Biology subjects

Christensen, A.

Publications and source records attributed to Christensen, A..

10 recordsLinked to original sources

bioRxiv2026

17α-Estradiol Confers Limited Protection Against APOE4 Phenotypes in Middle-Aged Female Mice

Longevity-promoting interventions represent a promising strategy to mitigate brain aging and reduce Alzheimers disease (AD) risk. The NIA Interventions Testing Program identified the weak estrogen 17-estradiol (17E2) as a compound that extends healthspan and lifespan in mice, with effects observed primarily in males. Our recent work demonstrated that 17E2 healthspan benefits were modulated by human apolipoprotein E (APOE) genotype such that aging phenotypes were improved more strongly in middle-aged male mice with targeted-replacement of the AD-associated APOE4 allele compared to APOE3, the risk neutral and most common APOE allele. Here, we tested whether APOE-dependent, AD-relevant benefits of 17E2 observed in males extend to females. Specifically, we treated 12-month-old APOE3 and APOE4 targeted-replacement female mice for 6 months with chow containing 0 or 14.4ppm 17E2. We find that relative to APOE3, APOE4 genotype largely exhibits more robust systemic phenotypes associated with aging, including increased adiposity, impaired glucose tolerance, and reduced energy expenditure. Further, we observe that treatment with 17E2 yields modest improvements in some outcomes, including decreased adiposity and increased lean mass, glucose tolerance, and energy expenditure, though significant benefits are found only in APOE4 females. In the CNS, we observed mixed effects of APOE genotype on behavioral performance and indices of brain aging, with APOE4 females performing worse in the Barnes Maze and having higher levels of the AD-related peptide soluble {beta}-amyloid, but no APOE genotype differences in cortical lipid raft oxidative damage. In contrast to its systemic effects, 17E2 did not significantly improve neural outcomes in APOE3 or APOE4 females. These findings address the impact of biological sex on established protective effects of a longevity-promoting intervention against APOE4 phenotypes, which have significant relevance to the prevention of age-related conditions including metabolic dysfunction, cognitive impairment and vulnerability to AD.

systems biology↗

bioRxiv2026

Females Adapt to Dietary Protein Restriction on Enhanced Gut-Brain Axis during Aging

Growing evidence supports a critical role for the gut-brain axis in regulating metabolic health, inflammation, and cognitive function during aging. Age-associated gut dysbiosis has been linked to metabolic dysfunction and cognitive decline, with females exhibiting increased susceptibility to these age-related impairments. Diet is a major determinant of gut microbiome composition and function. Previous studies from our laboratory demonstrated that dietary protein restriction (DPR) induces fibroblast growth factor 21 (FGF21), improves metabolic health, and extends lifespan in male mice. However, the effects of DPR on the gut microbiome and associated health outcomes in aged female mice remain poorly understood. Female mice were assigned at 16 months of age to either a normal-protein (NP) or low-protein (LP) diet for 26 weeks. Metabolic assessments included food intake, fasting glucose concentrations, and glucose tolerance testing. Senescence-associated markers in mesenteric white adipose tissue (mWAT), fecal microbiome composition, and behavioral outcomes were evaluated to determine relationships among dietary protein intake, microbial communities, metabolic health, and cognitive function. Low-protein diet significantly improved metabolic health in aged female mice, as evidenced by improved glucose regulation. Microbiome analyses revealed increased abundance of Akkermansia at 17 months and Faecalibaculum in LP-fed animals at 22 months of age. More so, functional profiling and gene set enrichment analyses indicated enrichment of microbial pathways associated with membrane integrity and metal ion binding. Lastly, LP-fed female mice displayed improved memory performance at 22 months of age compared with age-matched NP-fed controls. Collectively, these findings demonstrate that DPR remodels the gut microbiome and improves metabolic and cognitive health in aged female mice. The observed microbial adaptations may contribute to the beneficial effects of DPR on aging-related physiology, highlighting the gut microbiome as a potential mediator of dietary interventions that promote healthy aging.

physiology↗

bioRxiv2026

Powdery mildew fungi block plant vacuolar traffic to suppress immunity

Plant immunity can be activated by membrane-localized pattern recognition receptors or by cytosolic nucleotide-binding leucine-rich repeat (NLR) receptors, while it can be counteracted by pathogen secreted effectors. Manifestation of immunity often involves endomembrane traffic. However, limited evidence is available for such an involvement in NLR-mediated immunity, which typically includes a hypersensitive reaction (HR)-programmed cell death response. Here we show that the barley powdery mildew fungus uses several effectors to target and inhibit the vacuolar trafficking pathway, which causes endomembrane markers to stall in the endoplasmic reticulum (ER). We used this ER-stalling phenotype as a proxy to track fungal manipulation of the vacuolar pathway during different stages of the actual infection. Our data indicate that powdery mildew fungi interfere with the vacuolar pathway, but only temporarily, as the stalling is lifted once the fungal haustorial feeding structures are well-developed for nutrient uptake in epidermal cells. Notably, we show evidence that blocking the vacuolar pathway causes a general inhibition of NLR-mediated HR, and that this mechanism is taken advantage of by the pathogen. Finally, we provide an example that the fungus can secrete a different set of effectors at the haustorial stage that result in the re-opening of the vacuolar pathway by inhibiting the initial vacuolar traffic-suppressing effectors.

plant biology↗

bioRxiv2025

Murine peritoneal macrophages undergo female-specific remodeling with aging

Aging is a complex process characterized by a progressive decline in physiological functions. Immune function is strongly influenced by biological sex, affecting both innate and adaptive responses. Here, we investigated the effects of age and sex on mouse peritoneal immune cells and identified macrophages as the top affected cell type. Macrophages, as central components of the innate immune system, play critical roles in homeostasis maintenance and infection response. We found that aging induces sex-specific remodeling of mouse peritoneal macrophage omic landscapes, which is accompanied by female-specific age-related functional remodeling (i.e. decreased phagocysis, increased glycolysis). We show that age-related changes in circulating estrogen levels likely drive aspects of female-specific macrophage age-related changes, specifically age-related phagocytosis decline. By leveraging our multi-omic dataset, we identify transcription factors whose female-specific age-regulation may drive female-specific age-related changes in peritoneal macrophage phenotypes. Interestingly, Irf2 downregulation was sufficient to recapitulate aspects of female peritoneal macrophage aging phenotypes, including increased glycolysis. Mechanistically, decreased Irf2 expression leads to decreased binding to its target genes, including Hk3, which encodes hexokinase (the rate-limiting enzyme of glycolysis). Our findings support the notion that aging leads to female-specific remodeling of mouse peritoneal macrophages through hormone-dependent and -independent mechanisms.

immunology↗

bioRxiv2024

Intraflagellar transport protein IFT172 contains a C-terminal ubiquitin-binding U-box-like domain involved in ciliary signaling

Intraflagellar transport (IFT) is a fundamental process driving ciliogenesis in most eukaryotic organisms. IFT172, the largest protein of the IFT complex, plays a crucial role in cilium formation and several disease-causing IFT172 variants have been identified in ciliopathy patients. While IFT172 is tethered to the IFT-B complex via its N-terminal domains, the function of its C-terminal domains has remained elusive. Here, we reveal that the C-terminal part of IFT172 interacts with IFT-A complex subunits, providing a molecular basis for the role of IFT172 in bridging IFT-A and IFT-B complexes. We determine the crystal structure of the C-terminal part of IFT172, uncovering a conserved U-box-like domain often found in E3 ubiquitin ligases. This domain exhibits ubiquitin-binding properties and IFT172 undergoes ubiquitin conjugation in vitro, an activity which is reduced in the C1727R patient ciliopathy variant. We use CRISPR-engineered RPE-1 cells to demonstrate that the U-box-like domain is essential for IFT172 protein stability and proper cilium formation. Notably, RPE-1 cells with heterozygous deletion of the U-box domain show altered TGF-{beta} signaling responses, particularly in SMAD2 phosphorylation levels and AKT activation. Our findings suggest that IFT172, beyond its structural role in bridging IFT-A and IFT-B complexes within IFT trains, harbors a conserved U-box-like domain with potential involvement in ciliary ubiquitination processes and signaling, providing new insights into the molecular mechanisms underlying IFT172-related ciliopathies.

biochemistry↗

bioRxiv2024

Using Eye Gaze to Train an Adaptive Myoelectric Interface

Myoelectric interfaces hold promise in consumer and health applications, but they are currently limited by variable performance across users and poor generalizability across tasks. To address these limitations, we consider interfaces that continually adapt during operation. Although current adaptive interfaces can reduce inter-subject variability, they still generalize poorly between tasks because they make use of task-specific data during training. To address this limitation, we propose a new paradigm to adapt myoelectric interfaces using natural eye gaze as training data. We recruited 11 subjects to test our proposed method on a 2D computer cursor control task using high-density surface EMG signals measured from forearm muscles. We find comparable task performance between our gaze-trained paradigm and the current task-dependent method. This result demonstrates the feasibility of using eye gaze to replace task-specific training data in adaptive myoelectric interfaces, holding promise for generalization across diverse computer tasks. CCS Concepts* Human-centered computing [->] Interaction devices; Empirical studies in HCI.

bioengineering↗

bioRxiv2024

Protection against APOE4-associated aging phenotypes with the longevity-promoting intervention 17α-estradiol in male mice

The apolipoprotein {varepsilon}4 allele (APOE4) is associated with decreased longevity, increased vulnerability to age-related declines, and disorders across multiple systems. Interventions that promote healthspan and lifespan represent a promising strategy to attenuate the development of APOE4-associated aging phenotypes. Here we studied the ability of the longevity-promoting intervention 17-estradiol (17E2) to protect against age-related impairments in APOE4 versus the predominant APOE3 genotype using early middle-aged mice with knock-in of human APOE alleles. Beginning at age 10 months, male APOE3 or APOE4 mice were treated for 20 weeks with 17E2 or vehicle then compared for indices of aging phenotypes body-wide. Across peripheral and neural measures, APOE4 was associated with poorer outcomes. Notably, 17E2 treatment improved outcomes in a genotype-dependent manner favoring APOE4 mice. These data demonstrate a positive APOE4 bias in 17E2-mediated healthspan actions, suggesting that longevity-promoting interventions may be useful in mitigating deleterious age-related risks associated with APOE4 genotype.

systems biology↗

bioRxiv2023

Evolution of Rhodopseudomonas palustris to degrade halogenated aromatic compounds involves changes in pathway regulation and enzyme specificity

Halogenated aromatic compounds are used in a variety of industrial applications but can be harmful to humans and animals when released into the environment. Microorganisms that degrade halogenated aromatic compounds anaerobically have been isolated but the evolutionary path that they may have taken to acquire this ability is not well understood. A strain of the purple nonsulfur bacterium, Rhodopseudomonas palustris, RCB100, can use 3-chlorobenzoate (3-CBA) as a carbon source whereas a closely related strain, CGA009, cannot. To reconstruct the evolutionary events that enabled RCB100 to degrade 3-CBA, we selected for and isolated a CGA009 strain capable of growing on 3-CBA, although not as well as RCB100. Comparative whole-genome sequencing of the evolved strain and RCB100 revealed large deletions encompassing badM, a transcriptional repressor of genes for anaerobic benzoate degradation. It was previously shown that in strain RCB100, a single nucleotide change in an alicyclic acid coenzyme A ligase gene, named aliA, gives rise to a variant AliA enzyme that has high activity with 3-CBA. When we introduced the RCB100 aliA allele and a badM deletion into R. palustris CGA009, it grew on 3-CBA at a similar rate as RCB100. This work provides an example of pathway evolution that includes a variant of a promiscuous enzyme with enhanced substrate specificity and a regulatory mutation that leads to constitutive expression of a pathway that does not regulate the promiscuous enzyme. ImportanceBiodegradation of man-made compounds often involves the activity of promiscuous enzymes whose native substrate is structurally similar to the man-made compound. Based on the enzymes involved, it is possible to predict what microorganisms are likely involved in biodegradation of anthropogenic compounds. However, there are examples of organisms that contain the required enzyme(s) and yet cannot metabolize these compounds. We found that even when the purple nonsulfur bacterium, Rhodopseudomonas palustris, encodes all the enzymes required for degradation of a halogenated aromatic compound, it is unable to metabolize that compound. Using adaptive evolution, we found a regulatory mutation and a variant of promiscuous enzyme with increased substrate specificity were required, but the ability to metabolize a halogenated aromatic compound also resulted in reduced fitness on another aromatic compound. This work provides insight into how an environmental isolated evolved to use halogenated aromatic compounds and the potential ecological trade-offs associated with this adaptation.

microbiology↗

bioRxiv2023

Analysis of cortical cell polarity by imaging flow cytometry

Metastasis is the main cause of cancer-related death and therapies specifically targeting metastasis are highly needed. Cortical cell polarity (CCP) is a pro-metastatic property of circulating tumor cells (CTCs) affecting their ability to exit blood vessels and form new metastases that constitutes a promising point of attack to prevent metastasis. However, conventional fluorescence microscopy on single cells and manual quantification of CCP are time-consuming and unsuitable for screening of regulators. In this study, we developed an imaging flow cytometry (IFC)-based method for high-throughput screening of factors affecting CCP in melanoma cells. The artificial intelligence (AI)-supported analysis method we developed is highly reproducible, accurate, and orders of magnitude faster than manual quantification. Additionally, this method is flexible and can be adapted to include additional cellular parameters. In a small-scale pilot experiment using polarity-, cytoskeleton-or membrane-affecting drugs, we demonstrate that our workflow provides a straightforward and efficient approach for screening factors affecting CCP in cells in suspension and provide insights into the specific function of these drugs in this cellular system. The method and workflow presented here will facilitate large-scale studies to reveal novel cell-intrinsic as well as systemic factors controlling CCP during metastasis.

cell biology↗

bioRxiv2018

Do Plant Mitochondria Even Need Base Excision Repair?

Substitution rates in plant mitochondrial genes are extremely low, indicating strong selective pressure as well as efficient repair. Plant mitochondria possess base excision repair pathways, however, many repair pathways such as nucleotide excision repair and mismatch repair appear to be absent. In the absence of these pathways, many DNA lesions must be repaired by a different mechanism. To test the hypothesis that double-strand break repair (DSBR) is that mechanism, we maintained independent self-crossing lineages of plants deficient in uracil-N-glycosylase (UNG) for 11 generations to determine the repair outcomes when that pathway is missing. Surprisingly, no single nucleotide polymorphisms (SNPs) were fixed in any line in generation 11. The pattern of heteroplasmic SNPs was also unaltered through 11 generations. When the rate of cytosine deamination was increased by mitochondrial expression of the cytosine deaminase APOBEC3G, there was an increase in heteroplasmic SNPs, but only in mature leaves. Clearly DNA maintenance in reproductive meristem mitochondria is very effective in the absence of UNG, while mitochondrial genomes in differentiated tissue are maintained through a different mechanism, or not at all. Several genes involved in DSBR are upregulated in the absence of UNG, indicating that double strand break repair is a general system of repair in plant mitochondria. It is important to note that the developmental stage of tissues is critically important for these types of experiments.

genetics↗