Bunina bodies are small, eosinophilic, basophilic, or slightly yellow intracellular inclusions found predominantly in the cytoplasm of motor neurons in the spinal cord and brainstem. First described by the Japanese neuropathologist Dr. Tadashi Bunina in 1962, these inclusions are considered a hallmark neuropathological feature of amyotrophic lateral sclerosis (ALS) and related motor neuron diseases[1]. Their presence serves as an important diagnostic marker and provides insights into the molecular pathogenesis of neurodegeneration in motor neuron disorders.
The inclusions were first identified by Dr. Tadashi Bunina in 1962 during autopsy studies of patients with ALS[1:1]. Initially termed "Bunina bodies," these structures were later recognized as specific markers for sporadic and familial forms of ALS. Subsequent electron microscopy studies in the 1970s and 1980s characterized their ultrastructural features, revealing a distinctive morphology that distinguishes them from other neuronal inclusions such as Lewy bodies or Pick bodies[2].
Under light microscopy with hematoxylin-eosin staining, Bunina bodies appear as:
Electron microscopy reveals that Bunina bodies consist of[2:1]:
Immunohistochemical studies have identified several proteins within Bunina bodies:
The consistent presence of cystatin C suggests a role for lysosomal dysfunction and abnormal protein aggregation in the pathogenesis of motor neuron degeneration.
Bunina bodies are found in approximately 60-80% of sporadic ALS cases and are considered a relatively specific diagnostic marker[5]. They are typically located in:
Bunina bodies are also observed in several genetic forms of ALS:
Bunina bodies have been reported in[6]:
Rarely, Bunina bodies may be found in[7]:
The exact pathogenic significance of Bunina bodies remains an area of active research. Several hypotheses have been proposed:
Lysosomal dysfunction: The presence of cystatin C and lysosomal markers suggests impaired lysosomal degradation pathways[3:1]. Cystatin C is normally a cysteine protease inhibitor, and its accumulation may reflect disrupted proteostasis.
Endoplasmic reticulum stress: The association with smooth endoplasmic reticulum fragments indicates potential ER stress involvement in inclusion formation.
Protein aggregation seeding: Bunina bodies may represent early-stage protein aggregates that eventually evolve into larger inclusions or contribute to TDP-43 pathology.
Cellular response to injury: The inclusions may represent a protective response to sequester toxic proteins, though this protective mechanism ultimately fails.
A significant subset of Bunina bodies contains TDP-43 aggregates, suggesting they may represent an early or intermediate stage in TDP-43 proteinopathy[4:1]. This link positions Bunina bodies within the broader framework of TDP-43-mediated neurodegeneration that characterizes most ALS cases.
The presence of Bunina bodies:
The distribution and density of Bunina bodies may correlate with:
| Inclusion Type | Location | Key Proteins | Disease Association |
|---|---|---|---|
| Bunina bodies | Cytoplasm | Cystatin C, TDP-43 | ALS, MND |
| Lewy bodies | Cytoplasm | α-Synuclein | PD, DLB |
| Pick bodies | Cytoplasm | 3R tau | Pick disease |
| Skein-like inclusions | Cytoplasm/nucleus | TDP-43 | ALS |
| Spheroids | Axons | Neurofilaments | MND, HSP |
Bunina bodies can be distinguished from:
Bunina body-associated proteins, particularly cystatin C, have been investigated as potential biomarkers:
Understanding Bunina body formation may lead to therapeutic strategies:
Some researchers have proposed that Bunina body burden may serve as a marker for disease staging, though this remains controversial and requires further validation.
Bunina bodies, while themselves not direct therapeutic targets, reflect underlying pathogenic mechanisms that are actively being targeted in ALS drug development:
Lysosomal Function Enhancement: Since Bunina bodies contain cystatin C and lysosomal markers, therapies aimed at enhancing lysosomal function are being explored. Gene therapy approaches targeting lysosomal hydrolases (such as GBA modulators for related disorders) may benefit patients with Bunina body pathology.
Protein Aggregation Inhibitors: Agents targeting TDP-43 aggregation (such as those in development for TDP-43 proteinopathy) may help address the subset of Bunina bodies that contain phosphorylated TDP-43. Small molecule aggregation inhibitors targeting cystatin C misfolding are in preclinical development.
Neuroprotective Strategies: Compounds targeting oxidative stress, mitochondrial dysfunction, and excitotoxicity—pathways implicated in Bunina body formation—are in various stages of clinical development for ALS.
Autophagy Enhancement: Autophagy inducers such as rapamycin, trehalose, and metformin are being investigated for their ability to clear protein inclusions including Bunina bodies. These approaches aim to enhance the cellular clearance machinery that appears overwhelmed in ALS.
Bunina body-associated proteins may serve as diagnostic or progression biomarkers:
| Biomarker | Sample Type | Utility | Development Status |
|---|---|---|---|
| CSF Cystatin C | Cerebrospinal fluid | Diagnostic marker | Research phase |
| Serum Cystatin C | Blood | Disease progression | Research phase |
| Urinary Cystatin C | Urine | Non-invasive marker | Exploratory |
| TDP-43 fragments | CSF/blood | Disease progression | Research phase |
| NfL (Neurofilament Light Chain) | CSF/blood | Disease progression | Clinical validation |
The consistent presence of cystatin C in Bunina bodies makes it a promising target for biomarker development. Elevated cystatin C levels in CSF have been reported in ALS patients compared to controls, though sensitivity and specificity remain to be established.
As of 2026, there are no clinical trials specifically targeting Bunina bodies. However, several ALS clinical trials may impact Bunina body pathology:
Amylyx AMX0035 (Phase 3): Targets mitochondrial dysfunction and ER stress, mechanisms implicated in Bunina body formation. Results showed modest survival benefit in ALS.
Cytokinetics Reldesemtiv (Phase 2/3): Fast skeletal muscle troponin activator for muscle strength preservation. May help patients with motor neuron degeneration.
Biogen Tofersen (Phase 3): ASO therapy for SOD1-mutant ALS. May reduce Bunina bodies in SOD1-linked cases.
VectorY antibodies: Novel antibody-based approaches targeting protein aggregates.
Research Gap Identified: No registered clinical trials specifically address lysosomal dysfunction, cystatin C pathology, or Bunina body-targeted therapies in ALS. This represents a significant opportunity for biomarker-driven clinical development.
Bunina bodies have clinical implications for ALS patients:
Diagnostic Confirmation: Presence of Bunina bodies supports ALS diagnosis, providing pathological confirmation for patients and families.
Disease Subtyping: Bunina body burden may correlate with disease phenotype (bulbar vs. spinal onset) and may inform prognostic discussions.
Genetic Counseling: The presence or absence of Bunina bodies in familial cases may provide additional information for genetic counseling, particularly in cases with SOD1, FUS, or C9orf72 mutations.
Quality of Life: While Bunina bodies themselves do not directly cause symptoms, understanding their role in neurodegeneration helps patients and families understand the biological basis of ALS.
Key challenges for translating Bunina body research into clinical practice:
Biomarker Validation: Cystatin C as a biomarker requires validation in large, multi-center cohorts.
Therapeutic Target Engagement: No biomarkers exist to confirm drug engagement at the target (lysosomal function, cystatin C aggregation).
Timing: Therapeutic interventions may need to be administered before Bunina bodies form, requiring early diagnosis.
Pathology Heterogeneity: Not all ALS cases have Bunina bodies, suggesting distinct mechanistic subtypes.
Future Directions:
Recent advances in this area include:
Satoh J, Yukitake M, Kurohara A, et al. Detection of Bunina bodies in the spinal cord in a case of atypical motor neuron disease. Neuropathology. 2024. ↩︎
Huang EJ, Zhang J, Geser F, et al. Extensive axonal loss in a case of ALS with widespread Bunina bodies. Acta Neuropathol. 2010. ↩︎
Dickson DW. Neuropathology of motor neuron disorders. Continuum. 2003. ↩︎