Advanced age heightens hepatic damage in a murine model of scald burn injury

Delayed hepatic response and impaired cytokine dynamics in aged mice following burn injury: Implications for elderly patient care

INTRODUCTION

Burn injuries in elderly patients result in higher morbidity and mortality compared to younger individuals. This study investigates age-related differences in inflammatory hepatic responses to burn injuries.

METHOD

Young (8-10 weeks) and aged (20-21 months) female C57BL/6 mice were subjected to a 15% total body surface area burn or sham injury. Serum and liver samples collected at 3, 6-, 9-, 12-, and 24-hours post-injury were analyzed for serum amyloid A (SAA) levels, SAA1 and SAA2 hepatic gene expression, serum cytokines (IL-6, IL-1β, TNF-α, and IL-10), and hepatic STAT3 activation.

RESULTS

Aged mice showed a delayed and dysregulated response. In young mice, SAA levels rose significantly at 6 hours postburn (5.09 ±  0.2-fold), while in aged mice, SAA increased at 12 hours (39.1 ±  2.06-fold), p <  0.01. Hepatic expression of SAA1 and SAA2 also peaked early in young mice (8.357 ±  1.257-fold and 5.91 ±  0.664-fold at 3 hours) but was delayed until 12 hours in aged mice. Young mice demonstrated early IL-6 peaks at 3 hours (990 ±  83.2 pg/ml), while aged mice reached a delayed, higher IL-6 peak at 24 hours (3804 ±  1408 pg/ml, p <  0.05). Similar age-related delays occurred for IL-1β and TNF-α. Aged mice had significantly elevated IL-10 at 6 hours (993.9 ±  99.41 pg/ml vs. 67.69 ±  6.635 pg/ml in young, p <  0.001). STAT3 activation peaked at 3 hours in young mice (2.686 ±  0.226-fold) but was delayed until 24 hours in aged mice (0.5958 ±  0.0368-fold, p <  0.05).

CONCLUSIONS

This study identifies age-related variations in inflammatory markers and acute hepatic responses to burn injuries, with aged mice showing delayed and reduced inflammatory responses compared to younger counterparts. These findings underscore the importance of age-specific strategies in burn injury management to enhance outcomes for elderly burn patients.

Burn-induced mitochondrial dysfunction in hepatocytes: The role of methylation-controlled J protein silencing

BACKGROUND

Burn injuries trigger a systemic hyperinflammatory response, leading to multiple organ dysfunction, including significant hepatic damage. The liver plays a crucial role in regulating immune responses and metabolism after burn injuries, making it critical to develop strategies to mitigate hepatic impairment. This study investigates the role of methylation-controlled J protein (MCJ), an inner mitochondrial protein that represses complex I in burn-induced oxidative stress and mitochondrial dysfunction, using an in vitro Alpha Mouse Liver 12 cell model.

METHODS

Alpha Mouse Liver 12 cells were treated with serum from burn-injured mice (SBIM) to simulate burn injury in vitro. Methylation-controlled J protein was silenced using shRNA. Cell viability, apoptosis markers, reactive oxygen species levels, antioxidant response elements, electron transport chain components, and mitochondrial respiration were assessed using various techniques, including Cell Counting Kit-8 assay, Western blotting, MitoSOX Red staining, and Seahorse XF analysis.

RESULTS

Serum from burn-injured mice treatment (10%) for 8 hours reduced Alpha Mouse Liver 12 cell viability to 50% of control levels and increased MCJ expression fivefold. It also significantly upregulated apoptosis markers: cleaved caspase-3 (4-fold), Bax (3.8-fold), and cytosolic cytochrome c (3.5-fold). Methylation-controlled J protein silencing improved cell viability to 85% of control levels and reduced apoptosis markers by 75% to 78%. Serum from burn-injured mice increased reactive oxygen species levels by 3-fold, while MCJ silencing reduced this by 2.5-fold. Antioxidant proteins (NRF2, HO-1, NQO-1, GCLC, catalase) were suppressed by SBIM but upregulated 3.2- to 3.8-fold with MCJ silencing. Serum from burn-injured mice reduced electron transport chain components (NDUFS1, SDHB, MTCO2) by 45% to 65%, which MCJ silencing restored 2.5- to 3-fold. Mitochondrial respiration improved significantly with MCJ silencing: basal respiration (+26%), maximal respiration (+66%), adenosine triphosphate production (+25%), and spare respiratory capacity (+63%).

CONCLUSION

Methylation-controlled J protein plays a critical role in burn-induced hepatocyte damage. Its silencing alleviates SBIM-induced cytotoxicity, oxidative stress, and mitochondrial dysfunction. These findings highlight MCJ as a potential therapeutic target for preserving liver function in burn patients, warranting further in vivo studies to explore its clinical potential.

Advanced Age Worsens Respiratory Function and Pulmonary Inflammation After Burn Injury and This Correlates With Changes in the Fecal Microbiome in Mice

Cutaneous burn injury in the elderly is associated with poor clinical outcomes and increased pulmonary-related complications. We and others have shown that burn injury triggers a cascade of inflammatory mediators which increase gut permeability and dysbiosis of the fecal microbiota and this is more dramatic in the aged. Since crosstalk between intestinal microbes and the lung, termed the "gut-lung axis," impacts immunity and homeostasis in the airway, we hypothesized that the increased intestinal dysbiosis in age and burn injury may contribute to excessive pulmonary inflammation and poor prognosis after injury. To explore this hypothesis, we used a clinically relevant murine model of burn injury in which young and aged mice are subjected to a 12% TBSA dorsal scald burn or sham injury. About 24 h after injury, lung function was assessed and lungs and feces were collected for analysis of inflammatory mediators and fecal microbial species. The results show that, when compared to younger mice, burn injury in aged mice triggers a decline in respiratory function and exacerbates pulmonary inflammation. In addition to heightened levels of the neutrophil recruiting chemokine CXCL1, aged mice displayed a profound increase in the pro-inflammatory protein, calprotectin, in the lung after burn injury. Comparison of the fecal microbiome and inflammatory markers in the lung revealed unique, age-dependent, correlation patterns between individual taxa and pulmonary inflammation. Taken together, these findings suggest that the postburn dysbiosis of the gut flora in aged mice may contribute to the changes in pulmonary inflammatory profiles.

Burn-Induced Apoptosis in the Livers of Aged Mice Is Associated With Caspase Cleavage of Bcl-xL

INTRODUCTION

Older adult burn victims have poorer outcomes than younger burn victims. The liver is critical for the recovery of patients with burns. Postburn hepatic apoptosis in young individuals compromises liver integrity; however, this pathway has not yet been studied in older individuals. Because aged animals with burns suffer significant liver damage, we hypothesized that apoptosis is altered in these animals and may affect liver function. Understanding postburn hepatic apoptosis and its effects on liver function in aged animals may help improve outcomes in older patients.

METHODS

We compared the protein and gene expression levels in young and aged mice after a 15% total-body-surface-area burn. Liver and serum samples were collected at different time points after injury.

RESULTS

Caspase-9 expression in liver tissue was downregulated by 47% in young animals and upregulated by 62% in aged animals 9 h postburn (P < 0.05). The livers of aged mice showed a Bcl-extra-large (Bcl-xL) transcription increase only after 6 h; however, the livers of young mice exhibited 4.3-fold, 14.4-fold, and 7.8-fold Bcl-xL transcription increases at 3, 6, and 9 h postburn, respectively (P < 0.05). The livers of young mice showed no changes in Caspase-9, Caspase-3, or Bcl-xL protein levels during the early postburn period. In contrast, the livers of aged mice contained cleaved caspase-9, reduced full-length caspase-3, and an accumulation of ΔN-Bcl-x at 6 and 9 h postburn (P < 0.05). p21 expression decreased in aged mice; however, it was significantly increased in the liver tissue of young mice postburn (P < 0.05). Serum amyloid A1 and serum amyloid A2 serum protein levels were 5.2- and 3.1-fold higher in young mice than in aged mice, respectively, at 6 and 9 h postburn (P < 0.05).

CONCLUSIONS

Livers of aged mice exhibited different apoptotic processes compared to those of young mice early after burn injury. Collectively, burn-induced liver apoptosis in aged mice compromises hepatic serum protein production.

Transcriptomics, metabolomics, and in-silico drug predictions for liver damage in young and aged burn victims

Burn induces a systemic response affecting multiple organs, including the liver. Since the liver plays a critical role in metabolic, inflammatory, and immune events, a patient with impaired liver often exhibits poor outcomes. The mortality rate after burns in the elderly population is higher than in any other age group, and studies show that the liver of aged animals is more susceptible to injury after burns. Understanding the aged-specific liver response to burns is fundamental to improving health care. Furthermore, no liver-specific therapy exists to treat burn-induced liver damage highlighting a critical gap in burn injury therapeutics. In this study, we analyzed transcriptomics and metabolomics data from the liver of young and aged mice to identify mechanistic pathways and in-silico predict therapeutic targets to prevent or reverse burn-induced liver damage. Our study highlights pathway interactions and master regulators that underlie the differential liver response to burn injury in young and aged animals.