Biology subjects

Greer, L. K.

Publications and source records attributed to Greer, L. K..

3 recordsLinked to original sources

bioRxiv2026

Title: Unilateral loss of tyrosine hydroxylase in adult midbrain dopaminergic neurons reveals reduction to neuregulin1 in rat model of acute dopaminergic dysfunction

Dopamine, produced primarily in the midbrain, is required for movement and reward-based signaling all throughout life. Loss of dopaminergic function can result in changes to motor systems, mood, motivation, and cognition. Dopaminergic cell death or dopaminergic hypofunction are implicated in a variety of diseases including synucleinopathies, neuropsychiatric disorders, and substance use disorders. Loss of dopaminergic neurons (DANs) in the substantia nigra pars compacta (SNpc) and subsequent dysregulation of dopamine signaling in striatum are implicated to varying degrees in all synucleinopathies. By the time patients present with motor symptoms in Parkinson's disease, the most common synucleinopathy, >30% of DANs are lost in the SNpc because of ongoing degeneration for years prior to diagnosis. Studying the early consequences of dopamine loss is critical to understanding mechanisms of dopamine depletion disease progression and identifying biomarkers for earlier diagnosis so that effective treatment can ensue. Here, we created a model of dopamine loss in adult rats to study early transcriptional changes following loss of dopamine synthesis. We used CRISPR to knock out tyrosine hydroxylase (TH), the rate-limiting enzyme for dopamine synthesis, in the adult rat midbrain through injection of Th guide RNAs into transgenic rats expressing Cas9 nuclease specifically in dopamine transporter positive neurons and performed single nucleus RNA sequencing on midbrain and dorsal striatal tissue. Two weeks after injection, we measured a 90% loss of TH and dopamine in the midbrain, but striatal TH and dopamine were unaffected. Despite preceding striatal dopamine loss, our data identified alterations to genes involved in synaptic signaling, organization, and function in both midbrain and striatal neurons. We found the neurotrophic factor, neuregulin1, to be significantly reduced in dopaminergic neurons, which may account for transcriptional changes in surrounding cells that precede detectable reductions to striatal dopamine. These data establish a new rat model of adult TH loss and identify early transcriptional consequences of dopamine loss in the adult midbrain after normal development, providing potential biomarkers for early-stage dopamine loss in PD, synucleinopathies and related disorders of dopamine depletion.

neuroscience↗

bioRxiv2025

Inhibition of autophagy-lysosomal function exacerbates microglial and monocyte lipid metabolism reprograming and dysfunction after brain injury

CNS has an overall higher level of lipids than all tissues except adipose and contains up to 25% of total body cholesterol. Recent data demonstrate a complex crosstalk between lipid metabolism and inflammation, suggesting potential contribution of the lipid-rich brain environment to neuroinflammation. While recent data support the importance of brain lipid environment to inflammatory changes observed in age related chronic neurodegenerative diseases, in vivo interactions between lipid environment, lipid metabolism and neuroinflammation in acute brain disease and injury remain poorly understood. Here we utilize a mouse model of traumatic brain injury (TBI) to demonstrate that acute neurotrauma leads to widespread lipid metabolism reprograming in all microglial and brain associated and infiltrating monocyte populations. Additionally, we identify unique microglial and monocyte populations with higher degree of lipid metabolism reprograming and pronounced accumulation of neutral storage lipids, including cholesteryl esters and triglycerides. These lipids accumulate not only in lipid droplets but also in the microglial and monocyte lysosomes and are associated with lysosomal dysfunction and inhibition of autophagy after TBI. Our data indicate that lipid accumulation in these cells is the result of altered lipid handling rather than lipid synthesis and is triggered by phagocytosis of lipid-rich myelin debris generated after TBI. Finally, we use mice with autophagy defects in microglia and monocytes to demonstrate that further inhibition of autophagy leads to more pronounced lipid metabolism reprograming and exacerbated cellular lipid accumulation. Our data suggest a pathological feedback loop, where lipid phagocytosis causes inhibition of autophagy-lysosomal function, which in turn exacerbates cellular lipid retention, reprograming and inflammation.

neuroscience↗

bioRxiv2021

Identification of ER/SR resident proteins as biomarkers for ER/SR calcium depletion in skeletal muscle cells

Aberrations to endoplasmic/sarcoplasmic reticulum (ER/SR) calcium concentration can result in the departure of endogenous proteins in a phenomenon termed exodosis. Redistribution of the ER/SR proteome can have deleterious effects to cell function and cell viability, often contributing to disease pathogenesis. Many proteins prone to exodosis reside in the ER/SR via an ER retention/retrieval sequence (ERS) and are involved in protein folding, protein modification, and protein trafficking. While the consequences of their extracellular presence have yet to be fully delineated, the proteins that have undergone exodosis may be useful for biomarker development. Skeletal muscle cells rely upon tightly coordinated ER/SR calcium release for muscle contractions, and perturbations to calcium homeostasis can result in myopathies. Ryanodine receptor type-1 (RYR1) is a calcium release channel located in the SR. Mutations to the RYR1 gene can compromise calcium homeostasis leading to a vast range of clinical phenotypes that include hypotonia, myalgia, respiratory insufficiency, ophthalmoplegia, fatigue and malignant hyperthermia (MH). There are currently no FDA approved treatments for RYR1-related myopathies (RYR1-RM). Here we examine the exodosis profile of skeletal muscle cells following ER/SR calcium depletion. Proteomic analysis identified 4,465 extracellular proteins following ER/SR calcium depletion with 1,280 proteins significantly different than vehicle. A total of 54 ERS proteins were identified and 33 ERS proteins significantly increased following ER/SR calcium depletion. Specifically, ERS protein, mesencephalic astrocyte-derived neurotrophic factor (MANF), was elevated following calcium depletion, making it a potential biomarker candidate for human samples. Despite no significant elevation of MANF in plasma levels among healthy volunteers and RYR1-RM individuals, MANF plasma levels positively correlated with age in RYR1-RM individuals, presenting a potential biomarker of disease progression. Selenoprotein N (SEPN1) was also detected only in extracellular samples following ER/SR calcium depletion. This protein is integral to calcium handling and SEPN1 variants have a causal role in SEPN1-related myopathies (SEPN1-RM). Extracellular presence of ER/SR membrane proteins may provide new insight into proteomic alterations extending beyond ERS proteins. Pre-treatment of skeletal muscle cells with bromocriptine, an FDA approved drug recently found to have anti-exodosis effects, curbed exodosis of ER/SR resident proteins. Changes to the extracellular content caused by intracellular calcium dysregulation presents an opportunity for biomarker development and drug discovery.

cell biology↗