Biology subjects

Alassaf, M.

Publications and source records attributed to Alassaf, M..

7 recordsLinked to original sources

bioRxiv2024

Adipocyte metabolic state regulates glial phagocytic function

HighlightsO_LIProlonged exposure to an obesogenic diet result in a starvation-like metabolic response in adipose tissue. C_LIO_LIObesogenic diet-induced mitochondrial lipid catabolism in adipose tissue impacts glial phagocytic function. C_LIO_LIAdipocyte ApoB is a novel regulator of glial phagocytic function. C_LIO_LILpR1, on ensheathing glia, is required for glial response to axonal injury. C_LI Obesity and type 2 diabetes are well-established risk factors for neurodegenerative disorders1-4, yet the underlying mechanisms remain poorly understood. The adipocyte-brain axis is crucial for brain function, as adipocytes secrete signaling molecules, including lipids and adipokines, that impinge on neural circuits to regulate feeding and energy expenditure5. Disruptions in the adipocyte-brain axis are associated with neurodegenerative conditions6, but the causal links are not fully understood. Neural debris accumulates with age and injury, and glial phagocytic function is crucial for clearing this debris and maintaining a healthy brain microenvironment7-9. Using adult Drosophila, we investigate how adipocyte metabolism influences glial phagocytic activity in the brain. We demonstrate that a prolonged obesogenic diet increases adipocyte fatty acid oxidation and ketogenesis. Genetic manipulations that mimic obesogenic diet-induced changes in adipocyte lipid and mitochondrial metabolism unexpectedly reduce the expression of the phagocytic receptor Draper in Drosophila microglia-like cells in the brain. We identify Apolpp--the Drosophila equivalent of human apolipoprotein B (ApoB)--as a critical adipocyte-derived signal that regulates glial phagocytosis. Additionally, we show that Lipoprotein Receptor 1 (LpR1), the LDL receptor on phagocytic glia, is required for glial capacity to clear injury-induced neuronal debris. Our findings establish that adipocyte-brain lipoprotein signaling regulates glial phagocytic function, revealing a novel pathway that links adipocyte metabolic disorders with neurodegeneration. O_FIG O_LINKSMALLFIG WIDTH=164 HEIGHT=200 SRC="FIGDIR/small/614765v2_ufig1.gif" ALT="Figure 1"> View larger version (54K): org.highwire.dtl.DTLVardef@6698e4org.highwire.dtl.DTLVardef@1bfd855org.highwire.dtl.DTLVardef@13d732org.highwire.dtl.DTLVardef@9548ff_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical abstractC_FLOATNO C_FIG

neuroscience↗

bioRxiv2023

Atg8-LC3 controls systemic nutrient surplus signaling from flies to humans.

Organisms experience constant nutritional flux, and homeostatic mechanisms evolved to operate at the nexus of extreme nutritional states - scarcity and surplus. Thus, we surmised that decoding bidirectional molecular switches that operate at the interface of scarcity response and surplus signaling will enable the development of strategies to treat disorders that arise from nutrient imbalance states. Adipocytes secrete leptin, an interleukin protein, which signals nutrient surplus to the central brain to regulate feeding and energy expenditure. We report that Atg8-LC3-family proteins, best known for their role in autophagy, are required for leptin secretion in Drosophila and human adipocytes. Atg8-LC3 genetic knockdown and point mutations to the Atg8-LC3 interaction motif (AIM/LIR) of leptin, and its functional ortholog in Drosophila, Upd2, disrupt adipokine secretion and increase adipokine retention in human and fly cells. At an organismal level, Atg8-driven Upd2 retention increases organismal resilience to nutrient extremes by rewiring the transcriptome, organismal feeding behavior, and hunger response. Comparative proteomic analyses reveal that LC3 directs leptin to an exosome secretory pathway. We use genetic knockdown in primary human adipocytes to establish that LC3 is required for leptin secretion in a physiologically relevant mammalian system. Hence, we uncover a previously unknown and evolutionarily conserved role for Atg8-LC3 in promoting adipocyte-brain nutrient surplus signaling. We propose that Atg8-LC3s bidirectional role in nutrient sensing-conveying nutrient surplus and responding to nutrient deprivation-enables organisms to manage nutrient flux effectively.

physiology↗

bioRxiv2023

Diet-induced glial insulin resistance impairs the clearance of neuronal debris

Obesity significantly increases the risk of developing neurodegenerative disorders, yet the precise mechanisms underlying this connection remain unclear. Defects in glial phagocytic function are a key feature of neurodegenerative disorders, as delayed clearance of neuronal debris can result in inflammation, neuronal death, and poor nervous system recovery. Mounting evidence indicates that glial function can affect feeding behavior, weight, and systemic metabolism, suggesting that diet may play a role in regulating glial function. While it is appreciated that glial cells are insulin sensitive, whether obesogenic diets can induce glial insulin resistance and thereby impair glial phagocytic function remains unknown. Here, using a Drosophila model, we show that a chronic obesogenic diet induces glial insulin resistance and impairs the clearance of neuronal debris. Specifically, obesogenic diet exposure downregulates the basal and injury-induced expression of the glia-associated phagocytic receptor, Draper. Constitutive activation of systemic insulin release from Drosophila Insulin-producing cells (IPCs) mimics the effect of diet-induced obesity on glial draper expression. In contrast, genetically attenuating systemic insulin release from the IPCs rescues diet-induced glial insulin resistance and draper expression. Significantly, we show that genetically stimulating Phosphoinositide 3-kinase (PI3K), a downstream effector of Insulin receptor signaling, rescues HSD-induced glial defects. Hence, we establish that obesogenic diets impair glial phagocytic function and delays the clearance of neuronal debris.

neuroscience↗

bioRxiv2021

Fat Body Phospholipid State Dictates Hunger Driven Feeding Behavior

Diet-induced obesity (DIO) leads to dysfunctional feeding behavior. However, the precise molecular nodes underlying diet-induced dysregulation of satiety sensing and feeding motivation are poorly understood. The fruit fly is a simple genetic model system yet displays significant evolutionary conservation to mammalian nutrient sensing and energy balance. Using a longitudinal high sugar regime in Drosophila, we sought to address how lipid alteration in fat cells alters feeding behavior. We find that prolonged exposure to HSD degrades the hunger-driven feeding (HDF) response. Lipidomics analysis reveals that longitudinal exposure to HSD significantly alters whole body phospholipid profiles. By performing a systematic screen for phospholipid enzymes, we identify Pect as a critical regulator of hunger-driven feeding. Pect is a rate-limiting enzyme in the phosphatidylethanolamine (PE) biosynthesis pathway and the fly ortholog of human PCYT2. We show that disrupting Pect only in the fat body causes insulin-resistant phenotypes and a loss of hunger-driven feeding. Excitingly, we find that overexpression of Pect restores HSD-induced loss of hunger-driven feeding response. Strikingly human studies have noted a correlation between PCYT2/Pect levels and clinical obesity. Now, our unbiased studies in Drosophila provide specific genetic evidence for Pect in maintaining nutrient sensing during DIO. Our study provides novel insights into the role of phospholipids in interorgan communication of nutrient status. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=193 SRC="FIGDIR/small/472854v4_ufigA1.gif" ALT="Figure 1"> View larger version (66K): org.highwire.dtl.DTLVardef@1ecf3eorg.highwire.dtl.DTLVardef@b800f2org.highwire.dtl.DTLVardef@461a7eorg.highwire.dtl.DTLVardef@75651c_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2020

Pregnancy associated plasma protein-aa regulates endoplasmic reticulum-mitochondria associations

The endoplasmic reticulum (ER) and mitochondria form close physical associations to facilitate calcium transfer, thereby regulating mitochondrial function and dynamics. For neurons with high metabolic demands, such as sensory hair cells, precise regulation of ER-mitochondria associations is especially critical for cell survival. We previously identified the secreted metalloprotease Pregnancy associated plasma protein-aa (Pappaa) as a novel regulator of mitochondrial function in zebrafish lateral line hair cells (Alassaf et al., 2019). Here, we show that pappaa mutant hair cells exhibit excessive and abnormally close ER-mitochondria associations, suggesting increased ER-mitochondria calcium transfer. Indeed, we find that pappaa mutant hair cells are more vulnerable to pharmacological induction of ER-calcium release. Additionally, pappaa mutant hair cells display ER stress and dysfunctional downstream processes of the ER-mitochondria axis including mitochondrial fragmentation and autophagy. Together our results support a model in which Pappaa regulates mitochondrial function, at least in part, by regulating ER-mitochondria associations.

cell biology↗

bioRxiv2019

Pregnancy-associated plasma protein-aa supports hair cell survival by regulating mitochondrial function

To support cell survival, mitochondria must balance energy production with oxidative stress. Inner ear hair cells are particularly vulnerable to oxidative stress; thus require tight mitochondrial regulation. We identified a novel molecular regulator of the hair cells mitochondria and survival: Pregnancy-associated plasma protein-aa (Pappaa). Hair cells in zebrafish pappaa mutants exhibit mitochondrial defects, including elevated mitochondrial calcium, transmembrane potential, and reactive oxygen species (ROS) production and reduced antioxidant expression. In pappaa mutants, hair cell death is enhanced by stimulation of mitochondrial calcium or ROS production and suppressed by a mitochondrial ROS scavenger. As a secreted metalloprotease, Pappaa stimulates extracellular insulin-like growth factor 1 (IGF1) bioavailability. We found that the pappaa mutants enhanced hair cell loss can be suppressed by stimulation of IGF1 availability and that Pappaa-IGF1 signaling acts post-developmentally to support hair cell survival. These results reveal Pappaa as an extracellular regulator of hair cell survival and essential mitochondrial function.

cell biology↗

bioRxiv2018

Pregnancy-associated plasma protein-aa promotes neuron survival by regulating mitochondrial function

A neurons longevity is regulated by both extracellular molecular factors and the regulation of its intracellular functions, including mitochondrial activity. It remains poorly understood which extracellular factors promote neuron survival by influencing mitochondrial function. Through zebrafish mutant analysis, we reveal a novel extracellular neuronal survival factor: Pregnancy-associated plasma protein-aa (Pappaa). Neurons in pappaa mutant larvae die precociously and exhibit multiple mitochondrial defects, including elevated mitochondrial calcium, membrane potential, and reactive oxygen species production (ROS). In pappaa mutants, neuron loss is exacerbated by stimulation of mitochondrial calcium load or ROS production and suppressed by exposure to a mitochondrial ROS scavenger. As a secreted metalloprotease, Pappaa stimulates local insulin-like growth factor 1 (IGF1) signaling; a known regulator of mitochondrial function and neuron survival. In pappaa mutants, neurons show reduced IGF1-receptor activity and neuron loss is attenuated by stimulation of IGF1 signaling. These results suggest Pappaa-IGF1 signaling promotes neuron survival by regulating mitochondrial function.

neuroscience↗