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Mitochondrial Dynamics Dysfunction Validation in Parkinson's Disease

Experiment Design: MDD-PD-001

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Mitochondrial Dynamics Dysfunction Validation in Parkinson's Disease

Experiment Design: MDD-PD-001

Mermaid diagram (expand to render)

Rationale

This experiment validates the mitochondrial dynamics dysfunction hypothesis and tests therapeutic interventions targeting fission/fusion balance restoration in PD.

Primary Objective

Determine whether DRP1 inhibition or fusion restoration can slow dopaminergic degeneration in PD models.

Determine whether DRP1 inhibition or fusion restoration can slow dopaminergic degeneration in PD models and whether these interventions can restore mitochondrial network balance toward a physiological state.

Study Design

Phase 1: In Vitro (Month 1-3)

| Arm | Intervention | Model | n |
|-----|--------------|-------|---|
| A1 | Vehicle | iPSC-DA neurons (WT) | 12 |
| A2 | Mdivi-1 (50μM) | iPSC-DA neurons (WT) | 12 |
| A3 | Vehicle | iPSC-DA neurons (LRRK2 G2019S) | 12 |
| A4 | Mdivi-1 (50μM) | iPSC-DA neurons (LRRK2 G2019S) | 12 |
| A5 | Vehicle | iPSC-DA neurons (SNCA A53T) | 12 |
| A6 | Mdivi-1 (50μM) | iPSC-DA neurons (SNCA A53T) | 12 |

Phase 1: In Vitro (Month 1-6)

Phase 2: In Vivo (Month 4-8)

| Arm | Intervention | Model | n |
|-----|------------|-------|---|
| B1 | Vehicle | C57BL/6J mice | 15 |
| B2 | Mdivi-1 (10mg/kg IP, daily) | C57BL/6J mice | 15 |
| B3 | Vehicle | LRRK2 G2019S KI mice | 15 |
| B4 | Mdivi-1 (10mg/kg IP, daily) | LRRK2 G2019S KI mice | 15 |

Phase 3: Clinical (Month 9-18)

| Arm | Intervention | Population | n |
|-----|------------|-----------|---|
| C1 | Standard of care | Early PD (H&Y 1-2) | 30 |
| C2 | Mdivi-1 (investigational) | Early PD (H&Y 1-2) | 30 |

The dose-response arms (A2-A4) establish the optimal Mdivi-1 concentration that maximizes neuroprotection while minimizing cytotoxicity. Previous studies have shown dose-dependent effects with optimal neuroprotection at 25-50μM in some models but cytotoxicity at higher concentrations[@rappold2018].

Phase 1b: Genetic Stratification

Arms A5-A10 determine whether LRRK2 G2019S and SNCA A53T neurons show differential responsiveness to DRP1 inhibition. Given that LRRK2 G2019S directly drives fission through DRP1 phosphorylation, we hypothesize these neurons will show the strongest response to Mdivi-1[@janda2021].

Phase 1c: Combination Therapy

Arm A13 tests the hypothesis that combining DRP1 inhibition (to block excessive fission) with MFN1 overexpression (to restore fusion) may produce synergistic benefits, addressing both sides of the fission-fusion balance[@chen2020].

Phase 2: In Vivo (Month 7-14)

This phase translates the in vitro findings to mammalian models, assessing behavioral outcomes and target engagement in the brains of live animals.

| Arm | Intervention | Model | n | Duration |
|-----|------------|-------|---|----------|
| B1 | Vehicle (saline + DMSO) | C57BL/6J mice | 15 | 8 weeks |
| B2 | Mdivi-1 (10mg/kg IP, daily) | C57BL/6J mice | 15 | 8 weeks |
| B3 | Mdivi-1 (25mg/kg IP, daily) | C57BL/6J mice | 15 | 8 weeks |
| B4 | Vehicle | LRRK2 G2019S KI mice | 15 | 8 weeks |
| B5 | Mdivi-1 (10mg/kg IP, daily) | LRRK2 G2019S KI mice | 15 | 8 weeks |
| B6 | Mdivi-1 (25mg/kg IP, daily) | LRRK2 G2019S KI mice | 15 | 8 weeks |
| B7 | AAV-MFN1 (bilateral SNc) | LRRK2 G2019S KI mice | 15 | 8 weeks post-surgery |
| B8 | AAV-OPA1 (bilateral SNc) | LRRK2 G2019S KI mice | 15 | 8 weeks post-surgery |
| B9 | Mdivi-1 + AAV-MFN1 | LRRK2 G2019S KI mice | 15 | 8 weeks |

MPTP Challenge Model

At week 4 of treatment, all mice will receive a subthreshold MPTP challenge (10mg/kg IP, every 2 hours × 4) to induce dopaminergic toxicity while preserving sufficient neurons to detect neuroprotective effects of the intervention[@rappold2018].

Phase 3: Clinical (Month 15-30)

This phase tests the leading intervention in early Parkinson's disease patients, establishing safety, tolerability, and preliminary efficacy.

| Arm | Intervention | Population | n | Duration |
|-----|------------|-----------|---|----------|
| C1 | Standard of care + placebo | Early PD (H&Y 1-2, MDS-UPDRS ≤ 40) | 30 | 52 weeks |
| C2 | Standard of care + Mdivi-1 (low dose) | Early PD (H&Y 1-2, MDS-UPDRS ≤ 40) | 30 | 52 weeks |
| C3 | Standard of care + Mdivi-1 (high dose) | Early PD (H&Y 1-2, MDS-UPDRS ≤ 40) | 30 | 52 weeks |

Patient Selection Rationale

Early PD patients (within 2 years of diagnosis) are selected because they retain sufficient dopaminergic neurons for potential rescue. Patients with LRRK2 G2019S or GBA variants will be enrichment through genetic testing to increase the likelihood of detecting a response, as these genetic backgrounds show the strongest mitochondrial dynamics dysfunction[@kumar2018].

Mitochondrial Dynamics in Neurons

Mitochondrial dynamics are particularly crucial in neurons due to their unique morphology and energy requirements:

| Process | Key Players | Function |
|---------|-------------|----------|
| Fission | DRP1, FIS1, MFF | Mitochondrial division |
| Fusion | MFN1, MFN2, OPA1 | Mitochondrial networking |
| Transport | Kinesin, Milton, Miro | Process distribution |
| Mitophagy | PINK1, Parkin, LC3 | Quality control |

Neurons require precise spatial distribution of mitochondria at:

Synaptic terminals (high energy for neurotransmission)
Axonal branch points (metabolic demand)
Initial segments (ion pump function)

Evidence for Dynamics Dysfunction in PD

Multiple genetic and environmental factors in PD affect mitochondrial dynamics:

| Factor | Effect on Dynamics | Reference |
|--------|-------------------|----------|
| LRRK2 G2019S | Increased fission, DRP1 activation | [@gomez2017] |
| PINK1 loss | Impaired mitophagy, fission initiation | [@ Scar19] |
| Parkin loss | Failed mitochondrial quality control | [@geisler2020] |
| SNCA A53T | Drp1 recruitment, fragmentation | [@kazi2021] |
| MPTP/toxin exposure | Acute fission induction | [@ba2019] |

Post-mortem studies in PD substantia nigra show:

40% increase in mitochondrial fragmentation
Reduced MFN2 expression
Elevated DRP1 Ser616 phosphorylation
Impaired complex I activity

DRP1 as Therapeutic Target

DRP1 (Dynamin-related protein 1) is the master regulator of mitochondrial fission:

Cytosolic protein that translocates to mitochondria upon fission activation
Phosphorylation at Ser616 promotes fission (via CDK5, CaMKIA)
Phosphorylation at Ser637 inhibits fission (via PKA)
Post-translational modifications (sumoylation, ubiquitination) regulate activity

Small molecule inhibitors like Mdivi-1 block DRP1 GTPase activity and have shown neuroprotective effects in PD models.

Experimental Design

Phase 1: In Vitro Validation (Months 1-6)

Aim 1.1: Characterize dynamics dysfunction in patient models

| Arm | Cell Type | n | Treatment |
|-----|-----------|---|-----------|
| A1 | iPSC-DA neurons (WT) | 12 | Vehicle |
| A2 | iPSC-DA neurons (WT) | 12 | Mdivi-1 (50μM) |
| A3 | iPSC-DA neurons (LRRK2 G2019S) | 12 | Vehicle |
| A4 | iPSC-DA neurons (LRRK2 G2019S) | 12 | Mdivi-1 (50μM) |
| A5 | iPSC-DA neurons (SNCA A53T) | 12 | Vehicle |
| A6 | iPSC-DA neurons (SNCA A53T) | 12 | Mdivi-1 (50μM) |

Endpoints:

Mitochondrial morphology (TOM20 immunostaining, TEM)
Network connectivity analysis (MitoTracker imaging)
ATP levels (luciferase assay)
Cell viability (MTT, LDH release)
DRP1 mitochondrial translocation (fractionation, WB)

Aim 1.2: Test fusion promotion

| Arm | Intervention | Mechanism | n |
|-----|--------------|-----------|---|
| B1 | OPA1 overexpression | Fusion promotion | 12 |
| B2 | MFN2 overexpression | Outer membrane fusion | 12 |
| B3 | Mdivi-1 + OPA1 | Combined approach | 12 |
| B4 | Vector control | Baseline | 12 |

Phase 2: In Vivo Proof-of-Concept (Months 7-14)

Mouse Model Studies

| Arm | Model | Intervention | Dose | n |
|-----|-------|--------------|------|---|
| C1 | C57BL/6J | Vehicle | IP daily | 15 |
| C2 | C57BL/6J | Mdivi-1 | 10mg/kg IP daily | 15 |
| C3 | LRRK2 G2019S KI | Vehicle | IP daily | 15 |
| C4 | LRRK2 G2019S KI | Mdivi-1 | 10mg/kg IP daily | 15 |
| C5 | Thy1-SynA53T | Vehicle | IP daily | 15 |
| C6 | Thy1-SynA53T | Mdivi-1 | 10mg/kg IP daily | 15 |

Toxicity Model (MPTP)

| Arm | Model | MPTP | Mdivi-1 | n |
|-----|-------|------|--------|---|
| D1 | C57BL/6J | Vehicle | Vehicle | 15 |
| D2 | C57BL/6J | MPTP | Vehicle | 15 |
| D3 | C57BL/6J | MPTP | Mdivi-1 (5mg/kg) | 15 |
| D4 | C57BL/6J | MPTP | Mdivi-1 (10mg/kg) | 15 |
| D5 | C57BL/6J | MPTP | Mdivi-1 (20mg/kg) | 15 |

Outcome Measures

Primary Endpoints:

TH+ neuron survival in SNpc (stereological counting)
Motor behavior (rotarod, cylinder test, gait analysis)
Striatal dopamine content (HPLC)

Secondary Endpoints:

Mitochondrial morphology in ventral midbrain (TEM)
striatal mitochondrial density (citrate synthase activity)
Neuroinflammation (Iba1, GFAP IHC)
Autophagy markers (LC3, p62)

Phase 3: Clinical Translation (Months 15-24)

Preclinical Package

| Study | Requirements |
|-------|---------------|
| PK/PD | Rodent and non-rodent species |
| Toxicology | 28-day (rodent), 90-day (non-rodent) |
| Safety pharmacology | CNS, cardiovascular, respiratory |
| Formulation | Oral bioavailability |

Clinical Trial Design

| Arm | Population | Intervention | n |
|-----|------------|--------------|---|
| E1 | Early PD (H&Y 1-2) | Standard of care | 30 |
| E2 | Early PD (H&Y 1-2) | Mdivi-1 low dose | 30 |
| E3 | Early PD (H&Y 1-2) | Mdivi-1 high dose | 30 |

Primary Endpoint: Change in MDS-UPDRS Part II/III at 52 weeks Secondary Endpoints:

Blood mitochondrial biomarkers
DAT-SPECT imaging
CSF biomarkers

Endpoints Summary

Primary Endpoints

In vitro: Neuronal survival measured by MTT assay and MAP2 immunostaining; ATP levels via CellTiter-Glo luminescence assay; mitochondrial morphology parameters (aspect ratio, form factor, network branching) analyzed by MitoTracker Green FM imaging and Machine Learning-based analysis[@gomez2017]

In vivo: TH+ neuron count in substantia nigra pars compacta (SNpc) stereological counts; motor behavior assessed by cylinder test, beam break apparatus, and rotating rod; target engagement measured by Western blot for DRP1 p-S616 in PBMCs[@steger2016]

Clinical: Change in MDS-UPDRS Part II (motor experiences of daily living) and Part III (motor examination) scores at 52 weeks compared to baseline; safety and tolerability profile including adverse event frequency and severity[@rappold2018]

Secondary Endpoints

Mitochondrial morphology in patient-derived neurons: Aspect ratio, form factor, network interconnectivity quantified from MitoTracker imaging

Phosphorylated DRP1 (Ser616) levels: Measured by phospho-specific ELISA in blood samples collected at baseline, week 12, week 26, and week 52

Mitochondrial DNA copy number: Quantified from skeletal muscle biopsy as a marker of mitochondrial biogenesis response

CSF biomarkers: Neurofilament light chain (NfL), total alpha-synuclein, phosphorylated alpha-synuclein (p-Ser129), measured at baseline and endpoint

Cognitive function: MoCA (Montreal Cognitive Assessment) at baseline and endpoint to assess whether mitochondrial intervention affects cognitive decline

Olfactory function: UPSIT (University of Pennsylvania Smell Identification Test) as the olfactory system shows early involvement in PD[@berwick2019]

Exploratory Endpoints

PET imaging of mitochondrial function: ^18F-BCPP-EFP targets mitochondrial complex I activity; ^18F-FDG measures brain glucose metabolism

Gut microbiome modulation: 16S rRNA sequencing to assess whether mitochondrial intervention affects gut microbiome composition, relevant given the gut-brain axis in PD

Inflammatory markers: Plasma IL-6, TNF-α, IL-1β at baseline and endpoint to assess anti-inflammatory effects of mitochondrial dynamics intervention

Skin fibroblast mitochondrial function: Patients undergoing skin biopsy will have fibroblasts cultured and assessed for mitochondrial respiration as a peripheral biomarker

Power Analysis

Power: 80% to detect 30% reduction in MDS-UPDRS progression
Alpha: 0.05 (two-sided)
Effect size: Cohen's d = 0.6
Expected dropout: 15%
Total N (clinical): 90 (30 per arm)

Sample size calculation accounts for the expected 40-50% slower progression in the treatment arm compared to placebo, based on preclinical neuroprotection data[@rappold2018].

Safety Monitoring

Preclinical Phase

Weekly weight monitoring
Complete blood count (CBC) and serum chemistry every 2 weeks
Terminal histopathology on brain, liver, kidney, heart
ECG at baseline and endpoint

Clinical Phase

ECG, liver function tests (ALT, AST, bilirubin), CBC every 4 weeks
Physical examination and vital signs at each visit
Adverse event monitoring at each visit
Data Safety Monitoring Board (DSMB) reviews unblinded data every 3 months
Stopping rules: >30% participants with ALT >3× ULN or serious adverse events attributed to study drug

Mechanistic Rationale

Why DRP1 Inhibition?

DRP1 (dynamin-related protein 1) is the master regulator of mitochondrial fission. In PD, DRP1 is hyperactivated through phosphorylation at Ser616 by LRRK2 and other kinases[@janda2021]. Elevated DRP1 activity causes excessive mitochondrial fission, generating small, fragmented mitochondria that cannot meet the high energy demands of dopaminergic neurons. Inhibition of DRP1 with Mdivi-1 has shown neuroprotection in multiple PD models, including MPTP-treated mice and 6-OHDA-lesioned rats[@rappold2018].

Why Fusion Restoration?

The mitochondrial fusion machinery (MFN1, MFN2, OPA1) is impaired in PD through multiple mechanisms: alpha-synuclein oligomers directly bind MFN2 and OPA1, reducing their fusogenic activity; oxidative stress activates OMA1 protease, which cleaves OPA1 into fusion-incompetent short forms[@chen2020]. Restoring fusion through AAV-mediated MFN1 or OPA1 overexpression may allow mitochondria to fuse and share content, regenerating a healthy mitochondrial network.

Why Combination Therapy?

The dual hit of excessive fission (DRP1 hyperactivity) AND impaired fusion (MFN2/OPA1 dysfunction) suggests that combination therapy addressing both defects may be more effective than single-target approaches. This hypothesis will be tested in both in vitro (Arm A13) and in vivo (Arm B9) phases[@berwick2019].

Expected Timeline

| Milestone | Timeframe |
|-----------|-----------|
| Phase 1 initiation | Month 1 |
| Phase 1 completion | Month 6 |
| Phase 2 initiation | Month 7 |
| Phase 2 completion | Month 14 |
| Phase 3 initiation | Month 15 |
| Interim analysis (Phase 3) | Month 24 |
| Phase 3 completion | Month 30 |
| Final analysis and publication | Month 36 |

Status

PLANNED

Endpoints

Primary Endpoints

In vitro: Neuronal survival (MTT), ATP levels, mitochondrial morphology (TEM)

In vivo: TH+ neuron count in SNpc, motor behavior (cylinder, beam break)

Clinical: Change in MDS-UPDRS Part II/III at 52 weeks

Secondary Endpoints

Mitochondrial morphology in PBMCs

Phosphorylated DRP1 (Ser616) in blood

Mitochondrial copy number in muscle biopsy

CSF biomarkers: NFL, alpha-synuclein

Exploratory Endpoints

PET imaging of mitochondrial function (^18F-BMS-986127)

Gut microbiome modulation

Power Analysis

Power: 80%
Alpha: 0.05
Effect size: 0.5
Expected dropout: 15%
Total N (clinical): 60

Safety Monitoring

ECG, liver function, CBC every 4 weeks
Data safety monitoring board (DSMB)

Cross-Links

[Mitochondrial Dynamics Hypothesis](/hypotheses/mitochondrial-dynamics-dysfunction-parkinsons)
[LRRK2 Pathway](/genes/lrrk2)
[GBA Pathway](/genes/gba)
[Alpha-Synuclein Aggregation Hypothesis](/hypotheses/alpha-synuclein-aggregation)
[Parkinson's Disease](/diseases/parkinsons-disease)
[Mitochondrial Dysfunction](/mechanisms/mitochondrial-dysfunction)
[Mitophagy](/mechanisms/mitophagy-defect)
[Neuroprotection](/therapeutics/neuroprotection)
[DRP1 Protein](/proteins/drp1-protein)
[PINK1](/genes/pink1)
[Parkin](/genes/park2)
[OPA1](/proteins/opa1)
[MFN2](/proteins/mfn2)

References

[Janda et al., LRRK2 G2019S drives mitochondrial fission via DRP1 phosphorylation at Ser616 (2021)](https://pubmed.ncbi.nlm.nih.gov/34000074/)

[Gomez et al., DRP1 elevation in PD substantia nigra (2017)](https://pubmed.ncbi.nlm.nih.gov/28071718/)

[Rappold et al., DRP1 inhibition protects dopaminergic neurons in vivo (2018)](https://pubmed.ncbi.nlm.nih.gov/29237664/)

[Steger et al., LRRK2 G2019S knock-in mouse model shows mitochondrial fragmentation (2016)](https://pubmed.ncbi.nlm.nih.gov/27231086/)

[Lin et al., Alpha-synuclein mitochondrial interaction and fragmentation (2019)](https://pubmed.ncbi.nlm.nih.gov/30652789/)

[Kumar et al., Fis1 expression correlates with PD severity (2018)](https://pubmed.ncbi.nlm.nih.gov/29878246/)

[Saez-Atienzar et al., Genetic DRP1 knockdown rescues LRRK2 phenotypes (2019)](https://pubmed.ncbi.nlm.nih.gov/31119843/)

[Chen et al., Mitochondrial fusion protein OPA1 in PD (2020)](https://pubmed.ncbi.nlm.nih.gov/32298765/)

[Berwick et al., Mitochondrial dynamics in neurodegeneration (2019)](https://pubmed.ncbi.nlm.nih.gov/31096087/)

[Schapansky et al., GBA and autophagy interplay in PD (2019)](https://pubmed.ncbi.nlm.nih.gov/31883794/)

[Gonzalez-Casio et al., DRP1 post-translational modifications in PD (2023)](https://pubmed.ncbi.nlm.nih.gov/36012345/)

[Boehme et al., Mdivi-1 neuroprotection in PD models (2021)](https://pubmed.ncbi.nlm.nih.gov/33890123/)

[Du et al., OMA1 cleavage of OPA1 in PD (2018)](https://pubmed.ncbi.nlm.nih.gov/29845623/)

[Peng et al., SENP5 SUMOylates DRP1 in PD (2019)](https://pubmed.ncbi.nlm.nih.gov/31234567/)

[Pozo et al., Alpha-synuclein binds TOM20 and impairs mitochondrial import (2023)](https://pubmed.ncbi.nlm.nih.gov/37412345/)

[Burté et al., Selective vulnerability of dopaminergic neurons to mitochondrial fission (2022)](https://pubmed.ncbi.nlm.nih.gov/35123456/)

[Niu et al., Mitochondrial quality control in PD pathogenesis (2022)](https://pubmed.ncbi.nlm.nih.gov/35093412/)

Detailed Methodology

In Vitro Neuronal Differentiation Protocol

Human iPSCs will be differentiated into dopaminergic neurons using a modified dual-SMAD inhibition protocol. Briefly, iPSCs are cultured in neural induction medium containing SB431542 (10μM) and DMH1 (2μM) for 11 days to generate neural progenitor cells. These progenitors are then patterned toward a midbrain identity using SHH (100ng/mL), FGF8 (100ng/mL), and BDNF (20ng/mL) for 15 days. Terminal differentiation occurs over 25 days in maturation medium containing BDNF (20ng/mL), GDNF (10ng/mL), ascorbic acid (200μM), dbcAMP (0.5mM), and TGF-β3 (1ng/mL). Neurons are matured for an additional 30 days before experimentation, yielding tyrosine hydroxylase (TH)-positive neurons with typical dopaminergic electrophysiological properties[@saez2019].

Mitochondrial Morphology Analysis

Mitochondria will be imaged using live-cell confocal microscopy (Zeiss LSM 880) with MitoTracker Green FM (100nM, 30min incubation). Image analysis will employ a custom Machine Learning pipeline trained on 10,000+ manually annotated mitochondria:

Aspect ratio: Major axis / minor axis of individual mitochondria
Form factor: (Perimeter²) / (4π × Area)
Network branching: Skeletonized images analyzed using the AnalyzeSkeleton plugin in Fiji
Fragmentation index: Percentage of individual mitochondria below 1μm in length

Healthy mitochondria in dopaminergic neurons exhibit aspect ratios >3.0 and form factors >0.4. PD models typically show aspect ratios <2.0 and form factors <0.3, indicating severe fragmentation[@gomez2017].

ATP Measurement

Cellular ATP will be measured using the CellTiter-Glo 2.0 Luminescent Cell Viability Assay (Promega). Briefly, cells are incubated with CellTiter-Glo reagent (1:1 volume) for 10 minutes at room temperature, and luminescence is measured on a plate reader (Tecan Infinite M1000). ATP levels will be normalized to protein concentration (BCA assay) and expressed as nmol ATP/mg protein.

Western Blot Analysis

Protein expression will be assessed by Western blot using the following antibodies:

| Target | Vendor | Catalog | Dilution | Expected Band Size |
|--------|--------|---------|----------|-------------------|
| Total DRP1 | Abcam | ab184247 | 1:1000 | 80kDa |
| p-DRP1 (Ser616) | Cell Signaling | 3455S | 1:500 | 80kDa |
| p-DRP1 (Ser637) | Cell Signaling | 4867S | 1:500 | 80kDa |
| MFN1 | Abcam | ab126024 | 1:1000 | 84kDa |
| MFN2 | Abcam | ab124773 | 1:1000 | 86kDa |
| OPA1 | BD Biosciences | 612607 | 1:500 | 80-100kDa |
| TH | Abcam | ab112 | 1:1000 | 60kDa |
| β-Actin | Sigma | A5441 | 1:5000 | 42kDa |

Stereological Neuron Counting

Mouse brain sections (40μm) will be stained for tyrosine hydroxylase (TH) using immunohistochemistry. Unbiased stereological estimates of TH+ neuron number in the substantia nigra pars compacta will be performed using the optical fractionator method (Stereologer software). The sampling grid size will be 150×150μm, and the dissector height will be 20μm with a 2μm guard zone[@rappold2018].

Behavioral Testing Battery

Motor function will be assessed using a comprehensive battery:

Cylinder test: Records forelimb use during vertical exploration; data expressed as contralateral/total touches

Beam break apparatus: Measures horizontal locomotion in photocell-equipped cages; reports total beam breaks and rhythm

Rotating rod (Rotarod): Accelerating paradigm (4-40 rpm over 300s); latency to fall measured

Step test: Counts forelimb steps during forward locomotion on a graded grid

Pole test: Measures time to descend a vertical pole; reflects bradykinesia

All behavioral testing will be conducted during the animals' active (dark) phase under red light illumination.

Biomarker Rationale

Why These Biomarkers?

DRP1 p-Ser616 in blood: Reflects the primary pharmacological target of Mdivi-1. In PD patient blood, p-Ser616 levels correlate with disease severity and are elevated even in early stages[@janda2021].

Mitochondrial DNA copy number: Serves as a proxy for mitochondrial biogenesis. When fission is inhibited, mitochondria can fuse and undergo mitochondrial biogenesis, increasing mtDNA copy number as a compensatory response.

NfL in CSF: Non-specific marker of neuroaxonal injury but validated in PD progression. A decrease in NfL slope would suggest neuroprotection[@kumar2018].

p-Ser129 α-Syn in CSF: Disease-specific marker of alpha-synuclein pathology. If mitochondrial dynamics intervention reduces alpha-synuclein phosphorylation (through improved mitochondrial function), this would suggest disease modification.

Sample Collection Schedule

| Timepoint | Blood (EDTA) | CSF | Skin Biopsy | Muscle Biopsy |
|-----------|-------------|-----|------------|---------------|
| Baseline | ✓ | ✓ | ✓ | ✓ |
| Week 12 | ✓ | — | — | — |
| Week 26 | ✓ | ✓ | — | — |
| Week 52 (endpoint) | ✓ | ✓ | ✓ | ✓ |

Statistical Analysis Plan

Primary Analysis

The primary efficacy endpoint (change in MDS-UPDRS Parts II+III at 52 weeks) will be analyzed using a mixed-effects model for repeated measures (MMRM) with treatment arm, visit, treatment-by-visit interaction, and baseline MDS-UPDRS as covariates. An unstructured covariance matrix will model within-subject correlations.

Multiplicity Adjustment

The hierarchical testing procedure will control family-wise error rate:

First: High dose vs. placebo on primary endpoint

Second: Low dose vs. placebo on primary endpoint

Third: High dose vs. placebo on key secondary endpoint (MDS-UPDRS Part III)

Subgroup Analyses

Pre-specified subgroups based on genetic status:

LRRK2 G2019S carriers
GBA variant carriers
Sporadic (non-carrier)

Heterogeneity of treatment effect will be explored using treatment-by-subgroup interaction terms.

Sensitivity Analyses

Per-protocol analysis (excluding major protocol deviations)
Imputation of missing data using multiple imputation under MAR assumption
Tipping point analysis to assess robustness to unmeasured confounding

Risk Assessment

Potential Risks

Off-target effects: Mdivi-1 inhibits Drp1 but may have secondary targets. Preclinical toxicology will assess selectivity.

Cardiovascular effects: DRP1 is involved in mitochondrial dynamics in cardiac tissue. ECG monitoring will detect any cardiac toxicity.

Liver toxicity: Mdivi-1 is metabolized hepatically. Regular LFT monitoring will detect hepatotoxicity early.

BBB penetration: Current Mdivi-1 formulations have limited brain penetration. Future studies will use improved formulations or blood-brain barrier permeabilization strategies.

Risk Mitigation

Low starting dose in Phase 1 clinical trial
Frequent safety monitoring
Early stopping rules
DSMB oversight
Patient selection: exclude those with pre-existing liver disease

Future Directions

Next-Generation DRP1 Inhibitors

Mdivi-1 is a first-generation inhibitor with limitations (limited BBB penetration, potential off-target effects). Several next-generation compounds are in development:

| Compound | Company | Stage | Advantages |
|----------|---------|-------|------------|
| AT-158 | Internal | Preclinical | 10× potency, better selectivity |
| Dynasore analogs | Various | Discovery | Improved brain penetration |
| Small molecule Drp1 modulators | Merck | Preclinical | Allosteric modulation |

Gene Therapy Approaches

AAV-mediated delivery of MFN1, MFN2, or OPA1 directly to the substantia nigra could provide long-term restoration of mitochondrial fusion. This approach would require stereotactic neurosurgery but could provide sustained benefits.

Combination Strategies

Future trials may combine:

DRP1 inhibition + mitophagy enhancement (urolithin A)
DRP1 inhibition + α-Syn aggregation inhibition
Gene therapy (AAV-MFN1) + pharmacological intervention

Expected Timeline

Phase 1: 3 months
Phase 2: 5 months
Phase 3: 10 months
Total: 18 months

Status

PLANNED

References

[Janda et al., DRP1 inhibition in PD models (2021)](https://pubmed.ncbi.nlm.nih.gov/34000074/)

[Gomez et al., Mitochondrial dynamics in neurodegeneration (2019)](https://pubmed.ncbi.nlm.nih.gov/28071718/)

[Shields et al., Mdivi-1 clinical translation (2020)](https://pubmed.ncbi.nlm.nih.gov/32223456/)

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mitochondrial-dynamics-dysfunction-parkinsons

Mitochondrial Dynamics Dysfunction Validation in Parkinson's Disease

Experiment Design: MDD-PD-001

Mitochondrial Dynamics Dysfunction Validation in Parkinson's Disease

Experiment Design: MDD-PD-001

Rationale

Primary Objective

Study Design

Phase 1: In Vitro (Month 1-3)

Phase 1: In Vitro (Month 1-6)

Phase 2: In Vivo (Month 4-8)

Phase 3: Clinical (Month 9-18)

Phase 2: In Vivo (Month 7-14)

Phase 3: Clinical (Month 15-30)

Mitochondrial Dynamics in Neurons

Evidence for Dynamics Dysfunction in PD

DRP1 as Therapeutic Target

Experimental Design

Phase 1: In Vitro Validation (Months 1-6)

Aim 1.1: Characterize dynamics dysfunction in patient models

Aim 1.2: Test fusion promotion

Phase 2: In Vivo Proof-of-Concept (Months 7-14)

Mouse Model Studies

Toxicity Model (MPTP)

Outcome Measures

Phase 3: Clinical Translation (Months 15-24)

Preclinical Package

Clinical Trial Design

Endpoints Summary

Primary Endpoints

Secondary Endpoints

Exploratory Endpoints

Power Analysis

Safety Monitoring

Preclinical Phase

Clinical Phase

Mechanistic Rationale

Why DRP1 Inhibition?

Why Fusion Restoration?

Why Combination Therapy?

Expected Timeline

Status

Endpoints

Primary Endpoints

Secondary Endpoints

Exploratory Endpoints

Power Analysis

Safety Monitoring

Cross-Links

References

Detailed Methodology

In Vitro Neuronal Differentiation Protocol

Mitochondrial Morphology Analysis

ATP Measurement

Western Blot Analysis

Stereological Neuron Counting

Behavioral Testing Battery

Biomarker Rationale

Why These Biomarkers?

Sample Collection Schedule

Statistical Analysis Plan

Primary Analysis

Multiplicity Adjustment

Subgroup Analyses

Sensitivity Analyses

Risk Assessment

Potential Risks

Risk Mitigation

Future Directions

Next-Generation DRP1 Inhibitors

Gene Therapy Approaches

Combination Strategies

Expected Timeline

Status

References

See Also

💬 Discussion