Astrocyte-Derived Peptide Analog Shields Dopaminergic Neurons in Parkinson’s Mouse Model

A single injection of a synthetic analog of an astrocyte-derived neuropeptide protected dopaminergic neurons in the brains of mice treated with a Parkinson’s-like toxin, according to a new study published in Frontiers in Pharmacology. The peptide, called OP, is a modified version of octadecaneuropeptide (ODN), a small signaling molecule produced by astroglial cells in the central nervous system. When researchers delivered OP directly into the brain ventricles of mice exposed to the neurotoxin MPTP, the animals retained far more tyrosine hydroxylase-positive neurons in the substantia nigra and ventral tegmental area than toxin-treated mice that received no peptide, and the treatment also blunted oxidative damage, inflammation, and blood-brain barrier protein loss.

The research team, led by investigators at the University of Rouen Normandy in France and the University of Tunis El Manar in Tunisia, used an acute MPTP model of Parkinson’s disease. Ten-week-old male C57BL/6 mice were divided into four groups of eight animals each: a saline control group, a group receiving MPTP alone, a group receiving OP alone, and a group receiving both MPTP and OP. On the first day of treatment, mice in the toxin groups received three intraperitoneal injections of MPTP at 20 milligrams per kilogram, spaced two hours apart. One hour after the final injection, the peptide groups received a single intracerebroventricular injection of OP at a dose of 10 nanograms in 10 microliters. Seven days later, the animals were euthanized and their brains analyzed by real-time PCR, Western blotting, immunohistochemistry, and biochemical assays.

MPTP is a widely used neurotoxin in Parkinson's research because it induces dopaminergic neuron loss; in this study it reduced tyrosine hydroxylase expression in both the substantia nigra and the ventral tegmental area, regions affected in the human disease. In this study, the toxin produced a measurable toll within a week. Quantitative analysis of immunohistochemical sections showed a 1.61-fold decrease in mean tyrosine hydroxylase fluorescence intensity in the substantia nigra of MPTP-treated animals compared with saline controls. Western blotting confirmed significant reductions in tyrosine hydroxylase protein levels in both the substantia nigra, down 1.86-fold, and the ventral tegmental area, down 1.3-fold.

OP treatment markedly counteracted this damage. The peptide alone had no significant effect on tyrosine hydroxylase levels, but in toxin-exposed mice it attenuated the loss of tyrosine hydroxylase-immunoreactive neurons by 1.19-fold in the substantia nigra, as measured by fluorescence intensity. Western blot analysis showed that OP prevented the MPTP-evoked decline in tyrosine hydroxylase protein by 1.24-fold in the substantia nigra and 1.41-fold in the ventral tegmental area relative to the MPTP-only group. The treated animals also fared better systemically: MPTP caused a roughly 20 percent drop in body weight within two days of treatment, while mice given OP maintained a weight trajectory comparable to controls, and by day four the combined-treatment group weighed significantly more than the MPTP-only group.

A central mechanism behind MPTP toxicity is oxidative stress, and the peptide’s antioxidant effects were among the strongest findings. Using a fluorescent probe that detects reactive oxygen species, the researchers found that MPTP raised ROS levels in the substantia nigra by 1.51-fold compared with saline-treated mice. This was accompanied by a 3.69-fold elevation in malondialdehyde, a product of polyunsaturated fatty acid oxidation that serves as a marker of lipid peroxidation. Co-administration of OP cut ROS overproduction by 0.28-fold and reduced malondialdehyde levels to 0.4-fold of the MPTP-only values. The peptide also boosted catalase activity in the substantia nigra by 1.75-fold in toxin-exposed mice, suggesting a stimulation of endogenous antioxidant defenses rather than a simple scavenging effect.

The study also examined apoptotic signaling, the programmed cell death pathway that contributes to dopaminergic neuron loss. MPTP produced a non-significant reduction in the anti-apoptotic protein Bcl-2 in both the substantia nigra and the ventral tegmental area. OP administration in toxin-treated mice, however, significantly increased Bcl-2 protein levels by 1.48-fold in the substantia nigra and 1.54-fold in the ventral tegmental area. The peptide additionally engaged the MAPK/ERK signaling pathway: OP alone raised total ERK1/2 protein levels by 1.68-fold in the substantia nigra and by 48 percent in the ventral tegmental area, with parallel increases in ERK1/2 phosphorylation. MPTP alone reduced ERK1/2 phosphorylation in the ventral tegmental area to 0.5-fold of control, but in the presence of the toxin, OP maintained elevated levels of both total and phosphorylated ERK1/2 in both regions, at 1.65-fold and 2.66-fold respectively.

Inflammatory and barrier-related markers shifted in a protective direction as well. Seven days after MPTP exposure, tumor necrosis factor-alpha mRNA levels in the substantia nigra were elevated 3.01-fold compared with controls, while vascular endothelial growth factor expression fell to 0.83-fold of control. OP co-treatment significantly attenuated the TNF-alpha induction, to 0.56-fold of the MPTP-only value, and restored VEGF expression to 1.25-fold of the toxin group. Interleukin-10 protein, an anti-inflammatory cytokine, was not significantly altered by MPTP alone, but OP administration, both alone and with the toxin, raised IL-10 levels in the substantia nigra to 2.43-fold of control and 2.99-fold of the MPTP group. In the ventral tegmental area, neither MPTP nor the combined treatment changed IL-10 levels.

The blood-brain barrier findings add a distinctive dimension to the work. OP markedly enhanced occludin protein levels in the substantia nigra, to 1.88-fold of control and 92 percent above MPTP-treated mice, while occludin in the ventral tegmental area was unaffected by any treatment. At the mRNA level, MPTP reduced ZO-1 expression to 0.79-fold of control, whereas claudin-1 and E-cadherin were unchanged by the toxin. OP alone increased all three junctional genes, and in toxin-treated mice it maintained ZO-1 at 1.45-fold, claudin-1 at 1.99-fold, and E-cadherin at 1.44-fold relative to the MPTP group. Plasma levels of tissue inhibitor of metalloproteinase-1, which fell to 0.44-fold of control after MPTP, were restored to 1.78-fold of the toxin group by OP co-treatment, which the authors interpret as a sign of improved extracellular matrix homeostasis and vascular integrity.

Perhaps the most novel component of the study concerns microRNAs, the short non-coding RNAs that fine-tune gene expression and have been implicated in Parkinson’s pathology. Building on earlier in vitro work showing that ODN modulates miR-34b, miR-29a, and miR-21 in cultured astrocytes, the team measured three PD-related microRNAs in the substantia nigra. MPTP left miR-34b-5p unchanged but significantly upregulated miR-29a-5p by 1.55-fold and miR-21-3p by 2.24-fold. OP treatment in toxin-exposed mice normalized miR-29a-5p and miR-21-3p to near-control levels and markedly increased miR-34b-5p expression, to 3.11-fold of the MPTP group. The authors suggest this miRNA signature could eventually serve as a biomarker platform, though they caution that longitudinal studies in plasma and replication in human cohorts are needed before any translational use.

The authors are careful about the limits of the work. The acute MPTP paradigm does not fully recapitulate the chronic, progressive nature of human Parkinson’s disease, and no behavioral or motor testing was performed in this study, so functional benefits remain untested. The intracerebroventricular route used here, which bypasses the blood-brain barrier by injecting directly into the brain ventricles, is a proof-of-concept delivery method that is not clinically practical; the authors point to intranasal delivery as a more feasible strategy for future development, pending pharmacokinetic and dose-response studies in chronic models. Sex-specific effects were not assessed, since only male mice were used. Within those constraints, the study provides what the authors describe as the first in vivo evidence that an ODN analog can preserve dopaminergic neurons in the nigrostriatal system while simultaneously damping oxidative stress, inflammation, apoptotic signaling, and microRNA dysregulation, positioning OP as a multi-target candidate for further preclinical evaluation.

Subject of Research: Neuroprotective effects of an octadecaneuropeptide analog in an acute MPTP mouse model of Parkinson's disease

Article Title: Intracerebroventricular delivery of an ODN peptide analog protects dopaminergic neurons and modulates miRNA expression in a mouse model of Parkinson’s disease

Article References: Bourzam, A., Duraisamy, K., Dlimi, O., El Mehdi, M., Cherif, A., Arabo, A., Lizard, G., Ghrairi, T., Lefranc, B., Le Solliec, M.-A., Masmoudi-Kouki, O., & Leprince, J. (2026). Intracerebroventricular delivery of an ODN peptide analog protects dopaminergic neurons and modulates miRNA expression in a mouse model of Parkinson’s disease. Frontiers in Pharmacology, 17, Article 1933852. https://doi.org/10.3389/fphar.2026.1933852

Image Credits: AI Generated

DOI: 10.3389/fphar.2026.1933852

Keywords: Parkinson's disease, MPTP mouse model, octadecaneuropeptide, dopaminergic neurons, oxidative stress, neuroinflammation, microRNAs, blood-brain barrier, Bcl-2, ERK1/2 signaling, substantia nigra, neuroprotection