Research Projects

HIV and Cannabinoids

The endocannabinoid system has an important role in many neurodegenerative and neuroinflammatory processes/diseases including Parkinson’s disease, Alzheimer’s disease, and neuropathic pain. In the era of combined antiretroviral therapy (cART), human immunodeficiency virus type 1 (HIV-1) is now considered a chronic disease that specifically targets the brain and causes a high prevalence of mild forms of neurocognitive impairments, also referred to as HIV-associated neurocognitive disorders (HAND). The best correlate of HAND has been shown to be synaptodendritic damage with injury to synapses and dendrites underlying the neurocognitive impairments seen in HIV-1 positive individuals. We examine if increasing endocannabinoid signaling will be protective in models of such neuronal damage. Preliminary studies from our laboratory have shown that anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) used as direct ligands are neuroprotective against HIV-1 Tat-induced dysfunction and injury. However, use of endocannabinoids in vivo is not optimal/feasible because of their rapid degradation by catabolic enzymes: the main enzyme responsible for degradation of AEA, fatty acid amide hydrolase (FAAH), and the main enzyme responsible for degradation of 2-AG, monoacylglycerol lipase (MAGL). Recently, a new class of selective inhibitors of those enzymes have been developed that show neuroprotective, anti-inflammatory, antinociceptive and anxiolytic effects. Thus, the focus of our current work is to determine 1) the neuroprotective effects of endocannabinoids in HIV-1 Tat-induced injury using endocannabinoid catabolic enzyme inhibitors as a tool, and to define 2) the receptor-mediated mechanisms by which endocannabinoids are naturally protective in HIV-1 Tat neurotoxicity. New knowledge will be gained about how the endocannabinoid system protects neurons from HIV-1 Tat-induced toxicity by focusing on changes in vitro and in vivo on the cellular, molecular, functional, structural, and behavioral level. Understanding the effects of enzyme inhibitors in the context of neuroAIDS may uncover novel therapeutic targets for HAND and other diseases in which cognitive deficits occur.

Yadav-Samudrala, B. J., & Fitting, S. (2021). Mini-review: The therapeutic role of cannabinoids in neuroHIV. Neuroscience letters, 750, 135717. https://doi.org/10.1016/j.neulet.2021.135717

We use state-of-the-art live cell imaging and behavioral techniques:

Live Cell Imaging In Vivo and In Vitro.

To understand the differential responses to (endo)cannabinoids in the presence of HIV-1 proteins, we make use of in vivo calcium imaging techniques. The Fitting lab is the first to establish in vivo calcium imaging at the cellular level resolution in the field of neuroHIV and endocannabinoid research. This state-of-the-art technique utilizes genetically encoded calcium indicators (GECIs) to visualize dynamic neuronal activity in freely behaving mice. By employing a lightweight, head-mounted microscope, we can monitor real-time neuronal function during relatively unrestricted behavior, providing a powerful tool to explore brain activity in living organisms. We are using this approach to investigate how HIV-1 proteins alter neuronal signaling and influence behavior. By capturing the intricate relationship between neuronal activity and cognitive function, our research aims to uncover the mechanisms by which HIV affects the brain. These insights are crucial for understanding HIV-associated neurocognitive disorders and developing targeted therapeutic strategies.

Behavior In vivo movie.mp4

novel object recognition task recorded concurrently with in vivo calcium imaging footage

Calcium In vivo movie.mp4

in vivo calcium imaging footage from the medial prefrontal cortex (mPFC) in a Tat+ transgenic mouse

We also utilize an in vitro cell culture model, focusing on hippocampal neurons and prefrontal cortex neurons. Live cell imaging is conducted on the soma and dendrites of living cultured neurons using a Zeiss Axio Observer Z.1 inverted microscope (Carl Zeiss) with an automated, computer-controlled stage encoder with environmental control (37°C, 95% humidity, 5% CO2). We examine HIV/endocannabinoid-induced structural changes and functional changes in ion homeostasis, observing the imaging of [Na+]i and [Ca2+]i ions, mitochondrial membrane potential, and dendritic spines in living cultured neurons.

Estrous Cycle. HIV-1’s detrimental effects extend beyond neuroinflammation, profoundly disrupting the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes, leading to widespread neuroendocrine dysfunction. While extensive research has examined the interplay between the HIV-1 Tat protein and endocrine regulation, as well as the role of the endocannabinoid system (eCB) in HIV-associated neurocognitive disorders (HAND), a critical gap remains in understanding their interconnected influence. Our research aims to bridge this gap by investigating the intricate relationship between HIV-1 proteins, the eCB system, and the estrous cycle. By elucidating how these systems interact, we seek to uncover novel mechanisms through which HIV-1 disrupts neuroendocrine function and behavioral regulation. This work holds the potential to provide insights into sex-specific vulnerabilities in neuroHIV, paving the way for more targeted therapeutic strategies to mitigate its neurological and endocrine consequences.

Oral/Gut Microbiome. We use neuroHIV transgenic mouse models to understand the effects of long-term chronic cannabis (THC/CBD) and cannabis-associated Actinomyces species bacterial exposure on neurocognition and neuropathology. Additionally, we aim to determine the mechanisms of A. meyeri on neurocognition, myeloid cell infiltration, and endocannabinoids.

Behavioral Studies. To sort out the cellular sites of (endo)cannabinoids and HIV-1 protein interaction, we make use of transgenic and knockout mice. We conduct operant and classical conditioning behavioral tasks and other assays that involve the prefrontal cortex, hippocampus, and amygdala, including the Go/No-Go task, the Novel Object Recognition task, the Fear Conditioning task, Elevated Plus Maze (EPM), T maze, and others.

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