Cells must duplicate their mass in order to proliferate. Glucose and glutamine are the major nutrients consumed by proliferating mammalian cells, but the extent to which these and other nutrients ...contribute to cell mass is unknown. We quantified the fraction of cell mass derived from different nutrients and found that the majority of carbon mass in cells is derived from other amino acids, which are consumed at much lower rates than glucose and glutamine. While glucose carbon has diverse fates, glutamine contributes most to protein, suggesting that glutamine's ability to replenish tricarboxylic acid cycle intermediates (anaplerosis) is primarily used for amino acid biosynthesis. These findings demonstrate that rates of nutrient consumption are indirectly associated with mass accumulation and suggest that high rates of glucose and glutamine consumption support rapid cell proliferation beyond providing carbon for biosynthesis.
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•Glucose and glutamine are not the sources of the majority of mammalian cell mass•Non-glutamine amino acids provide abundant carbon and nitrogen to proliferating cells•Non-proliferating mammalian cells exhibit variable degrees of cell mass turnover•Nutrient fates are determined, showing that glutamine contributes primarily to protein
Hosios et al. analyze nutrient contributors to cell mass and find that although glucose and glutamine have the highest consumption rates, the majority of proliferative cell mass actually derives from non-glutamine amino acids. This quantitative analysis provides a framework for understanding proliferative metabolism of mammalian cells and cancer metabolism.
Cell therapy can improve cardiac function in animals and humans after injury, but the mechanism is unclear. We performed cell therapy experiments in genetically engineered mice that permanently ...express green fluorescent protein (GFP) only in cardiomyocytes after a pulse of 4-OH-tamoxifen. Myocardial infarction diluted the GFP
+ cardiomyocyte pool, indicating refreshment by non-GFP
+ progenitors. Cell therapy with bone marrow-derived c-kit
+ cells, but not mesenchymal stem cells, further diluted the GFP
+ pool, consistent with c-kit
+ cell-mediated augmentation of cardiomyocyte progenitor activity. This effect could not be explained by transdifferentiation to cardiomyocytes by exogenously delivered c-kit
+ cells or by cell fusion. Therapy with c-kit
+ cells but not mesenchymal stem cells improved cardiac function. These findings suggest that stimulation of endogenous cardiogenic progenitor activity is a critical mechanism of cardiac cell therapy.
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► c-kit
+ cell therapy stimulates endogenous cardiomyocyte progenitors ► Nkx2.5- and Gata4-expressing progenitors increase in the infarct border zone ► c-kit
+ cell therapy leads to improved cardiac function ► No evidence for cardiomyocyte transdifferentiation by bone marrow progenitors
Long noncoding RNAs (lncRNAs) are often expressed in a development-specific manner, yet little is known about their roles in lineage commitment. Here, we identified Braveheart (Bvht), a ...heart-associated lncRNA in mouse. Using multiple embryonic stem cell (ESC) differentiation strategies, we show that Bvht is required for progression of nascent mesoderm toward a cardiac fate. We find that Bvht is necessary for activation of a core cardiovascular gene network and functions upstream of mesoderm posterior 1 (MesP1), a master regulator of a common multipotent cardiovascular progenitor. We also show that Bvht interacts with SUZ12, a component of polycomb-repressive complex 2 (PRC2), during cardiomyocyte differentiation, suggesting that Bvht mediates epigenetic regulation of cardiac commitment. Finally, we demonstrate a role for Bvht in maintaining cardiac fate in neonatal cardiomyocytes. Together, our work provides evidence for a long noncoding RNA with critical roles in the establishment of the cardiovascular lineage during mammalian development.
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► Braveheart (Bvht) is a heart-associated long noncoding RNA in the mouse ► In embryonic stem cells, Bvht is necessary for cardiovascular lineage commitment ► Bvht functions upstream of MesP1 to regulate a core cardiac gene network ► Bvht interacts with PRC2 to mediate epigenetic activation of the cardiac program
Braveheart (Bvht) is a heart-associated long noncoding RNA that is necessary for cardiovascular lineage commitment in embryonic stem cells. Its interaction with the polycomb complex suggests that it may regulate the cardiac program epigenetically.
Although recent studies have revealed that heart cells are generated in adult mammals, the frequency of generation and the source of new heart cells are not yet known. Some studies suggest a high ...rate of stem cell activity with differentiation of progenitors to cardiomyocytes. Other studies suggest that new cardiomyocytes are born at a very low rate, and that they may be derived from the division of pre-existing cardiomyocytes. Here we show, by combining two different pulse-chase approaches--genetic fate-mapping with stable isotope labelling, and multi-isotope imaging mass spectrometry--that the genesis of cardiomyocytes occurs at a low rate by the division of pre-existing cardiomyocytes during normal ageing, a process that increases adjacent to areas of myocardial injury. We found that cell cycle activity during normal ageing and after injury led to polyploidy and multinucleation, but also to new diploid, mononucleate cardiomyocytes. These data reveal pre-existing cardiomyocytes as the dominant source of cardiomyocyte replacement in normal mammalian myocardial homeostasis as well as after myocardial injury.
Fat mass expansion occurs by adipocyte hypertrophy or recruitment of differentiating adipocyte progenitors, the relative balance of which may impact systemic metabolism. We measured adipogenesis in ...murine subcutaneous (sWAT) and visceral white adipose tissue (vWAT) using stable isotope methodology and then modeled adipocyte turnover. Birth and death rates were similar within depots; however, turnover was higher in vWAT relative to sWAT. In juvenile mice, obesity increased adipogenesis, but in adults, this was only seen in vWAT after prolonged high-fat feeding. Statistical modeling suggests differentiation of adipocyte progenitors without an accompanying self-renewing division step may partially explain the age-dependent decline in hyperplastic potential. Additional metabolic interrogation of obese mice demonstrated an association between adipocyte turnover and insulin sensitivity. These data therefore identify adipocyte hypertrophy as the dominant mechanism of adult fat mass expansion and support the paradoxical concept that metabolic disease ensues due to a failure of adipose tissue plasticity.
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•Stable isotopes can be used to quantitatively track adipogenesis in vivo•Visceral fat is more plastic than subcutaneous fat•Fat cell hypertrophy is the dominant mechanism of fat mass expansion in the adult•Subcutaneous adipogenesis is associated with measures of insulin sensitivity
The role of new fat cell generation in obesity is unclear. Using stable isotope methodology, Kim et al. demonstrate age-dependent decline in adipogenesis. Obesity increased adipogenesis during postnatal development, but this plasticity disappeared in adulthood. A positive association between adipocyte turnover and metabolic health suggests that adipogenesis is an adaptive response.
In mice, FGF21 is rapidly induced by fasting, mediates critical aspects of the adaptive starvation response, and displays a number of positive metabolic properties when administered ...pharmacologically. In humans, however, fasting does not consistently increase FGF21, suggesting a possible evolutionary divergence in FGF21 function. Moreover, many key aspects of FGF21 function in mice have been identified in the context of transgenic overexpression or administration of supraphysiologic doses, rather than in a physiologic setting. Here, we explored the dynamics and function of FGF21 in human volunteers during a 10-day fast. Unlike mice, which show an increase in circulating FGF21 after only 6 hours, human subjects did not have a notable surge in FGF21 until 7 to 10 days of fasting. Moreover, we determined that FGF21 induction was associated with decreased thermogenesis and adiponectin, an observation that directly contrasts with previous reports based on supraphysiologic dosing. Additionally, FGF21 levels increased after ketone induction, demonstrating that endogenous FGF21 does not drive starvation-mediated ketogenesis in humans. Instead, a longitudinal analysis of biologically relevant variables identified serum transaminases--markers of tissue breakdown--as predictors of FGF21. These data establish FGF21 as a fasting-induced hormone in humans and indicate that FGF21 contributes to the late stages of adaptive starvation, when it may regulate the utilization of fuel derived from tissue breakdown.
The most common form of heart failure occurs with normal systolic function and often involves cardiac hypertrophy in the elderly. To clarify the biological mechanisms that drive cardiac hypertrophy ...in aging, we tested the influence of circulating factors using heterochronic parabiosis, a surgical technique in which joining of animals of different ages leads to a shared circulation. After 4 weeks of exposure to the circulation of young mice, cardiac hypertrophy in old mice dramatically regressed, accompanied by reduced cardiomyocyte size and molecular remodeling. Reversal of age-related hypertrophy was not attributable to hemodynamic or behavioral effects of parabiosis, implicating a blood-borne factor. Using modified aptamer-based proteomics, we identified the TGF-β superfamily member GDF11 as a circulating factor in young mice that declines with age. Treatment of old mice to restore GDF11 to youthful levels recapitulated the effects of parabiosis and reversed age-related hypertrophy, revealing a therapeutic opportunity for cardiac aging.
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•Heterochronic parabiosis reverses age-related cardiac hypertrophy•The antihypertrophic effect is not due to hemodynamic or behavioral factors•GDF11 is a circulating TGF-β family member that declines with age•Restoration of youthful GDF11 levels reverses age-related cardiac hypertrophy
Parabiosis experiments in mice unravel a role for the TGF-β family member GDF-11 as a negative regulator of age-associated cardiac hypertrophy.
Loss of cardiomyocytes is a major cause of heart failure, and while the adult heart has a limited capacity for cardiomyogenesis, little is known about what regulates this ability or whether it can be ...effectively harnessed. Here we show that 8 weeks of running exercise increase birth of new cardiomyocytes in adult mice (~4.6-fold). New cardiomyocytes are identified based on incorporation of
N-thymidine by multi-isotope imaging mass spectrometry (MIMS) and on being mononucleate/diploid. Furthermore, we demonstrate that exercise after myocardial infarction induces a robust cardiomyogenic response in an extended border zone of the infarcted area. Inhibition of miR-222, a microRNA increased by exercise in both animal models and humans, completely blocks the cardiomyogenic exercise response. These findings demonstrate that cardiomyogenesis can be activated by exercise in the normal and injured adult mouse heart and suggest that stimulation of endogenous cardiomyocyte generation could contribute to the benefits of exercise.
Mass spectrometry with stable isotope labels has been seminal in discovering the dynamic state of living matter, but is limited to bulk tissues or cells. We developed multi-isotope imaging mass ...spectrometry (MIMS) that allowed us to view and measure stable isotope incorporation with submicrometre resolution. Here we apply MIMS to diverse organisms, including Drosophila, mice and humans. We test the 'immortal strand hypothesis', which predicts that during asymmetric stem cell division chromosomes containing older template DNA are segregated to the daughter destined to remain a stem cell, thus insuring lifetime genetic stability. After labelling mice with (15)N-thymidine from gestation until post-natal week 8, we find no (15)N label retention by dividing small intestinal crypt cells after a four-week chase. In adult mice administered (15)N-thymidine pulse-chase, we find that proliferating crypt cells dilute the (15)N label, consistent with random strand segregation. We demonstrate the broad utility of MIMS with proof-of-principle studies of lipid turnover in Drosophila and translation to the human haematopoietic system. These studies show that MIMS provides high-resolution quantification of stable isotope labels that cannot be obtained using other techniques and that is broadly applicable to biological and medical research.
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