Cell-penetrating peptides and homeoproteins translocate into cells via submillisecond transient pores
Background
Cell-penetrating peptides (CPPs) and homeoproteins (HPs) are vital for intracellular drug delivery, yet their direct membrane crossing, termed translocation, remains largely uncharacterized. While endocytosis is a known entry pathway, understanding translocation is crucial to bypass endosomal entrapment and degradation, thereby optimizing the delivery of therapeutic cargos. This study addresses the fundamental gap in characterizing the biophysical events underlying this rapid, non-endocytic cellular entry mechanism.
Study Design
Researchers employed an electrophysiological approach to assess the internalization of CPPs (Tat, R9, penetratin, R6W3) and HPs (Otx2, En2). They measured single-cell unitary transient currents in mammalian cells at resting membrane potential, and under hyperpolarization and depolarization. The study also investigated the role of specific membrane glycosaminoglycans and confirmed the translocation of a CPP-conjugated bioactive cargo. Finally, similar HP-evoked transient pores were observed in brain cortical pyramidal cells to establish physiological relevance.
Results
At resting membrane potential, CPPs and HPs induced submillisecond transient pores, revealing rapid peptide passage across the membrane via translocation. Expression of specific membrane glycosaminoglycans was found to be mandatory for the induction of these translocation-induced transient pores. Associated transient currents were supralinearly enhanced by hyperpolarization, while depolarization had only a poor effect. Furthermore, a CPP-conjugated bioactive cargo demonstrated similar translocation into the cytosol, confirming the utility of this mechanism for delivery. The study also identified similar HP-evoked transient pores in brain cortical pyramidal cells, underscoring the physiological relevance of this translocation pathway in neural tissue.
These transient pores were significantly faster than any known endocytosis event, highlighting a distinct and rapid cellular entry mechanism.
Key Findings
- CPPs and HPs form submillisecond transient pores for rapid cellular entry.
- Translocation via these pores is faster than any endocytosis event.
- Specific membrane glycosaminoglycans are mandatory for transient pore formation.
- Transient currents are supralinearly enhanced by hyperpolarization.
- CPP-conjugated bioactive cargos also translocate into the cytosol.
Why It Matters
This research fundamentally redefines how CPPs and HPs enter cells, revealing a rapid, direct membrane translocation mechanism via transient pores. Understanding this mechanism could revolutionize intracellular drug delivery strategies, allowing for more efficient and targeted transport of therapeutic cargos, bypassing limitations of endosomal degradation. For peptide users and biohackers, this insight suggests that optimizing peptide design to leverage glycosaminoglycan interactions and membrane potential could significantly enhance cellular uptake and efficacy. The finding of similar transient pores in brain cells highlights the potential for improved delivery of neurotherapeutics across the blood-brain barrier, opening new avenues for treating neurological disorders. This work moves us closer to designing peptides with predictable and superior cellular penetration, impacting future protocols for direct cytosolic delivery.
cell-penetrating-peptides
homeoproteins
drug-delivery
translocation
electrophysiology
membrane-transport