Biology subjects

Schwartz, G. J.

Publications and source records attributed to Schwartz, G. J..

12 recordsLinked to original sources

bioRxiv2026

NgBR controls hepatic adiponectin signaling competence through KAT7-dependent chromatin regulation

Adiponectin signaling is essential for hepatic glucose homeostasis, yet the molecular basis of adiponectin receptor responsiveness remains incompletely understood. Here, we identify the Nogo-B receptor (NgBR; NUS1) as a regulator of hepatic adiponectin sensitivity. Across human, cynomolgus monkey, and mouse datasets, hepatic NgBR expression is consistently reduced in obesity-associated diabetes, indicating a conserved metabolic signature. Hepatocyte-specific NgBR deletion abolishes the metabolic effects of the adiponectin agonist AdipoRon, resulting in impaired AMPK activation, persistent gluconeogenesis, and ceramide accumulation. Mechanistically, NgBR loss suppresses KAT7 expression and reduces histone acetylation at AdipoR1 and AdipoR2 promoters, thereby limiting receptor expression. Adeno-associated virus (AAV)-mediated restoration of hepatic NgBR reinstates KAT7-dependent chromatin activation, adiponectin receptor expression, and glucose homeostasis. These findings support a hepatocellular mechanism in which NgBR maintains adiponectin receptor competence and suggest a potential therapeutic strategy for restoring adiponectin responsiveness in metabolic disease. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=115 SRC="FIGDIR/small/726643v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@117fa66org.highwire.dtl.DTLVardef@1385297org.highwire.dtl.DTLVardef@b64369org.highwire.dtl.DTLVardef@3dd55_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2026

A novel subset of hepatocytes is simultaneously gluconeogenic and de novo lipogenic in the fed state and is naturally insulin resistant

It is generally accepted that hepatic gluconeogenesis, the synthesis of glucose from non-carbohydrate substrates is active in the fasted state and inactive in the fed state. In contrast, de novo lipogenesis is active in the fed state and is inactive in the fasted state. Here, we used targeted single cell RNA-seq, HCR RNA-FISH, and PrimeFlow in normal physiological mouse liver, and identified a subpopulation of periportal hepatocytes that simultaneously co-express both gluconeogenic and lipogenic genes in the fed state. Euglycemic-hyperinsulinemic clamps further demonstrated that this novel hepatocyte subpopulation is naturally insulin resistant. Spatial metabolic imaging coupled with stable isotope tracing analyses revealed individual hepatocytes that simultaneously undergo both gluconeogenesis and de novo lipogenesis. These dual-positive hepatocytes were also present in human hepatocytes from humanized mouse livers. Moreover, the number of dual-positive hepatocytes increased in high-fat diet-fed mice, suggesting a paradigm shift in our understanding of how the liver becomes insulin resistant.

molecular biology↗

bioRxiv2024

Slit3 Fragments Orchestrate Neurovascular Expansion and Thermogenesis in Brown Adipose Tissue

Brown adipose tissue (BAT) is an evolutionary innovation that enables placental mammals to regulate body temperature through adaptive thermogenesis. Brown adipocytes are embedded within an intricate network of blood vessels and sympathetic nerves that support their development and thermogenic function. Cold exposure activates BAT thermogenesis through the coordinated induction of brown adipogenesis, angiogenesis, and sympathetic innervation. However, how these distinct processes are coordinated remains unclear. Here, we show that fragments of Slit guidance ligand 3 (Slit3) drive crosstalk among adipocyte progenitors, endothelial cells, and sympathetic nerves. We demonstrate that adipocyte progenitors secrete Slit3, which regulates both angiogenesis and sympathetic innervation in BAT and is essential for BAT thermogenesis in vivo. Proteolytic cleavage of Slit3 generates secreted Slit3-N and Slit3-C fragments, which bind distinct receptors to stimulate angiogenesis and sympathetic innervation, respectively. We identify Plxna1 as a previously unrecognized receptor for Slit3-C and show that it is essential for sympathetic innervation and cold-induced neurite expansion in BAT. Moreover, we introduce bone morphogenetic protein 1 (Bmp1) as the first Slit protease identified in vertebrates. In summary, this work establishes a mechanistic framework for the coordinated regulation of sympathetic innervation and angiogenesis to enhance thermogenic function. The co-regulation of neurovascular expansion by distinct Slit3 fragments offers a bifurcated yet harmonized mechanism to ensure a synchronized BAT response to environmental challenges. Finally, this study provides the first evidence that adipocyte progenitors regulate tissue innervation, revealing a previously unrecognized dimension of cellular interaction within adipose tissue.

physiology↗

bioRxiv2024

Liver-innervating vagal sensory neurons play an indispensable role in the development of hepatic steatosis in mice fed a high-fat diet.

The visceral organ-brain axis, mediated by vagal sensory neurons, is essential for maintaining various physiological functions. Here, we investigate the impact of liver-projecting vagal sensory neurons on energy balance, hepatic steatosis, and anxiety-like behavior in mice under obesogenic conditions. A small subset of vagal sensory neurons in both the left and right ganglia innervate the liver and project centrally to the nucleus of the tractus solitarius, area postrema, and dorsal motor nucleus of the vagus, and peripherally to the periportal areas in the liver. Surprisingly, the loss of liver-projecting vagal sensory neurons via caspase-induced selective destruction of advillin-positive neurons prevents diet-induced obesity, and these outcomes are associated with increased energy expenditure. Although males and females exhibit improved glucose homeostasis following disruption of liver-projecting vagal sensory neurons, only male mice display increased insulin sensitivity. Furthermore, the loss of liver-projecting vagal sensory neurons limits the progression of hepatic steatosis in mice fed a steatogenic diet. Intriguingly, mice lacking liver-innervating vagal sensory neurons also exhibit less anxiety-like behavior compared to control mice. Therefore, modulation of the liver-brain axis may aid in designing effective treatments for both psychiatric and metabolic disorders associated with obesity and MAFLD.

neuroscience↗

bioRxiv2024

Development of novel tools for dissection of central versus peripheral dopamine D2-like receptor signaling in dysglycemia

Dopamine (DA) D2-like receptors in both the central nervous system (CNS) and the periphery are key modulators of metabolism. Moreover, disruption of D2-like receptor signaling is implicated in dysglycemia. Yet, the respective metabolic contributions of CNS versus peripheral D2-like receptors including D2 (D2R) and D3 (D3R) receptors remain poorly understood. To address this, we developed new pharmacological tools, D2-like receptor agonists with diminished and delayed blood-brain barrier capability, to selectively manipulate D2R/D3R signaling in the periphery. We designated bromocriptine methiodide (BrMeI), a quaternary methiodide analogue of D2/3R agonist and diabetes drug bromocriptine, as our lead compound based on preservation of D2R/D3R binding and functional efficacy. We then used BrMeI and unmodified bromocriptine to dissect relative contributions of CNS versus peripheral D2R/D3R signaling in treating dysglycemia. Systemic administration of bromocriptine, with unrestricted access to CNS and peripheral targets, significantly improved both insulin sensitivity and glucose tolerance in obese, dysglycemic mice in vivo. In contrast, metabolic improvements were attenuated when access to bromocriptine was restricted either to the CNS through intracerebroventricular administration or delayed access to the CNS via BrMeI. Our findings demonstrate that the coordinated actions of both CNS and peripheral D2-like receptors are required for correcting dysglycemia. Ultimately, the development of a first-generation of drugs designed to selectively target the periphery provides a blueprint for dissecting mechanisms of central versus peripheral DA signaling and paves the way for novel strategies to treat dysglycemia.

neuroscience↗

bioRxiv2023

Ablation of parasympathetic cholinergic innervation of the liver prevents diet-induced obesity and hepatic steatosis in mice.

Hepatic lipid metabolism is regulated by the autonomic nervous system of the liver, with the sympathetic innervation being extensively studied, while the parasympathetic efferent innervation is less understood despite its potential importance. In this study, we investigate the consequences of disrupted brain-liver communication on hepatic lipid metabolism in mice exposed to obesogenic conditions. We found that a subset of hepatocytes and cholangiocytes are innervated by parasympathetic nerve terminals originating from the dorsal motor nucleus of the vagus. The elimination of the brain-liver axis by deleting parasympathetic cholinergic neurons innervating the liver prevents hepatic steatosis and promotes browning of inguinal white adipose tissue (ingWAT). The loss of liver-innervating cholinergic neurons increases hepatic Cyp7b1 expression and fasting serum bile acid levels. Furthermore, knockdown of the G protein-coupled bile acid receptor 1 gene in ingWAT reverses the beneficial effects of the loss of liver-innervating cholinergic neurons, leading to the reappearance of hepatic steatosis. Deleting liver-innervating cholinergic neurons has a small but significant effect on body weight, which is accompanied by an increase in energy expenditure. Taken together, these data suggest that targeting the parasympathetic cholinergic innervation of the liver is a potential therapeutic approach for enhancing hepatic lipid metabolism in obesity and diabetes.

physiology↗

bioRxiv2022

DISRUPTION OF SYMPATHETIC OUTFLOW TO INTRA-ABDOMINAL ORGANS EMULATES THE METABOLIC EFFECTS OF SLEEVE GASTRECTOMY IN OBESE MICE

Although sleeve gastrectomy (SG) is the most commonly performed bariatric surgery in the US, its mechanistic underpinnings have not been fully determined. Thus, we set out to investigate whether SGs effects on the peripheral sympathetic system could mediate the metabolic effects of SG. The celiac-superior mesenteric ganglia (CSMG) lie juxtaposed to the stomach and supply the sympathetic innervation of the stomach, as well as to numerous intra-abdominal organs relevant to metabolism. Here we investigated the effects of SG on the CSMG. SG led to the degeneration of neurons in the CSMG, as evidenced by chromatolysis, which was not found in control mice. Furthermore, CSMG ablation (CGX) completely recapitulated the glycemic and weight loss effects of SG, promoting weight loss at the expense of fat mass in both males and females. Glycemic improvement was robust in males but much more modest in female mice. Norepinephrine tissue content measurement by high performance liquid chromatography revealed that liver, duodenum, and ileum were organs where both SG and CGX displayed evidence of significant sympathetic denervation. Both SG and CGX were associated with increased levels of glucagon-like peptide 1 (GLP-1) and high free fatty acid content in the stools. In conclusion, CSMG neuronal degeneration caused by SG appears to be a mediator of the metabolic effects of this type of bariatric surgery.

neuroscience↗

bioRxiv2021

Neuronal glucose metabolism sets cholinergic tone and controls thermo-regulated signaling at the neuromuscular junction

Cholinergic and sympathetic counter-regulatory networks control numerous physiologic functions including learning/memory/cognition, stress responsiveness, blood pressure, heart rate and energy balance. As neurons primarily utilize glucose as their primary metabolic energy source, we generated mice with increased glycolysis in cholinergic neurons by specific deletion of the fructose-2,6-phosphatase protein TIGAR. Steady-state and stable isotope flux analyses demonstrated increased rates of glycolysis, acetyl-CoA production, acetylcholine levels and density of neuromuscular synaptic junction clusters with enhanced acetylcholine release. The increase in cholinergic signaling reduced blood pressure and heart rate with a remarkable resistance to cold-induced hypothermia. These data directly demonstrate that increased cholinergic signaling through the modulation of glycolysis has several metabolic benefits particularly to increase energy expenditure and heat production upon cold exposure. HighlightsO_LIDeficiency of a negative regulator of glycolysis (TIGAR) in cholinergic neurons increases the biosynthesis and content of the neurotransmitter acetylcholine. C_LIO_LIIncreased cholinergic tone reduces blood pressure and heart rate while enhancing signaling at neuromuscular junction. C_LIO_LIUpregulation of neuromuscular junction activation provides protection against the paralytic curare and cold-induced hypothermia. C_LIO_LIModulation of cholinergic neuron glycolysis may provide a novel therapeutic approach for treatment of diseases stemming from reduced acetylcholine signaling such as myasthenia gravis and sarcopenic pre-synaptic dysfunction. C_LI

cell biology↗

bioRxiv2020

Fat Mass Regain in Middle-Aged Mice after Sleeve Gastrectomy is divergent from plasma leptin levels

BackgroundSome degree of weight regain is typically observed in human patients who undergo Sleeve Gastrectomy (SG), even if the majority of them do not return to their presurgical body weight. Although the majority of bariatric surgery patients are middle aged, most preclinical models of bariatric surgery utilize juvenile male mice. A long-term characterization of the response of mature, wild type, obese male mice to SG has not been performed. MethodsEight-month old C57bl/6J obese male mice were randomized to undergo SG, sham surgery without caloric restriction (SH) or sham surgery with caloric restriction to match body weight to the SG group (SWM). Body weight, body composition and glucose tolerance were matched at baseline. Mice were followed for 60 days following their respective surgeries. ResultsSG mice had a more pronounced percent weight loss than the SH group in the first post-operative month (p<0.05), along with fat mass loss (p<0.01). By the second post-operative month, the SG group started to regain fat mass, although it continued to be statistically lower than the SH group (p<0.05). Cumulative food intake was significantly lower in the SG group compared to SH group only in the first post-operative week (p<0.05), with both groups having similar cumulative food intake thereafter (p>0.05). SWM group had a significantly lower cumulative food intake throughout the study, except for week 1 (p<0.01). Glucose tolerance was only demonstrably better in the SG group compared to SH group at 8 weeks post-operatively (p<0.01). Plasma leptin was significantly lower in the SG group compared to both SWM and SH groups group by the second post-operative month (p<0.01), in spite of SGs increasing fat mass accumulation. In the second post-operative month, both FGF-21 and GDF-15 were increased in the SH group compared to the SG and SWM groups (p<0.05), while there was no difference in plasma insulin among the three groups. Heat production was surprisingly higher in the SH group compared to the other two groups (p<0.05), even though brown adipose tissue Peroxisome Proliferator-Activated Receptor Gamma (PPARg) and Cidea mRNA expression were significantly higher in SG and SWM compared to SH (p<0.01). There was no change in BAT UCP-1 mRNA expression among the groups (p>0.05). There was also no change in fecal lipid content among the groups (p>0.05). ConclusionsSG in obese, middle aged male mice leads is accompanied by fat mass regain in the second post-operative month, while plasma leptin levels continue to be significantly lower. This raises the question of whether the observed fat mass regain consists mostly of visceral adipose tissue.

physiology↗

bioRxiv2020

Sleeve gastrectomy promotes sustained weight loss while increasing heat production in middle aged, obese female mice

BackgroundSleeve gastrectomy (SG) is currently the most frequently performed bariatric surgery in the United States. The majority of patients undergoing SG are middle aged women. Most preclinical models of bariatric surgery, however, utilize juvenile male mice. A long-term characterization of the response of mature wild type, obese female mice to SG has not been performed. Thus, we set out to characterize the response of middle aged obese female mice to SG. MethodsTen-month old C57bl/6J obese female mice were randomized to undergo SG, sham surgery without caloric restriction (SH) or sham surgery with caloric restriction to match body weight to the SG group (SWM). Body weight, body composition and glucose tolerance were matched at baseline. Mice were followed for 60 days following their respective surgeries. ResultsThe SG group had a more pronounced percent weight loss than the SH and SWM control groups (p<0.05), while consuming more calories than the SWM group (p<0.05). The SG group had a significant improvement in glucose tolerance compared to the SH control group (p<0.05). Plasma leptin was significantly decreased in the SG and SWM group, compared to the SH group (p<0.01). Unexpectedly, FGF-21 was increased in the SH group compared to the SG and SWM groups (p<0.01), while there was no difference in plasma insulin among the three groups. Heat production was increased in the SG group compared to SWM and SH groups (p<0.001). SG also had a significantly increased mRNA expression of Uncoupling Protein 1 (UCP-1), Adiponectin and Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha (PGC1-alpha) in brown adipose tissue (BAT), compared to SWM and SH groups. Both SG and SWM groups had increased fecal lipid excretion (p<0.05), compared to the SH group. ConclusionsSG in obese, middle aged female mice leads to sustained weight loss and blood glucose improvement. It appears that increased metabolism in BAT may be linked to these effects.

physiology↗

bioRxiv2020

Adipose tissue-derived neurotrophic factor 3 regulates sympathetic innervation and thermogenesis in adipose tissue

Activation of brown fat thermogenesis increases energy expenditure and alleviates obesity. Sympathetic nervous system (SNS) is important in brown/beige adipocyte thermogenesis. Here we discover a novel fat-derived “adipokine” neurotrophic factor neurotrophin 3 (NTF3) and its receptor Tropomyosin receptor kinase C (TRKC) as key regulators of SNS growth and innervation in adipose tissue. NTF3 is highly expressed in brown/beige adipocytes, and potently stimulates sympathetic neuron neurite growth. NTF3/TRKC regulates a plethora of pathways in neuronal axonal growth and elongation. Adipose tissue sympathetic innervation is significantly increased in mice with adipocyte-specific NTF3 overexpression, but profoundly reduced in mice with TRKC haploinsufficiency (TRKC+/-). Increasing NTF3 via pharmacological or genetic approach promotes beige adipocyte development, enhances cold-induced thermogenesis and protects against diet-induced obesity (DIO); whereas TRKC+/- mice or SNS TRKC deficient mice are cold intolerant and prone to DIO. Thus, NTF3 is an important fat-derived neurotrophic factor regulating SNS innervation, energy metabolism and obesity.Competing Interest StatementThe authors have declared no competing interest.View Full Text

physiology↗

bioRxiv2019

Inhibiting the prostaglandin transporter PGT induces non-canonical thermogenesis at thermoneutrality

ABSTRACT / SUMMARYProstaglandins play fundamental roles in adipose tissue function. While prostaglandin F2 inhibits adipogenesis, prostaglandin E2 promotes adipose beiging. PGF2 and PGE2 are both inactivated through uptake by the plasma membrane transporter (PGT). We hypothesized that inhibiting PGT would increase PGF2 and PGE2 levels, thereby reducing white fat expansion and inducing beiging. Consistent with this hypothesis, inhibiting PGT in mice on high fat diet via genetic knockout or pharmacological blockade reduced body fat stores and induced thermogenesis at thermoneutrality. Inguinal white adipose tissue (iWAT) of these mice exhibited robust UCP1-independent thermogenesis characterized by mitochondrial expansion, coupling of O2 consumption to ATP synthesis, and induction of the creatine pathway. Enhanced coupled respiration persisted in PGT-KO iWAT adipocytes in a creatine shuttle-dependent manner. Thus, inhibiting PGT increases mitochondrial biogenesis and coupled respiration--each supported by the creatine pathway in a system lacking UCP1 expression--revealing PGT as a promising drug target against obesity.

physiology↗