Pancreatic Biology

iPSC-Derived β-Islet Cells

Differentiation, functional characterization, and pharmacological interrogation of human iPSC-derived pancreatic β-islet cells. Originally generated as endodermal control lineages for the Parkin agonist study, these cultures revealed unexpected off-target E3 ligase–mediated effects of Compound X1 on insulin-secreting cells—opening a new axis of investigation into pancreatic vulnerability to neuro-targeted therapeutics.

iPSC-Derived β-Cells Pancreatic Islets Insulin Secretion GSIS E3 Ubiquitin Ligase Compound X1 Parkin Off-Target Effects

Differentiation

Directed Differentiation to β-Islet Cells

Human iPSCs were directed through definitive endoderm → pancreatic progenitor → endocrine precursor → β-like cell stages using a 28-day stepwise protocol. Cultures transitioned from 2D monolayer (Stages 1–3) to 3D suspension aggregates (Stages 4–5) to promote islet-like cluster formation. Final cultures were assessed for C-peptide, NKX6.1, PDX1, and insulin co-expression.

Days to Maturity

>65%

C-Peptide+ Cells

iPSC Lines Validated

Differentiation Stages

Stage Progression & Marker Expression

Stage 1 (Days 0–3): Definitive endoderm induction with Activin A + CHIR99021 → SOX17+/FOXA2+ (>90%). Stage 2 (Days 3–7): Primitive gut tube with FGF10 + KGF → HNF4α+. Stage 3 (Days 7–12): Posterior foregut with RA + Noggin + SANT-1 + TPB → PDX1+ (>75%). Stage 4 (Days 12–20): Pancreatic endocrine transition in 3D suspension with ALK5 inhibitor + T3 + Betacellulin + γ-secretase inhibitor → NKX6.1+/NGN3+ (>55%). Stage 5 (Days 20–28): β-cell maturation in 3D with T3 + N-acetyl cysteine → INS+/NKX6.1+/C-PEP+ (>65%).

Stage-Specific Marker Expression (%)

Flow cytometry and immunofluorescence quantification across differentiation stages

n=3 lines per stage. Mean ± SEM. SOX17/FOXA2 (endoderm), PDX1 (pancreatic progenitor), NKX6.1 (endocrine precursor), C-Peptide (mature β-cell).

Function

Functional Characterization & GSIS

Glucose-stimulated insulin secretion (GSIS) confirmed functional maturity of iPSC-derived β-like cells. Clusters were challenged with basal (2.8 mM) and stimulatory (16.7 mM) glucose, with insulin and C-peptide quantified by ELISA. Stimulation index (SI) of 2.4 ± 0.3 across three iPSC lines, approaching primary human islet benchmarks (SI ~3–5). KCl depolarization (30 mM) elicited robust insulin release, confirming functional KATP channels.

2.4 ± 0.3

Stimulation Index

16.7 mM

Glucose Challenge

850 ± 120

Insulin (µIU/mL/cluster)

30 mM

KCl Depolarization

Glucose-Stimulated Insulin Secretion (GSIS)

Insulin response across three validated iPSC lines (KOLF2, WTC11, NCRM5) at basal, stimulated, and depolarized conditions

ELISA quantification. n=3 biological replicates per line. Stimulation index = stimulated / basal glucose insulin levels. KCl (30 mM) evokes maximal depolarization response.

Calcium Imaging

Live calcium imaging with Fluo-4 AM revealed synchronized oscillatory Ca²⁺ transients upon glucose stimulation (16.7 mM). Oscillation frequency: 3.2 ± 0.8 peaks/min. Amplitude: 1.8 ± 0.4 ΔF/F₀. Response latency: 45 ± 12 seconds post-glucose addition. GLP-1 receptor agonist (exendin-4, 10 nM) potentiated calcium response amplitude by 40%.

Compound X1

Compound X1 Off-Target Effects on β-Islet Cells

Compound X1 — a small-molecule Parkin agonist developed for neuroprotection — was tested in iPSC-derived β-islet cells as endodermal control cultures for the Parkin study. Unexpectedly, Compound X1 produced dose-dependent effects on β-cell function and viability through its E3 ubiquitin ligase activity. Parkin (PARK2) is expressed in pancreatic β-cells, and its activation by Compound X1 triggered enhanced mitophagy and altered insulin granule dynamics, reducing glucose-stimulated insulin secretion at higher doses while paradoxically improving β-cell survival under glucolipotoxic stress.

35%

GSIS Reduction (10 µM)

2.8×

Mitophagy Induction

EC₅₀ 3.2 µM

β-Cell E3 Activity

42%

Improved Survival (Stress)

Compound X1 Dose-Response in β-Islet Cells

GSIS, viability, and mitophagy induction as a function of Compound X1 concentration

GSIS measured by ELISA (% of vehicle control). Viability by CellTiter-Glo at 48h. Mitophagy by MitoTracker-Red+ vesicle quantification. EC₅₀ ~3.2 µM for GSIS reduction; therapeutic window 0.1–3 µM shows cytoprotection without functional impairment.

Mechanistic Pathway

Western blot analysis confirmed Compound X1 activates Parkin E3 ligase activity in β-cells (increased ubiquitin-Ser65 phosphorylation, PINK1 stabilization). Downstream effects: TFEB nuclear translocation increased 2.1-fold (autophagy/lysosomal biogenesis), mitochondrial membrane potential decreased 18% (indicating selective mitophagy of damaged mitochondria), and insulin granule density decreased 25% at 10 µM (assessed by zinc-binding dye Zinquin). Critically, under palmitate-induced glucolipotoxicity (0.5 mM, 48h), Compound X1 pre-treatment (3 µM) improved β-cell survival by 42% via enhanced clearance of damaged mitochondria.

Compound X1 Molecular Effects in β-Cells (10 µM, 24h)

Western blot densitometry, imaging analysis, and functional readouts normalized to vehicle control

Ub-Ser65 phosphorylation (anti-phospho-ubiquitin Western), PINK1 stabilization (full-length PINK1 band), TFEB nuclear translocation (immunofluorescence), mitophagy induction (MitoTracker red colocalization), insulin granule density (Zinquin fluorescence), ATP/ADP ratio (luciferase assay), and glucolipotoxic survival (CellTiter-Glo under 0.5 mM palmitate stress).

Omics

Transcriptomic Profiling & Pathway Analysis

Bulk RNA-seq of Compound X1–treated (3 µM, 24h) vs vehicle-treated β-islet cells identified 1,847 differentially expressed genes (padj <0.05, |log2FC| >1). GSEA revealed enrichment of autophagy/lysosomal pathways (NES = 2.4, FDR <0.001) and downregulation of insulin secretion machinery (NES = −1.8, FDR = 0.003). Key upregulated genes: PARK2, PINK1, TFEB, LAMP1, SQSTM1/p62. Key downregulated genes: INS, GCK, SLC30A8, ABCC8, KCNJ11.

1,847

DE Genes

NES 2.4

Autophagy Enrichment

NES −1.8

Insulin Pathway

padj <0.001

Significance

Volcano Plot — Compound X1 vs Vehicle in β-Islet Cells

Log2 fold change vs −log10(p-value) for 1,847 differentially expressed genes

RNA-seq of n=3 biological replicates. Red points: upregulated genes (PARK2, PINK1, TFEB, LAMP1, ULK1, ATG5, BECN1). Blue points: downregulated genes (INS, GCK, ABCC8, KCNJ11, SLC30A8, PCSK1). Gray: non-significant (padj >0.05 or |log2FC| <1).

GSEA Pathway Enrichment

Normalized Enrichment Score (NES) for canonical pathways affected by Compound X1

Positive NES (red): pathways enriched in Compound X1-treated cells. Negative NES (blue): pathways suppressed. FDR <0.01 threshold for significance. Autophagy, Lysosome, Mitophagy, and Ubiquitin-Proteasome pathways are highly upregulated; metabolic and insulin secretion pathways are suppressed.

Impact

Translational Implications & Safety Pharmacology

These findings demonstrate that neuro-targeted E3 ligase agonists can produce significant off-target effects in pancreatic β-cells. This has implications for: (1) safety pharmacology — pancreatic function should be monitored in clinical trials of Parkin agonists; (2) drug repurposing — controlled Parkin activation may protect β-cells under metabolic stress (diabetes); (3) mechanistic biology — the PINK1/Parkin mitophagy axis operates differently in β-cells vs neurons, with divergent effects on organelle dynamics and secretory function.

Therapeutic Implications

Disease Areas (Neuro + Metabolic)

PARK2

Shared Target

β + DA

Cell Types Affected

Key Conclusions