Exogenous progesterone is neuroprotective following injury to the male zebra finch brain

Chondroitin sulfate proteoglycans mRNA expression and degradation in the zebra finch following traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of fatality and disability worldwide. From minutes to months following damage, injury can result in a complex pathophysiology that can lead to temporary or permanent deficits including an array of neurodegenerative symptoms. These changes can include behavioral dysregulation, memory dysfunctions, and mood changes including depression. The nature and severity of impairments resulting from TBIs vary widely given the range of injury type, location, and extent of brain tissue involved. In response to the injury, the brain induces structural and functional changes to promote repair and minimize injury size. Despite its high prevalence, effective treatment strategies for TBI are limited. PNNs are part of the neuronal extracellular matrix (ECM) that mediate synaptic stabilization in the adult brain and thus neuroplasticity. They are associated mostly with inhibitory GABAergic interneurons and are thought to be responsible for maintaining the excitatory/inhibitory balance of the brain. The major structural components of PNNs include multiple chondroitin sulfate proteoglycans (CSPGs) as well as other structural proteins. Here we examine the effects of injury on CSPG expression, specifically around the changes in the side change moieties. To investigate CSPG expression following injury, adult male and female zebra finches received either a bilateral penetrating, or no injury and qPCR analysis and immunohistochemistry for components of the CSPGs were examined at 1- or 7-days post-injury. Next, to determine if CSPGs and thus PNNs should be a target for therapeutic intervention, CSPG side chains were degraded at the time of injury with chondroitinase ABC (ChABC) CSPGs moieties were examined. Additionally, GABA receptor mRNA and aromatase mRNA expression was quantified following CSPG degradation as they have been implicated in neuronal survival and neurogenesis. Our data indicate the CSPG moieties change following injury, potentially allowing for a brief period of synaptic reorganization, and that treatments that target CSPG side chains are successful in further targeting this brief critical period by decreasing GABA mRNA receptor expression, but also decreasing aromatase expression.

Effects of Progesterone on Preclinical Animal Models of Traumatic Brain Injury: Systematic Review and Meta-analysis

Since the publication of two phase III clinical trials not supporting the use of progesterone in patients with traumatic brain injury (TBI), several possible explanations have been postulated, including limitations in the analysis of results from preclinical evidence. Therefore, to address this question, a systematic review and meta-analysis was performed to evaluate the effects of progesterone as a neuroprotective agent in preclinical animal models of TBI. A total of 48 studies were included for review: 29 evaluated brain edema, 21 evaluated lesion size, and 0 studies reported the survival rate. In the meta-analysis, it was found that progesterone reduced brain edema (effect size - 1.73 [- 2.02, - 1.44], p < 0.0001) and lesion volume (effect size - 0.40 [- 0.65, - 0.14], p = 0.002). Lack of details in the studies hindered the assessment of risk of bias (through the SYRCLE tool). A funnel plot asymmetry was detected, suggesting a possible publication bias. In conclusion, preclinical studies show that progesterone has an anti-edema effect in animal models of TBI, decreasing lesion volume or increasing remaining tissue. However, more studies are needed using assessing methods with lower risk of histological artifacts.

Steroid profiling in brain and plasma of adult zebra finches following traumatic brain injury

Traumatic brain injury (TBI) is a serious health concern and a leading cause of death. Emerging evidence strongly suggests that steroid hormones (estrogens, androgens, and progesterone) modulate TBI outcomes by regulating inflammation, oxidative stress, free radical production, and extracellular calcium levels. Despite this growing body of evidence on steroid-mediated neuroprotection, very little is known about the local synthesis of these steroids following injury. Here, we examine the effect of TBI on local neurosteroid levels around the site of injury and in plasma in adult male and female zebra finches. Using ultrasensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS), we examined estrogens, androgens, and progesterone in the entopallium and plasma of injured and uninjured animals. Three days after injury, elevated levels of 17β-estradiol (E₂ ), estrone (E₁ ), and testosterone (T) were detected near injured brain tissue with a corresponding increase in E₂ also detected in plasma. Taken together, these results provide further evidence that TBI alters neurosteroid levels and are consistent with studies showing that neurosteroids provide neuroprotection following injury.

Estrogen Formation and Inactivation Following TBI: What we Know and Where we Could go

Traumatic brain injury (TBI) is responsible for various neuronal and cognitive deficits as well as psychosocial dysfunction. Characterized by damage inducing neuroinflammation, this response can cause an acute secondary injury that leads to widespread neurodegeneration and loss of neurological function. Estrogens decrease injury induced neuroinflammation and increase cell survival and neuroprotection and thus are a potential target for use following TBI. While much is known about the role of estrogens as a neuroprotective agent following TBI, less is known regarding their formation and inactivation following damage to the brain. Specifically, very little is known surrounding the majority of enzymes responsible for the production of estrogens. These estrogen metabolizing enzymes (EME) include aromatase, steroid sulfatase (STS), estrogen sulfotransferase (EST/SULT1E1), and some forms of 17β-hydroxysteroid dehydrogenase (HSD17B) and are involved in both the initial conversion and interconversion of estrogens from precursors. This article will review and offer new prospective and ideas on the expression of EMEs following TBI.

Progesterone receptor-mediated actions and the treatment of central nervous system disorders: An up-date of the known and the challenge of the unknown

Progesterone has been shown to exert a wide range of remarkable protective actions in experimental models of central nervous system injury or disease. However, the intimate mechanisms involved in each of these beneficial effects are not fully depicted. In this review, we intend to give the readers a thorough revision on what is known about the participation of diverse receptors and signaling pathways in progesterone-mediated neuroprotective, pro-myelinating and anti-inflammatory outcomes, as well as point out to novel regulatory mechanisms that could open new perspectives in steroid-based therapies.

Neurosteroids as regulators of neuroinflammation

Neuroinflammation is a physiological protective response in the context of infection and injury. However, neuroinflammation, especially if chronic, may also drive neurodegeneration. Neurodegenerative diseases, such as multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease (PD) and traumatic brain injury (TBI), display inflammatory activation of microglia and astrocytes. Intriguingly, the central nervous system (CNS) is a highly steroidogenic environment synthesizing steroids de novo, as well as metabolizing steroids deriving from the circulation. Neurosteroid synthesis can be substantially affected by neuroinflammation, while, in turn, several steroids, such as 17β-estradiol, dehydroepiandrosterone (DHEA) and allopregnanolone, can regulate neuroinflammatory responses. Here, we review the role of neurosteroids in neuroinflammation in the context of MS, AD, PD and TBI and describe underlying molecular mechanisms. Moreover, we introduce the concept that synthetic neurosteroid analogues could be potentially utilized for the treatment of neurodegenerative diseases in the future.