Adipose tissue is a major site of energy storage and has a role in the regulation of metabolism through the release of adipokines. Here we show that mice with an adipose-tissue-specific knockout of the microRNA (miRNA)-processing enzyme Dicer (ADicerKO), as well as humans with lipodystrophy, exhibit a substantial decrease in levels of circulating exosomal miRNAs. Transplantation of both white and brown adipose tissue—brown especially—into ADicerKO mice restores the level of numerous circulating miRNAs that are associated with an improvement in glucose tolerance and a reduction in hepatic Fgf21 mRNA and circulating FGF21. This gene regulation can be mimicked by the administration of normal, but not ADicerKO, serum exosomes. Expression of a human-specific miRNA in the brown adipose tissue of one mouse in vivo can also regulate its 3′ UTR reporter in the liver of another mouse through serum exosomal transfer. Thus, adipose tissue constitutes an important source of circulating exosomal miRNAs, which can regulate gene expression in distant tissues and thereby serve as a previously undescribed form of adipokine.

Both intrinsic cell state changes and variations in the composition of stem cell populations have been implicated as contributors to aging. We used single-cell RNA-seq to dissect variability in hematopoietic stem cell (HSC) and hematopoietic progenitor cell populations from young and old mice from two strains. We found that cell cycle dominates the variability within each population and that there is a lower frequency of cells in the G1 phase among old compared with young long-term HSCs, suggesting that they traverse through G1 faster. Moreover, transcriptional changes in HSCs during aging are inversely related to those upon HSC differentiation, such that old short-term (ST) HSCs resemble young long-term (LT-HSCs), suggesting that they exist in a less differentiated state. Our results indicate both compositional changes and intrinsic, population-wide changes with age and are consistent with a model where a relationship between cell cycle progression and self-renewal versus differentiation of HSCs is affected by aging and may contribute to the functional decline of old HSCs.

The considerable potential of Cre recombinase as a tool for in vivo fate‐mapping studies depends on the availability of reliable reporter mice. By targeting a tandem‐dimer red fluorescent protein (tdRFP) with advanced spectral and biological properties into the ubiquitously expressed ROSA26 locus of C57BL/6‐ES cells, we have generated a novel inbred Cre‐reporter mouse with several unique characteristics. We directly demonstrate the usefulness of our reporter strain in inter‐crosses with a “universal Cre‐deleter” strain and with mice expressing Cre recombinase in a T lineage‐specific manner. Cytofluorometric and histological analyses illustrate: (i) non‐toxicity and extraordinary brightness of the fluorescent reporter, allowing quantitative detection and purification of labeled cells with highest accuracy, (ii) reliable Cre‐mediated activation of tdRFP from an antisense orientation relative to ROSA26 transcription, effectively excluding “leaky” reporter expression, (iii) absence of gene expression variegation effects, (iv) quantitative detection of tdRFP‐expressing cells even in paraformaldehyde‐fixed tissue sections, and (v) full compatibility with GFP/YFP‐based fluorescent markers in multicolor experiments. Taken together, the data show that our C57BL/6‐inbred reporter mice are ideally suited for sophisticated lineage‐tracing experiments requiring sensitive and quantitative detection/purification of live Cre‐expressing cells and their progeny.

Overconsumption of high-fat diet (HFD) and sugar-sweetened beverages are risk factors for developing obesity, insulin resistance, and fatty liver disease. Here we have dissected mechanisms underlying this association using mice fed either chow or HFD with or without fructose- or glucose-supplemented water. In chow-fed mice, there was no major physiological difference between fructose and glucose supplementation. On the other hand, mice on HFD supplemented with fructose developed more pronounced obesity, glucose intolerance, and hepatomegaly as compared to glucose-supplemented HFD mice, despite similar caloric intake. Fructose and glucose supplementation also had distinct effects on expression of the lipogenic transcription factors ChREBP and SREBP1c. While both sugars increased ChREBP-β, fructose supplementation uniquely increased SREBP1c and downstream fatty acid synthesis genes, resulting in reduced liver insulin signaling. In contrast, glucose enhanced total ChREBP expression and triglyceride synthesis but was associated with improved hepatic insulin signaling. Metabolomic and RNA sequence analysis confirmed dichotomous effects of fructose and glucose supplementation on liver metabolism in spite of inducing similar hepatic lipid accumulation. Ketohexokinase, the first enzyme of fructose metabolism, was increased in fructose-fed mice and in obese humans with steatohepatitis. Knockdown of ketohexokinase in liver improved hepatic steatosis and glucose tolerance in fructose-supplemented mice. Thus, fructose is a component of dietary sugar that is distinctively associated with poor metabolic outcomes, whereas increased glucose intake may be protective.

In chronic kidney disease, fibroblast dysfunction causes renal fibrosis and renal anemia. Renal fibrosis is mediated by the accumulation of myofibroblasts, whereas renal anemia is mediated by the reduced production of fibroblast-derived erythropoietin, a hormone that stimulates erythropoiesis. Despite their importance in chronic kidney disease, the origin and regulatory mechanism of fibroblasts remain unclear. Here, we have demonstrated that the majority of erythropoietin-producing fibroblasts in the healthy kidney originate from myelin protein zero–Cre (P0-Cre) lineage-labeled extrarenal cells, which enter the embryonic kidney at E13.5. In the diseased kidney, P0-Cre lineage-labeled fibroblasts, but not fibroblasts derived from injured tubular epithelial cells through epithelial-mesenchymal transition, transdifferentiated into myofibroblasts and predominantly contributed to fibrosis, with concomitant loss of erythropoietin production. We further demonstrated that attenuated erythropoietin production in transdifferentiated myofibroblasts was restored by the administration of neuroprotective agents, such as dexamethasone and neurotrophins. Moreover, the in vivo administration of tamoxifen, a selective estrogen receptor modulator, restored attenuated erythropoietin production as well as fibrosis in a mouse model of kidney fibrosis. These findings reveal the pathophysiological roles of P0-Cre lineage-labeled fibroblasts in the kidney and clarify the link between renal fibrosis and renal anemia.