HSPA1A Protects Cells from Thermal Stress by Impeding ESCRT-0-Mediated Autophagic Flux in Epidermal Thermoresistance.

Thermoresistance is a physiological phenomenon relevant to noninvasive laser treatments for skin esthetics and tumor removal, although the underlying mechanism remains elusive. We hypothesized that HSPA1A may regulate autophagy by reducing ESCRT-0 and/or STAM2 levels, which could lead to thermal protection from cell death. In this study, we showed that thermoresistance was induced in mouse epidermal tissue and HaCaT cells by heating at 45 °C for 10 minutes. Moreover, HSPA1A levels were increased in thermoresistant mouse epidermis and HaCaT cells. HSPA1A was highly involved in protecting cells from thermal cytotoxicity, as evidenced by the knockdown or overexpression assays of the HSPA1A gene. In addition, ESCRT-0 and STAM2 levels were dramatically decreased in thermoresistant cells, which was mediated by HSPA1A binding to STAM2, particularly through HSPA1A amino acids 395‒509. Furthermore, the loss of ESCRT-0 and/or STAM2 in response to HSPA1A-STAM2 binding regulated autophagy by impeding autophagosome‒lysosome fusion and abolishing autophagic flux in cellular thermoresistance, significantly reducing thermal cytotoxicity and promoting cell survival. To our knowledge, it is previously unreported that HSPA1A-ESCRT-0 and/or STAM2 modulates heat-induced resistance by inhibiting autophagic flux. In summary, the results of this study demonstrate that the mechanisms of thermoresistance may have clinical relevance for noninvasive or minimally invasive thermal therapeutics.

Low molecular weight chitosan-coated silver nanoparticles are effective for the treatment of MRSA-infected wounds.

Silver nanoparticles (AgNPs) are being widely applied as topical wound materials; however, accumulated deposition of silver in the liver, spleen, and other main organs may lead to organ damage and dysfunction. We report here that low molecular weight chitosan-coated silver nanoparticles (LMWC-AgNPs) are effective against methicillin-resistant Staphylococcus aureus (MRSA), have better biocompatibility, and have lower body absorption characteristics when compared with polyvinylpyrrolidone-coated silver nanoparticles (PVP-AgNPs) and silver nanoparticles without surface stabilizer (uncoated-AgNPs) in a dorsal MRSA wound infection mouse model. LMWC-AgNPs were synthesized by reducing silver nitrate with low molecular weight chitosan as a stabilizer and reducing agent, while PVP-AgNPs were synthesized using polyvinylpyrrolidone as a stabilizer and ethanol as a reducing agent. AgNPs with different surface stabilizers were identified by UV-visible absorption spectrometry, and particle size was determined by transmission electron microscopy. UV-visible absorption spectra of LMWC-AgNPs, PVP-AgNPs and uncoated-AgNPs were similar and their sizes were in the range of 10-30 nm. In vitro experiments showed that the three types of AgNPs had similar MRSA-killing effects, with obvious effect at 4 µg/mL and 100% effect at 8 µg/mL. Bacteriostatic annulus experiments also showed that all the three types of AgNPs had similar antibacterial inhibitory effect at 10 µg/mL. Cell counting kit-8 assay and Hoechst/propidium iodide (PI) staining showed that LMWC-AgNPs were significantly less toxic to human fibroblasts than PVP-AgNPs and uncoated-AgNPs. Treatment of mice with MRSA wound infection demonstrated that the three types of AgNPs effectively controlled MRSA wound infection and promoted wound healing. After continuous application for 14 days, LMWC-AgNPs-treated mice showed significantly reduced liver dysfunction as demonstrated by the reduced alanine aminotransferase and aspartate aminotransferase levels and liver deposition of silver, in comparison to mice treated with uncoated-AgNPs or PVP-AgNPs. Our results demonstrated that LMWC-AgNPs had good anti-MRSA effects, while harboring a better biocompatibility and lowering the body's absorption characteristics.