Ming-Lei Guo

Substance use disorders ( SUDs ) remain major public health concerns worldwide, particularly in developed countries. SUDs are characterized by persistent neuroinflammation and synaptic dysfunction in the brain. Despite decades of extensive investigation, the detailed mechanisms underlying SUDs remain elusive. Ferroptosis is a highly regulated cell death process deeply affected by iron metabolism, lipid peroxidation, reactive oxygen species ( ROS ) production, and antioxidant systems. It has been implicated in multiple neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, multiple sclerosis, and ischemic stroke. Recently, emerging evidence has highlighted the role of ferroptosis in drug-induced pathological changes. Various types of abused substances including alcohol, cocaine, methamphetamine ( METH) nicotine, cannabis, and opioids have been shown to disrupt ferroptosis-relevant pathways, leading to microglial activation and neuronal injury. Inhibition of ferroptosis could mitigate these pathological changes in preclinical models. Here, we summarize current evidence demonstrating the effects of abused drugs on ferroptosis pathways. Collectively, these findings underscore the potential role of ferroptosis in the pathophysiology of SUDs. Targeting ferroptosis may represent a promising therapeutic strategy for alleviating drug-induced neurological damage and improving recovery outcomes such as cognitive and memory deficiency in individuals with addiction.

A novel subtype of microglia, lipid droplet accumulation microglia (LDAMs), has been identified in the aged brain, which is characterized by sustained inflammation and senescent-like phenotypes. LDAMs are deeply involved in promoting brain aging as well as the pathogenesis of multiple neurodegenerative diseases. Cocaine can alter brain lipidomic profiles, induce microglial activation, and accelerate brain aging. This suggests that cocaine might affect microglial lipid metabolism, which ultimately aggravates aging-related neurological disorders in people with addictions. In this study, we explored the effects of cocaine on microglial lipid metabolism. Our results showed that chronic cocaine administration altered brain lipid profiles and increased LDAM formation in vivo. The increase in LDAMs was accompanied by the upregulation of the senescent marker p53 in the brain. Cocaine also increased lipid droplet (LD) formation in BV2 microglia and primary microglia in vitro. A mechanism study revealed that cocaine increased the levels of SREBP1/2, HMGCR, DGAT1, and FASN, which are critical for lipid synthesis. Overall, our findings demonstrate that cocaine increases LDAM formation in vitro and in vivo. These results indicate that targeting microglia lipid metabolism might be a promising therapeutic approach to mitigate aging-related neurological syndromes in people with cocaine addictions.

In the era of combined antiretroviral therapy, around 50% of chronic HIV (+) individuals show varying degrees of memory and cognitive deficiency (NeuroHIV), a phenomenon of accelerated brain aging. HIV protein transactivator of transcription (TAT) has been well-accepted as a risk factor contributing to NeuroHIV through dysregulating microglia (Mg) functions. Previous studies have demonstrated that HIV-TAT can affect lipid metabolism, immune responses, autophagy, and senescence in rodent Mg. However, due to the significant species differences between rodent and human Mg (hMg), it is essential to take caution when interpreting the results obtained from rodent models into human conditions. For the unanswered questions, we generated hMg from human inducible pluripotent stem cells (iPSCs) and exposed them to HIV-TAT. The results obtained from Flow analysis and immunostaining experiments reveal that TAT can induce LD accumulation and increase perilipin-2 (Plin2) levels in hMg. Meanwhile, HIV-TAT can upregulate autophagosome formation and p53 levels. Through human immune array assay, we showed that TAT can increase the expression of multiple pro-inflammatory mediators, cytokines, and chemokines in hMg. Extensive bioinformatic analysis shows that HIV-TAT can affect multiple neuroimmune signaling pathways and indicates that microRNAs (miRNAs) are coherently involved in such dysregulation. Overall, our findings provide direct evidence showing that HIV-TAT can affect lipid metabolism, autophagy, senescence signaling, and multiple neuroimmune-related pathways in hMg and indicate the roles of novel miRNAs on NeuroHIV pathogenesis, which deserves further investigations.

Abnormal microglial activation has been suggested as “driven force” promoting brain aging. Lipid droplets accumulating microglia (LDAM), identified as a novel inflammatory phenotype, elevate neuroinflammation and exaggerate neuronal injuries in aging and multiple neurodegenerative diseases. Since chronic HIV (human immunodeficiency virus) (+) individuals show an accelerated brain aging and higher incidence of neurological symptoms compared to age-matched HIV (-) population, we hypothesize that LDAM are also involved in such phenomenon. For validating the hypothesis, we employed HIV transgenic (HIV-Tg) and wilt type (WT) rats to check lipid droplets (LDs) accumulation in the brains at mature (6 months) and middle age (12 months). Our results showed that HIV-Tg rats possess higher levels of LDs formation in the hippocampus (HP) and prefrontal cortex (PFc) than controls at middle age. Increased LDs are mainly presented in microglia in the HP but largely co-localized with astrocytes in the PFc. Interestingly, increased LDs are associated with upregulation on Iba1 but not with GFAP levels. HIV-Tg rats reveal an accelerated LDs accumulation during normal aging. Purified microglia from HIV-Tg rats (12 month) show higher expression of neuroimmune signaling than microglia from controls. HIV-Tg rats showed dysregulation on cholesterol synthesis in the brain HP as well as deficiency on locomotion coordination compared to controls. Overall, our results demonstrate substantial LDs accumulation in the brains of HIV-Tg rats which is associated with abnormal microglial activation and accelerated decline on locomotion coordination during aging. Dysregulation on lipid metabolism might underlie accelerated brain aging in the context of chronic HIV infection.

Cocaine, one of the most abused drugs worldwide, is capable of activating microglia in vitro and in vivo. Several neuroimmune pathways have been suggested to play roles in cocaine-mediated microglial activation. Previous work showed that cocaine activates microglia in a region-specific manner in the brains of self-administered mice. To further characterize the effects of cocaine on microglia and neuroimmune signaling in vivo, we utilized the brains from both sexes of outbred rats with cocaine self-administration to explore the activation status of microglia, NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome activity, corticotropin-releasing factor (CRF) signaling, and NF-κB levels in the striatum and hippocampus (HP). Age-matched rats of the same sex (drug naïve) served as controls. Our results showed that cocaine increased neuroinflammation in the striatum and HP of both sexes with a relatively higher increases in male brains. In the striatum, cocaine upregulated NLRP3 inflammasome activity and CRF levels in males but not in females. In contrast, cocaine increased NLRP3 inflammasome activity in the HP of females but not in males, and no effects on CRF signaling were observed in this region of either sex. Interestingly, cocaine increased NF-κB levels in the striatum and HP with no sex difference. Taken together, our results provide evidence that cocaine can exert region- and sex-specific differences in neuroimmune signaling in the brain. Targeting neuroimmune signaling has been suggested as possible treatment for cocaine use disorders (CUDs). Our current results indicate that sex should be taken into consideration when determining the efficacy of these new therapeutic approaches.

During the last decade, substance use disorders (SUDs) have been increasingly recognized as neuroinflammation-related brain diseases. Various types of abused drugs (cocaine, methamphetamine, alcohol, opiate-like drugs, marijuana, etc.) can modulate the activation status of microglia and neuroinflammation levels which are involved in the pathogenesis of SUDs. Several neuroimmune signaling pathways, including TLR/NF-кB, reactive oxygen species, mitochondria dysfunction, as well as autophagy defection, etc., have been implicated in promoting SUDs. Recently, inflammasome-mediated signaling has been identified as playing critical roles in the microglia activation induced by abused drugs. Among the family of inflammasomes, NOD-, LRR-, and pyrin-domain-containing protein 3 (NLRP3) serves the primary research target due to its abundant expression in microglia. NLRP3 has the capability of integrating multiple external and internal inputs and coordinately determining the intensity of microglia activation under various pathological conditions. Here, we summarize the effects of abused drugs on NLRP3 inflammasomes, as well as others, if any. The research on this topic is still at an infant stage; however, the readily available findings suggest that NLRP3 inflammasome could be a common downstream effector stimulated by various types of abused drugs and play critical roles in determining abused-drug-mediated biological effects through enhancing glia–neuron communications. NLRP3 inflammasome might serve as a novel target for ameliorating the development of SUDs.

Despite the ability of combination antiretroviral therapy (cART) to suppress viremia, there is persistence low levels of HIV proteins such as Transactivator of transcription (Tat) in the central nervous system (CNS), contributing to glial activation and neuroinflammation. Accumulating evidence also implicates the role of drugs of abuse in exacerbating neurological complications associated with HIV-1. The combined effects of HIV Tat, drugs of abuse, and cART can thus create a toxic milieu in the CNS. The present study investigated the combinatorial effects of HIV-Tat, cocaine, and cART on autophagy and NLRP3 inflammasome activation. We selected a combination of three commonly used cART regimens: tenofovir, emtricitabine, and dolutegravir. Our results demonstrated that exposure of mouse primary microglia (MPMs) to these agents—HIV Tat (25 ng/ml), cocaine (1 μM), and cART (1 μM each) resulted in upregulation of autophagy markers: Beclin1, LC3B-II, and SQSTM1 with impaired lysosomal functioning involving increased lysosomal pH, decreased LAMP2 and cathepsin D, ultimately leading to dysregulated autophagy. Our findings also demonstrated activation of the NLRP3 signaling in microglia exposed to these agents. We further demonstrated that gene silencing of key autophagy protein BECN1 significantly blocked NLRP3-mediated activation of microglia. Silencing of NLRP3, however, failed to block HIV Tat, cocaine, and cART-mediated dysregulation of the autophagy-lysosomal axis; these in vitro phenomena were also validated in vivo using iTat mice administered cocaine and cART. This study thus underscores the cooperative effects of HIV Tat, cocaine, and cART in exacerbating microglial activation involving dysregulated autophagy and activation of the NLRP3 inflammasome signaling. Graphical Abstract

Objectives: The current study was undertaken to understand the underlying molecular mechanism(s) by which HIV Transactivator of transcription (Tat) alters oligodendrocyte maturation through the generation of reactive oxygen species (ROS), impairment of lysosomal functioning, and dysregulation of autophagy. Methods: We exposed primary rat immature oligodendrocytes to HIV Tat and utilized various experimental techniques to assess its effects on oligodendrocytes maturation. We measured ROS levels, assessed lysosomal membrane potential, determined cathepsin D activity, and analyzed the expression of autophagy-related markers. Furthermore, we investigated the potential of ROS scavengers and lysosomal protectants to mitigate the damaging effects of HIV Tat on oligodendrocytes maturation. Results: Exposure of primary rat immature oligodendrocytes to HIV Tat significantly increased ROS levels, indicating the induction of oxidative stress. This oxidative stress impaired lysosomal functioning, as evidenced by a substantial increase in lysosomal membrane potential and a decrease in cathepsin D activity. Compromised lysosomal function resulted in dysregulated autophagy, which was confirmed by increased expression of SQSTM1. However, the administration of ROS scavengers and lysosomal protectants effectively attenuated the detrimental effects of HIV Tat on oligodendrocytes maturation. Conclusions: Our findings demonstrate that HIV Tat exposure induces oxidative stress, impairs lysosomal functioning, and dysregulates autophagy in oligodendrocytes. These molecular changes likely contribute to the altered maturation of oligodendrocytes observed in HIV-infected individuals. Understanding these underlying mechanisms provides valuable insights into the pathogenesis of HIV-associated neurocognitive disorders and highlights the potential of therapeutic strategies targeting ROS scavenging and lysosomal protection as adjunctive approaches for managing such complications in HIV +ve individuals.

Chronic sleep disturbances (CSDs) including insomnia, insufficient sleep time, and poor sleep quality are major public health concerns around the world, especially in developed countries. CSDs are major health risk factors linked to multiple neurodegenerative and neuropsychological diseases. It has been suggested that CSDs could activate microglia (Mg) leading to increased neuroinflammation levels, which ultimately lead to neuronal dysfunction. However, the detailed mechanisms underlying CSD-mediated microglial activation remain mostly unexplored. In this study, we used mice with three-weeks of sleep fragmentation (SF) to explore the underlying pathways responsible for Mg activation. Our results revealed that SF activates Mg in the hippocampus (HP) but not in the striatum and prefrontal cortex (PFc). SF increased the levels of corticotropin-releasing hormone (CRH) in the HP. In vitro mechanism studies revealed that CRH activation of Mg involves galectin 3 (Gal3) upregulation and autophagy dysregulation. CRH could disrupt lysosome membrane integrity resulting in lysosomal cathepsins leakage. CRHR2 blockage mitigated CRH-mediated effects on microglia in vitro. SF mice also show increased Gal3 levels and autophagy dysregulation in the HP compared to controls. Taken together, our results show that SF-mediated hippocampal Mg activation involves CRH mediated galectin 3 and autophagy dysregulation. These findings suggest that targeting the hippocampal CRH system might be a novel therapeutic approach to ameliorate CSD-mediated neuroinflammation and neurodegenerative diseases.