Obesity differentially effects the somatosensory cortex and striatum of TgF344-AD rats

Lifestyle choices leading to obesity, hypertension and diabetes in mid-life contribute directly to the risk of late-life Alzheimer's disease (AD). However, in late-life or in late-stage AD conditions, obesity reduces the risk of AD and disease progression. To examine the mechanisms underlying this paradox, TgF344-AD rats were fed a varied high-carbohydrate, high-fat (HCHF) diet to induce obesity from nine months of age representing early stages of AD to twelve months of age in which rats exhibit the full spectrum of AD symptomology. We hypothesized regions primarily composed of gray matter, such as the somatosensory cortex (SSC), would be differentially affected compared to regions primarily composed of white matter, such as the striatum. We found increased myelin and oligodendrocytes in the somatosensory cortex of rats fed the HCHF diet with an absence of neuronal loss. We observed decreased inflammation in the somatosensory cortex despite increased AD pathology. Compared to the somatosensory cortex, the striatum had fewer changes. Overall, our results suggest that the interaction between diet and AD progression affects myelination in a brain region specific manner such that regions with a lower density of white matter are preferentially affected. Our results offer a possible mechanistic explanation for the obesity paradox.

Obesity differentially effects the somatosensory cortex and striatum of TgF344-AD rats

Lifestyle choices leading to obesity, hypertension and diabetes in mid-life contribute directly to the risk of late-life Alzheimer's disease (AD). However, in late-life or in late-stage AD conditions, obesity reduces the risk of AD and disease progression. To examine the mechanisms underlying this paradox, TgF344-AD rats were fed a varied high-carbohydrate, high-fat (HCHF) diet to induce obesity from nine months of age representing early stages of AD to twelve months of age in which rats exhibit the full spectrum of AD symptomology. We hypothesized regions primarily composed of gray matter, such as the somatosensory cortex (SSC), would be differentially affected compared to regions primarily composed of white matter, such as the striatum. We found increased myelin and oligodendrocytes in the somatosensory cortex of rats fed the HCHF diet with an absence of neuronal loss. We observed decreased inflammation in the somatosensory cortex despite increased AD pathology. Compared to the somatosensory cortex, the striatum had fewer changes. Overall, our results suggest that the interaction between diet and AD progression affects myelination in a brain region specific manner such that regions with a lower density of white matter are preferentially effected. Our results offer a possible mechanistic explanation for the obesity paradox.

Obesity Facilitates Sex-Specific Improvement In Cognition And Neuronal Function In A Rat Model Of Alzheimer's Disease

Obesity reduces or increases the risk of developing Alzheimer's disease (AD) depending on whether it is assessed in mid-life or late-life. There is currently no consensus on the relationship between obesity and AD or the mechanism or their interaction. Here, we aim to differentiate the cause-and-effect relationship between obesity and AD in a controlled rat model of AD. We induced obesity in 9-month-old TgF344-AD rats, that is pathology-load wise similar to early symptomatic phase of human AD. To more accurately model human obesity, we fed both TgF344-AD and non-transgenic littermates a varied high-carbohydrate-high-fat diet consisting of human food for 3 months. Obesity increased overall glucose metabolism and slowed cognitive decline in TgF344-AD rats, specifically executive function, without affecting non-transgenic rats. Pathological analyses of prefrontal cortex and hippocampus showed that obesity in TgF344-AD rats produced varied effects, with increased density of myelin and oligodendrocytes, lowered density and activation of microglia that we propose contributes to the cognitive improvement. However, obesity also decreased neuronal density, and promoted deposition of amyloid-beta plaques and tau inclusions. After 6 months on the high-carbohydrate-high-fat diet, detrimental effects on density of neurons, amyloid-beta plaques, and tau inclusions persisted while the beneficial effects on myelin, microglia, and cognitive functions remained albeit with a lower effect size. By examining the effect of sex, we found that both beneficial and detrimental effects of obesity were stronger in female TgF344-AD rats indicating that obesity during early symptomatic phase of AD is protective in females.

Trends in Negative Emotions Throughout the COVID-19 Pandemic in the United States

Objectives

Study design

Methods

Results

Conclusions

Compromised Cortical-Hippocampal Network Function From Transient Hypertension: Linking Mid-Life Hypertension to Late Life Dementia Risk

Mid-life hypertension is a major risk factor for developing dementia later in life. While anti-hypertensive drugs restore normotension, dementia risk remains above baseline suggesting that brain damage sustained during transient hypertension is irreversible. The current study characterized a rat model of transient hypertension with an extended period of normotensive recovery: F344 rats were treated with L-NG-Nitroarginine methyl ester (L-NAME) for 1 month to induce hypertension then allowed up to 4 months of recovery. With respect to cognitive deficits, comparison between 1 month and 4 months of recovery identified initial deficits in spatial memory that resolved by 4 months post-hypertension; contrastingly, loss of cognitive flexibility did not. The specific cells and brain regions underlying these cognitive deficits were investigated. Irreversible structural damage to the brain was observed in both the prefrontal cortex and the hippocampus, with decreased blood vessel density, myelin and neuronal loss. We then measured theta-gamma phase amplitude coupling as a readout for network function, a potential link between the observed cognitive and pathological deficits. Four months after hypertension, we detected decreased theta-gamma phase amplitude coupling within each brain region and a concurrent increase in baseline connectivity between the two regions reflecting an attempt to maintain function that may account for the improvement in spatial memory. Our results demonstrate that connectivity between prefrontal cortex and hippocampus is a vulnerable network affected by transient hypertension which is not rescued over time; thus demonstrating for the first time a mechanistic link between the long-term effects of transient hypertension and dementia risk.

Myelopreservation with the CDK4/6 inhibitor trilaciclib in patients with small-cell lung cancer receiving first-line chemotherapy: a phase Ib/randomized phase II trial

BACKGROUND

Chemotherapy-induced damage of hematopoietic stem and progenitor cells (HSPC) causes multi-lineage myelosuppression. Trilaciclib is an intravenous CDK4/6 inhibitor in development to proactively preserve HSPC and immune system function during chemotherapy (myelopreservation). Preclinically, trilaciclib transiently maintains HSPC in G1 arrest and protects them from chemotherapy damage, leading to faster hematopoietic recovery and enhanced antitumor immunity.

PATIENTS AND METHODS

This was a phase Ib (open-label, dose-finding) and phase II (randomized, double-blind placebo-controlled) study of the safety, efficacy and PK of trilaciclib in combination with etoposide/carboplatin (E/P) therapy for treatment-naive extensive-stage small-cell lung cancer patients. Patients received trilaciclib or placebo before E/P on days 1-3 of each cycle. Select end points were prespecified to assess the effect of trilaciclib on myelosuppression and antitumor efficacy.

RESULTS

A total of 122 patients were enrolled, with 19 patients in part 1 and 75 patients in part 2 receiving study drug. Improvements were seen with trilaciclib in neutrophil, RBC (red blood cell) and lymphocyte measures. Safety on trilaciclib+E/P was improved with fewer ≥G3 adverse events (AEs) in trilaciclib (50%) versus placebo (83.8%), primarily due to less hematological toxicity. No trilaciclib-related ≥G3 AEs occurred. Antitumor efficacy assessment for trilaciclib versus placebo, respectively, showed: ORR (66.7% versus 56.8%, P = 0.3831); median PFS [6.2 versus 5.0 m; hazard ratio (HR) 0.71; P = 0.1695]; and OS (10.9 versus 10.6 m; HR 0.87; P = 0.6107).

CONCLUSION

Trilaciclib demonstrated an improvement in the patient's tolerability of chemotherapy as shown by myelopreservation across multiple hematopoietic lineages resulting in fewer supportive care interventions and dose reductions, improved safety profile, and no detriment to antitumor efficacy. These data demonstrate strong proof-of-concept for trilaciclib's myelopreservation benefits.

CLINICAL TRAIL NUMBER

NCT02499770.

Early-stage attenuation of phase-amplitude coupling in the hippocampus and medial prefrontal cortex in a transgenic rat model of Alzheimer's disease

Alzheimer's disease (AD) is pathologically characterized by amyloid-β peptide (Aβ) accumulation, neurofibrillary tangle formation, and neurodegeneration. Preclinical studies on neuronal impairments associated with progressive amyloidosis have demonstrated some Aβ-dependent neuronal dysfunction including modulation of gamma-aminobutyric acid-ergic signaling. The present work focuses on the early stage of disease progression and uses TgF344-AD rats that recapitulate a broad repertoire of AD-like pathologies to investigate the neuronal network functioning using simultaneous intracranial recordings from the hippocampus (HPC) and the medial prefrontal cortex (mPFC), followed by pathological analyses of gamma-aminobutyric acid (GABA_A ) receptor subunits α1_, α5, and δ, and glutamic acid decarboxylases (GAD65 and GAD67). Concomitant to amyloid deposition and tau hyperphosphorylation, low-gamma band power was strongly attenuated in the HPC and mPFC of TgF344-AD rats in comparison to those in non-transgenic littermates. In addition, the phase-amplitude coupling of the neuronal networks in both areas was impaired, evidenced by decreased modulation of theta band phase on gamma band amplitude in TgF344-AD animals. Finally, the gamma coherence between HPC and mPFC was attenuated as well. These results demonstrate significant neuronal network dysfunction at an early stage of AD-like pathology. This network dysfunction precedes the onset of cognitive deficits and is likely driven by Aβ and tau pathologies. This article is part of the Special Issue "Vascular Dementia".

Rho-associated protein kinases as therapeutic targets for both vascular and parenchymal pathologies in Alzheimer's disease

The causes of late-onset Alzheimer's disease are unclear and likely multifactorial. Rho-associated protein kinases (ROCKs) are ubiquitously expressed signaling messengers that mediate a wide array of cellular processes. Interestingly, they play an important role in several vascular and brain pathologies implicated in Alzheimer's etiology, including hypertension, hypercholesterolemia, blood-brain barrier disruption, oxidative stress, deposition of vascular and parenchymal amyloid-beta peptides, tau hyperphosphorylation, and cognitive decline. The current review summarizes the functions of ROCKs with respect to the various risk factors and pathologies on both sides of the blood-brain barrier and present support for targeting ROCK signaling as a multifactorial and multi-effect approach for the prevention and amelioration of late-onset Alzheimer's disease. This article is part of the Special Issue "Vascular Dementia".

Early neurovascular dysfunction in a transgenic rat model of Alzheimer's disease

Alzheimer's disease (AD), pathologically characterized by amyloid-β peptide (Aβ) accumulation, neurofibrillary tangle formation, and neurodegeneration, is thought to involve early-onset neurovascular abnormalities. Hitherto studies on AD-associated neurovascular injury have used animal models that exhibit only a subset of AD-like pathologies and demonstrated some Aβ-dependent vascular dysfunction and destabilization of neuronal network. The present work focuses on the early stage of disease progression and uses TgF344-AD rats that recapitulate a broader repertoire of AD-like pathologies to investigate the cerebrovascular and neuronal network functioning using in situ two-photon fluorescence microscopy and laminar array recordings of local field potentials, followed by pathological analyses of vascular wall morphology, tau hyperphosphorylation, and amyloid plaques. Concomitant to widespread amyloid deposition and tau hyperphosphorylation, cerebrovascular reactivity was strongly attenuated in cortical penetrating arterioles and venules of TgF344-AD rats in comparison to those in non-transgenic littermates. Blood flow elevation to hypercapnia was abolished in TgF344-AD rats. Concomitantly, the phase-amplitude coupling of the neuronal network was impaired, evidenced by decreased modulation of theta band phase on gamma band amplitude. These results demonstrate significant neurovascular network dysfunction at an early stage of AD-like pathology. Our study identifies early markers of pathology progression and call for development of combinatorial treatment plans.

Venular degeneration leads to vascular dysfunction in a transgenic model of Alzheimer's disease

Most patients with Alzheimer's disease exhibit accumulation of amyloid-β peptide on leptomeningeal and cortical arterioles, or cerebral amyloid angiopathy, which is associated with impaired vascular reactivity and accelerated cognitive decline. Despite widespread recognition of the significance of vascular dysfunction in Alzheimer's disease aetiology and progression, much uncertainty still surrounds the mechanism underlying Alzheimer's disease vascular injury. Studies to date have focused on amyloid-β-induced damage to capillaries and plaque-associated arterioles, without examining effects across the entire vascular bed. In the present study, we investigated the structural and functional impairment of the feeding arteriolar versus draining venular vessels in a transgenic murine Alzheimer's disease model, with a particular focus on the mural cell populations that dictate these vessels' contractility. Although amyloid-β deposition was restricted to arterioles, we found that vascular impairment extended to the venules, which showed significant depletion of their mural cell coverage by the mid-stage of Alzheimer's disease pathophysiology. These structural abnormalities were accompanied by an abolishment of the normal vascular network flow response to hypercapnia: this functional impairment was so severe as to result in hypercapnia-induced flow decreases in the arterioles. Further pharmacological depletion of mural cells using SU6668, a platelet-derived growth factor receptor-β antagonist, resulted in profound structural abnormalities of the cortical microvasculature, including vessel coiling and short-range looping, increased tortuosity of the venules but not of the arterioles, increased amyloid-β deposition on the arterioles, and further alterations of the microvascular network cerebral blood flow response to hypercapnia. Together, this work shows hitherto unrecognized structural alterations in penetrating venules, demonstrates their functional significance and sheds light on the complexity of the relationship between vascular network structure and function in Alzheimer's disease.

scyllo-Inositol promotes robust mutant Huntingtin protein degradation

Huntington disease is characterized by neuronal aggregates and inclusions containing polyglutamine-expanded huntingtin protein and peptide fragments (polyQ-Htt). We have used an established cell-based assay employing a PC12 cell line overexpressing truncated exon 1 of Htt with a 103-residue polyQ expansion that yields polyQ-Htt aggregates to investigate the fate of polyQ-Htt-drug complexes. scyllo-Inositol is an endogenous inositol stereoisomer known to inhibit accumulation and toxicity of the amyloid-β peptide and α-synuclein. In light of these properties, we investigated the effect of scyllo-inositol on polyQ-Htt accumulation. We show that scyllo-inositol lowered the number of visible polyQ-Htt aggregates and robustly decreased polyQ-Htt protein abundance without concomitant cellular toxicity. We found that scyllo-inositol-induced polyQ-Htt reduction was by rescue of degradation pathways mediated by the lysosome and by the proteasome but not autophagosomes. The rescue of degradation pathways was not a direct result of scyllo-inositol on the lysosome or proteasome but due to scyllo-inositol-induced reduction in mutant polyQ-Htt protein levels.

Distinct activation profiles in microglia of different ages: a systematic study in isolated embryonic to aged microglial cultures

Microglia have been implicated in disease progression for several age-related brain disorders. However, while microglia's contribution to the progression of these disorders is accepted, the effect of aging on their endogenous cellular characteristics has received limited attention. In fact, a comprehensive study of how the structure and function of microglia changes as a function of developmental age has yet to be performed. Here, we describe the functional response characteristics of primary microglial cultures prepared from embryonic, neonatal (Neo), 2-3month-old, 6-8month-old, 9-11month-old, and 13-15month-old rats. Microglial morphology, glutamate (GLU) uptake, and release of trophic and inflammatory factors were assessed under basal conditions and in microglia activated with adenosine 5'-triphosphate (ATP) or lipopolysaccharide. We found that microglia from different age groups were both morphologically and functionally distinct. Upon activation by ATP, Neo microglia were the most reactive, upregulating nitric oxide, tumor necrosis factor-α, and brain-derived neurotrophic factor release as well as GLU uptake. This upregulation translated into neurotoxicity in microglia-neuron co-cultures that were not observed with microglia of different developmental ages. Interestingly, 13-15month-old microglia exhibited similar activation profiles to Neo microglia, whereas microglia from younger adults and embryos were activated less by ATP. Our data also identify age-dependent differences in purinergic receptor subtype expression that contribute to the regulation of neuronal survival. Combined, our data demonstrate that microglial activation and purinergic receptor profiles vary non-linearly with developmental age, a potentially important finding for studies examining the role of microglia in neurodegenerative disorders.

Clearance of amyloid-β peptides by microglia and macrophages: the issue of what, when and where

Accumulation of senile plaques consisting of amyloid-β peptide (Aβ) aggregates is a prominent pathological feature in Alzheimer's disease. Effective clearance of Aβ from the brain parenchyma is thought to regulate the development and progression of the disease. Macrophages in the brain play an important role in Aβ clearance by a variety of phagocytic and digestive mechanisms. Subpopulations of macrophages are heterogeneous such that resident microglia in the parenchyma, blood macrophages infiltrating from the periphery, and perivascular macrophages residing along cerebral vessels make functionally distinct contributions to Aβ clearance. Despite phenotypic similarities between the different macrophage subsets, a series of in vivo models have been derived to differentiate their relative impacts on Aβ dynamics as well as the molecular mechanisms underlying their activities. This review discusses the key findings from these models and recent research efforts to selectively enhance macrophage clearance of Aβ.

Mechanisms of amyloid-Beta Peptide uptake by neurons: the role of lipid rafts and lipid raft-associated proteins

A hallmark pathological feature of Alzheimer's disease (AD) is the accumulation of extracellular plaques composed of the amyloid-beta (Aβ) peptide. Thus, classically experiments were designed to examine Aβ toxicities within the central nervous system (CNS) from the extracellular space. However, a significant amount of evidence now suggests that intraneuronal accumulation of Aβ is neurotoxic and may play an important role in the disease progression of AD. One of the means by which neurons accumulate intracellular Aβ is through uptake of extracellular Aβ peptides, and this process may be a potential link between Aβ generation, synaptic dysfunction, and AD pathology. Recent studies have found that neuronal internalization of Aβ involves lipid rafts and various lipid raft-associated receptor proteins. Uptake mechanisms independent of lipid rafts have also been implicated. The aim of this paper is to summarize these findings and discuss their significance in the pathogenesis of AD.

Effects of sciatic nerve axotomy on excitatory synaptic transmission in rat substantia gelatinosa

Injury or section of a peripheral nerve can promote chronic neuropathic pain. This is initiated by the appearance and persistence of ectopic spontaneous activity in primary afferent neurons that promotes a secondary, enduring increase in excitability of sensory circuits in the spinal dorsal horn ("central sensitization"). We have previously shown that 10-20 days of chronic constriction injury (CCI) of rat sciatic nerve produce a characteristic "electrophysiological signature" or pattern of changes in synaptic excitation of five different electrophysiologically defined neuronal phenotypes in the substantia gelatinosa of the dorsal horn. Although axotomy and CCI send different signals to the dorsal horn, we now find, using whole cell recording, that the "electrophysiological signature" produced 12-22 days after sciatic axotomy is quite similar to that seen with CCI. Axotomy thus has little effect on resting membrane potential, rheobase, current-voltage characteristics, or excitability of most neuron types; however, it does decrease excitatory synaptic drive to tonic firing neurons, while increasing that to delay firing neurons. Since many tonic neurons are GABAergic, whereas delay neurons do not contain gamma-aminobutyric acid, axotomy may reduce synaptic excitation of inhibitory neurons while increasing that of excitatory neurons. Further analysis of spontaneous and miniature (tetrodotoxin-resistant) excitatory postsynaptic currents is consistent with the possibility that decreased excitation of tonic neurons reflects loss of presynaptic contacts. By contrast, increased excitation of "delay" neurons may reflect increased frequency of discharge of presynaptic action potentials. This would explain how synaptic excitation of tonic cells decreases despite the fact that axotomy increases spontaneous activity in primary afferent neurons.

Brain-derived neurotrophic factor drives the changes in excitatory synaptic transmission in the rat superficial dorsal horn that follow sciatic nerve injury

Peripheral nerve injury can promote neuropathic pain. The basis of the 'central sensitization' that underlies this often intractable condition was investigated using 14-20-day chronic constriction injury (CCI) of the sciatic nerve of 20-day-old rats followed by electrophysiological analysis of acutely isolated spinal cord slices. In addition, defined-medium organotypic spinal cord slice cultures were exposed for 5-6 days to brain-derived neurotrophic factor (BDNF, 200 ng ml(-1)) or to medium conditioned with activated microglia (aMCM). Since microglial activation is an early consequence of CCI, the latter manipulation allowed us to model the effect of peripheral nerve injury on the dorsal horn in vitro. Using whole-cell recording from superficial dorsal horn neurons, we found that both BDNF and CCI increased excitatory synaptic drive to putative excitatory 'radial delay' neurons and decreased synaptic excitation of inhibitory 'tonic islet/central' neurons. BDNF also attenuated synaptic excitation of putative GABAergic neurons identified by glutamic acid decarboxylase (GAD) immunoreactivity. Intrinsic neuronal properties (rheobase, input resistance and action potential discharge rates) were unaffected. Exposure of organotypic cultures to either BDNF or aMCM increased overall excitability of the dorsal horn, as seen by increased cytoplasmic Ca(2+) responses to 35 mm K(+) as monitored by confocal Fluo-4AM imaging. The effect of aMCM was attenuated by the recombinant BDNF binding protein TrkBd5 and the effect of BDNF persisted when GABAergic inhibition was blocked with SR95531. These findings suggest that CCI enhances excitatory synaptic drive to excitatory neurons but decreases that to inhibitory neurons. Both effects are mediated by nerve injury-induced release of BDNF from microglia.

Differential regulation of trophic and proinflammatory microglial effectors is dependent on severity of neuronal injury

Microglial activation has been reported to promote neurotoxicity and also neuroprotective effects. A possible contributor to this dichotomy of responses may be the degree to which proximal neurons are injured. The aim of this study was to determine whether varying the severity of neuronal injury influenced whether microglia were neuroprotective or neurotoxic. We exposed cortical neuronal cultures to varying degrees of hypoxia thereby generating mild (<20% death, 30 min hypoxia), moderate (40-60% death, 2 h hypoxia), or severe (>70% death, 6 h hypoxia) injuries. Twenty-four hours after hypoxia, the media from the neuronal cultures was collected and incubated with primary microglial cultures for 24 h. Results showed that the classic microglial proinflammatory mediators including inducible nitric oxide synthase, tumor necrosis factor alpha, and interleukin-1-beta were upregulated only in response to mild neuronal injuries, while the trophic microglial effectors brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor were upregulated in response to all degrees of neuronal injury. Microglia stimulated with media from damaged neurons were co-cultured with hypoxic neurons. Microglia stimulated by moderate, but not mild or severe damage were neuroprotective in these co-cultures. We also showed that the severity-dependent phenomenon was not related to autocrine microglial signaling and was dependent on the neurotransmitters released by neurons after injury, namely glutamate and adenosine 5'-triphosphate. Together our results show that severity of neuronal injury is an important factor in determining microglial release of "toxic" versus "protective" effectors and the resulting neurotoxicity versus neuroprotection.

Microglia in cerebral ischemia: molecular actions and interactions

The precise role of microglia in stroke and cerebral ischemia has been the subject of debate for a number of years. Microglia are capable of synthesizing numerous soluble and membrane-bound biomolecules, some known to be neuroprotective, some neurotoxic, whereas others have less definitive bioactivities. The molecular mechanisms through which microglia activate these molecules have thus become an important area of ischemia research. Here we provide a survey review that summarizes the key actions of microglial factors in cerebral ischemia including complement proteins, chemokines, pro-inflammatory cytokines, neurotrophic factors, hormones, and proteinases, as well several important messenger molecules that play a part in how these factors respond to extracellular signals during ischemic injuries. We also provide some new perspectives on how microglial intracellular signaling may contribute to the seemingly contradictory roles of several microglial effector molecules.

Interleukin-1 beta modulates AMPA receptor expression and phosphorylation in hippocampal neurons

Interleukin (IL)-1beta is a pro-inflammatory cytokine involved in modulating inflammation and stress responses in the brain. Central administration of IL-1beta impairs both memory functions and long-term potentiation (LTP) induction. However, the molecular events responsible for the downstream effects of IL-1beta are not fully understood. Given the potential regulatory role of IL-1beta in LTP, we assessed whether IL-1beta influences surface expression and phosphorylation of glutamate receptors. We found that IL-1beta, but not IL-10 or tumour necrosis factor (TNF)-alpha, down-regulated the surface expression and Ser831 phosphorylation of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit GluR1. Agents that block IL-1beta receptor activity abolished these effects. In contrast, no change in the surface expression of the N-methyl-d-aspartate (NMDA) receptor subunit NR1 was observed. The inhibition of NMDA receptor activity or depletion of extracellular calcium blocked IL-1beta effects on GluR1 phosphorylation and surface expression. NMDA-mediated calcium influx was also regulated by IL-1beta. These findings suggest that IL-1beta selectively regulates AMPA receptor phosphorylation and surface expression through extracellular calcium and an unknown mechanism involving NMDA receptor activity.

Hypoxia-activated microglial mediators of neuronal survival are differentially regulated by tetracyclines

The tetracycline derivatives minocycline (MINO) and doxycycline (DOXY) have been shown to be neuroprotective in in vivo and in vitro models of stroke. This neuroprotection is thought to be due to the suppression of microglial activation. However, the specific molecular parameters in microglia of the tetracyclines' effect are not understood. We subjected cultured rat microglial and neuronal cells to in vitro hypoxia and examined the effects of MINO and DOXY pre-treatments. Our data showed that MINO and DOXY protect against hypoxia-induced neuronal death by a mechanism dependent on regulation of microglial factors, but likely unrelated to regulation of microglial proliferation/viability. Both MINO and DOXY suppressed the hypoxic activation of ED-1, a marker for microglial activation. Morphological analyses of hypoxic microglia using the microglial marker Iba1 revealed that treatment with MINO and DOXY caused a higher percentage of microglia to remain in a non-activated state. MINO suppressed the hypoxic upregulation of pro-inflammatory agents nitric oxide (NO), interleukin-1 beta (IL-1beta), and tumor necrosis factor alpha (TNF-alpha), while DOXY down-regulated only NO and IL-1beta. In contrast, the hypoxic activation of pro-survival/neuroprotective microglial proteins, such as brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF), were unaffected by tetracycline treatments. Taken together, these results suggest that MINO and DOXY may provide neuroprotection against stroke by selectively down-regulating microglial toxic factors while maintaining functional pro-survival factors.