Biology subjects

Middleton, F. A.

Publications and source records attributed to Middleton, F. A..

5 recordsLinked to original sources

bioRxiv2026

ADRA2B genetic polymorphism modulates vagus nerve stimulation response

Introduction. Given interest in vagus nerve stimulation (VNS) as a potential therapy for Alzheimer's disease, due to its hypothesized influence on the noradrenergic (NA) system, there is a need to understand the pronounced individual differences in responsiveness to VNS in aging. We tested whether a genetic polymorphism related to NA signaling, the {Delta}301-303 deletion in the ADRA2B receptor, modulates transcutaneous auricular (taVNS) effects on task-related pupillary responses or pupil-linked cortical activity in noradrenergic projection territory. Methods. Forty-one adults (61% deletion carriers; ages 19-79) performed a visual oddball task during a sham-controlled single-blind crossover taVNS trial. Of these people, 25 (68% deletion carriers) also performed the same task with simultaneous fMRI. Results. ADRA2B genotype predicted the taVNS effect on oddball pupillary responses (t(37) = 3.03, p = .004, d = 0.84). Deletion carrier responses were more likely to increase, while non-carrier responses decreased. Carriers showed stronger spatial alignment between pupil-BOLD coupling and cortical norepinephrine transporter (NET) expression (t(22) = 2.82, p = .010, adjusted d = 1.21). This difference was selective to NET among 19 PET maps (all other p > .11). The individual effect of taVNS predicted NET alignment of pupil-BOLD coupling ({rho} = .45, p = .023). Conclusions. ADRA2B {Delta}301-303 deletion status, which is thought to increase NA availability, predicts the direction of the pupillary response to taVNS and how tightly pupil-linked BOLD activity aligns with cortical noradrenergic projection territory.

neuroscience↗

bioRxiv2024

Dengue virus structural proteins are expressed on the surface of DENV-infected cells and are a target for antibody-dependent cellular phagocytosis

Dengue virus (DENV) is an arboviral pathogen found in over 100 countries and a source of significant morbidity and mortality. While the mechanisms underpinning the pathophysiology of severe dengue are incompletely understood, it has been previously suggested that antibodies directed against the DENV envelope (E) protein can facilitate antibody dependent enhancement (ADE) of the infection, increasing the number of infected cells and the severity of infection in an exposed individual. Accordingly, there is interest in defining mechanisms for directly targeting DENV-infected cells for immunologic clearance, an approach that bypasses the risk of ADE. We have previously demonstrated that antibodies specific for DENV non-structural protein 1 (NS1) can opsonize and facilitate the phagocytic clearance of DENV infected cells. However, it is currently unclear if other DENV antigens are expressed on the surface of infected cells, and if these antigens can be targeted by antibody-dependent clearance mechanisms. In this study, we demonstrate that DENV structural proteins are expressed on the surface of DENV-infected cells, and that these antigens can be opsonized by both DENV-immune sera and monoclonal antibodies. In addition, DENV E-specific antibodies can facilitate phagocytic uptake of DENV-infected cells, resulting in the target-cell membrane localizing to endosomes of the engulfing phagocyte. Notably, no DENV genetic material was observed localizing to the engulfing phagocyte, suggesting that horizontal transfer of DENV from the infecting cell is an unlikely occurrence. In their totality, these data reinforce the concept that DENV E-reactive antibodies have a multifaceted role in DENV immunity and pathogenesis beyond neutralization and/or infection-enhancement.

immunology↗

bioRxiv2022

Mitochondrial protein import clogging as a mechanism of disease

Mitochondrial biogenesis requires the import of >1,000 mitochondrial preproteins from the cytosol. Most studies on mitochondrial protein import are focused on the core import machinery. Whether and how the biophysical properties of substrate preproteins affect overall import efficiency is underexplored. Here, we show that protein traffic into mitochondria is disrupted by amino acid substitutions in a single substrate preprotein. Pathogenic missense mutations in adenine nucleotide translocase 1 (Ant1), and its yeast ortholog Aac2, cause the protein to accumulate along the protein import pathway, thereby obstructing general protein translocation into mitochondria. This impairs mitochondrial respiration, cytosolic proteostasis and cell viability independent of Ant1s nucleotide transport activity. The mutations act synergistically, as double mutant Aac2/Ant1 cause severe clogging primarily at the Translocase of the Outer Membrane (TOM) complex. This confers extreme toxicity in yeast. In mice, expression of a super-clogger Ant1 variant led to an age-dependent dominant myopathy that phenocopies Ant1-induced human disease, suggesting clogging as a mechanism of disease. We propose that secondary structures of mitochondrial preproteins play an essential role in preventing clogging and disease.

biochemistry↗

bioRxiv2022

Mitochondrial protein import stress potentiates neurodegeneration in a mouse model of Parkinson disease

Several genetic and environmental risk factors for Parkinsons disease have been identified that converge on mitochondria as central elements in the disease process. However, the mechanisms by which mitochondrial dysfunction contributes to neurodegeneration remain incompletely understood. Non-bioenergetic pathways of the mitochondria are increasingly appreciated, but confounding bioenergetic defects are a major barrier to experimental validation. Here, we describe a novel bioenergetics-independent mechanism by which mild mitochondrial protein import stress augments neurodegeneration. We induced this mitochondrial protein import stress in an established mouse model of Parkinsons disease expressing the A53T mutated form of -synuclein (SNCA). Mice with import stress in addition to the A53T mutation demonstrated increased size of -synuclein aggregates, co-aggregation of mitochondrial preproteins with -synuclein, and worsened neurodegeneration. Importantly, we found no evidence of bioenergetic defects in any of the mutant mice, even with the added import stress. These data suggest that mitochondrial protein import stress contributes to neurodegeneration through cytosolic proteostatic stress and co-aggregation of mitochondrial and neuropathogenic proteins independent of bioenergetics. Given that protein import efficiency is affected by many types of mitochondrial stress, our findings add a new layer to understanding why the pathogenic mitochondrial dysfunction and cytosolic protein misfolding pathways converge in neurodegenerative diseases such as Parkinsons disease.

biochemistry↗

bioRxiv2019

Cytosolic Proteostatic Adaptation to Mitochondrial Stress Causes Progressive Muscle Wasting

Mitochondrial dysfunction causes muscle wasting (or atrophy) in many diseases and probably also during aging. The underlying mechanism is unclear. Accumulating evidence suggests that substantial levels of bioenergetic deficiency and oxidative stress are insufficient by themselves to intrinsically cause muscle wasting, raising the possibility that non-bioenergetic factors may contribute to mitochondria-induced muscle wasting. In this report, we show that chronic adaptation to mitochondria-induced proteostatic stress in the cytosol induces muscle wasting. We generated transgenic mice with unbalanced mitochondrial protein loading and import, by a two-fold increase in the expression of the nuclear-encoded mitochondrial carrier protein, Ant1. We found that the ANT1-transgenic mice progressively lose muscle mass. Skeletal muscle is severely atrophic in older mice without affecting the overall lifespan. Mechanistically, Ant1 overloading induces aggresome-like structures and the expression of small heat shock proteins in the cytosol. The data support mitochondrial Precursor Overaccumulation Stress (mPOS), a recently discovered cellular stress mechanism caused by the toxic accumulation of unimported mitochondrial precursors/preproteins. Importantly, the ANT1-transgenic muscles have a drastically remodeled transcriptome that appears to be trying to counteract mPOS, by repressing protein synthesis, and by stimulating proteasomal function, autophagy and lysosomal amplification. These anti-mPOS responses collectively reduce protein content, which is known to decrease myofiber size and muscle mass. Our work therefore revealed that a subtle imbalance between mitochondrial protein load and import is sufficient to induce mPOS in vivo, and that anti-mPOS adaptation is a robust mechanism of muscle wasting. This finding may help improve the understanding of how mitochondria contribute to muscle wasting. It could have direct implications for several human diseases associated with ANT1 overexpression, including Facioscapulohumeral Dystrophy (FSHD). One Sentence SummaryProteostatic adaptations to proteostatic stress in the cytosol caused by unbalanced mitochondrial protein loading and import lead to progressive muscle wasting.

cell biology↗