Biology subjects

Garcia, A. J.

Publications and source records attributed to Garcia, A. J..

14 recordsLinked to original sources

bioRxiv2026

Locus Coeruleus activity correlates with transient elevations in breathing during opioid-induced respiratory depression

A history of use remains a key risk factor for opioid-related overdose deaths in the ongoing opioid epidemic. The locus coeruleus (LC) is the principal source of noradrenergic tone and a site for opioid neuromodulation and tolerance. How a history of opioid use affects LC activity and shapes opioid-induced respiratory depression (OIRD) remains poorly understood. Using plethysmography and fiber photometry, we assessed how fentanyl affects LC activity and OIRD before and after five days of repeat opioid use (ROU). Fentanyl increased the frequency of LC bursts independent of exposure history and was coupled to transient elevations in breathing. LC coupled ventilation (LC-Ve) persisted through ROU. After ROU, OIRD magnitude diverged across mice. Mice developing an adaptive ventilatory response (AVR) showed a smaller OIRD that coincided with improved ventilation outside LC bursts and reduced LC-Ve gain. Mice with the non-adaptive response (NVR) show no improvement in OIRD or ventilation outside LC bursts, resulting in an unchanged reliance on LC-Ve. While LC-Ve reflexively counters OIRD acutely, it may also drive oscillations to destabilize blood gas homeostasis, perpetuating pathophysiology with repeat use. Thus, LC-coupled breathing appears to be a physiological signature of divergent respiratory responses with a history of fentanyl exposure.

physiology↗

bioRxiv2026

Mueller glia-vasculature interactions in the developing retina

Coordinated signaling among neurons, glia, and the vasculature is essential for the formation of a functional nervous system, yet how these relationships emerge during development remains unclear. Here, we investigated the developmental interplay between neural activity, Muller glia, and the retina vasculature in mice. Using quantitative confocal imaging from postnatal day 5 to eye-opening, we mapped the emergence of the superficial, intermediate, and deep vasculature layers and found that they emerged normally in mice lacking the {beta}2-containing nicotinic acetylcholine receptors, despite a dramatic reduction in cholinergic signaling. Tip cell density and overall vessel growth were unchanged, indicating cholinergic wave activity is not required for the emergence of retinal vasculature. We next defined the developmental timeline of Muller glia-vascular interactions. Sparse labeling and immunohistochemistry revealed that Muller glial lateral processes closely associate with endothelial tip cells during intermediate- and deep-layer angiogenesis and establish Aquaporin-4-enriched endfeet at vascular contact sites from the earliest stages of growth, even when vessel trajectories are perturbed. Finally, two-photon calcium imaging combined with simultaneous electrophysiology demonstrated that Muller glial endfeet exhibit robust, compartmentalized calcium transients during development. Although a subset of events was temporally correlated with retinal waves, enhancing neurotransmitter spillover selectively increased wave-associated activity in glial stalks but not endfeet. These findings indicate that calcium signaling at the glial-vascular interface is largely independent of spontaneous neuronal activity. Together, our results support a model in which Muller glia engage growing vessels through an activity-independent, parallel developmental program that may provide instructive cues for retinal angiogenesis.

neuroscience↗

bioRxiv2025

Repeat Opioid Use Modulates Microglia Activity and Amyloid Beta Clearance in a Mouse Model of Alzheimer's Disease

In addition to driving dependency and overdose, illicit use of opioids, such as fentanyl, is linked to the risk for cognitive decline and dementia. Growing evidence also indicates that opioid use is associated with pathological features, paralleled early in Alzheimers disease (AD), which raises the possibility of the involvement of mechanistic interactions between opioid use and AD progression. Here, we investigate how chronic fentanyl use (i.e., 20 days) influences the neuroimmune state, microglial activity, and amyloid burden in wildtype and APPPS1-21 mice, a transgenic model of AD. In wild-type mice, fentanyl use promoted a pro-inflammatory state without increasing the incidence of disease-associated microglia. In APPPS1-21 mice, chronic fentanyl use led to a shift favoring an anti-inflammatory state, which was associated with increased microglia clustering and activation at A{beta} plaques, increased A{beta} internalization in plaque-associated activated microglia, decreased soluble A{beta}, and decreased plaque burden. Our findings indicate that chronic fentanyl use fundamentally changes the trajectory of neuroimmune activity and features characteristic of early AD by enabling microglia to enhance A{beta} clearance. The interactions demonstrate how substance use can reshape the neuroimmune landscape in neurodegenerative disease, emphasizing the importance of tailored treatment strategies.

neuroscience↗

bioRxiv2025

Hydrogel microdroplet based glioblastoma drug screening platform

Glioblastoma is the most common primary malignant brain tumor with a five-year survival rate less than 5%. The standard of care involves surgical resection followed by treatment with the alkylating agent temozolomide (TMZ). GBM cells that evade surgery eventually become resistant to TMZ and lead to recurrence of tumors in patients. With only four drugs currently FDA-approved for GBM treatment, there is a need for a clinically relevant model capable of accelerating the identification of new therapies. Microgels are microscale ([~]10-1,000 m) hydrogel particles that can be used to encapsulate cells in a tailorable 3D matrix. Microdroplets offer short diffusion lengths relative to conventional hydrogel constructs (>1 mm) to limit spatial distributions of hypoxia and potentially screen therapeutics in a controlled and physiologically relevant environment. Here, we establish a method to encapsulate GBM cells in gelatin and polyethylene glycol (PEG) microgels. We show that microgel composition can affect cell morphology and further, that collections of GBM-laden hydrogels can be used to quantify the effect of single vs. metronomic doses of TMZ. GBM metabolic activity is maintained in microgel culture and GBM cells display drug response kinetics similar to previously established literature using macro-scale hydrogel constructs. Finally, we show microgels can be integrated with a liquid handler to enable high-throughput screening using cell-laden microgels.

bioengineering↗

bioRxiv2024

Improving Functional Muscle Regeneration in Volumetric Muscle Loss Injuries by Shifting the Balance of Inflammatory and Pro-Resolving Lipid Mediators

Severe tissue loss resulting from extremity trauma, such as volumetric muscle loss (VML), poses significant clinical challenges for both general and military populations. VML disrupts the endogenous tissue repair mechanisms, resulting in acute and unresolved chronic inflammation and immune cell presence, impaired muscle healing, scar tissue formation, persistent pain, and permanent functional deficits. The aberrant healing response is preceded by acute inflammation and immune cell infiltration which does not resolve. We analyzed the biosynthesis of inflammatory and specialized pro-resolving lipid mediators (SPMs) after VML injury in two different models; muscle with critical-sized defects had a decreased capacity to biosynthesize SPMs, leading to dysregulated and persistent inflammation. We developed a modular poly(ethylene glycol)-maleimide hydrogel platform to locally release a stable isomer of Resolvin D1 (AT-RvD1) and promote endogenous pathways of inflammation resolution in the two muscle models. The local delivery of AT-RvD1 enhanced muscle regeneration, improved muscle function, and reduced pain sensitivity after VML by promoting molecular and cellular resolution of inflammation. These findings provide new insights into the pathogenesis of VML and establish a pro-resolving hydrogel therapeutic as a promising strategy for promoting functional muscle regeneration after traumatic injury.

bioengineering↗

bioRxiv2024

Global coordination of protrusive forces in migrating immune cells

Efficient immune responses rely on the capacity of leukocytes to traverse diverse and complex tissues. To meet such changing environmental conditions, leukocytes usually adopt an amoeboid configuration, utilizing their forward-positioned nucleus as a probe to identify and follow the path of least resistance among pre-existing pores. We show that in dense environments, where even the largest pores preclude free passage, leukocytes switch polarity and position their nucleus behind centrosome and organelles. In this mesenchymal configuration, local compression of the cell body triggers assembly of a central F-actin pool, located between cell front and nucleus. Central actin pushes outward to transiently dilate a path for organelles and nucleus. Pools of central and front actin are tightly coupled and experimental depletion of the central pool enhances actin accumulation and protrusion formation at the cell front. Although this shifted balance speeds up cells in permissive environments, migration in restrictive environments is impaired, as the unleashed leading edge dissociates from the trapped cell body. Our findings establish an actin regulatory loop that balances path dilation with advancement of the leading edge to maintain cellular coherence.

cell biology↗

bioRxiv2022

Astrocyte-like CEPsh glia responds to the stressful environments

While astrocytes are known to be important for development and nourishment of the nervous system, the field is just beginning to explore how astrocytes respond to environmental stimuli. Using Caenorhabditis elegans and their astrocyte-equivalent, CEPsh, we asked whether astrocyte-like glia respond to odor exposure. We found one day-old adult C. elegans decrease hlh-17 promoter (CEPsh glia marker) mediated fluorescent expression when trained with an innately attractive odor butanone. Moreover, the olfactory training paradigm itself affects phlh-17 expression, but in a different way. This suggests astrocyte-like CEPsh glia can integrate environmental information to respond to changes in the environment, which enhances survival.

animal behavior and cognition↗

bioRxiv2020

JAGGED1 Stimulates Cranial Neural Crest Cell Osteoblast Commitment Pathways and Bone Regeneration Independent of Canonical NOTCH Signaling

Craniofacial bone loss is a complex clinical problem with limited regenerative solutions. Currently, BMP2 is used as a bone-regenerative therapy in adults, but in pediatric cases of bone loss, it is not FDA-approved due to concerns of life-threatening inflammation and cancer. Development of a bone-regenerative therapy for children will transform our ability to reduce the morbidity associated with current autologous bone grafting techniques. We discovered that JAGGED1 (JAG1) induces cranial neural crest (CNC) cell osteoblast commitment during craniofacial intramembranous ossification, suggesting that exogenous JAG1 delivery is a potential craniofacial bone-regenerative approach. In this study, we found that JAG1 delivery using synthetic hydrogels containing O9-1 cells, a CNC cell line, into critical-sized calvarial defects in C57BL/6 mice provided robust bone-regeneration. Since JAG1 signals through canonical (Hes1/Hey1) and non-canonical (JAK2) NOTCH pathways in CNC cells, we used RNAseq to analyze transcriptional pathways activated in CNC cells treated with JAG1{+/-}DAPT, a NOTCH-canonical pathway inhibitor. JAG1 upregulated expression of multiple NOTCH canonical pathway genes (Hes1), which were downregulated in the presence of DAPT. JAG1 also induced bone chemokines (Cxcl1), regulators of cytoskeletal organization and cell migration (Rhou), signaling targets (STAT5), promoters of early osteoblast cell proliferation (Prl2c2, Smurf1 and Esrra), and, inhibitors of osteoclasts (Id1). In the presence of DAPT, expression levels of Hes1 and Cxcl1 were decreased, whereas, Prl2c2, Smurf1, Esrra, Rhou and Id1 remain elevated, suggesting that JAG1 induces osteoblast proliferation through these non-canonical genes. Pathway analysis of JAG1+DAPT-treated CNC cells revealed significant upregulation of multiple non-canonical pathways, including the cell cycle, tubulin pathway, regulators of Runx2 initiation and phosphorylation of STAT5 pathway. In total, our data show that JAG1 upregulates multiple pathways involved in osteogenesis, independent of the NOTCH canonical pathway. Moreover, our findings suggest that JAG1 delivery using a synthetic hydrogel, is a bone-regenerative approach with powerful translational potential.

genomics↗

bioRxiv2020

Highly multiplexed immune profiling throughout adulthood reveals kinetics of lymphocyte infiltration in the aging mouse prostate

Aging is a significant risk factor for cancer in several tissues, including the prostate. Defining the kinetics of age-related changes in these tissues is critical for identifying regulators of aging and evaluating interventions to slow the aging process and reduce disease risk. An altered microenvironment is characteristic of prostatic aging in mice. Whether features of aging in the prostate emerge predominantly in old age or earlier in adulthood has not previously been established. Using comprehensive immune profiling and time-course analysis, we show that populations of T and B lymphocytes increase in the mouse prostate between 6 and 12 months of age. When comparing the prostate to other urogenital tissues, we found similar features of age-related inflammation in the mouse bladder. In summary, our study offers new insight into the kinetics of prostatic inflammaging and the window when interventions to slow down age-related changes may be most effective.

immunology↗

bioRxiv2020

Transplantation of muscle stem cell mitochondria rejuvenates the bioenergetic function of dystrophic muscle

Mitochondrial dysfunction has been implicated in various pathologies, including muscular dystrophies. During muscle regeneration, resident stem cells, also known as muscle satellite cells (MuSCs), undergo myogenic differentiation to form de novo myofibers or fuse to existing syncytia. Leveraging this cell-cell fusion process, we postulated that mitochondria stemming from MuSCs could be transferred to myofibers during muscle regeneration to remodel the mitochondrial network and restore bioenergetic function. Here, we report that dystrophic MuSCs manifest significant mitochondrial dysfunction and fuse with existing dystrophic myofibers to propagate mitochondrial dysfunction during muscle repair. We demonstrate that by transplanting healthy donor MuSCs into dystrophic host muscle, the mitochondrial network (reticulum) and bioenergetic function can be rejuvenated. Conversely, when bioenergetically-compromised donor MuSCs are transplanted, improvements in mitochondrial organization and bioenergetic function were ablated in the dystrophic recipient. Overall, these data reveal a unique role of muscle stem cells as an essential regulator of myofiber mitochondrial homeostasis and a potential therapeutic target against mitochondrial myopathies.

cell biology↗

bioRxiv2020

Optoregulated force application to cellular receptors using molecular motors

Mechanotransduction events in physiological environments are difficult to investigate, in part due to the lack of experimental tools to apply forces to mechanosensitive receptors remotely. Inspired by cellular mechanisms for force application (i.e. motor proteins pulling on cytoskeletal fibers), here we present a unique molecular machine that can apply forces at cell-matrix and cell-cell junctions using light as an energy source. The key actuator is a light-driven rotatory molecular motor linked to polymer chains, which is intercalated between a membrane receptor and an engineered biointerface. The light-driven actuation of the molecular motor is converted in mechanical twisting of the polymer chains, which will in turn effectively "pulls" on engaged cell membrane receptors (integrins, cadherins...) within the illuminated area. Applied forces have the adequate magnitude and occur at time scales within the relevant ranges for mechanotransduction at cell-friendly exposure conditions, as demonstrated in forcedependent focal adhesion maturation and T cell activation experiments. Our results reveal the potential of nanomotors for the manipulation of living cells at the molecular scale and demonstrate, for the first time, a functionality which at the moment cannot be achieved by any other means.

cell biology↗

bioRxiv2020

Material-Driven Fibronectin Assembly Rescues Matrix Defects due to Mutations in Collagen IV in Fibroblasts

Basement membranes (BMs) provide structural support to tissues and influence cell signaling. Mutations in COL4A1/COL4A2, a major BM component, cause eye, kidney and cerebrovascular disease, including stroke. Common variants in these genes are risk factors for intracerebral hemorrhage in the general population. However, the contribution of the matrix to the disease mechanism(s) and its effects on the biology of cells harboring a collagen IV mutation remain poorly understood. To shed light on this, we engineered controlled microenvironments using polymer biointerfaces coated with ECM proteins laminin or fibronectin (FN), to investigate the cellular phenotype of primary fibroblasts harboring a COL4A2+/G702D mutation. FN nanonetworks assembled on poly(ethyl acrylate) (PEA) induced increased deposition and assembly of collagen IV in COL4A2+/G702D cells, which was associated with reduced ER size and enhanced levels of protein chaperones such as BIP, suggesting increased protein folding capacity of cells. FN nanonetworks on PEA also partially rescued the reduced stiffness of the deposited matrix and cells, and enhanced cell adhesion through {beta}1-mediated signaling and actin-myosin contractility, effectively rescuing some of the cellular phenotypes associated with COL4A1/4A2 mutations. Collectively, these results suggest that biomaterials are able to shape the matrix and cellular phenotype of the COL4A2+/G702D mutation in patient-derived cells.

bioengineering↗

bioRxiv2019

A role for Hypoxia Inducible Factor 1a (HIF1a) in intermittent hypoxia-dependent changes in spatial memory and synaptic plasticity

Intermittent hypoxia (IH), a key feature of sleep apnea, increases the oxygen regulated transcription factor Hypoxia Inducible Factor 1a (HIF1a). Although recognized for its role in IH-dependent changes in cardio-respiratory physiology, it remains unclear how IH-dependent HIF1a signaling affects neurophysiology underlying learning and memory. This study examines how IH affects hippocampal associated learning and memory in wildtype mice and mice heterozygous for the HIF1a gene (HIF1a+/-). In wild-type mice, ten days of IH impaired performance in the Barnes maze increased hippocampal HIF1a and elevated protein carbonyls. These behavioral and biochemical effects of IH were accompanied by a decrease in the N-Methyl-D-Aspartate receptor (NMDAr) and an attenuation of long-term potentiation (LTP) in area CA1. In HIF1a+/-, IH did not impair Barnes maze performance, increase hippocampal HIF1a, or enhance protein carbonyl content. At the network level, IH neither led to a decrease in NMDAr nor impaired LTP. Concurrent antioxidant treatment during IH mitigated the IH-dependent effects on the Barnes maze performance and LTP in wildtype mice. Our findings indicate that IH-dependent HIF1a signaling leads to oxidative stress and reduces NMDAr to impair LTP in area CA1, which contributes to IH-dependent deficits in learning and memory associated with the hippocampus.\n\nSignificanceIntermittent Hypoxia is a hallmark of sleep apnea and decreases the threshold for cognitive deficit. We demonstrate that intermittent hypoxia-dependent HIF1a signaling contributes to impairments in hippocampal associated memory. This is co-incidental with HIF1a-mediated alternations in synaptic physiology and increased oxidative stress.\n\nKey pointsO_LIIntermittent hypoxia (IH) is a hallmark of sleep apnea and is known to cause learning and memory deficits.\nC_LIO_LIHypoxia Inducible Factor 1a (HIF1a), is associated with IH-dependent changes in physiology.\nC_LIO_LIIH exposure causes increased hippocampal HIF1a in wild type mice and is associated with elevated oxidative stress, impairments to spatial memory, and suppression of long term potentiation (LTP).\nC_LIO_LIIH-dependent suppression of LTP is co-incidental with diminished NMDA receptor contribution to glutamatergic transmission.\nC_LIO_LIFollowing IH, mice heterozygous for HIF1a (HIF1a+/-) do not show an increase in HIF1a and oxidative stress, or changes in either behavior or glutamatergic transmission.\nC_LI

neuroscience↗

bioRxiv2019

Wnt7a-releasing synthetic hydrogel enhances local skeletal muscle regeneration and muscle stem cell engraftment

Skeletal muscle possesses efficient ability to regenerate upon minor injuries, but its capacity to regenerate is severely compromised with traumatic injuries and muscle-associated diseases. Recent evidence suggests that skeletal muscle regeneration can be accelerated by transplantation of muscle satellite cells (MuSCs) or treatment with promyogenic factors, such as Wingless-type MMTV Integrated 7a (Wnt7a) protein. Although direct intramuscular injection is the simplest method to deliver MuSCs and Wnt7a for regenerative therapy, direct injection is not viable in many clinical cases where the structural integrity is severely compromised. To address this challenge, we engineered a synthetic poly(ethylene glycol) (PEG)-based hydrogel to facilitate the co-delivery of pro-myogenic factors, such as Wnt7a, and MuSCs to skeletal muscles affected by severe trauma or muscular dystrophies. Wnt7a release rate can be controlled by modulating the polymer density of the hydrogel, and this release rate can be further accelerated through the proteolytic degradation of the hydrogel. Treating cryo-injured tibialis anterior (TA) muscles with Wnt7a-loaded hydrogels resulted in an accelerated regenerative response, measured by increased muscle fiber cross-sectional area, bulk TA mass, and number of Pax7+ MuSCs at the injury site, compared to the TA muscles treated with Wnt7a-free hydrogels. Co-delivery of Wnt7a and primary MuSCs using the synthetic hydrogel to the cryo-injured TA muscles significantly increased cellular migration during the engraftment process. This work provides a synthetic biomaterial platform for advancing treatment strategies of skeletal muscle trauma and diseases, specifically in conditions where direct intramuscular injection may be challenging.

bioengineering↗