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As the obesity epidemic worsens, the prevalence of maternal obesity is expected to rise. Both high-fat and high-sucrose diets are known to promote maternal obesity and several studies have elucidated the molecular influence of high-fat feeding on female reproduction. However, to date, the molecular impact of a high-sucrose diet on maternal obesity remains to be investigated. Using our previously reported Drosophila high-sucrose maternal obesity model, we sought to determine how excess dietary sucrose impacted the ovary. High-sucrose diet (HSD) fed adult females developed systemic insulin resistance and exhibited an ovarian phenotype characterized by excess accumulation of lipids and cholesterol in the ovary, decreased ovary size, and impaired egg maturation. We also observed decreased expression of antioxidant genes and increased protein carbonylation in the ovaries of HSD females. HSD females laid fewer eggs; however, the overall survival of offspring was unchanged relative to lean control females. Ovaries of HSD females had increased mitochondrial DNA copy number and decreased expression of key mitochondrial regulators, suggestive of an ineffective compensatory response to mitochondrial dysfunction. Mitochondrial alterations were also observed in male offspring of obese females. This study demonstrates that high-sucrose-induced maternal obesity promotes insulin resistance, while disrupting ovarian metabolism and function.

Lipin 1 is a bifunctional protein that is a transcriptional regulator and has phosphatidic acid (PA) phosphohydrolase activity, which dephosphorylates PA to generate diacylglycerol. Human lipin 1 mutations lead to episodic rhabdomyolysis, and some affected patients exhibit cardiac abnormalities, including exercise-induced cardiac dysfunction and cardiac triglyceride accumulation. Furthermore, lipin 1 expression is deactivated in failing heart, but the effects of lipin 1 deactivation in myocardium are incompletely understood. We generated mice with cardiac-specific lipin 1 KO (cs- Lpin1 –/– ) to examine the intrinsic effects of lipin 1 in the myocardium. Cs- Lpin1 –/– mice had normal systolic cardiac function but mild cardiac hypertrophy. Compared with littermate control mice, PA content was higher in cs- Lpin1 –/– hearts, which also had an unexpected increase in diacylglycerol and triglyceride content. Cs- Lpin1 –/– mice exhibited diminished cardiac cardiolipin content and impaired mitochondrial respiration rates when provided with pyruvate or succinate as metabolic substrates. After transverse aortic constriction–induced pressure overload, loss of lipin 1 did not exacerbate cardiac hypertrophy or dysfunction. However, loss of lipin 1 dampened the cardiac ionotropic response to dobutamine and exercise endurance in association with reduced protein kinase A signaling. These data suggest that loss of lipin 1 impairs cardiac functional reserve, likely due to effects on glycerolipid homeostasis, mitochondrial function, and protein kinase A signaling.

Understanding how cells remember previous mechanical environments to influence their fate, or mechanical memory, informs the design of biomaterials and therapies in medicine. Current regeneration therapies require two-dimensional (2D) cell expansion processes to achieve large cell populations critical for the repair of damaged (e.g. connective and musculoskeletal) tissues. However, the influence of mechanical memory on cell fate following expansion is unknown, and mechanisms defining how physical environments influence the therapeutic potential of cells remain poorly understood. Here, we show that the organization of histone H3 trimethylated at lysine 9 (H3K9me3) and expression of tissue-identifying genes in primary cartilage cells (chondrocytes) transferred to three-dimensional (3D) hydrogels depends on the number of previous population doublings on tissue culture plastic during 2D cell expansion. Decreased levels of H3K9me3 occupying promoters of dedifferentiation genes after the 2D culture were also retained in 3D culture. Suppression of H3K9me3 during expansion of cells isolated from a murine model similarly resulted in the loss of the chondrocyte phenotype and global remodeling of nuclear architecture. In contrast, increasing levels of H3K9me3 through inhibiting H3K9 demethylases partially rescued the chondrogenic nuclear architecture and gene expression, which has important implications for tissue repair therapies, where expansion of large numbers of phenotypically-suitable cells is required. Overall, our findings indicate mechanical memory in primary cells is encoded in the chromatin architecture, which impacts cell fate and the phenotype of expanded cells.SIGNIFICANCE STATEMENTTissue regeneration procedures, such as cartilage defect repair (e.g. Matrix-induced Autologous Chondrocyte Implantation) often require cell expansion processes to achieve sufficient cells to transplant into an in vivo environment. However, the chondrocyte cell expansion on 2D stiff substrates induces epigenetic changes that persist even when the chondrocytes are transferred to a different (e.g. 3D) or in vivo environment. Treatments to alter epigenetic gene regulation may be a viable strategy to improve existing cartilage defect repair procedures and other tissue engineering procedures that involve cell expansion.

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