Cell-permeable peptide-based delivery vehicles useful for subcellular targeting and beyond

Disruption of G3BP1 granules promotes mammalian CNS and PNS axon regeneration

Depletion or inhibition of core stress granule proteins, G3BP1 in mammals and TIAR-2 in Caenorhabditis elegans, increases the growth of spontaneously regenerating axons. Inhibition of G3BP1 by expression of its acidic or "B-domain" accelerates axon regeneration after nerve injury, bringing a potential therapeutic strategy for peripheral nerve repair. Here, we asked whether G3BP1 inhibition is a viable strategy to promote regeneration in injured mammalian central nervous system (CNS) where axons do not regenerate spontaneously. G3BP1 B-domain expression was found to promote axon regeneration in the transected spinal cord provided with a permissive peripheral nerve graft (PNG) as well as in crushed optic nerve. Moreover, a cell-permeable peptide (CPP) to a subregion of B-domain (rodent G3BP1 amino acids 190 to 208) accelerated axon regeneration after peripheral nerve injury and promoted regrowth of reticulospinal axons into the distal transected spinal cord through a bridging PNG. G3BP1 CPP promoted axon growth from rodent and human neurons cultured on permissive substrates, and this function required alternating Glu/Asp-Pro repeats that impart a unique predicted tertiary structure. The G3BP1 CPP disassembles axonal G3BP1, G3BP2, and FMRP, but not FXR1, granules and selectively increases axonal protein synthesis in cortical neurons. These studies identify G3BP1 granules as a key regulator of axon growth in CNS neurons and demonstrate that disassembly of these granules promotes retinal axon regeneration in injured optic nerve and reticulospinal axon elongation into permissive environments after CNS injury. This work highlights G3BP1 granule disassembly as a potential therapeutic strategy for enhancing axon growth and neural repair.

Disruption of G3BP1 Granules Promotes Mammalian CNS and PNS Axon Regeneration

Depletion or inhibition of core stress granule proteins, G3BP1 in mammals and TIAR-2 in C. elegans , increases axon regeneration in injured neurons, showing spontaneous regeneration. Inhibition of G3BP1 by expression of its acidic or 'B-domain' accelerates axon regeneration after nerve injury, bringing a potential therapeutic intervention to promote neural repair in the peripheral nervous system. Here, we asked if G3BP1 inhibition is a viable strategy to promote regeneration in injured mammalian central nervous system where axons do not regenerate spontaneously. G3BP1 B-domain expression was found to promote axon regeneration in the transected spinal cord provided with a permissive peripheral nerve graft (PNG) as well as in crushed optic nerve. Moreover, a cell-permeable peptide (CPP) to a subregion of B-domain (rodent G3BP1 amino acids 190-208) accelerated axon regeneration after peripheral nerve injury and promoted regrowth of reticulospinal axons into the distal transected spinal cord through a bridging PNG. G3BP1 CPP promoted axon growth from rodent and human neurons cultured on permissive substrates, and this function required alternating Glu/Asp-Pro repeats that impart a unique predicted tertiary structure. The G3BP1 CPP disassembles axonal G3BP1, G3BP2, and FMRP, but not FXR1, granules and selectively increases axonal protein synthesis in cortical neurons. These studies identify G3BP1 granules as a key regulator of axon growth in CNS neurons and demonstrate that disassembly of these granules promotes retinal axon regeneration in injured optic nerve and reticulospinal axon elongation into permissive environments after CNS injury. This work highlights G3BP1 granule disassembly as a potential therapeutic strategy for enhancing axon growth and neural repair.

SIGNIFICANCE STATEMENT

The central nervous system (CNS) axon does not have the capacity for spontaneous axon regeneration, as seen in the peripheral nervous system (PNS). We previously showed that stress granule-like aggregates of G3BP1 are present in uninjured PNS axons, and these slow nerve regeneration. We now report that CNS axons contain G3BP1 granules, and G3BP1 granule disassembling strategies promote axon regeneration in the injured sciatic nerve, transected spinal cord with a peripheral nerve graft, and injured optic nerve. Thus, G3BP1 granules are a barrier to axon regeneration and can be targeted for stimulating neural repair following traumatic injury, including in the regeneration refractory CNS.

A Hybrid Nanotube Stamp System in Intracellular Protein Delivery for Cancer Treatment and NMR Analytical Techniques

In contrast to intracellular gene transfer, the direct delivery of expressed proteins is a significantly challenging yet essential technique for elucidating cellular functions, including protein complex structure, liquid-liquid phase separation, therapeutic applications, and reprogramming. In this study, we developed a hybrid nanotube (HyNT) stamp system that physically inserts the HyNTs into adhesive cells, enabling the injection of target molecules through HyNT ducts. This system demonstrates the capability to deliver multiple proteins, such as lactate oxidase (LOx) and ubiquitin (UQ), to approximately 1.8 × 107 adhesive cells with a delivery efficiency of 89.9% and a viability of 97.1%. The delivery of LOx enzyme into HeLa cancer cells induced cell death, while enzyme-delivered healthy cells remained viable. Furthermore, our stamp system can deliver an isotope-labeled UQ into adhesive cells for detection by nuclear magnetic resonance (NMR).

Recent Progress in the Endosomal Escape Mechanism and Chemical Structures of Polycations for Nucleic Acid Delivery

Nucleic acid-based therapies are seeing a spiralling surge. Stimuli-responsive polymers, especially pH-responsive ones, are gaining widespread attention because of their ability to efficiently deliver nucleic acids. These polymers can be synthesized and modified according to target requirements, such as delivery sites and the nature of nucleic acids. In this regard, the endosomal escape mechanism of polymer-nucleic acid complexes (polyplexes) remains a topic of considerable interest owing to various plausible escape mechanisms. This review describes current progress in the endosomal escape mechanism of polyplexes and state-of-the-art chemical designs for pH-responsive polymers. The importance is also discussed of the acid dissociation constant (i.e., pKa) in designing the new generation of pH-responsive polymers, along with assays to monitor and quantify the endosomal escape behavior. Further, the use of machine learning is addressed in pKa prediction and polymer design to find novel chemical structures for pH responsiveness. This review will facilitate the design of new pH-responsive polymers for advanced and efficient nucleic acid delivery.

Enhancing the activity of β-lactamase inhibitory protein-II with cell-penetrating peptide against KPC-2-carrying Klebsiella pneumoniae

Carbapenem-resistant Enterobacterales (CRE) is considered a paramount threat due to its rapid spread and high mortality rate. Klebsiella pneumoniae carbapenemases (KPCs), specifically KPC-2, are prevalent enzymes responsible for carbapenem resistance in many countries. While combinations of antibiotics are commonly used, they must be tailored to match the remaining susceptibility of the infecting strains. Therefore, there is a need to develop the β-lactamase inhibitor to effectively address this issue. β-lactamase inhibitor protein (BLIP) and its variants, BLIP-I and BLIP-II, have demonstrated the ability to inhibit class A β-lactamases. In particular, BLIP-II shows strong binding to the KPC-2 carbapenemase, making it a potential candidate for inhibition. To improve the intracellular penetration of BLIP-II, a cell-penetrating peptide (CPP) was employed. In this study, a KRK-rich peptide was introduced at either the N-terminal or C-terminal region of tBLIP-II, excluding the signal sequence of the BLIP-II protein. tBLIP-II, tBLIP-II-CPP, and CPP-BLIP-II were successfully expressed, and the chimeric proteins retained inhibitory activity compared to tBLIP-II alone. It is apparent that homology modeling demonstrated neither the poly-histidine tag nor the CPP interfered with the essential interaction residues of tBLIP-II. Interestingly, BLIP-II-CPP exhibited the highest inhibitory activity, reducing the minimal inhibitory concentration (MIC) of meropenem by 8 folds. Moreover, the combination of tBLIP-CPP with meropenem significantly decreased the viable bacterial cell count compared to the combination of tBLIP-II with meropenem or meropenem alone. These findings suggest that tBLIP-CPP is a promising candidate for restoring carbapenem susceptibility against CRE and provides a valuable therapeutic option for infections caused by CRE.