Senescence in a cell culture model for burn wounds

Box A of HMGB1 improves second-degree burn wound healing in rats

BACKGROUND

DNA damage accumulation delays burn wound healing. Our previous research demonstrated the function of Box A of HMGB1 in DNA protection, generating youth-DNA gaps. Overexpression of youth-DNA gaps enhances DNA durability and decreases endogenous DNA damage. Box A-expressing plasmid transfection is a new DNA-editing technology that prevents DNA damage. Thus, we hypothesized that Box A is a curative agent that improves burn wound healing.

METHODS

In this study, we used a Box A plasmid coated with calcium phosphate nanoparticles (Ca-P) to treat burn wounds in rats. Second-degree burns were created on the backs of the rats. Three groups were used in this study: control (saline), saline + Ca-P (control), and Box A plasmid (n = 15 rats/group). The wounds were photographed 0, 7, 14, 21, and 28 days after wound induction and the burned areas were measured using Image J software. Burned skin tissue sections were analyzed for youth-DNA gap levels, subjected to histological and immunochemical analyses, and then scored according to the expression level of the DNA damage markers γH2AX and 8-OhdG.

RESULTS

We observed improved wound healing in Box A plasmid-treated wounds from days 14 to 28 after injury (P < 0.001). A significant improvement in the total pathological score and DNA gaps in the Box A plasmid-treated group was observed at 14-28 days, with a peak on day 14 (P < 0.01) compared with that of the normal saline and calcium phosphate nanoparticle treated group. The expression of γH2AX and 8-OhdG was also decreased in the Box A group compared to controls on days 14-28, with the largest differences in expression levels observed on days 14 and 21.

CONCLUSIONS

Our results demonstrated that by producing youth-DNA gaps, Box A plasmid may be a potential therapeutic target in burn wound treatment.

THE USE OF POLOXAMER 188 IN BURN INJURY TREATMENT: A SYSTEMATIC LITERATURE REVIEW

ABSTRACT

Although there have been numerous advancements in burn wound management, burn injuries are still a major cause of morbidity and mortality in the United States, and novel therapeutics are still needed to improve outcomes. Poloxamer 188 (P188) is a synthetic copolymer with Food and Drug Administration (FDA) approval that has many biological applications. This study aimed to review the literature on P188 in burn injuries and its effects based on burn mechanisms. We employed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to complete this systematic literature review. We searched the databases of Google Scholar, PubMed, and SCOPUS using the keywords burn, p188, poloxamer 188, and pluronic F68 in combination. Two reviewers independently screened the articles for inclusion. Articles that were not in English, were book chapters or conference proceedings, or did not evaluate P188 in the setting of burn injuries were excluded. We included a total of 33 full-text articles with both in vivo and in vitro preclinical studies. P188 was found to be beneficial in animal and cell studies evaluating electrical and thermal burn injuries. P188 was also found to be useful in burn wound management. Although its utility may be limited in radiation injuries, P188 may be helpful in delaying the initial damage caused by radiation burns. P188 therefore has the potential to be used as a therapy in both burn wound management and in the treatment of systemic injuries sustained through burns. Future studies should aim to assess the efficacy of P188 in clinical models of burn injury.

Repression motif in HSF1 regulated by phosphorylation

The heat shock factor 1 (HSF1) is a transcription factor that itself is a sensor for stress and integrates various intrinsic or environmental stress sensing pathways. Thus HSF1 orchestrates the heat shock response (HSR) by translating these pathways into a distinct transcriptional program that aids the cells to cope with and adapt to proteotoxic stress. Although heavily researched the regulation of HSF1 activation is still not completely understood. A conserved reaction to stress is the hyperphosphorylation of the otherwise confined constitutive phosphorylated HSF1. Therefore, this stress specific phosphorylation is believed to be involved in the regulatory mechanism and hence, was and is focus of many studies, ascribing various effects to single phosphorylation sites. To gain additional insight into effects of phosphorylation, HSF1 carrying amino acid substitutions on up to 18 amino acids were tested for their transactivation potential on an HSR reporter plasmid. A pattern of eleven phosphor-mimicking and diminishing amino acid substitutions on well-known phosphorylation sites of HSF1 were introduced to produce transcriptional active [11 M(+)] or repressed [11 M(-)] phenotypes. It could be confirmed that heat activates HSF1 regardless of phosphorylation. Distinct cellular stress, obtained by chemical HSR inducers or mimicked by a constitutively active HSF1, showed clear differences in the activation potential of HSF1-11 M(+) and 11 M(-). Further refinement to the single amino acid level identified the S303/307 double-phosphorylation motif, wherein phosphorylation of S303 was sole responsible for the repressing effect. The effect could be reproduced in different cell lines and is not entirely based on degradation. A small repression motif could be dissociated from the HSF1 context, which is still capable of repressing the background transcription of a specifically designed reporter plasmid. Taken together these results indicate, that besides already described mechanisms of pS303/307 mediated repression of HSF1 activation, an additional mechanism repressing the transcriptional output of the entire HSE containing promoter is mediated by this small repressive motif.

Senescence induces fundamental changes in the secretome of mesenchymal stromal cells (MSCs): implications for the therapeutic use of MSCs and their derivates

Mesenchymal stromal cells (MSCs) are a heterogeneous population containing multipotent adult stem cells with a multi-lineage differentiation capacity, which differentiated into mesodermal derivatives. MSCs are employed for therapeutic purposes and several investigations have demonstrated that the positive effects of MSC transplants are due to the capacity of MSCs to modulate tissue homeostasis and repair via the activity of their secretome. Indeed, the MSC-derived secretomes are now an alternative strategy to cell transplantation due to their anti-inflammatory, anti-apoptotic, and regenerative effects. The cellular senescence is a dynamic process that leads to permanent cell cycle arrest, loss of healthy cells' physiological functions and acquiring new activities, which are mainly accrued through the release of many factors, indicated as senescence-associated secretory phenotype (SASP). The senescence occurring in stem cells, such as those present in MSCs, may have detrimental effects on health since it can undermine tissue homeostasis and repair. The analysis of MSC secretome is important either for the MSC transplants and for the therapeutic use of secretome. Indeed, the secretome of MSCs, which is the main mechanism of their therapeutic activity, loses its beneficial functions and acquire negative pro-inflammatory and pro-aging activities when MSCs become senescent. When MSCs or their derivatives are planned to be used for therapeutic purposes, great attention must be paid to these changes. In this review, we analyzed changes occurring in MSC secretome following the switch from healthy to senescence status.

Link between senescence and cell fate: Senescence-associated secretory phenotype (SASP) and its effects on stem cell fate transition

Senescence is a form of durable cell cycle arrest elicited in response to a wide range of stimuli. Senescent cells remain metabolically active and secrete a variety of factors collectively termed senescence-associated secretory phenotype (SASP). SASP is highly pleiotropic and can impact numerous biological processes in which it has both beneficial and deleterious roles. The underlying mechanisms by which SASP exerts its pleiotropic influence remain largely unknown. SASP serves as an environmental factor, which regulates stem cell differentiation and alters its routine. The latter can potentially be accomplished through dedifferentiation, transdifferentiation, or reprogramming. Behavioral changes that cells undergo when exposed to SASP are involved in several senescence-associated physiological and pathological phenomena. These findings provide clues for identifying possible interventions to reduce the deleterious effects without interfering in the beneficial outcomes. Here, we discuss the multifaced effects of SASP and the changes occurring in cellular states upon exposure to SASP factors.