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Pathologic expansion of white adipose tissue (WAT) in obesity is characterized by adipocyte hypertrophy, inflammation, and fibrosis; however, factors triggering this maladaptive remodeling are largely unknown. Here, we test the hypothesis that the potential to recruit new adipocytes from Pdgfrβ + preadipocytes determines visceral WAT health in obesity. We manipulate levels of Pparg , the master regulator of adipogenesis, in Pdgfrβ + precursors of adult mice. Increasing the adipogenic capacity of Pdgfrβ + precursors through Pparg overexpression results in healthy visceral WAT expansion in obesity and adiponectin-dependent improvements in glucose homeostasis. Loss of mural cell Pparg triggers pathologic visceral WAT expansion upon high-fat diet feeding. Moreover, the ability of the TZD class of anti-diabetic drugs to promote healthy visceral WAT remodeling is dependent on mural cell Pparg . These data highlight the protective effects of de novo visceral adipocyte differentiation in these settings, and suggest Pdgfrβ + adipocyte precursors as targets for therapeutic intervention in diabetes. Adipocyte hyperplasia is thought to have beneficial metabolic effects in obesity, but definitive evidence is lacking. Here, Shao et al. promote de novo formation of adipocytes in visceral white adipose tissue (WAT) of adult mice through inducible overexpression of Pparg in Pdgfrβ + preadipocytes and show that this protects from pathological WAT remodeling.

Adiponectin is a secretory protein, primarily produced in adipocytes. However, low but detectable expression of adiponectin can be observed in cell types beyond adipocytes, particularly in kidney tubular cells, but its local renal role is unknown. We assessed the impact of renal adiponectin by utilizing male inducible kidney tubular cell-specific adiponectin overexpression or knockout mice. Kidney-specific adiponectin overexpression induces a doubling of phosphoenolpyruvate carboxylase expression and enhanced pyruvate-mediated glucose production, tricarboxylic acid cycle intermediates and an upregulation of fatty acid oxidation (FAO). Inhibition of FAO reduces the adiponectin-induced enhancement of glucose production, highlighting the role of FAO in the induction of renal gluconeogenesis. In contrast, mice lacking adiponectin in the kidney exhibit enhanced glucose tolerance, lower utilization and greater accumulation of lipid species. Hence, renal adiponectin is an inducer of gluconeogenesis by driving enhanced local FAO and further underlines the important systemic contribution of renal gluconeogenesis. Adiponectin is a widely studied secretory protein produced by adipocytes. Here, the authors show that adiponectin is also expressed in the kidney where it is a major driver of fatty acid oxidation, from which the kidney derives energy for gluconeogenesis.

Insulin monotherapy can neither maintain normoglycemia in type 1 diabetes (T1D) nor prevent the long-term damage indicated by elevated glycation products in blood, such as glycated hemoglobin (HbA1c). Here we find that hyperglycemia, when unaccompanied by an acute increase in insulin, enhances itself by paradoxically stimulating hyperglucagonemia. Raising glucose from 5 to 25 mM without insulin enhanced glucagon secretion ∼two- to fivefold in InR1-G9 α cells and ∼18-fold in perfused pancreata from insulin-deficient rats with T1D. Mice with T1D receiving insulin treatment paradoxically exhibited threefold higher plasma glucagon during hyperglycemic surges than during normoglycemic intervals. Blockade of glucagon action with mAb Ac, a glucagon receptor (GCGR) antagonizing antibody, maintained glucose below 100 mg/dL and HbA1c levels below 4% in insulin-deficient mice with T1D. In rodents with T1D, hyperglycemia stimulates glucagon secretion, up-regulating phosphoenolpyruvate carboxykinase and enhancing hyperglycemia. GCGR antagonism in mice with T1D normalizes glucose and HbA1c, even without insulin. Significance Subcutaneous injections of insulin sustain life in mammals unable to produce insulin (type 1 diabetes) but do not prevent hyperglycemic and hypoglycemic swings or decrease hemoglobin A1c levels to normal amounts. In mice treated with insulin alone, repeated episodes of transient elevated blood glucose cause long-term damage. We show that in mice with type 1 diabetes treated with insulin, the transient high blood glucose levels require production of glucagon, a hormone that will cause the liver to produce more glucose. Blocking the action of glucagon with an antibody to the glucagon receptor completely normalizes blood glucose and hemoglobin A1c in the complete absence of insulin therapy. Suppressing glucagon action in combination with low-dose insulin would be a superior treatment for type 1 diabetes.

Proinflammatory signaling in adipocytes is essential for healthy adipose expansion, remodeling, and tissue integrity. We investigated the effects of targeting inflammation in either adipocytes or mammary gland epithelial cells, in the context of mammary tumor development, by locally expressing the antiinflammatory adenoviral RIDα/β protein complex in a cell type–specific manner. Suppression of adipocyte inflammation (RID ad mice) in a mammary tumor model driven by MMTV-PyMT (PyMT-RID ad mice) led to an elevated number of tumor-associated macrophages and upregulation of immunoregulatory molecules in the mammary fat pad. This was accompanied by metabolic dysfunction and abnormal mammary gland development. Importantly, this phenotype correlated with accelerated mammary tumor onset, enhanced growth, and lung metastasis. Tumors in PyMT-RID ad mice exhibited upregulated CD36 expression, suggesting enhanced fatty acid uptake. Conversely, suppression of inflammation in mammary gland epithelial cells by RIDα/β expression (RID MMTV mice) decelerated mammary tumor growth without affecting tumor onset or macrophage accumulation. These findings highlight the differential impact on tumor development exerted through the suppression of inflammatory signals in different cell types in the microenvironment. Our results underscore the role of the suppression of adipocyte inflammation leading to a tumor-friendly microenvironment, promoting mammary cancer progression. This study sheds light on the complex interplay between inflammation, specifically driven by the adipocyte, in breast cancer pathogenesis.

Extracellular vesicles (EVs) are nano-sized, membrane-delimited, particles released by cells that carry signaling macromolecules. A major pathway of EV production is potentiated by neutral sphingomyelinase 2 (SMPD3/nSMAse2), an enzyme that generates ceramide from sphingomyelin. In our attempt to study this pathway in adipocytes of male mice, we discover that the elimination of SMPD3 from adipocytes in vivo triggers a signal to surrounding immune cell-like preadipocytes to release EVs that carry SMPD3 mRNA. This results in a widespread increase in SMPD3 mRNA in purified null adipocytes without a change in the transcripts of other enzymes involved in ceramide metabolism. These results point to a selective mechanism by which specific mRNA molecules are acquired from the microenvironment to a level that can restore expression of mRNA and protein in a cell that is depleted of the corresponding genetic information. Extracellular vesicles (EVs) mediate intercellular communication by transferring signaling macromolecules. Unexpectedly, the author here identifies that adipocyte-specific loss of SMPD3 triggers neighboring preadipocytes to release EVs containing SMPD3 mRNA, restoring SMPD3 expression in genetically null adipocytes.

The G protein-coupled receptor 84 (GPR84), a medium-chain fatty acid receptor, has garnered attention because of its potential involvement in a range of metabolic conditions. However, the precise mechanisms underlying this effect remain elusive. Our study has shed light on the pivotal role of GPR84, revealing its robust expression and functional significance within brown adipose tissue (BAT). Mice lacking GPR84 exhibited increased lipid accumulation in BAT, rendering them more susceptible to cold exposure and displaying reduced BAT activity compared with their WT counterparts. Our in vitro experiments with primary brown adipocytes from GPR84-KO mice revealed diminished expression of thermogenic genes and reduced O2 consumption. Furthermore, the application of the GPR84 agonist 6-n-octylaminouracil (6-OAU) counteracted these effects, effectively reinstating the brown adipocyte activity. These compelling in vivo and in vitro findings converge to highlight mitochondrial dysfunction as the primary cause of BAT anomalies in GPR84-KO mice. The activation of GPR84 induced an increase in intracellular Ca2+ levels, which intricately influenced mitochondrial respiration. By modulating mitochondrial Ca2+ levels and respiration, GPR84 acts as a potent molecule involved in BAT activity. These findings suggest that GPR84 is a potential therapeutic target for invigorating BAT and ameliorating metabolic disorders.

Current methods of monitoring insulin secretion lack the required spatial and temporal resolution to adequately map the dynamics of exocytosis of native insulin granules in intact cell populations in three dimensions. Exploiting the fact that insulin granules contain a high level of Zn2+, and that Zn2+ is coreleased with insulin during secretion, we have developed a fluorescent, cell surface-targeted zinc indicator for monitoring induced exocytotic release (ZIMIR). ZIMIR displayed a robust fluorescence enhancement on Zn2+ chelation and bound Zn2+ with high selectivity against Ca2+ and Mg2+. When added to cultured β cells or intact pancreatic islets at low micromolar concentrations, ZIMIR labeled cells rapidly, noninvasively, and stably, and it reliably reported changes in Zn2+ concentration near the sites of granule fusion with high sensitivity that correlated well with membrane capacitance measurement. Fluorescence imaging of ZIMIR-labeled β cells followed the dynamics of exocytotic activity at subcellular resolution, even when using simple epifluorescence microscopy, and located the chief sites of insulin release to intercellular junctions. Moreover, ZIMIR imaging of intact rat islets revealed that Zn2+/insulin release occurred largely in small groups of adjacent β cells, with each forming a \"secretory unit.\" Concurrent imaging of ZIMIR and Fura-2 showed that the amplitude of cytosolic Ca2+ elevation did not necessarily correlate with insulin secretion activity, suggesting that events downstream of Ca2+ signaling underlie the cell-cell heterogeneity in insulin release. In addition to studying stimulation-secretion coupling in cells with Zn2+-containing granules, ZIMIR may find applications in β-cell engineering and screening for molecules regulating insulin secretion on high-throughput platforms.

The molecular mechanisms underlying obesity-induced increases in ß cell mass and the resulting ß cell dysfunction need to be elucidated further. Our study revealed that GPR92, expressed in islet macrophages, is modulated by dietary interventions in metabolic tissues. Therefore, we aimed to define the role of GPR92 in islet inflammation by using a high-fat diet-induced (HFD-induced) obese mouse model. GPR92-KO mice exhibited glucose intolerance and reduced insulin levels - despite the enlarged pancreatic islets - as well as increased islet macrophage content and inflammation level compared with WT mice. These results indicate that the lack of GPR92 in islet macrophages can cause ß cell dysfunction, leading to disrupted glucose homeostasis. Alternatively, stimulation with the GPR92 agonist farnesyl pyrophosphate results in the inhibition of HFDinduced islet inflammation and increased insulin secretion in WT mice, but not in GPR92-KO mice. Thus, our study suggests that GPR92 can be a potential target to alleviate ß cell dysfunction via the inhibition of islet inflammation associated with the progression of diabetes.

Homeothermic vertebrates produce heat in cold environments through thermogenesis, in which brown adipose tissue (BAT) increases mitochondrial oxidation along with uncoupling of the electron transport chain and activation of uncoupling protein 1 (UCP1). Although the transcription factors regulating the expression of UCP1 and nutrient oxidation genes have been extensively studied, only a few other proteins essential for BAT function have been identified. We describe the discovery of FAM195A, a BAT-enriched RNA binding protein, which is required for cold-dependent thermogenesis in mice. FAM195A knockout (KO) mice display whitening of BAT and an inability to thermoregulate. In BAT of FAM195A KO mice, enzymes involved in branched-chain amino acid (BCAA) metabolism are down-regulated, impairing their response to cold. Knockdown of FAM195A in brown adipocytes in vitro also impairs expression of leucine oxidation enzymes, revealing FAM195A to be a regulator of BCAA metabolism and a potential target for metabolic disorders.

Endotrophin (ETP), a cleavage product of the C5 domain of collagen VI α3 (COL6A3), plays a crucial role in extracellular matrix remodeling. Previously established Col6a3 -knockout mouse models primarily reflect the consequences of COL6A3 loss rather than the specific effects of ETP depletion, making it challenging to directly assess the functions of ETP. These models either disrupt COL6A3 along with ETP production or express functionally defective COL6A3 while maintaining ETP production. Here we developed and validated a novel ETP-knockout (ETP KO ) mouse model that selectively ablates ETP while preserving Col6a3 expression to address these limitations. To generate the ETP KO model, we introduced lox2272 sites and a fluorescent mCherryCAAX reporter into the Col6a3 locus, ensuring that ETP expression is turned off and reporter expression is turned on upon Cre-mediated recombination. Crossing the Col6a3-Etp+mCherryCAAX mouse line with CMV-Cre mice yielded ETP KO mice, in which successful ETP deletion was confirmed by sequencing of genomic DNA and analysis of mCherryCAAX expression. Using this model, we investigated the role of ETP in kidney fibrosis. ETP KO mice subjected to unilateral or bilateral kidney ischemia–reperfusion injury exhibited complete Etp messenger RNA ablation with only a partial reduction in Col6a3 mRNA. Notably, ETP depletion significantly attenuated fibrosis progression, demonstrating a critical contribution of ETP to the pathogenesis of kidney fibrosis. The ETP KO mouse model provides a targeted and specific approach to study ETP function independently of COL6A3 expression. These findings establish ETP as a key driver of fibrosis and position ETP KO mice as a valuable tool for elucidating ETP-mediated mechanisms in preclinical disease models. ETP KO mice reveal ETP’s role in kidney fibrosis Collagen type VI is important for tissue structure. It consists of three chains, including COL6A3, which produces a fragment called endotrophin (ETP). Previous mouse models could not isolate the role of ETP without affecting its parent molecule COL6A3. To address this, researchers created a new mouse model that can specifically remove ETP using a technique called CRISPR–Cas9. In this study, researchers used this new model to study kidney fibrosis. They induced kidney injury in mice and found that removing ETP reduced fibrosis and improved kidney function. This suggests ETP plays a key role not only in fibrosis in the kidneys but also in many other tissues. The study used methods such as immunostaining and genetic analysis to confirm these findings. The results show that targeting ETP could be a potential therapeutic approach to fibrotic diseases, which are very difficult to treat. Future research could explore the role of ETP in other conditions and its potential as a therapeutic target. This summary was initially drafted using artificial intelligence, then revised and fact-checked by the author.