Programmed Death-1 Deficiency Aggravates Motor Dysfunction in MPTP Model of Parkinson's Disease by Inducing Microglial Activation and Neuroinflammation in Mice

Mesenchymal stem cell-derived extracellular vesicles alleviate autism by regulating microglial glucose metabolism reprogramming and neuroinflammation through PD-1/PD-L1 interaction

Neuroinflammation triggered by microglia activation is hallmark of autism spectrum disorder (ASD), and this process includes crucial metabolic reprogramming from oxidative phosphorylation to glycolysis, which may cause neuron loss and functional impairment. The inhibitory immune checkpoint programmed cell death protein 1 (PD-1) on immune cells is an important target for tumor immunotherapy. However, the immunomodulatory effects of PD-1 in ASD remains to be elusive. Mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) exhibit immunomodulatory capabilities in a range of neurological diseases. Our findings indicated the expression of PD-L1 on MSC-EVs, potentially facilitating signaling to PD-1-expressing microglia. Here, we showed how MSC-EVs activated of PD-L1/PD-1 axis and ameliorated glycolysis, neuroinflammation and autism-like behaviors. After first detecting elevated glycolysis and neuroinflammation in prefrontal cortex (PFC) tissue from the maternal immune activation (MIA) mice, we also demonstrated that PD-1 expression level was upregulated in microglia. Following given MSC-EVs carried PD-L1 into adult MIA offspring mice via intranasal administration, which bound with PD-1 on microglia and then the autism-like behaviors were alleviated as well. Further experiments verified that MSC-EVs could decreased the level of glycolysis and neuroinflammation by PD-1/ERK/HIF-1α pathway in the primary microglia in PFC of MIA offspring mice. Pharmacological blockade and genetic inhibition of PD-1 could weaken the effect of MSC-EVs and aggravate microglial dysfunction, glycolysis and autism-like behaviors in MIA offspring mice. Futhermore, PD-L1 deficient weakened the effect of MSC-EVs on neuroinflammation, glycolysis and autism-like behaviors in MIA offspring mice. Our research indicated the significant immunomodulatory capabilities of MSC-EVs, which play an important role in reprogramming microglial glucose metabolism and suppressing neuroinflammation in ASD. By activating the PD-L1/PD-1 axis and inhibiting the downstream ERK/HIF-1α pathway, MSC-EVs were found to alleviate autism-like behaviors, which revealing a novel pathological mechanism and offering promising therapeutic insights into ASD.

PD-L1: From cancer immunotherapy to therapeutic implications in multiple disorders

The PD-L1/PD-1 signaling pathway is the gold standard for cancer immunotherapy. Therapeutic antibodies targeting PD-1, such as nivolumab (Opdivo) and pembrolizumab (Keytruda), and PD-L1, including atezolizumab (Tecentriq), durvalumab (Imfinzi), and avelumab (Bavencio) have received Food and Drug Administration approval and are currently being used to treat various cancers. Traditionally, PD-L1 is known as an immune checkpoint protein that binds to the PD-1 receptor on its surface to inhibit the activity of T cells, which are the primary effector cells in antitumor immunity. However, it also plays a role in cancer progression, which goes beyond traditional understanding. Here, we highlight the multifaceted mechanisms of action of PD-L1 in cancer cell proliferation, transcriptional regulation, and systemic immune suppression. Moreover, we consider the potential role of PD-L1 in the development and pathogenesis of diseases other than cancer, explore PD-L1-focused therapeutic approaches for these diseases, and assess their clinical relevance. Through this review, we hope to provide deeper insights into the PD-L1/PD-1 signaling pathway and present a broad perspective on potential therapeutic approaches for cancer and other diseases.

Neuronal-enriched small extracellular vesicles trigger a PD-L1-mediated broad suppression of T cells in Parkinson's disease

Many clinical studies indicate a significant decrease of peripheral T cells in Parkinson's disease (PD). There is currently no mechanistic explanation for this important observation. Here, we found that small extracellular vesicles (sEVs) derived from in vitro and in vivo PD models suppressed IL-4 and INF-γ production from both purified CD4+ and CD8+ T cells and inhibited their activation and proliferation. Furthermore, neuronal-enriched sEVs (NEEVs) isolated from plasma of A53T-syn mice and culture media of human dopaminergic neurons carrying A53T-syn mutation also suppressed Th1 and Th2 differentiation of naive CD4+ T cells. Mechanistically, the suppressed phenotype induced by NEEVs was associated with altered programmed death ligand 1 (PD-L1) level in T cells. Blocking PD-L1 with an anti-PD-L1 antibody or a small molecule inhibitor BMS-1166 reversed T cell suppression. Our study provides the basis for exploring peripheral T cells in PD pathogenesis and as biomarkers or therapeutic targets for the disease.

Vincamine alleviates brain injury by attenuating neuroinflammation and oxidative damage in a mouse model of Parkinson's disease through the NF-κB and Nrf2/HO-1 signaling pathways

Parkinson's disease (PD) is a neurodegenerative disease featured by progressive loss of nigrostriatal dopaminergic neurons, the etiology of which is associated with the existence of neuroinflammatory response and oxidative stress. Vincamine is an indole alkaloid that was reported to exhibit potent anti-inflammatory and antioxidant properties in many central and/or peripheral diseases. Nevertheless, the specific role of vincamine in PD development remains unknown. In our study, dopaminergic neuron loss was determined through immunohistochemistry staining and western blot analysis of tyrosine hydroxylase (TH) expression in the substantia nigra (SN) of PD mice. Reactive oxygen species (ROS) production and malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione (GSH) levels were detected through DHE staining and commercially available kits to assess oxidative stress. Pro-inflammatory cytokine (TNF-α, IL-1β, and IL-6) levels in the SN were measured via RT-qPCR and western blot analysis. Microglial and astrocyte activation was examined through immunofluorescence staining of Iba-1 (microglia marker) and GFAP (astrocyte marker) in the SN. The regulation of vincamine on the NF-κB and Nrf2/HO-1 pathway was estimated through western blot analysis. Our results showed that vincamine treatment decreased TNF-α, IL-1β, and IL-6 mRNA and protein levels, reduced GFAP and Iba-1 expression, decreased ROS production and MDA level, and increased SOD activity and GSH level in the SN of PD mice. Mechanically, vincamine repressed the phosphorylation levels of p65, IKKβ, and IκBα but enhanced the protein levels of Nrf2 and HO-1 in PD mice. Collectively, vincamine plays a neuroprotective role in PD mouse models by alleviating neuroinflammation and oxidative damage via suppressing the NF-κB pathway and activating the Nrf2/HO-1 pathway.

Immunological dimensions of neuroinflammation and microglial activation: exploring innovative immunomodulatory approaches to mitigate neuroinflammatory progression

The increasing life expectancy has led to a higher incidence of age-related neurodegenerative conditions. Within this framework, neuroinflammation emerges as a significant contributing factor. It involves the activation of microglia and astrocytes, leading to the release of pro-inflammatory cytokines and chemokines and the infiltration of peripheral leukocytes into the central nervous system (CNS). These instances result in neuronal damage and neurodegeneration through activated nucleotide-binding domain and leucine-rich repeat containing (NLR) family pyrin domain containing protein 3 (NLRP3) and nuclear factor kappa B (NF-kB) pathways and decreased nuclear factor erythroid 2-related factor 2 (Nrf2) activity. Due to limited effectiveness regarding the inhibition of neuroinflammatory targets using conventional drugs, there is challenging growth in the search for innovative therapies for alleviating neuroinflammation in CNS diseases or even before their onset. Our results indicate that interventions focusing on Interleukin-Driven Immunomodulation, Chemokine (CXC) Receptor Signaling and Expression, Cold Exposure, and Fibrin-Targeted strategies significantly promise to mitigate neuroinflammatory processes. These approaches demonstrate potential anti-neuroinflammatory effects, addressing conditions such as Multiple Sclerosis, Experimental autoimmune encephalomyelitis, Parkinson's Disease, and Alzheimer's Disease. While the findings are promising, immunomodulatory therapies often face limitations due to Immune-Related Adverse Events. Therefore, the conduction of randomized clinical trials in this matter is mandatory, and will pave the way for a promising future in the development of new medicines with specific therapeutic targets.

PD-1/PD-L Axis in Neuroinflammation: New Insights

The approval of immune checkpoint inhibitors (ICIs) by the Food and Drug Administration (FDA) led to an improvement in the treatment of several types of cancer. The main targets of these drugs are cytotoxic T-lymphocyte antigen 4 (CTLA-4) and programmed cell death protein-1/programmed death-ligand 1 pathway (PD-1/PD-L1), which are important inhibitory molecules for the immune system. Besides being generally safer than common chemotherapy, the use of ICIs has been associated with several immune-related adverse effects (irAEs). Although rare, neurological adverse effects are reported within the irAEs in clinical trials, particularly in patients treated with anti-PD-1 antibodies or a combination of both anti-CTLA-4 and PD-1 drugs. The observations obtained from clinical trials suggest that the PD-1 axis may play a remarkable role in the regulation of neuroinflammation. Moreover, numerous studies in preclinical models have demonstrated the involvement of PD-1 in several neurological disorders. However, a comprehensive understanding of these cellular mechanisms remains elusive. Our review aims to summarize the most recent evidence concerning the regulation of neuroinflammation through PD-1/PD-L signaling, focusing on cell populations that are involved in this pathway.