Mitochondrial dysfunction in sepsis is associated with diminished intramitochondrial TFAM despite its increased cellular expression

Tim Rahmel,Michael Adamzik,Sebastian Kreimendahl,Björn Koos,Katharina Rump,Jürgen Peters,Hartmuth Nowak,Mervyn Singer,Joachim Rassow,Britta Marko,Lars Bergmann,Patrick Thon

doi:10.1038/s41598-020-78195-4

Abstract

Sepsis is characterized by a dysregulated immune response, metabolic derangements and bioenergetic failure. These alterations are closely associated with a profound and persisting mitochondrial dysfunction. This however occurs despite increased expression of the nuclear-encoded transcription factor A (TFAM) that normally supports mitochondrial biogenesis and functional recovery. Since this paradox may relate to an altered intracellular distribution of TFAM in sepsis, we tested the hypothesis that enhanced extramitochondrial TFAM expression does not translate into increased intramitochondrial TFAM abundance. Accordingly, we prospectively analyzed PBMCs both from septic patients (n = 10) and lipopolysaccharide stimulated PBMCs from healthy volunteers (n = 20). Extramitochondrial TFAM protein expression in sepsis patients was 1.8-fold greater compared to controls (p = 0.001), whereas intramitochondrial TFAM abundance was approximate 80% less (p < 0.001). This was accompanied by lower mitochondrial DNA copy numbers (p < 0.001), mtND1 expression (p < 0.001) and cellular ATP content (p < 0.001) in sepsis patients. These findings were mirrored in lipopolysaccharide stimulated PBMCs taken from healthy volunteers. Furthermore, TFAM-TFB2M protein interaction within the human mitochondrial core transcription initiation complex, was 74% lower in septic patients (p < 0.001). In conclusion, our findings, which demonstrate a diminished mitochondrial TFAM abundance in sepsis and endotoxemia, may help to explain the paradox of lacking bioenergetic recovery despite enhanced TFAM expression.

Highlights

Sepsis is defined as an acute organ dysfunction caused by a dysregulated immune response to an infection, affecting millions of individuals per year worldwide and representing a major healthcare c oncern[1,2]
To test the hypothesis that enhanced TFAM gene expression does not translate into an increased abundance of intramitochondrial TFAM and maintenance of mitochondrial dysfunction, we studied both blood mononuclear cells (PBMCs) from sepsis patients and lipopolysaccharide (LPS)-stimulated Peripheral blood mononuclear cells (PBMCs) drawn from healthy volunteers
We found a 1.8-fold greater extramitochondrial TFAM protein expression in sepsis patients compared to healthy controls (p = 0.001; Fig. 1f)

Summary

Introduction

Sepsis is defined as an acute organ dysfunction caused by a dysregulated immune response to an infection, affecting millions of individuals per year worldwide and representing a major healthcare c oncern[1,2]. Mitochondria generate most of the adenosine triphosphate (ATP) required for normal cellular function, but are involved in multiple intracellular signaling and regulatory processes such as intracellular calcium regulation and production of reactive oxygen species[5,6,7] These important regulatory mechanisms seems to be profoundly disturbed in human sepsis, which can ensue mitochondrial dysfunction and reduced oxidative ATP p roduction[3,4,8]. Provide growing evidence that activation of mitochondrial biogenesis in sepsis, associated with an increased intracellular TFAM expression, is not necessarily accompanied by recovery of mitochondrial function[10,26,27,28] This raises the question as to whether steps in TFAMs production and activity, from nuclear transcription to intramitochondrial actions, are disturbed. To test the hypothesis that enhanced TFAM gene expression does not translate into an increased abundance of intramitochondrial TFAM and maintenance of mitochondrial dysfunction, we studied both blood mononuclear cells (PBMCs) from sepsis patients and lipopolysaccharide (LPS)-stimulated PBMCs drawn from healthy volunteers

Methods

Results

Discussion

Conclusion