide insight into the relationship between nigrostriatal dopamine (DA) signaling and locomotor function. Although toxin-based rat models produce frank nigrostriatal neuron loss and eventual motor decline characteristic of PD, the rapid nature of neuronal loss may not adequately translate premotor traits, such as cognitive decline. Unfortunately, rodent genetic PD models, like the Pink1 knockout (KO) rat, often fail to replicate the differential severity of striatal DA and tyrosine hydroxylase (TH) loss, and a bradykinetic phenotype, reminiscent of human PD. To elucidate this inconsistency, we evaluated aging as a progression factor in the timing of motor and non-motor cognitive impairments. Male PINK1 KO and age-matched wild type (WT) rats were evaluated in a longitudinal study from 3 to 16 months old in one cohort, and in a cross-sectional study of young adult (6-7 months) and aged (18-19 months) in another cohort. Young adult PINK1 KO rats exhibited hyperkinetic behavior associated with elevated DA and TH in the substantia nigra (SN), which decreased therein, but not striatum, in the aged KO rats. Additionally, norepinephrine levels decreased in aged KO rats in the prefrontal cortex (PFC), paired with a higher DA levels in young and aged KO. Although a younger age of onset characterizes familial forms of PD, our results underscore the critical need to consider age-related factors. Moreover, the results indicate that compensatory mechanisms may exist to preserve locomotor function, evidenced by increased DA in the SN early in the lifespan, in response to deficient PINK1 function, which declines with aging and the onset of motor decline.
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Affiliation(s)
- Isabel Soto
- Department of Pharmacology & Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76107, United States of America
| | - Robert McManus
- Department of Pharmacology & Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76107, United States of America
| | - Walter Navarrete
- Department of Pharmacology & Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76107, United States of America
| | - Ella A Kasanga
- Department of Pharmacology & Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76107, United States of America
| | - Kirby Doshier
- Department of Pharmacology & Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76107, United States of America
| | - Vicki A Nejtek
- Department of Pharmacology & Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76107, United States of America
| | - Michael F Salvatore
- Department of Pharmacology & Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76107, United States of America.
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Soto I, McManus R, Navarrete-Barahona W, Kasanga EA, Doshier K, Nejtek VA, Salvatore MF. Aging hastens locomotor decline in PINK1 knockout rats in association with decreased nigral, but not striatal, dopamine and tyrosine hydroxylase expression. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.01.578317. [PMID: 38352365 PMCID: PMC10862808 DOI: 10.1101/2024.02.01.578317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/16/2024]
Abstract
Parkinson's disease (PD) rodent models provide insight into the relationship between nigrostriatal dopamine (DA) signaling and locomotor function. Although toxin-based rat models produce frank nigrostriatal neuron loss and eventual motor decline characteristic of PD, the rapid nature of neuronal loss may not adequately translate premotor traits, such as cognitive decline. Unfortunately, rodent genetic PD models, like the Pink1 knockout (KO) rat, often fail to replicate the differential severity of striatal DA and tyrosine hydroxylase (TH) loss, and a bradykinetic phenotype, reminiscent of human PD. To elucidate this inconsistency, we evaluated aging as a progression factor in the timing of motor and non-motor cognitive impairments. Male PINK1 KO and age-matched wild type (WT) rats were evaluated in a longitudinal study from 3 to 16 months old in one cohort, and in a cross-sectional study of young adult (6-7 months) and aged (18-19 months) in another cohort. Young adult PINK1 KO rats exhibited hyperkinetic behavior associated with elevated DA and TH in the substantia nigra (SN), which decreased therein, but not striatum, in the aged KO rats. Additionally, norepinephrine levels decreased in aged KO rats in the prefrontal cortex (PFC), paired with a higher DA content in young and aged KO. Although a younger age of onset characterizes familial forms of PD, our results underscore the critical need to consider age-related factors. Moreover, the results indicate that compensatory mechanisms may exist to preserve locomotor function, evidenced by increased DA in the SN early in the lifespan, in response to deficient PINK1 function, which declines with aging and the onset of motor impairment.
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Salvatore MF. Dopamine Signaling in Substantia Nigra and Its Impact on Locomotor Function-Not a New Concept, but Neglected Reality. Int J Mol Sci 2024; 25:1131. [PMID: 38256204 PMCID: PMC10815979 DOI: 10.3390/ijms25021131] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2023] [Revised: 01/11/2024] [Accepted: 01/13/2024] [Indexed: 01/24/2024] Open
Abstract
The mechanistic influences of dopamine (DA) signaling and impact on motor function are nearly always interpreted from changes in nigrostriatal neuron terminals in striatum. This is a standard practice in studies of human Parkinson's disease (PD) and aging and related animal models of PD and aging-related parkinsonism. However, despite dozens of studies indicating an ambiguous relationship between changes in striatal DA signaling and motor phenotype, this perseverating focus on striatum continues. Although DA release in substantia nigra (SN) was first reported almost 50 years ago, assessment of nigral DA signaling changes in relation to motor function is rarely considered. Whereas DA signaling has been well-characterized in striatum at all five steps of neurotransmission (biosynthesis and turnover, storage, release, reuptake, and post-synaptic binding) in the nigrostriatal pathway, the depth of such interrogations in the SN, outside of cell counts, is sparse. However, there is sufficient evidence that these steps in DA neurotransmission in the SN are operational and regulated autonomously from striatum and are present in human PD and aging and related animal models. To complete our understanding of how nigrostriatal DA signaling affects motor function, it is past time to include interrogation of nigral DA signaling. This brief review highlights evidence that changes in nigral DA signaling at each step in DA neurotransmission are autonomous from those in striatum and changes in the SN alone can influence locomotor function. Accordingly, for full characterization of how nigrostriatal DA signaling affects locomotor activity, interrogation of DA signaling in SN is essential.
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Affiliation(s)
- Michael F Salvatore
- Department of Pharmacology & Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76107, USA
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Kasanga EA, Han Y, Shifflet MK, Navarrete W, McManus R, Parry C, Barahona A, Nejtek VA, Manfredsson FP, Kordower JH, Richardson JR, Salvatore MF. Nigral-specific increase in ser31 phosphorylation compensates for tyrosine hydroxylase protein and nigrostriatal neuron loss: Implications for delaying parkinsonian signs. Exp Neurol 2023; 368:114509. [PMID: 37634696 DOI: 10.1016/j.expneurol.2023.114509] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Revised: 08/08/2023] [Accepted: 08/23/2023] [Indexed: 08/29/2023]
Abstract
Compensatory mechanisms that augment dopamine (DA) signaling are thought to mitigate onset of hypokinesia prior to major loss of tyrosine hydroxylase (TH) in striatum that occurs in Parkinson's disease. However, the identity of such mechanisms remains elusive. In the present study, the rat nigrostriatal pathway was unilaterally-lesioned with 6-hydroxydopamine (6-OHDA) to determine whether differences in DA content, TH protein, TH phosphorylation, or D1 receptor expression in striatum or substantia nigra (SN) aligned with hypokinesia onset and severity at two time points. In striatum, DA and TH loss reached its maximum (>90%) 7 days after lesion induction. However, in SN, no DA loss occurred, despite ∼60% TH loss. Hypokinesia was established at 21 days post-lesion and maintained at 28 days. At this time, DA loss was ∼60% in the SN, but still of lesser magnitude than TH loss. At day 7 and 28, ser31 TH phosphorylation increased only in SN, corresponding to less DA versus TH protein loss. In contrast, ser40 TH phosphorylation was unaffected in either region. Despite DA loss in both regions at day 28, D1 receptor expression increased only in lesioned SN. These results support the concept that augmented components of DA signaling in the SN, through increased ser31 TH phosphorylation and D1 receptor expression, contribute as compensatory mechanisms against progressive nigrostriatal neuron and TH protein loss, and may mitigate hypokinesia severity.
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Affiliation(s)
- Ella A Kasanga
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76117, USA
| | - Yoonhee Han
- Robert Stempel School of Public Health and Social Work, Florida International University, Miami, FL 33199, USA
| | - Marla K Shifflet
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76117, USA
| | - Walter Navarrete
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76117, USA
| | - Robert McManus
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76117, USA
| | - Caleb Parry
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76117, USA
| | - Arturo Barahona
- Robert Stempel School of Public Health and Social Work, Florida International University, Miami, FL 33199, USA
| | - Vicki A Nejtek
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76117, USA
| | - Fredric P Manfredsson
- Parkinson's Disease Research Unit, Department of Translational Neuroscience, Barrow Neurological Institute, Phoenix, AZ 85013, USA
| | - Jeffrey H Kordower
- ASU-Banner Neurodegenerative Disease Research Center, Arizona State University, Tempe, AZ 85287, USA
| | - Jason R Richardson
- Robert Stempel School of Public Health and Social Work, Florida International University, Miami, FL 33199, USA
| | - Michael F Salvatore
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76117, USA.
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Kasanga EA, Soto I, Centner A, McManus R, Shifflet MK, Navarrete W, Han Y, Lisk J, Wheeler K, Mhatre-Winters I, Richardson JR, Bishop C, Nejtek VA, Salvatore MF. Moderate intensity aerobic exercise in 6-OHDA-lesioned rats alleviates established motor deficits and reduces neurofilament light and glial fibrillary acidic protein serum levels without increased striatal dopamine or tyrosine hydroxylase protein. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.11.548638. [PMID: 37502851 PMCID: PMC10369940 DOI: 10.1101/2023.07.11.548638] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/29/2023]
Abstract
Background Alleviation of motor impairment by aerobic exercise (AE) in Parkinson's disease (PD) points to a CNS response that could be targeted by therapeutic approaches, but recovery of striatal dopamine (DA) or tyrosine hydroxylase (TH) has been inconsistent in rodent studies. Objective To increase translation of AE, 3 components were implemented into AE design to determine if recovery of established motor impairment, concomitant with >80% striatal DA and TH loss, was possible. We also evaluated if serum levels of neurofilament light (NfL) and glial fibrillary acidic protein (GFAP), blood-based biomarkers of disease severity in human PD, were affected. Methods We used a 6-OHDA hemiparkinson rat model featuring progressive nigrostriatal neuron loss over 28 days, with impaired forelimb use 7 days post-lesion, and hypokinesia onset 21 days post-lesion. After establishing forelimb use deficits, moderate intensity AE began 1-3 days later, 3x per week, for 40 min/session. Motor assessments were conducted weekly for 3 wks, followed by determination of striatal DA, TH protein and mRNA, and NfL and GFAP serum levels. Results Seven days after 6-OHDA lesion, recovery of depolarization-stimulated extracellular DA and DA tissue content was <10%, representing severity of DA loss in human PD, concomitant with 50% reduction in forelimb use. Despite severe DA loss, recovery of forelimb use deficits and alleviation of hypokinesia progression began after 2 weeks of AE and was maintained. Increased NfLand GFAP levels from lesion were reduced by AE. Despite these AE-driven changes, striatal DA tissue and TH protein levels were unaffected. Conclusions This proof-of-concept study shows AE, using exercise parameters within the capabilities most PD patients, promotes recovery of established motor deficits in a rodent PD model, concomitant with reduced levels of blood-based biomarkers associated with PD severity, without commensurate increase in striatal DA or TH protein.
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Kelley DP, Albrechet‐Souza L, Cruise S, Maiya R, Destouni A, Sakamuri SSVP, Duplooy A, Hibicke M, Nichols C, Katakam PVG, Gilpin NW, Francis J. Conditioned place avoidance is associated with a distinct hippocampal phenotype, partly preserved pattern separation, and reduced reactive oxygen species production after stress. GENES, BRAIN, AND BEHAVIOR 2023; 22:e12840. [PMID: 36807494 PMCID: PMC10067435 DOI: 10.1111/gbb.12840] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Revised: 01/23/2023] [Accepted: 01/23/2023] [Indexed: 02/20/2023]
Abstract
Stress is associated with contextual memory deficits, which may mediate avoidance of trauma-associated contexts in posttraumatic stress disorder. These deficits may emerge from impaired pattern separation, the independent representation of similar experiences by the dentate gyrus-Cornu Ammonis 3 (DG-CA3) circuit of the dorsal hippocampus, which allows for appropriate behavioral responses to specific environmental stimuli. Neurogenesis in the DG is controlled by mitochondrial reactive oxygen species (ROS) production, and may contribute to pattern separation. In Experiment 1, we performed RNA sequencing of the dorsal hippocampus 16 days after stress in rats that either develop conditioned place avoidance to a predator urine-associated context (Avoiders), or do not (Non-Avoiders). Weighted genome correlational network analysis showed that increased expression of oxidative phosphorylation-associated gene transcripts and decreased expression of gene transcripts for axon guidance and insulin signaling were associated with avoidance behavior. Based on these data, in Experiment 2, we hypothesized that Avoiders would exhibit elevated hippocampal (HPC) ROS production and degraded object pattern separation (OPS) compared with Nonavoiders. Stress impaired pattern separation performance in Non-Avoider and Avoider rats compared with nonstressed Controls, but surprisingly, Avoiders exhibited partly preserved pattern separation performance and significantly lower ROS production compared with Non-Avoiders. Lower ROS production was associated with better OPS performance in Stressed rats, but ROS production was not associated with OPS performance in Controls. These results suggest a strong negative association between HPC ROS production and pattern separation after stress, and that stress effects on these outcome variables may be associated with avoidance of a stress-paired context.
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Affiliation(s)
- D. Parker Kelley
- Comparative Biomedical SciencesLouisiana State University School of Veterinary MedicineBaton RougeLouisianaUSA
- Department of PhysiologyLouisiana State University Health Sciences CenterNew OrleansLouisianaUSA
| | - Lucas Albrechet‐Souza
- Department of Cell Biology & AnatomyLouisiana State University Health Sciences CenterNew OrleansLouisianaUSA
- Alcohol & Drug Abuse Center of ExcellenceLouisiana State University Health Sciences CenterNew OrleansLouisianaUSA
| | - Shealan Cruise
- Department of PhysiologyLouisiana State University Health Sciences CenterNew OrleansLouisianaUSA
| | - Rajani Maiya
- Department of PhysiologyLouisiana State University Health Sciences CenterNew OrleansLouisianaUSA
| | - Aspasia Destouni
- Comparative Biomedical SciencesLouisiana State University School of Veterinary MedicineBaton RougeLouisianaUSA
| | | | - Alexander Duplooy
- Comparative Biomedical SciencesLouisiana State University School of Veterinary MedicineBaton RougeLouisianaUSA
| | - Meghan Hibicke
- Department of Pharmacology and Experimental TherapeuticsLouisiana State University Health Sciences CenterNew OrleansLouisianaUSA
| | - Charles Nichols
- Alcohol & Drug Abuse Center of ExcellenceLouisiana State University Health Sciences CenterNew OrleansLouisianaUSA
- Department of Pharmacology and Experimental TherapeuticsLouisiana State University Health Sciences CenterNew OrleansLouisianaUSA
| | - Prasad V. G. Katakam
- Department of PharmacologyTulane University School of MedicineNew OrleansLouisianaUSA
| | - Nicholas W. Gilpin
- Department of PhysiologyLouisiana State University Health Sciences CenterNew OrleansLouisianaUSA
- Alcohol & Drug Abuse Center of ExcellenceLouisiana State University Health Sciences CenterNew OrleansLouisianaUSA
- Neuroscience Center of ExcellenceLouisiana State University Health Sciences CenterNew OrleansLouisianaUSA
- Southeast Louisiana VA Healthcare System (SLVHCS)New OrleansLouisianaUSA
| | - Joseph Francis
- Comparative Biomedical SciencesLouisiana State University School of Veterinary MedicineBaton RougeLouisianaUSA
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Kasanga EA, Han Y, Navarrete W, McManus R, Shifflet MK, Parry C, Barahona A, Manfredsson FP, Nejtek VA, Richardson JR, Salvatore MF. Differential expression of RET and GDNF family receptor, GFR-α1, between striatum and substantia nigra following nigrostriatal lesion: a case for diminished GDNF-signaling. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.01.530671. [PMID: 36909534 PMCID: PMC10002742 DOI: 10.1101/2023.03.01.530671] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/07/2023]
Abstract
Although glial cell line-derived neurotrophic factor (GDNF) showed efficacy in preclinical and early clinical studies to alleviate parkinsonian signs in Parkinson's disease (PD), later trials did not meet primary endpoints, giving pause to consider further investigation. While GDNF dose and delivery methods may have contributed to diminished efficacy, one crucial aspect of these clinical studies is that GDNF treatment across all studies began ∼8 years after PD diagnosis; a time point representing several years after near 100% depletion of nigrostriatal dopamine markers in striatum and at least 50% in substantia nigra (SN), and is later than the timing of GDNF treatment in preclinical studies. With nigrostriatal terminal loss exceeding 70% at PD diagnosis, we utilized hemi-parkinsonian rats to determine if expression of GDNF family receptor, GFR-α1, and receptor tyrosine kinase, RET, differed between striatum and SN at 1 and 4 weeks following a 6-hydroxydopamine (6-OHDA) lesion. Whereas GDNF expression changed minimally, GFR-α1 expression decreased progressively in striatum and in tyrosine hydroxylase positive (TH+) cells in SN, correlating with reduced TH cell number. However, in nigral astrocytes, GFR-α1 expression increased. RET expression decreased maximally in striatum by 1 week, whereas in the SN, a transient bilateral increase occurred that returned to control levels by 4 weeks. Expression of brain-derived neurotrophic factor (BDNF) or its receptor, TrkB, were unchanged throughout lesion progression. Together, these results reveal that differential GFR-α1 and RET expression between the striatum and SN, and cell-specific differences in GFR-α1 expression in SN, occur during nigrostriatal neuron loss. Targeting loss of GDNF receptors appears critical to enhance GDNF therapeutic efficacy against nigrostriatal neuron loss. Significance Statement Although preclinical evidence supports that GDNF provides neuroprotection and improves locomotor function in preclinical studies, clinical data supporting its efficacy to alleviate motor impairment in Parkinson's disease patients remains uncertain. Using the established 6-OHDA hemi-parkinsonian rat model, we determined whether expression of its cognate receptors, GFR-α1 and RET, were differentially affected between striatum and substantia nigra in a timeline study. In striatum, there was early and significant loss of RET, but a gradual, progressive loss of GFR-α1. In contrast, RET transiently increased in lesioned substantia nigra, but GFR-α1 progressively decreased only in nigrostriatal neurons and correlated with TH cell loss. Our results indicate that direct availability of GFR-α1 may be a critical element that determines GDNF efficacy following striatal delivery. Highlights GDNF expression was minimally affected by nigrostriatal lesionGDNF family receptor, GFR-α1, progressively decreased in striatum and in TH neurons in SN.GFR-α1 expression decreased along with TH neurons as lesion progressedGFR-α1 increased bilaterally in GFAP+ cells suggesting an inherent response to offset TH neuron lossRET expression was severely reduced in striatum, whereas it increased in SN early after lesion induction.
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