Nose-to-Brain Protein Delivery Shows Promise for Protecting Dopamine Neurons in Parkinson’s Models

Parkinson’s disease remains one of the most stubborn challenges in modern neurology. Its hallmark, the progressive death of dopaminergic neurons in the substantia nigra pars compacta, unfolds silently for years before tremors, rigidity, and slowness of movement announce its presence. By the time clinical diagnosis is possible, a large fraction of these critical neurons has already been lost, and current therapies such as levodopa can only replace missing dopamine rather than halt the underlying degeneration. A new study published in BMC Medicine by Shuyi Liu, Yuan Deng, Wei Si, Zhengbo Wang, and colleagues at Kunming University of Science and Technology now reports that delivering recombinant BMP2 and BMP6 proteins directly into the nose can slow the degeneration of these vulnerable neurons in mouse models of Parkinsonian pathology, offering an early-stage neuroprotective strategy built on a developmental signaling pathway that the brain already uses.

The therapeutic logic of the study rests on the biology of bone morphogenetic proteins, or BMPs, which belong to the transforming growth factor beta superfamily. Although their name reflects their original discovery as inducers of bone and cartilage formation, BMPs are far more versatile than that label suggests. In the developing and mature central nervous system, they act as morphogens and survival factors, shaping neural fate decisions, guiding differentiation, and maintaining the functional integrity of neuronal circuits. The BMP2/6-SMAD1 signaling axis, in particular, has been shown to play a pivotal role in the development and functional maturation of nigrostriatal dopaminergic circuits, the very circuitry that degenerates in Parkinson’s disease. Because SMAD1 is the canonical intracellular mediator downstream of BMP receptors, activation of this pathway in dopaminergic neurons can trigger transcriptional programs that support cell survival, resilience against stress, and proper neuronal differentiation.

Translating that developmental biology into a therapy for an adult neurodegenerative disease, however, requires solving two problems at once. First, the protein must reach the target cells inside the brain. Second, it must do so in a way that is compatible with repeated, long-term administration in patients. Recombinant proteins are large, hydrophilic molecules that do not cross the blood-brain barrier in meaningful quantities, and invasive delivery into the brain parenchyma is impractical for a chronic disease. The research team addressed this by choosing the intranasal route, in which proteins administered into the nasal cavity can reach the central nervous system along olfactory and trigeminal nerve-associated pathways, bypassing the blood-brain barrier entirely. Intranasal delivery is non-invasive, can be self-administered, and has emerged in recent years as a practical gateway for biologics that would otherwise be excluded from the brain.

On the laboratory side, the investigators began with a cellular model designed to reproduce a key molecular insult of Parkinson’s disease. Neural stem cells were transduced with a lentiviral vector carrying A53T-mutant alpha-synuclein, a form of the protein linked to familial Parkinson’s disease and notorious for its propensity to misfold and aggregate. Overexpression of A53T alpha-synuclein in these cells creates a toxic intracellular environment that compromises viability, proliferation, and the capacity of the cells to differentiate along neuronal lineages. When the researchers treated these stressed neural stem cells with recombinant BMP2 and BMP6, they observed a clear rescue: the treated cells showed improved viability, better proliferation, and restored differentiation capacity. This set of results suggested that BMP2/6 signaling can counteract some of the damage inflicted by alpha-synuclein pathology and may exert protective effects on the survival and differentiation of dopaminergic neurons themselves.

Encouraged by the in vitro findings, the team moved into animal models that are standard for preclinical Parkinson’s research. They used two complementary lesion paradigms in mice. The first relied on 6-hydroxydopamine, a catecholaminergic neurotoxin that is taken up selectively by dopaminergic neurons and destroys them through oxidative stress, producing a rapid and reproducible loss of nigrostriatal neurons. The second used alpha-synuclein preformed fibrils, synthetic seeds of misfolded alpha-synuclein that, when introduced into the brain, recruit endogenous alpha-synuclein into pathological aggregates and trigger a slower, more disease-like progressive neurodegeneration accompanied by phosphorylated alpha-synuclein inclusions. Using both models matters because they probe different aspects of the disease: one tests whether neurons can be protected from acute chemical insult, while the other tests whether the treatment can interfere with the protein aggregation cascade that defines Parkinson’s pathology in patients.

In both lesioned mouse groups, the treatment consisted of mouse BMP2/6 recombinant proteins delivered intranasally. The results were consistent across the paradigms. Intranasal BMP2/6 significantly delayed the degeneration of dopaminergic neurons compared with control animals that received the same lesions without the protein therapy. Histological assessment of the substantia nigra and striatum showed that more dopaminergic neurons survived in the treated animals, and the preservation of neurons translated into functional benefit. On the rotarod test, a standard measure of motor coordination and balance in which mice must remain on a rotating rod for as long as possible, the BMP2/6-treated mice performed better than their untreated counterparts. The apomorphine-induced rotation test, which measures asymmetric turning behavior caused by dopamine imbalance between the two sides of the brain after apomorphine administration, likewise showed improvement in treated animals. Together, these behavioral assays demonstrated that the neuronal protection achieved at the cellular level was sufficient to preserve motor function, the clinical dimension that matters most to patients.

The mechanistic thread running through the study is the reactivation of SMAD1 signaling in a context where it has been weakened or overwhelmed by pathological stress. During normal development, BMP2 and BMP6 help dopaminergic neurons acquire their mature identity and maintain their circuitry, and the authors argue that this same pathway can be recruited therapeutically in the adult brain. By supplying recombinant ligands through the nose, the treatment effectively amplifies an endogenous survival signal at a time when alpha-synuclein toxicity, oxidative damage, and inflammatory stress are pushing neurons toward degeneration. The improved survival and differentiation of A53T alpha-synuclein-overexpressing neural stem cells in vitro further hints that BMP2/6 may support not only the survival of existing neurons but also the health of the neural stem cell compartment, a possibility with implications for endogenous repair mechanisms.

Several features of this work make it noteworthy in the crowded field of Parkinson’s neuroprotection. Most candidate neuroprotective agents tested in animal models have failed to translate into humans, often because of delivery problems, dosing limitations, or the fact that interventions began too late in the disease process. The intranasal approach sidesteps the blood-brain barrier without requiring surgery or implanted devices, and protein-based therapy avoids some of the off-target concerns associated with small molecules. Moreover, because BMP2/6 acts on a pathway intrinsic to dopaminergic neuron maintenance rather than on a single pathological species such as aggregated alpha-synuclein, it could in principle complement therapies aimed at aggregation, inflammation, or other disease mechanisms. The authors frame their findings as evidence for a potential role in early neuroprotection, which aligns with the growing consensus that disease-modifying treatment in Parkinson’s must begin before extensive neuronal loss has occurred.

Important caveats remain before this approach can be considered for clinical development. The study was conducted in mice, and rodent models of Parkinson’s disease, while informative, do not fully capture the complexity of the human illness, which involves multiple brain regions, non-motor symptoms, and decades of progression. The dose, frequency, and duration of intranasal protein delivery that would be required in humans are unknown, and the long-term safety of repeatedly activating BMP signaling in the adult brain will need careful evaluation, since BMP pathways participate in diverse processes beyond neuronal survival. It is also not yet established how much of the intranasally delivered protein reaches the human substantia nigra, a deep midbrain structure, although the olfactory route has been shown to deliver biologics to the central nervous system in other contexts. The published version of the study is open access and carries the DOI 10.1186/s12916-026-05269-x, allowing the scientific community to examine the full data, including the supplementary figures and original western blot images that the authors have made available.

Even with those caveats, the study adds a compelling entry to the short list of strategies aimed at protecting rather than replacing dopaminergic neurons. It demonstrates that a signaling axis borrowed from neural development can be harnessed in the adult brain through a practical, non-invasive delivery route, and that the resulting protection is measurable both in surviving neurons and in the motor behavior of living animals. If follow-up studies in larger animals confirm the effect and establish a safe dosing profile, intranasal BMP2/6 could eventually join the growing toolkit of biologics delivered nose-to-brain, shifting the therapeutic goal in Parkinson’s disease from managing symptoms to preserving the neurons that produce dopamine in the first place. For a disease in which every preserved neuron counts, that shift would represent a meaningful step forward.

Subject of Research: Intranasal BMP2/6 recombinant protein therapy for neuroprotection of dopaminergic neurons in Parkinson's disease models

Article Title: Intranasal delivery of BMP2/6 recombinant proteins attenuating Parkinsonian pathology-induced neuronal degeneration

Article References: Liu, S., Deng, Y., Si, W., & Wang, Z. (2026). Intranasal delivery of BMP2/6 recombinant proteins attenuating Parkinsonian pathology-induced neuronal degeneration. BMC Medicine. https://doi.org/10.1186/s12916-026-05269-x

Image Credits: AI Generated

DOI: 10.1186/s12916-026-05269-x

Keywords: Parkinson's disease, dopaminergic neurons, BMP2/6, intranasal delivery, neuroprotection, SMAD1 signaling, alpha-synuclein, neural stem cells, 6-hydroxydopamine, preformed fibrils, substantia nigra, recombinant protein therapy