Biology subjects

Lutkewitte, A. J.

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

11 recordsLinked to original sources

bioRxiv2025

Loss of ovarian function and estrogen therapy remodel the brain's synaptic and metabolic proteome

Menopause is linked to cognitive decline and reduced brain metabolism, while estrogen (E2) therapy has been shown to mitigate these effects. Understanding the molecular mechanisms by which ovarian hormones and E2 influence neuroprotection is essential for developing strategies to maintain brain health in women. In this study, we examined how the loss of ovarian hormones, with or without E2 treatment, affects the brain proteome and mitochondrial energy production in aged female C57BL/6J mice (36-40 weeks). The mice underwent sham or ovariectomy (OVX) surgery and were fed a high-fat diet for 10 weeks; six weeks after surgery, OVX mice received either sesame oil or E2 treatment for four weeks. Proteomic analysis of brain homogenates revealed 4,992 proteins regulated by E2, with pathway analysis showing increased signaling proteins related to synaptogenesis. OVX reduced proteins involved in synaptic function, branched-chain amino acid and ketone metabolism, the TCA cycle, and oxidative phosphorylation (Complexes I, IV, and V), while E2 restored protein expression within these pathways. Despite alterations in OxPhos proteins, basal and state 3 mitochondrial respiration remained unchanged, although notable impairments to Complex IV enzymatic activity were apparent in OVX, but not following E2 replacement. Overall, these results indicate that E2 supports brain health by maintaining proteins crucial for synaptic integrity and metabolism, and by reducing the decline in mitochondrial bioenergetics associated with menopause.

neuroscience↗

bioRxiv2025

The Impact of a Western Diet with High Salt on Metabolic Outcomes in Male C57bl/6J Mice

ObjectiveThe Western diet promotes obesity and metabolic disease by increasing caloric intake and systemic inflammation. The typical Western diet is high in saturated fats, sugars, and salt. In pre-clinical rodent studies, the "Western" diet (also called the high-fat high-sucrose diet (HFHS)) is high in saturated fats and sugars (typically sucrose) but low in salt (<1% salt). As such, we sought investigate the impact of a chronic 3% NaCl Western diet (high-fat, high-sucrose + high salt (HFHS + Salt)) diet on systemic organ metabolism, liver mitochondrial function, and adipose tissue. MethodsThirty-six 8 week-old C57Bl/6J male mice were fed either a low-fat diet (LFD), a HFHS, or a HFHS + Salt diet for 16 weeks. Body weight, body composition, and food intake were monitored weekly. Glucose tolerance tests (GTT) and insulin concentrations were measured after 8 weeks of diet intervention to assess glucose and insulin homeostasis. Mice were euthanized at 16 weeks for liver mitochondrial respiration and tissue analysis. ResultsOver 16 weeks, the HFHS fed group gained significantly more weight than the other diet groups. Liver weights were similar in LFD and HFHS + Salt groups but higher in the HFHS group. Liver triglycerides (TAGs) were also similar between LFD and HFHS + Salt groups, while HFHS had elevated liver TAGs. Inguinal and brown adipose tissue depots were larger in both HFHS and HFHS + Salt vs. LFD. Surprisingly, the gonadal adipose tissue was significantly larger in the HFHS + Salt compared to HFHS and LFD groups - suggesting that a HFHS + Salt exacerbates gonadal adipose expansion more than typical rodent HFHS. Paradoxically, the addition of salt appears to have dampened expression of inflammation related genes (Ccl2 & Adgre1) in adipose tissue compared to HFHS alone. Metabolically, the HFHS+ Salt fed mice showed the highest glucose intolerance, followed by HFHS and then LFD groups. Liver mitochondrial respiration, assessed by changing ATP/ADP ratios, showed the HFHS group with the highest oxygen consumption, followed by HFHS + Salt, then LFD groups, highlighting differences in respiration with additional salt (HFHS vs HFHS + Salt). ConclusionWhile the excess salt mitigated some HFHS effects on weight gain and hepatic lipid accumulation, it exacerbated gonadal adipose expansion and impaired glucose tolerance. HFHS increased mitochondrial respiration, but salt addition appeared to dampen this effect. Dietary salt, within a high-fat/high-sucrose context, has differential impacts on metabolic outcomes compared to HFHS alone, underscoring the need for further research to fully understand how Western diets (high-fat, high-sucrose, and high salt) impact all aspects of metabolic health.

physiology↗

bioRxiv2023

Effects of hepatic mitochondrial pyruvate carrier deficiency on de novo lipogenesis and glycerol-mediated gluconeogenesis in mice

The liver coordinates the systemic response to nutrient deprivation and availability by producing glucose from gluconeogenesis during fasting and synthesizing lipids via de novo lipogenesis (DNL) when carbohydrates are abundant. Mitochondrial pyruvate metabolism is thought to play important roles in both gluconeogenesis and DNL. We examined the effects of hepatocyte-specific mitochondrial pyruvate carrier (MPC) deletion on the fasting-refeeding response. Rates of DNL during refeeding were impaired by liver MPC deletion, but this did not reduce intrahepatic lipid content. During fasting, glycerol is converted to glucose by two pathways; a direct cytosolic pathway essentially reversing glycolysis and an indirect mitochondrial pathway requiring the MPC. MPC deletion reduced the incorporation of 13C-glycerol into TCA cycle metabolites but not into newly synthesized glucose. However, suppression of glycerol metabolism did not affect glucose concentrations in fasted hepatocyte-specific MPC-deficient mice. Thus, glucose production by kidney and intestine may compensate for MPC deficiency in hepatocytes.

physiology↗

bioRxiv2023

Mitochondrial Pyruvate Carrier Inhibition in Hepatic Stellate Cells Attenuates Fibrosis in Nonalcoholic Steatohepatitis in Mice

Hepatic stellate cells (HSC) are non-parenchymal liver cells that produce extracellular matrix comprising fibrotic lesions in chronic liver diseases. Prior work demonstrated that mitochondrial pyruvate carrier (MPC) inhibitors suppress HSC activation and fibrosis in a mouse model of metabolic dysfunction-associated steatohepatitis (MASH). In the present study, pharmacologic or genetic inhibition of the MPC in HSC decreased expression of markers of activation in vitro. MPC knockdown also reduced the abundance of several intermediates of the TCA cycle, and diminished -ketoglutarate played a key role in attenuating HSC activation by suppressing hypoxia inducible factor-1 signaling. On high fat diets, mice with HSC-specific MPC deletion exhibited reduced circulating transaminases, numbers of HSC, and hepatic expression of markers of HSC activation and inflammation compared to wild-type mice. These data suggest that MPC inhibition modulates HSC metabolism to attenuate activation and illuminate mechanisms by which MPC inhibitors could prove therapeutically beneficial for treating MASH.

physiology↗

bioRxiv2023

Adipocyte lipin 1 is positively associated with metabolic health in humans and regulates systemic metabolism in mice.

Dysfunctional adipose tissue is believed to promote the development of hepatic steatosis and systemic insulin resistance, but many of the mechanisms involved are still unclear. Lipin 1 catalyzes the conversion of phosphatidic acid to diacylglycerol (DAG), the penultimate step of triglyceride synthesis, which is essential for lipid storage. Herein we found that adipose tissue LPIN1 expression is decreased in people with obesity compared to lean subjects and low LPIN1 expression correlated with multi-tissue insulin resistance and increased rates of hepatic de novo lipogenesis. Comprehensive metabolic and multi-omic phenotyping demonstrated that adipocyte-specific Lpin1-/- mice had a metabolically-unhealthy phenotype, including liver and skeletal muscle insulin resistance, hepatic steatosis, increased hepatic de novo lipogenesis, and transcriptomic signatures of nonalcoholic steatohepatitis that was exacerbated by high-fat diets. We conclude that adipocyte lipin 1-mediated lipid storage is vital for preserving adipose tissue and systemic metabolic health and its loss predisposes mice to nonalcoholic steatohepatitis.

physiology↗

bioRxiv2022

Dynamic changes in the mouse hepatic lipidome following warm ischemia reperfusion injury

Liver failure secondary to nonalcoholic fatty liver disease (NAFLD) has become the most common cause for liver transplantation in many parts of the world. Moreover, the prevalence of NAFLD not only increases the demand for liver transplantation, but also limits the supply of suitable donor organs because steatosis predisposes grafts to ischemia-reperfusion injury (IRI). There are currently no pharmacological interventions to limit hepatic IR injury because the mechanisms by which steatosis leads to increased injury are unclear. To identify potential novel mediators of IR injury, we used liquid chromatography and mass spectrometry to assess temporal changes in the hepatic lipidome in steatotic and non-steatotic livers after warm IRI in mice. Our untargeted analyses revealed distinct differences between the steatotic and non-steatotic response to IRI and highlighted dynamic changes in lipid composition with marked changes in glycerolipids and glycerophospholipids. These findings enhance our knowledge of the lipidomic changes that occur following IRI and provide a foundation for future mechanistic studies. A better understanding of the mechanisms underlying such changes will lead to novel therapeutic strategies to combat IR injury.

biochemistry↗

bioRxiv2022

Monoacylglycerol O-acyltransferase 1 is required for adipocyte differentiation in vitro but does not affect adiposity in mice

ObjectiveMonoacylglycerol O-acyltransferase 1 (Mogat1), a lipogenic enzyme that converts monoacylglycerol to diacylglycerol, is highly expressed in adipocytes and may regulate lipolysis by re-esterifying fatty acids released during times when lipolytic rates are low. However, the role of Mogat1 in regulating adipocyte fat storage during differentiation and diet-induced obesity is relatively understudied. MethodsHere we generated adipocyte-specific Mogat1 knockout mice and subjected them to a high-fat diet to determine the effects of Mogat1 deficiency on diet-induced obesity. We also used Mogat1 floxed mice to develop preadipocyte cell lines wherein Mogat1 could be conditionally knocked out to study adipocyte differentiation in vitro. ResultsIn preadipocytes, we found that Mogat1 knockout at the onset of preadipocyte differentiation prevented the accumulation of glycerolipids and reduced the differentiation capacity of preadipocytes. However, the loss of adipocyte Mogat1 did not affect weight gain or fat mass induced by high-fat diet in mice. Furthermore, loss of Mogat1 in adipocytes did not affect plasma lipid or glucose concentrations or insulin tolerance. ConclusionsThese data suggest Mogat1 may play a role in adipocyte differentiation in vitro but not adipose tissue expansion in response to nutrient overload in mice. STUDY IMPORTANCEO_ST_ABSWhat is already known?C_ST_ABSO_LIAdipose tissue expansion through adipocyte precursor cell differentiation is critical for proper lipid storage during nutrient overload. C_LIO_LIMonoacylglycerol O-acyltransferase 1 (Mogat1), a lipogenic enzyme, is highly induced during adipocyte differentiation of human and mouse precursor cells and is reduced in patients with obesity and metabolic dysfunction. C_LI What does this study add?O_LIMogat1 deletion during early adipocyte differentiation reduces differentiation capacity, adipogenic gene expression and lowers glycerolipid content of differentiated adipocytes. C_LIO_LIAdipocyte Mogat1 expression is dispensable for adiposity and metabolic outcomes high-fat fed mice and suggests compensation from other glycerolipid synthesis enzymes. C_LI How might these results change the direction of research?O_LIUnderstanding the molecular mechanisms of glycerolipid metabolism healthy adipose tissue expansion. C_LI

molecular biology↗

bioRxiv2021

Silencing alanine transaminase 2 in diabetic liver attenuates hyperglycemia by reducing gluconeogenesis from amino acids

Hepatic gluconeogenesis from amino acids contributes significantly to diabetic hyperglycemia, but the molecular mechanisms involved are incompletely understood. Alanine transaminases (ALT1 and ALT2) catalyze the interconversion of alanine and pyruvate, which is required for gluconeogenesis from alanine. We found that ALT2 was overexpressed in liver of diet-induced obese and db/db mice and that the expression of the gene encoding ALT2 (GPT2) was downregulated following bariatric surgery in people with obesity. The increased hepatic expression of Gpt2 in db/db liver was mediated by activating transcription factor 4; an endoplasmic reticulum stress-activated transcription factor. Hepatocyte-specific knockout of Gpt2 attenuated incorporation of 13C-alanine into newly synthesized glucose by hepatocytes. In vivo Gpt2 knockdown or knockout in liver had no effect on glucose concentrations in lean mice, but Gpt2 suppression alleviated hyperglycemia in db/db mice. These data suggest that ALT2 plays a significant role in hepatic gluconeogenesis from amino acids in diabetes.

physiology↗

bioRxiv2020

Glucolipotoxicity-induced Mig6 desensitizes EGFR signaling and promotes pancreatic beta cell death

A loss of functional beta cell mass is a final etiological event in the development of frank type 2 diabetes (T2D). To preserve or expand beta cells and therefore treat/prevent T2D, growth factors have been considered therapeutically but have largely failed to achieve robust clinical success. The molecular mechanisms preventing the activation of mitogenic signaling pathways from maintaining functional beta cell mass during the development of T2D remain unknown. We speculated that endogenous negative effectors of mitogenic signaling cascades impede beta cell survival/expansion. Thus, we tested the hypothesis that a stress-inducible epidermal growth factor receptor (EGFR) inhibitor, Mitogen-inducible gene 6 (Mig6), regulates beta cell fate in a T2D milieu. To this end, we determined that: 1) glucolipotoxicity (GLT) induces Mig6, thereby blunting EGFR signaling cascades, and 2) Mig6 mediates molecular events regulating beta cell survival/death. We discovered that GLT impairs EGFR activation, and Mig6 is elevated in human islets from T2D donors as well as GLT-treated rodent islets and 832/13 INS-1 beta cells. Mig6 is essential for GLT-induced EGFR desensitization, as Mig6 suppression rescued the GLT-impaired EGFR and ERK1/2 activation. Further, Mig6 mediated EGFR but not insulin-like growth factor-1 receptor nor hepatocyte growth factor receptor activity in beta cells. Finally, we identified that elevated Mig6 augmented beta cell apoptosis, as Mig6 suppression reduced apoptosis during GLT. In conclusion, we established that T2D and GLT induce Mig6 in pancreatic beta cells. The elevated Mig6 desensitizes EGFR signaling and induces beta cell death. Our findings suggest that Mig6 could be a novel therapeutic target for T2D, as blocking Mig6 could possibly enhance mitogenic signaling cascades in a diabetic milieu to promote beta cell survival and prevent beta cell death.

cell biology↗

bioRxiv2020

Mig6 decreases hepatic EGFR activation and survival during saturated fatty acid-induced endoplasmic reticulum stress

Hyperlipidemia associated with obesity and type 2 diabetes (T2D) promotes excess hepatic lipid storage (steatosis) and endoplasmic reticulum (ER) stress, thereby reducing hepatic cell proliferation and survival. An important receptor tyrosine kinase controlling liver proliferation and survival is the epidermal growth factor receptor (EGFR). EGFR expression and activation are decreased during steatosis in humans and several animal models of obesity. Therefore, restoring EGFR activation in obesity-induced ER stress and diabetes could restore the livers capacity for survival and regeneration. As an inducible feedback inhibitor of EGFR activity, mitogen-inducible gene 6 (Mig6) is a novel target for enhancing EGFR signaling during diet-induced obesity (DIO) and T2D. Thus, we hypothesized hepatic ER stress induces Mig6 expression and decreases EGFR activation during DIO and diabetes. We identified that Mig6 expression was increased during obesity-induced insulin resistance in C57Bl/6J mice fed a high fat diet. We also discovered that both pharmacological- and fatty acid-driven ER stress increased Mig6 expression and decreased EGF-mediated EGFR activation in primary rat hepatocytes and cell lines. Furthermore, siRNA-mediated Mig6 knockdown restored EGFR signaling and reduced caspase 3/7 activation during ER stress. Therefore, we conclude Mig6 is increased during ER stress in DIO, thereby reducing EGFR activation and enhancing cell death. The implications are the induction of Mig6 during DIO and diabetes may decrease hepatocyte survival, thus hindering cellular repair and regenerative mechanisms.

physiology↗

bioRxiv2020

Antisense oligonucleotides against monoacylglycerol acyltransferase 1 (Mogat1) improve glucose metabolism independently of Mogat1

ObjectiveMonoacylglycerol acyltransferase (MGAT) enzymes catalyze the synthesis of diacylglycerol from monoacylglycerol. Previous work has suggested the importance of MGAT activity in the development of obesity-related hepatic insulin resistance. Indeed, antisense oligonucleotide (ASO)-mediated knockdown of the gene encoding MGAT1, Mogat1, reduced hepatic MGAT activity and improved glucose tolerance and insulin resistance in high fat diet (HFD) fed mice. However, recent work has suggested that some ASOs may have off-target effects on body weight and metabolic parameters via activation of the interferon alpha/beta receptor 1 (IFNAR-1) pathway. MethodsMice with whole-body Mogat1 knockout or a floxed allele for Mogat1 to allow for liver-specific Mogat1-knockout (by either a liver-specific transgenic or adeno-associated virus-driven Cre recombinase) were generated. These mice were placed on a high fat diet and glucose metabolism and insulin sensitivity was assessed after 16 weeks on diet. In some experiments, mice were treated with control or Mogat1 or control ASOs in the presence or absence of IFNAR-1 neutralizing antibody. ResultsGenetic deletion of hepatic Mogat1, either acutely or chronically, did not improve hepatic steatosis, glucose tolerance, or insulin sensitivity in HFD-fed mice. Furthermore, constitutive Mogat1 knockout in all tissues actually exacerbated HFD-induced weight gain, insulin resistance, and glucose intolerance on a HFD. Despite markedly reduced Mogat1 expression, liver MGAT activity was unaffected in all knockout mouse models. Mogat1 overexpression hepatocytes increased liver MGAT activity and TAG content in low-fat fed mice, but did not cause insulin resistance. Interestingly, Mogat1 ASO treatment improved glucose tolerance in both wild-type and Mogat1 null mice, suggesting an off target effect. Inhibition of IFNAR-1 did not block the effect of Mogat1 ASO on glucose homeostasis. ConclusionThese results indicate that genetic loss of Mogat1 does not affect hepatic MGAT activity or metabolic homeostasis on HFD and show that Mogat1 ASOs improve glucose metabolism through effects independent of targeting Mogat1 or activation of IFNAR-1 signaling. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=65 SRC="FIGDIR/small/238535v1_ufig1.gif" ALT="Figure 1"> View larger version (18K): org.highwire.dtl.DTLVardef@18d43c4org.highwire.dtl.DTLVardef@15c1974org.highwire.dtl.DTLVardef@18b396dorg.highwire.dtl.DTLVardef@16745bf_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIMogat1 liver-specific KO or KD does not improve metabolism in HFD fed mice. C_LIO_LIWhole-body Mogat1-deletion impairs insulin tolerance in HFD fed mice. C_LIO_LIMogat1 ASOs improves whole body metabolism independently of gene knockdown. C_LIO_LIBlockade of the INFR response does not prevent off-target effects of Mogat1 ASOs. C_LI

physiology↗