Testosterone Administration after Traumatic Brain Injury Reduces Mitochondrial Dysfunction and Neurodegeneration

Abstract

Traumatic brain injury (TBI) increases Ca 2+ influx into neurons and desynchronizes mitochondrial function leading to energy depletion and apoptosis. This process may be influenced by brain testosterone (TS) levels, which are known to decrease after TBI. We hypothesized that a TS-based therapy could preserve mitochondrial neuroenergetics after TBI, thereby reducing neurodegeneration. C57BL/6J mice were submitted to sham treatment or severe parasagittal controlled cortical impact (CCI) and were subcutaneously injected with either vehicle (VEH-SHAM and VEH-CCI) or testosterone cypionate (15 mg/kg, TS-CCI) for 10 days. Cortical tissue homogenates ipsilateral to injury were used for neurochemical analysis. The VEH-CCI group displayed an increased Ca 2+-induced mitochondrial swelling after the addition of metabolic substrates (pyruvate, malate, glutamate, succinate, and adenosine diphosphate [PMGSA]). The addition of Na + stimulated mitochondrial Ca 2+ extrusion through Na + /Ca 2+ /Li + exchanger (NCLX) in VEH-SHAM and TS-CCI, but not in the VEH-CCI group. Reduction in Ca 2+ efflux post-injury was associated with impaired mitochondrial membrane potential formation/dissipation, and decreased mitochondrial adenosine triphosphate (ATP)-synthase coupling efficiency. Corroborating evidence of mitochondrial uncoupling was observed with an increase in H 2 O 2 production post-injury, but not in superoxide dismutase (SOD2) protein levels. TS administration significantly reduced these neuroenergetic alterations. At molecular level, TS prevented the increase in pTau Ser396 and alpha-Spectrin fragmentation by the Ca 2+ dependent calpain-2 activation, and decreased both caspase-3 activation and Bax/BCL-2 ratio, which suggests a downregulation of mitochondrial apoptotic signals. Search Tool for the Retrieval of Interacting Genes/Proteins database provided two distinct gene/protein clusters, ''upregulated and downregulated,'' interconnected through SOD2. Therefore, TS administration after a severe CCI improves the mitochondrial Ca 2+ extrusion through NCLX exchanger and ATP synthesis efficiency, ultimately downregulating the overexpression of molecular drivers of neurodegeneration.

Pyruvate Dehydrogenase and Tricarboxylic Acid Cycle Enzymes Are Sensitive Targets of Traumatic Brain Injury Induced Metabolic Derangement

“…TBI has been shown to cause significant changes in various mitochondrial functions, including the transport of electrons through the ETC [26,27], the permeability of the mitochondrial membranes [28], and the mitochondrial quality control system [19,29,30]. These phenomena, besides triggering oxidative/nitrosative stress [20,31] and the intrinsic pathway of apoptosis [32], generate a profound derangement of energy metabolism, leading to inadequate ATP supply for the brain’s energy demands [12,15,16,17,25,33]. Given that the brain mostly utilizes glucose as the fuel for its oxidative metabolism [4,5,34], it is highly relevant to elucidate which steps of glucose oxidation TBI principally affects.…”

Low Molecular Weight Dextran Sulfate (ILB®) Administration Restores Brain Energy Metabolism Following Severe Traumatic Brain Injury in the Rat

“…The rat skull cap was carefully removed, the brain was exposed, rapidly removed, the cerebral hemispheres dissected and placed on aluminium tongues pre-cooled in liquid nitrogen, freeze-clamped, and then immersed in liquid nitrogen. The freeze-clamping procedure was introduced to accelerate freezing of the tissue, thus minimizing potential metabolite loss [9,12,15,16]. Tissue homogenization for metabolite analyses was effected as described below.…”

“…The severity of this cellular and molecular damage depends on the impact force acting on the cerebral tissue [12]. Mitochondrial dysfunction occurs in the post-injured brain [13,14], causing an imbalance of ATP production and consumption, with consequent energy crisis [15]. This triggers the intrinsic apoptotic pathway [16], and increasing levels of reactive oxygen species (ROS) and reactive nitrogen species (RNS) with associated decreased levels of cell antioxidants [17] causing an insurgence of oxidative/nitrosative stress [18].…”

Vagus Nerve Stimulation Attenuates Early Traumatic Brain Injury by Regulating the NF-κB/NLRP3 Signaling Pathway

“…Studies have reported that the expression of Bax is significantly upregulated, and the expression of Bcl-2 is downregulated in the TBI model. 48 The NLRP3 inflammasome is a multiprotein oligomer activated by NF-κB and promotes the secretion of IL-1β and IL-18. These cytokines induce pro-inflammatory cell death by activating Bax.…”