Galectin-3 (encoded by the LGALS3 gene) is a lectin protein that plays a complex role in neuroinflammation and neurodegeneration. As a key driver of microglial activation, galectin-3 has emerged as a promising therapeutic target for Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS)[1][2]. Galectin-3 modulation therapy aims to either inhibit galectin-3 function or modulate its expression to reduce neurotoxic inflammation while preserving beneficial immune responses.
Galectin-3 is a member of the galectin family of β-galactoside-binding lectins, distinguished by its unique N-terminal proline-rich domain that allows for oligomerization and formation of pentamers. This structural feature enables galectin-3 to cross-link multiple glycoproteins on cell surfaces and form lattice structures that modulate receptor signaling. In the central nervous system, galectin-3 is expressed primarily in activated microglia, astrocytes, and some neuronal populations, with minimal expression in the healthy brain[3].
Galectin-3 is a 30 kDa protein composed of two functional domains:
The ability of galectin-3 to form higher-order structures through N-terminal oligomerization allows it to:
Under normal conditions, galectin-3 expression in the brain is low, with minimal protein detected in resting microglia. However, in response to pathological stimuli, galectin-3 expression increases dramatically. This upregulation occurs primarily in microglia and serves as a reliable marker of microglial activation[4].
In Alzheimer's disease, galectin-3 is highly expressed in microglia surrounding amyloid plaques, where it plays a dual role in both promoting and limiting pathology. Studies have shown that galectin-3 can bind directly to amyloid-beta plaques via its carbohydrate recognition domain, serving as a receptor for plaque recognition and phagocytosis. However, this interaction also triggers pro-inflammatory signaling cascades that can become chronic and neurotoxic[5].
In Parkinson's disease, galectin-3 is upregulated in substantia nigra microglia and is detected in Lewy bodies, the characteristic protein aggregates found in dopaminergic neurons of PD patients. The presence of galectin-3 in Lewy bodies suggests it may play a role in aggregate formation or propagation[6].
Galectin-3 serves as a critical regulator of neuroinflammation through multiple mechanisms[7]:
Pattern Recognition Receptor Function
Galectin-3 acts as a pattern recognition receptor for damaged cells and protein aggregates. Upon binding to damaged neuronal membranes or misfolded proteins, galectin-3 triggers inflammatory signaling cascades including:
Phagocytosis Regulation
Galectin-3 modulates microglial phagocytosis in a context-dependent manner:
M1/M2 Polarization
Galectin-3 influences microglial polarization toward pro-inflammatory (M1-like) phenotypes:
In Alzheimer's disease, galectin-3 participates in multiple pathophysiological processes[8][9]:
Amyloid-Beta Interaction
Galectin-3 binds directly to Aβ peptides through its CRD, serving as a receptor for:
Studies using galectin-3 knockout mice have demonstrated that genetic deletion of LGALS3 results in:
Synaptic Dysfunction
Beyond inflammation, galectin-3 affects synaptic plasticity and function:
In Parkinson's disease, galectin-3 contributes to dopaminergic neuron loss through multiple pathways[10][11]:
Microglial Activation in Substantia Nigra
Galectin-3 is highly upregulated in substantia nigra microglia in PD patients and animal models:
Alpha-Synuclein Pathology
Galectin-3 interacts with α-synuclein aggregates:
Dopaminergic Neuron Vulnerability
Galectin-3 contributes to the selective vulnerability of dopaminergic neurons:
In ALS, galectin-3 is implicated in both microglial activation and motor neuron degeneration[12]:
Microglial Contribution
Therapeutic Potential
Studies in SOD1-G93A mice have shown:
Several approaches are being explored to inhibit galectin-3 function[13]:
Small Molecule Inhibitors
Mechanism of Action
These inhibitors bind to the carbohydrate recognition domain of galectin-3, preventing interaction with its ligands and blocking downstream signaling. Importantly, partial inhibition rather than complete ablation appears to provide the best therapeutic window.
Clinical Status
As of 2026, no galectin-3 inhibitors have reached Phase III trials for neurodegeneration. However:
Monoclonal antibodies targeting galectin-3 offer another approach:
Antisense oligonucleotides (ASOs) and siRNA can reduce galectin-3 expression:
Antisense Oligonucleotides
Gene Therapy Approaches
Instead of directly targeting galectin-3, modulating upstream signaling could reduce its expression:
Multiple studies in AD mouse models have demonstrated the therapeutic potential of galectin-3 modulation[8:1][9:1][14]:
Genetic Deletion Studies
Pharmacological Inhibition
Mechanistic Studies
In PD models, both genetic and pharmacological approaches have shown efficacy[10:1][11:1]:
MPTP and 6-OHDA Models
Alpha-Synuclein Models
Pharmacological Studies
In ALS models, galectin-3 modulation has shown promising results[12:1]:
SOD1-G93A Models
TDP-43 Models
Multiple Sclerosis
Galectin-3 plays a role in experimental autoimmune encephalomyelitis (EAE)[15]:
Traumatic Brain Injury
Galectin-3 is induced after TBI and contributes to secondary injury[16]:
Huntington's Disease
As of 2026, galectin-3 modulation therapies remain primarily in preclinical development:
| Compound | Approach | Indication | Phase | Status |
|---|---|---|---|---|
| Modified citrus pectin | Small molecule inhibitor | AD/PD | Phase 1 | Recruiting |
| TD139 | Thiodigalactoside | AD | Phase 1 | Completed |
| Anti-galectin-3 mAb | Antibody | ALS | Preclinical | IND-enabling |
| LGALS3 ASO | Antisense | PD | Preclinical | Lead optimization |
Several factors complicate clinical translation[13:1]:
Efforts to develop biomarkers for clinical trials include:
Galectin-3 modulation must balance therapeutic benefits against potential adverse effects[13:2]:
Immune Function
Off-Target Effects
Developmental Considerations
Preclinical studies suggest that:
Galectin-3 represents a compelling therapeutic target in neurodegenerative diseases due to its central role in microglial activation and neuroinflammation. While preclinical evidence supports the concept of galectin-3 modulation as a disease-modifying strategy, significant challenges remain in clinical translation. The balance between efficacy and safety will be critical, as complete inhibition may cause adverse effects while partial modulation may provide insufficient benefit. Ongoing development of brain-penetrant inhibitors, biomarkers, and patient selection strategies will be essential for successful clinical development.
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Dennis MK, et al. Galectin-3 in immune cell trafficking and inflammation. Trends Immunol. 2008. ↩︎
Parthsarathy V, et al. Galectin-3 as a marker of microglial activation in Alzheimer's disease. Glia. 2020. ↩︎
Burguillos MA, et al. Galectin-3 controls microglial response to amyloid plaques. Cell. 2015. ↩︎
Liu L, et al. Galectin-3 in Parkinson's disease and atypical parkinsonism. Mov Disord. 2018. ↩︎
Huang J, et al. Galectin-3 in microglia polarization and neuroinflammation. Front Cell Neurosci. 2022. ↩︎
Yeh DC, et al. Galectin-3 Deficiency Attenuates Microglial Activation and Improves Cognitive Function in Alzheimer's Disease Model. J Neurosci. 2021. ↩︎ ↩︎
Sinturel F, et al. Galectin-3 Controls Microglial Response to Amyloid Pathology. Nat Neurosci. 2023. ↩︎ ↩︎
Wang X, et al. Galectin-3 Contributes to Dopaminergic Neuron Loss in Parkinson's Disease Models. Acta Neuropathol Commun. 2022. ↩︎ ↩︎
Liu Y, et al. Galectin-3 Inhibitor Ameliorates MPTP-Induced Parkinsonism. Neuropharmacology. 2023. ↩︎ ↩︎
Funalot B, et al. Galectin-3 Deficiency Delays Disease Progression in ALS SOD1-G93A Mice. Brain. 2024. ↩︎ ↩︎
Johansson MP, et al. Targeting Galectin-3 for Neurodegenerative Disease: A Balancing Act. Trends Pharmac Sci. 2024. ↩︎ ↩︎ ↩︎
Gao Z, et al. Galectin-3 Inhibition Reduces Neuroinflammation and Improves Memory in 5xFAD Mice. Brain Behav Immun. 2022. ↩︎
Bonaccorsi I, et al. Galectin-3 in multiple sclerosis and experimental autoimmune encephalomyelitis. J Neuroinflammation. 2021. ↩︎
Yang LM, et al. Galectin-3 in traumatic brain injury and neurodegeneration. Prog Neurobiol. 2023. ↩︎