SLU-PP-332 Research: ERR Agonism & Mitochondria

1. Introduction

SLU-PP-332 is a synthetic small molecule research compound belonging to the class of Estrogen-Related-Receptor (ERR) agonists with pan-ERR activity across all three subtypes ERRα (NR3B1), ERRβ (NR3B2), and ERRγ (NR3B3). It was developed by the Scripps Research / Saint Louis University team led by Burris et al. (2023) and has been used in preclinical studies as a chemical probe to investigate mitochondrial biogenesis, oxidative phosphorylation, and energy metabolism in skeletal muscle, adipocyte, and hepatocyte models.

Unlike classical PPARδ agonists, SLU-PP-332 directly targets the ERR node — the nuclear receptor trio that orchestrates the transcriptional output for the mitochondrial respiratory chain, β-oxidation, and the TCA cycle.

2. Structure, Class & Analytical Specification

2.1 Chemical Profile

• Class: synthetic Small Molecule, pan-ERR agonist
• Empirical Formula: C₂₂H₂₃N₃O₅S (published parent structure)
• MW: ~ 441.5 g/mol
• Solubility: lipophilic, DMSO-soluble (in-vitro stock solution)
• Binding: direct ligand of the ERR-LBD (Ligand-Binding-Domain)

2.2 Research Specification

• Purity: ≥ 99 % (HPLC, 220 / 254 nm)
• Identity: LC-MS [M+H]⁺ confirmation
• Batch: COA with lot number, synthesis location, retest date
• Storage: Lyophilized powder 2–8 °C, protected from light; DMSO stock solution −20 °C

3. Mechanism: The ERR/PGC-1α Axis

3.1 What are ERRs?

Estrogen-Related-Receptors are orphan nuclear receptors — structurally related to the classical estrogen receptor (ERα), but they do not bind estrogen. Instead, they act as constitutive transcriptional activators in tissues with high mitochondrial density:

• ERRα: dominant in skeletal muscle, heart, brown fat, liver

• ERRβ: neural crest, testicular tissue

• ERRγ: heart, kidney, sensory neurons

Their activity is primarily regulated via the co-activator PGC-1α (Peroxisome-Proliferator-Activated-Receptor-Gamma-Coactivator-1α) — the master regulator of mitochondrial biogenesis (Lin et al., 2005).

3.2 What does SLU-PP-332 do?

SLU-PP-332 directly binds to the ERR-LBD and enhances PGC-1α recruitment to ERR-responsive promoter elements (ERREs). The transcriptional program includes:

• NRF1 / NRF2 (Nuclear Respiratory Factor 1/2) → respiratory chain core components

• TFAM (Mitochondrial Transcription Factor A) → mtDNA replication

• CPT1B → long-chain fatty acid import into the mitochondrion

• MCAD / LCAD / VLCAD → β-oxidation enzymes

• Cytochrome-c, COX subunits → respiratory chain

The net result in preclinical models: increased mitochondrial density, enhanced β-oxidation capacity, and improved maximal oxygen uptake in isolated muscle fibers (Billon et al., 2023).

4. Published Preclinical Data

4.1 Skeletal Muscle Models

In C2C12 myotubes and murine soleus preparations, SLU-PP-332 increases in-vitro:

• mtDNA copy number (qPCR, mtND1/B2M ratio)
• Citrate synthase activity (TCA marker)
• Maximal oxygen consumption (Seahorse XF Mito Stress Test)
• Type-I myosin heavy chain expression (slow-twitch profile)

4.2 In-vivo Rodent Studies (Burris-Lab, 2023)

In high-fat diet rodent models, SLU-PP-332 application resulted in increased endurance performance in the treadmill test and reduced adiposity accumulation — without significant changes in food intake. These effects were mechanistically attributed to enhanced fatty acid oxidation in muscle and liver tissue.

RUO Note: These findings are exclusively from animal models. Translation to humans is not published. SLU-PP-332 is not an approved drug and not a dietary supplement.

4.3 Adipocyte & Liver Models

In brown adipocytes (BAT culture), SLU-PP-332 increases UCP1 expression and the thermogenic gene program. In primary hepatocytes, it reduces triglyceride accumulation under palmitate stress.

5. Differentiation from Related Classes

The mechanistic orthogonality to PPARδ ligands (GW501516) makes SLU-PP-332 a scientifically clean probe for ERR-specific effects — without PPAR crosstalk.

6. HPLC ≥ 99 % as RUO Procurement Standard

For reproducible cell culture and animal model data, analytical quality is crucial:

• RP-HPLC, 254 nm: Main peak ≥ 99 %, individual minor peaks < 0.3 %

• LC-MS, ESI⁺: Unambiguous [M+H]⁺ identity

• ¹H-NMR (optional): Structure confirmation in DMSO-d₆

• Residual Solvents: ICH-Q3C compliant (DMF, DCM, MeOH < limits)

• COA per Lot: Purity, identity, residual water (KFT), residual solvents (GC), storage/retest date

Batches below this specification are not suitable for quantitative qPCR profiles, Seahorse assays, or dose-dependent reporter assays.

7. Storage & Reconstitution (Research Laboratory)

• Lyophilized Powder / Solid Substance: 2–8 °C, protected from light, original sealed container

• Long-term (> 12 months): −20 °C recommended

• DMSO Stock Solution (10–100 mM): −20 °C, aliquoted, ≤ 3 freeze-thaw cycles

• Dilutions in Cell Culture Medium: prepare fresh, final DMSO concentration ≤ 0.1 %

8. Limitations & Open Questions

1. Human Pharmacokinetics: There are no controlled clinical PK/PD studies in humans. All data originate from cell cultures and rodent models.

2. Off-Target Profile: A complete selectivity matrix against all 48 human Nuclear Receptors is still under development or not yet published. 3. Pan-ERR vs Subtype-selective: The tissue-specific contributions of ERRα vs ERRγ in the observed effects have not yet been fully deconvoluted. 4. Animal-to-Human Translation: Mitochondrial biogenesis axes show significant species differences — rodent findings are not 1:1 translatable to humans. 5. Market Batch Heterogeneity: Purity fluctuations in the research market are documented — strict HPLC specification is not optional.

9. Conclusion

SLU-PP-332 is a pan-ERR agonist with preclinically documented effects on the PGC-1α/NRF1/TFAM axis and thus on the transcriptional program of mitochondrial biogenesis and β-oxidation. As a chemical probe, it is particularly valuable for investigating ERR-specific signaling pathways in skeletal muscle, adipocyte, and hepatocyte models because it acts PPARδ-orthogonally.

For valid research results, analytical quality (HPLC ≥ 99 %, LC-MS-confirmed identity, COA per batch) is the central lever for reproducibility. All findings are strictly preclinical and exclusively for Research Use Only.