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Hepatic mitochondrial bioenergetics in aged C57BL/6 mice exhibit delayed recovery from severe burn injury.

ABSTRACT: Severe burn injuries initiate a cascade of downstream events, culminating in multiple organ dysfunction, sepsis, and even death. The elderly are in particular vulnerable to such outcomes, due primarily to a scarcity of knowledge on trauma progression at the biomolecular level in this population. Mitochondria, the cellular powerhouses, have been increasingly scrutinized recently for their contribution to trauma outcomes. We hypothesized that elderly have a worse outcome compared to adult patients due to failed recovery of hepatic mitochondria. Using a murine model of burn injury, Seahorse respirometry and functional proteomic assays, we demonstrate the impact of thermal trauma on hepatic mitochondrial respiration in adult and aged mice. While the mitochondria in adults rebound from the initial insult within 7days of the injury, the older animals display delayed recovery of mitochondrial bioenergetics accompanied by uncoupling and an oxidative environment. This is associated with a state of increased protein oxidation and nitrosylation, along with increases in circulating mtDNA, a known damage-associated molecular pattern. These findings suggest that hepatic mitochondria fail to normalize after trauma in aged mice and we suggest that this cellular failure is associated with organ damage and subsequently increased morbidity and mortality in elderly burn patients.

SUBMITTER: Auger C

PROVIDER: S-EPMC5659908 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature

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Hepatic mitochondrial bioenergetics in aged C57BL/6 mice exhibit delayed recovery from severe burn injury.

Auger Christopher C Sivayoganathan Thibacg T Abdullahi Abdikarim A Parousis Alexandra A Jeschke Marc G MG

Biochimica et biophysica acta. Molecular basis of disease 20170713 11

Severe burn injuries initiate a cascade of downstream events, culminating in multiple organ dysfunction, sepsis, and even death. The elderly are in particular vulnerable to such outcomes, due primarily to a scarcity of knowledge on trauma progression at the biomolecular level in this population. Mitochondria, the cellular powerhouses, have been increasingly scrutinized recently for their contribution to trauma outcomes. We hypothesized that elderly have a worse outcome compared to adult patients ...[more]

PMID: 28711594

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Project description:BackgroundHuman mitochondrial DNA mutations are associated with common to rare mitochondrial disorders, which are multisystemic with complex clinical pathologies. The pathologies of these diseases are poorly understood and have no FDA-approved treatments leading to symptom management. Leigh syndrome (LS) is a pediatric mitochondrial disorder that affects the central nervous system during early development and causes death in infancy. Since there are no adequate models for understanding the rapid fatality associated with LS, human-induced pluripotent stem cell (hiPSC) technology has been recognized as a useful approach to generate patient-specific stem cells for disease modeling and understanding the origins of the phenotype.MethodshiPSCs were generated from control BJ and four disease fibroblast lines using a cocktail of non-modified reprogramming and immune evasion mRNAs and microRNAs. Expression of hiPSC-associated intracellular and cell surface markers was identified by immunofluorescence and flow cytometry. Karyotyping of hiPSCs was performed with cytogenetic analysis. Sanger and next-generation sequencing were used to detect and quantify the mutation in all hiPSCs. The mitochondrial respiration ability and glycolytic function were measured by the Seahorse Bioscience XFe96 extracellular flux analyzer.ResultsReprogrammed hiPSCs expressed pluripotent stem cell markers including transcription factors POU5F1, NANOG and SOX2 and cell surface markers SSEA4, TRA-1-60 and TRA-1-81 at the protein level. Sanger sequencing analysis confirmed the presence of mutations in all reprogrammed hiPSCs. Next-generation sequencing demonstrated the variable presence of mutant mtDNA in reprogrammed hiPSCs. Cytogenetic analyses confirmed the presence of normal karyotype in all reprogrammed hiPSCs. Patient-derived hiPSCs demonstrated decreased maximal mitochondrial respiration, while mitochondrial ATP production was not significantly different between the control and disease hiPSCs. In line with low maximal respiration, the spare respiratory capacity was lower in all the disease hiPSCs. The hiPSCs also demonstrated neural and cardiac differentiation potential.ConclusionOverall, the hiPSCs exhibited variable mitochondrial dysfunction that may alter their differentiation potential and provide key insights into clinically relevant developmental perturbations.

Project description:BackgroundThe lack of better understanding of the pathophysiology and cellular mechanisms associated with high mortality seen in hepatic encephalopathy (HE), a neurological complication arising from acute hepatic failure, remains a challenging medical issue. Clinical reports showed that the degree of baroreflex dysregulation is related to the severity of HE. Furthermore, mitochondrial dysfunction in the rostral ventrolateral medulla (RVLM), a key component of the baroreflex loop that maintains blood pressure and sympathetic vasomotor tone, is known to underpin impairment of baroreflex. Realizing that in addition to angiogenic and vasculogenic effects, by acting on its key receptor (VEGFR2), vascular endothelial growth factor (VEGF) elicits neuroprotection via maintenance of mitochondrial function, the guiding hypothesis of the present study is that the VEGF/VEGFR2 signaling plays a protective role against mitochondrial dysfunction in the RVLM to ameliorate baroreflex dysregulation that underpins the high fatality associated with HE.MethodsPhysiological, pharmacological and biochemical investigations were carried out in proof-of-concept experiments using an in vitro model of HE that involved incubation of cultured mouse hippocampal neurons with ammonium chloride. This was followed by corroboratory experiments employing a mouse model of HE, in which adult male C57BL/6 mice and VEGFR2 wild-type and heterozygous mice received an intraperitoneal injection of azoxymethane, a toxin used to induce acute hepatic failure.ResultsWe demonstrated that VEGFR2 is present in cultured neurons, and observed that whereas recombinant VEGF protein maintained cell viability, gene-knockdown of vegfr2 enhanced the reduction of cell viability in our in vitro model of HE. In our in vivo model of HE, we found that VEGFR2 heterozygous mice exhibited shorter survival rate and time when compared to wild-type mice. In C57BL/6 mice, there was a progressive reduction in VEGFR2 mRNA and protein expression, mitochondrial membrane potential and ATP levels, alongside augmentation of apoptotic cell death in the RVLM, accompanied by a decrease in baroreflex-mediated sympathetic vasomotor tone and hypotension. Immunoneutralization of VEGF exacerbated all those biochemical and physiological events.ConclusionsOur results suggest that, acting via VEGFR2, the endogenous VEGF plays a protective role against high fatality associated with HE by amelioration of the dysregulated baroreflex-mediated sympathetic vasomotor tone through sustaining mitochondrial bioenergetics functions and eliciting antiapoptotic action in the RVLM.

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Hepatic mitochondrial bioenergetics in aged C57BL/6 mice exhibit delayed recovery from severe burn injury.

Publications

Hepatic mitochondrial bioenergetics in aged C57BL/6 mice exhibit delayed recovery from severe burn injury.

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