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Microcystin-LR (MCLR) is a hepatotoxic cyanotoxin reported to cause a phenotype similar to nonalcoholic steatohepatitis (NASH). NASH is a common progressive liver disease that advances in severity due to exogenous stressors such as poor diet and toxicant exposure. Our objective was to determine how sub-chronic MCLR toxicity affects preexisting diet-induced NASH. Sprague-Dawley rats were fed one of three diets for 10 weeks: control, methionine and choline deficient (MCD), or high fat/high cholesterol (HFHC). After six weeks of diet, animals received vehicle, 10 µg/kg, or 30 µg/kg MCLR via intraperitoneal injection every other day for the final 4 weeks. Incidence and severity scoring of histopathology endpoints suggested that MCLR toxicity drove NASH to a less fatty and more fibrotic state. In general, expression of genes involved in de novo lipogenesis and fatty acid esterification were altered in favor of decreased steatosis. The higher MCLR dose increased expression of genes involved in fibrosis and inflammation in the control and HFHC groups. These data suggest MCLR toxicity in the context of preexisting NASH may drive the liver to a more severe phenotype that resembles burnt-out NASH.

Neurofibrillary tangles are a pathological hallmark of Alzheimer’s disease, and their levels correlate with the severity of cognitive dysfunction in humans. However, experimental evidence suggests that soluble tau species cause cognitive deficits and memory impairment. Our recent study suggests that caspase-2 (Casp2)-catalyzed tau cleavage at aspartate 314 mediates synaptic dysfunction and memory impairment in mouse and cellular models of neurodegenerative disorders. Δtau314, the C-terminally-truncated cleavage products, are soluble and present in human brain. In addition, levels of Δtau314 proteins are elevated in the brain of the cognitively impaired individuals compared to the cognitively normal individuals, indicating a possible role for Δtau314 proteins in cognitive deterioration. Here we show that (1) Δtau314 proteins are present in the inferior temporal gyrus of human brains; (2) Δtau314 proteins are generated from all six tau splicing isoforms, (3) levels of both Casp2 and Δtau314 proteins are elevated in cognitively impaired individuals compared to cognitively normal individuals, and (4) levels of Δtau314 proteins show a modest predictive value for dementia. These findings advance our understanding of the characteristics of Δtau314 proteins and their relevance to cognitive dysfunction and shed light on the contribution of Casp2-mediated Δtau314 production to cognitive deterioration.

The central integration of peripheral neural signals is one mechanism by which systemic energy homeostasis is regulated. Previously, increased acute food intake following the chemical reduction of hepatic fatty acid oxidation and ATP levels was prevented by common hepatic branch vagotomy (HBV). However, possible offsite actions of the chemical compounds confound the precise role of liver energy metabolism. Herein, we used a hepatocyte PGC1a heterozygous (LPGC1a) mouse model, with associated reductions in mitochondrial fatty acid oxidation and respiratory capacity, to assess the role of liver energy metabolism in systemic energy homeostasis. LPGC1a male, but not female, mice had a 70% greater high-fat/high-sucrose (HFHS) diet-induced weight gain compared to wildtype (WT) mice (p < 0.05). The greater weight gain was associated with altered feeding behavior and lower activity energy expenditure during the HFHS diet in LPGC1a males. WT and LPGC1a mice underwent sham surgery or HBV to assess whether vagal signaling was involved in the HFHS-induced weight gain of male LPGC1a mice. HBV increased HFHS-induced weight gain (85%, p < 0.05) in male WT mice, but not LPGC1a mice. These data demonstrate a sex-specific role of reduced liver energy metabolism in acute diet-induced weight gain, and the need for a more nuanced assessment of the role of vagal signaling in short-term diet-induced weight gain.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Abstract Central integration of peripheral neural signals is one mechanism by which systemic energy homeostasis is regulated. Previous work described increased acute food intake following chemical reduction of hepatic fatty acid oxidation and ATP levels, which was prevented by common hepatic branch vagotomy (HBV). However, possible offsite actions of the chemical compounds confound the precise role of liver energy metabolism. Herein, we used a liver-specific PGC1a heterozygous (LPGC1a) mouse model, with associated reductions in mitochondrial fatty acid oxidation and respiratory capacity, to assess the role of liver energy metabolism in systemic energy homeostasis. LPGC1a male mice have 70% greater high-fat/high-sucrose (HFHS) diet-induced weight gain and 35% greater positive energy balance compared to wildtype (WT) (p<0.05). The greater energy balance was associated with altered feeding behavior and lower activity energy expenditure during HFHS in LPGC1a males. Importantly, no differences in HFHS-induced weight gain or energy metabolism was observed between female WT and LPGC1a mice. WT and LPGC1a mice underwent sham or HBV to assess whether vagal signaling was involved in HFHS-induced weight gain of male LPGC1a mice. HBV increased HFHS-induced weight gain (85%, p<0.05) in male WT, but not LPGC1a mice. As above, sham LPGC1a males gain 70% more weight during short-term HFHS feeding than sham WT (p<0.05). These data demonstrate a sexspecific role of reduced liver energy metabolism in acute diet-induced weight gain, and the need of more nuanced assessment of the role of vagal signaling in short-term diet-induced weight gain. Key Points Summary * Reduced liver PGC1a expression results in reduced mitochondrial fatty acid oxidation and respiratory capacity in male mice. * Male mice with reduced liver PGC1a expression (LPGC1a) demonstrate greater short-term high-fat/high-sucrose diet-induced weight gain compared to wildtype. * Greater positive energy balance during HFHS feeding in male LPGC1a mice is associated with altered food intake patterns and reduced activity energy expenditure. * Female LPGC1a mice do not have differences in short-term HFHS-induced body weight gain or energy metabolism compared to wildtype. * Disruption of vagal signaling through common hepatic branch vagotomy increases short-term HFHS-induced weight gain in male wildtype mice, but does not alter male LPGC1a weight gain. Competing Interest Statement The authors have declared no competing interest. Footnotes * Disclosures – The authors have no conflicts of interest to disclose for this research. * Grants and Support: This work was partially supported by NIH grants K01DK112967 (EMM), AHA 14POST20110034 (EMM), R01KD121497 (JPT), and VA Merit grant 1I01BX002567 (JPT).