In vivo partial reprogramming by bacteria promotes adult liver organ growth without fibrosis and tumorigenesis

Opportunities and challenges of bacterial extracellular vesicles in regenerative medicine

Extracellular vesicles (EVs) are membrane-bound vesicles that are shed or secreted from the cell membrane and enveloped by a lipid bilayer. They possess stability, low immunogenicity, and non-cytotoxicity, exhibiting extensive prospects in regenerative medicine (RM). However, natural EVs pose challenges, such as insufficient targeting capabilities, potential biosafety concerns, and limited acquisition pathways. Although engineered EVs demonstrate excellent therapeutic efficacy, challenges such as low production yield and the complexity of engineering modifications constrain their further clinical applications. Bacteria have advantages such as rapid proliferation, diverse gene editing methods, mature cultivation techniques, and relatively easy preparation of bacterial EVs (BEVs), which can be used to effectively address the challenges currently encountered in the field of EVs. This review provides a description of the biogenesis and pathophysiological functions of BEVs, and strategies for optimizing BEVs preparation to attain efficiency and safety are discussed. An analysis of natural characteristics of BEVs is also conducted to explore how to leverage their advantages or mitigate their limitations, thereby overcoming constraints on the application of BEVs in RM. In summary, engineered BEVs possess characteristics such as high production yield, excellent stability, and high drug-delivering capabilities, laying the foundation for their application in RM.

Liver Extracellular Vesicles and Particles Enriched β-Sitosterol Effectively Promote Liver Regeneration in Mice

Background

The liver's regenerative capacity allows it to repair itself after injury. Extracellular vesicles and particles (EVPs) in the liver's interstitial space are crucial for signal transduction, metabolism, and immune regulation. Understanding the role and mechanism of liver-derived EVPs in regeneration is significant, particularly after partial hepatectomy, where the mechanisms remain unclear.

Methods

A 70% hepatectomy model was established in mice, and EVPs were isolated and characterized using electron microscopy, nanocharacterization, and Western blot analysis. Combined metabolomic and transcriptomic analyses revealed β-sitosterol enrichment in EVPs and activation of the Hedgehog signaling pathway during regeneration. The role of β-sitosterol in EVPs on the Hedgehog pathway and its targets were identified using qRT-PCR, Western blot analysis. The regulation of carnitine synthesis by this pathway was determined using a dual luciferase assay. The effect of a β-sitosterol diet on liver regeneration was verified in mice.

Results

After 70% hepatectomy, the liver successfully regenerated without liver failure or death. At 24 hours post-surgery, tissue staining showed transient regeneration-associated steatosis (TRAS), with increased Ki67 positivity at 48 hours. EVPs displayed a spherical lipid bilayer structure with particle sizes of 70-130 nm. CD9, CD63, and CD81 in liver-derived EVPs were confirmed. Transcriptomic and metabolomic analyses showed EVPs supplementation significantly promoted carnitine synthesis and fatty acid oxidation. Tissue staining confirmed accelerated TRAS resolution and enhanced liver regeneration with EVP supplementation. Mass spectrometry identified β-sitosterol in EVPs, which binds to Smo protein, activating the Hedgehog pathway. This led to the nuclear transport of Gli3, stimulating Setd5 transcription and inducing carnitine synthesis, thereby accelerating fatty acid oxidation. Mice with increased β-sitosterol intake showed faster TRAS resolution and liver regeneration compared to controls.

Conclusion

Liver-derived EVPs promote regeneration after partial hepatectomy. β-sitosterol from EVPs accelerates fatty acid oxidation and promotes liver regeneration by activating Hedgehog signaling pathway.

Coupling of SARS-CoV-2 to Aβ Amyloid Fibrils

The COVID-19 infection has been more problematic for individuals with certain health predispositions. Coronaviruses could also interfere with neural diseases if the viruses succeed in entering the brain. Therefore, it might be of principal interest to examine a possible coupling of coronaviruses and amyloid fibrils. Here, molecular dynamics simulations were used to investigate direct coupling of SARS-CoV-2 and Aβ fibrils, which play a central role in neural diseases. The simulations revealed several stable binding configurations and their dynamics of Aβ42 fibrils attached to spike proteins of the Omicron and Alpha variants of SARS-CoV-2.

Microbiota in promoting liver regeneration

Extensive work has revealed well-coordinated mechanisms that underlie liver regeneration, albeit with a focus on intrinsic interactions within hepatic cells. Here, Hess et al.¹ demonstrate that Mycobacterium leprae infection can induce liver growth of nine-banded armadillo without obvious side effects.