Shao-Jun Tang

Imbalance of excitatory and inhibitory neuronal activity (E/I imbalance) plays a critical role in pain pathogenesis. Recent studies have identified a novel form of E/I imbalance in the spinal dorsal horn (SDH) of animal models of HIV-associated pain, manifesting as increased spontaneous excitatory postsynaptic current (sEPSC) frequency in excitatory neurons alongside decreased sEPSC frequency in inhibitory neurons and hence termed neural circuitry polarization (NCP). However, how the opposite forms of synaptic plasticity in NCP is coordinated in the pain neural circuit is unclear. Here, we show that in the SDH of a mouse model of HIV-associated pain, potentiation of excitatory synapses on excitatory neurons (ESE) and depression of excitatory synapses on inhibitory neurons (ESI) employ distinct mechanisms to support their expression. We found the increase of sEPSC frequency in excitatory neurons induced by HIV1 gp120 was mediated by a postsynaptic mechanism, whereas decrease of sEPSC frequency in inhibitory neurons by a presynaptic mechanism. Our studies showed that pharmacological inhibition of calcium-permeable AMPA (CP-AMPA) receptors selectively attenuated potentiation of ESE without significantly affecting ESI depression. We also observed that GluA1 was upregulated in excitatory but not inhibitory neurons, indicating selective CP-AMPA receptor formation in excitatory neurons. Furthermore, we identified a new pain-related signaling pathway in ESE: Wnt5a-PKCδ-GluA1. We elucidated that the GluA1 upregulation and ESE potentiation were controlled by neuronal Wnt5a signaling via protein kinase C delta (PKCδ). Our findings reveal that ESE and ESI in the SDH of HIV pain models use distinct synaptic and molecular mechanisms to support their expression in NCP, demonstrating specialized regulatory pathways for the plasticity of excitatory synapses targeting different neuron types during the pain pathogenesis.

Pain is a common complication in individuals with HIV, yet the underlying pathogenic mechanisms remain poorly understood. Reactive astrocytes are selectively activated in the spinal dorsal horn of HIV patients experiencing pathological pain, implicating their potential role in pain pathogenesis. However, the specific pathogenic subtype of these reactive astrocytes has not been defined. Here, we identify a distinct subpopulation of pain-associated reactive astrocytes in the lumbar spinal cord of HIV-1 gp120 transgenic mice using single-nucleus RNA sequencing. This astrocyte subpopulation displays transcriptomic features associated with phagocytosis and inflammation and depends on galectin-3 for its formation. Both global and astrocyte-specific heterozygous knockout of Lgals3 (galectin-3) markedly reduce mechanical allodynia in gp120 transgenic mice. These findings reveal a subset of reactive astrocytes that play a role in remodeling the spinal pain circuitry underlying HIV-associated pain.

Synapse loss is a common neuropathology in the CNS of HIV patients, likely contributing to neurological complications such as neurocognitive disorders and pain. However, the underlying mechanism remains poorly understood. Here, we show microglia- and astrocyte-mediated synaptic pruning of excitatory and inhibitory synapses in the frontal cortex (FC) and spinal dorsal horn (SDH) of HIV-1 gp120 transgenic (gp120Tg) mice compared with the wild-type (WT). Confocal imaging and 3D reconstruction revealed a significant increase of internalized synaptic elements in microglia and astroglia in gp120Tg mice, in a region- and synapse-type-specific manner. Microglia in the FC of gp120Tg mice showed increased pruning activity on the pre-synaptic but not post-synaptic compartment of both excitatory and inhibitory synapses. In contrast, microglia in the SDH of gp120Tg mice had increased pruning activity of both pre- and post-synaptic compartments excitatory and inhibitory compartments in the SDH. However, astrocytes in the gp120 transgenic model increased their pruning activity of both the pre- and post-synaptic compartments of excitatory but not inhibitory synapses in the FC and the SDH. We confirmed synaptic engulfment in viral reservoirs in the brain tissues of human HIV patients. These findings provide important insights into the pathogenic mechanism of synapse loss induced by HIV.

Imaging technologies have revolutionized the study of the tumor microenvironment (TME) by leveraging spatial analysis, which enables the exploration of tissue organization and cellular communication, as well as aiding cancer diagnosis and prognosis. However, while many advanced spatial analysis methods have been recently published, they are enmeshed with specific imaging technology. An opportunity exists to develop a technology-agnostic methodology that captures complex spatial patterns in the TME as phenotypes to use in downstream tasks. In this paper, we present a novel variation of spatial g-function and a comprehensive imaging-technologyagnostic framework that identifies rich spatial phenotypes that can be used in survival analysis and classification tasks. Applying our methodology to breast cancer, we uncover spatial phenotypes with significance to survival across racial groups and molecular subtypes of breast cancer. We find other phenotypes that are significant to the survival of specific patient categories (such as African American). We also demonstrate that our phenotypes reflect specific biological contexts. These results highlight the relevance of our proposed spatial analysis and phenotype discovery pipeline and demonstrate the benefits of the systematic exploration of spatial phenotypes for more personalized diagnosis and treatments.

The development of combination antiretroviral therapy (cART) has transformed human immunodeficiency virus (HIV) infection from a lethal diagnosis into a chronic disease, and people living with HIV on cART can experience an almost normal life expectancy. However, these individuals often develop various complications that lead to a decreased quality of life, some of the most significant of which are neuropathic pain and the development of painful peripheral sensory neuropathy (PSN). Critically, although cART is thought to induce pain pathogenesis, the relative contribution of different classes of antiretrovirals has not been systematically investigated. In this study, we measured the development of pathological pain and peripheral neuropathy in mice orally treated with distinct antiretrovirals at their translational dosages. Our results show that only nucleoside reverse transcriptase inhibitors (NRTIs), not other types of antiretrovirals such as proteinase inhibitors, non-nucleoside reverse transcriptase inhibitors, integrase strand transfer inhibitors, and CCR5 antagonists, induce pathological pain and PSN. Thus, these findings suggest that NRTIs are the major class of antiretrovirals in cART that promote the development of neuropathic pain. As NRTIs form the essential backbone of multiple different current cART regimens, it is of paramount clinical importance to better understand the underlying mechanism to facilitate the design of less toxic forms of these drugs and/or potential mitigation strategies.

Pathological pain emerges from nociceptive system dysfunction, resulting in heightened pain circuit activity. Various forms of circuitry plasticity, such as central sensitization, synaptic plasticity, homeostatic plasticity, and excitation/inhibition balance, contribute to the malfunction of neural circuits during pain pathogenesis. Recently, a new form of plasticity in the spinal dorsal horn (SDH), named neural circuit polarization (NCP), was discovered in pain models induced by HIV-1 gp120 and chronic morphine administration. NCP manifests as an increase in excitatory postsynaptic currents (EPSCs) in excitatory neurons and a decrease in EPSCs in inhibitory neurons, presumably facilitating hyperactivation of pain circuits. The expression of NCP is associated with astrogliosis. Ablation of reactive astrocytes or suppression of astrogliosis blocks NCP and, concomitantly, the development of gp120- or morphine-induced pain. In this review, we aim to compare and integrate NCP with other forms of plasticity in pain circuits to improve the understanding of the pathogenic contribution of NCP and its cooperation with other forms of circuitry plasticity during the development of pathological pain.

Chronic pain is a prevalent neurological complication among individuals living with human immunodeficiency virus (PLHIV) in the post-combination antiretroviral therapy (cART) era. These individuals experience malfunction in various cellular and molecular pathways involved in pain transmission and modulation, including the neuropathology of the peripheral sensory neurons and neurodegeneration and neuroinflammation in the spinal dorsal horn. However, the underlying etiologies and mechanisms leading to pain pathogenesis are complex and not fully understood. In this review, we aim to summarize recent progress in this field. Specifically, we will begin by examining neuropathology in the pain pathways identified in PLHIV and discussing potential causes, including those directly related to HIV-1 infection and comorbidities, such as antiretroviral drug use. We will also explore findings from animal models that may provide insights into the molecular and cellular processes contributing to neuropathology and chronic pain associated with HIV infection. Emerging evidence suggests that viral proteins and/or antiretroviral drugs trigger a complex pathological cascade involving neurons, glia, and potentially non-neural cells, and that interactions between these cells play a critical role in the pathogenesis of HIV-associated pain.

Pathological pain is a frequent complication in HIV patients, yet the underlying mechanism remains elusive, and effective therapeutic targets have not been identified. Reactive astrocytes are specifically activated in the spinal dorsal horn (SDH) of HIV patients with pathological pain and required for HIV-associated pain development in mouse models. These findings suggest that reactive astrocytes play a crucial role in the pathogenesis of HIV-associated pain. However, due to the heterogeneity of reactive astrocytes, the pathogenic subtype remains unknown. In this study, we used single-nucleus RNA-seq (snRNA-seq) transcriptomic analysis to identify a novel subtype of HIV-pain-associated astrocytes (HIPAs) in the lumbar spinal cord of HIV-1 gp120 transgenic models and in the spinal cord of HIV patients. HIPAs express galectin 3 (Gal3) and exhibit transcriptomic signatures of phagocytosis and inflammation. We demonstrated that HIPAs phagocytose neuronal components and are associated with neuronal degeneration. We also found that knockout (KO) of Gal3 in gp120 transgenic mice reduced the number of HIPAs. Furthermore, Gal3 KO inhibited the expression of mechanical allodynia and HIV pain-related pathogenic processes, including neuronal degeneration and neuroinflammation, in gp120 transgenic mice. Our data collectively suggest that HIPAs are a novel Gal3-expressing astrocytic subtype that plays a critical role in gp120-induced pathogenesis in the spinal pain neural circuit. Targeting HIPAs may provide a potential therapeutic strategy for treating HIV-associated pain.