A Notch toward Progenitor D(G)FRentiation: Defining a NOTCH-PDGFR axis in brown adipogenesis.

Brown adipocytes are found in several fat depots, however, the origins and contributions of different lineages of adipogenic progenitor cells (APCs) to these depots are unclear. In this issue of Developmental Cell, Shi et al. show that platelet-derived growth factor receptor ß (PDGFRß)-lineage and T-box transcription factor 18 (TBX18)-lineage APCs differentially contribute to brown adipogenesis across these depots.

Association of Lipoprotein-associated phospholipase A2 With Carotid Intima-Media Thickness in Acute Cerebral Infarction Patients.

Lipoprotein-associated phospholipase A2 (Lp-PLA2) is an inflammatory marker associated with atherosclerotic and cardiovascular diseases. This study aimed to explore the association of Lp-PLA2 with carotid intima-media thickness (cIMT) in patients with acute ischemic stroke (AIS) and explore a threshold level to predict the risk of vulnerable plaques. This retrospective observational study included patients with AIS in the Neurology Department of our Hospital between January 2018 and December 2019. The study included 293 patients aged 65.29 ± 12.11 years, including 212 males, of whom 124 had carotid intima-media thickening (42.32%). Multivariable logistic regression showed that Lp-PLA2 level was an independent risk factor for cIMT (odds ratio [OR] = 1.004, 95% confidence interval [95% CI] 1.001-1.008, P = .008). Threshold effect analysis showed that the risk of vulnerable carotid plaque occurrence increased by 2% for every 1 ng/mL increase in Lp-PLA2 level with serum Lp-PLA2 levels between 157 and 279 ng/mL; this increase was statistically significant (OR = 1.02, 95% CI 1.01-1.03, P < .001). Serum Lp-PLA2 is an independent risk factor for increased cIMT in patients with AIS, and a threshold Lp-PLA2 level between 157 and 279 ng/mL showed a higher risk of carotid plaque rupture.

FAM210A is essential for cold-induced mitochondrial remodeling in brown adipocytes.

Cold stimulation dynamically remodels mitochondria in brown adipose tissue (BAT) to facilitate non-shivering thermogenesis in mammals, but what regulates mitochondrial plasticity is poorly understood. Comparing mitochondrial proteomes in response to cold revealed FAM210A as a cold-inducible mitochondrial inner membrane protein. An adipocyte-specific constitutive knockout of Fam210a (Fam210aAKO) disrupts mitochondrial cristae structure and diminishes the thermogenic activity of BAT, rendering the Fam210aAKO mice vulnerable to lethal hypothermia under acute cold exposure. Induced knockout of Fam210a in adult adipocytes (Fam210aiAKO) does not affect steady-state mitochondrial structure under thermoneutrality, but impairs cold-induced mitochondrial remodeling, leading to progressive loss of cristae and reduction of mitochondrial density. Proteomics reveals an association between FAM210A and OPA1, whose cleavage governs cristae dynamics and mitochondrial remodeling. Mechanistically, FAM210A interacts with mitochondrial protease YME1L and modulates its activity toward OMA1 and OPA1 cleavage. These data establish FAM210A as a key regulator of mitochondrial cristae remodeling in BAT and shed light on the mechanism underlying mitochondrial plasticity in response to cold.

Atypical peripheral actin band formation via overactivation of RhoA and nonmuscle myosin II in mitofusin 2-deficient cells.

Cell spreading and migration play central roles in many physiological and pathophysiological processes. We have previously shown that MFN2 regulates the migration of human neutrophil-like cells via suppressing Rac activation. Here, we show that in mouse embryonic fibroblasts, MFN2 suppresses RhoA activation and supports cell polarization. After initial spreading, the wild-type cells polarize and migrate, whereas the Mfn2-/- cells maintain a circular shape. Increased cytosolic Ca2+ resulting from the loss of Mfn2 is directly responsible for this phenotype, which can be rescued by expressing an artificial tether to bring mitochondria and endoplasmic reticulum to close vicinity. Elevated cytosolic Ca2+ activates Ca2+/calmodulin-dependent protein kinase II, RhoA, and myosin light-chain kinase, causing an overactivation of nonmuscle myosin II, leading to a formation of a prominent F-actin ring at the cell periphery and increased cell contractility. The peripheral actin band alters cell physics and is dependent on substrate rigidity. Our results provide a novel molecular basis to understand how MFN2 regulates distinct signaling pathways in different cells and tissue environments, which is instrumental in understanding and treating MFN2-related diseases.

FAM210A mediates an inter-organelle crosstalk essential for protein synthesis and muscle growth in mouse.

Mitochondria are not only essential for energy production in eukaryocytes but also a key regulator of intracellular signaling. Here, we report an unappreciated role of mitochondria in regulating cytosolic protein translation in skeletal muscle cells (myofibers). We show that the expression of mitochondrial protein FAM210A (Family With Sequence Similarity 210 Member A) is positively associated with muscle mass in mice and humans. Muscle-specific Myl1Cre-driven Fam210a knockout (Fam210aMKO) in mice reduces mitochondrial density and function, leading to progressive muscle atrophy and premature death. Metabolomic and biochemical analyses reveal that Fam210aMKO reverses the oxidative TCA cycle towards the reductive direction, resulting in acetyl-CoA accumulation and hyperacetylation of cytosolic proteins. Specifically, hyperacetylation of several ribosomal proteins leads to disassembly of ribosomes and translational defects. Transplantation of Fam210aMKO mitochondria into wildtype myoblasts is sufficient to elevate protein acetylation in recipient cells. These findings reveal a novel crosstalk between the mitochondrion and ribosome mediated by FAM210A.

PRMT5 links lipid metabolism to contractile function of skeletal muscles.

Skeletal muscle plays a key role in systemic energy homeostasis besides its contractile function, but what links these functions is poorly defined. Protein Arginine Methyl Transferase 5 (PRMT5) is a well-known oncoprotein but also expressed in healthy tissues with unclear physiological functions. As adult muscles express high levels of Prmt5, we generated skeletal muscle-specific Prmt5 knockout (Prmt5MKO ) mice. We observe reduced muscle mass, oxidative capacity, force production, and exercise performance in Prmt5MKO mice. The motor deficiency is associated with scarce lipid droplets in myofibers due to defects in lipid biosynthesis and accelerated degradation. Specifically, PRMT5 deletion reduces dimethylation and stability of Sterol Regulatory Element-Binding Transcription Factor 1a (SREBP1a), a master regulator of de novo lipogenesis. Moreover, Prmt5MKO impairs the repressive H4R3 symmetric dimethylation at the Pnpla2 promoter, elevating the level of its encoded protein ATGL, the rate-limiting enzyme catalyzing lipolysis. Accordingly, skeletal muscle-specific double knockout of Pnpla2 and Prmt5 normalizes muscle mass and function. Together, our findings delineate a physiological function of PRMT5 in linking lipid metabolism to contractile function of myofibers.

Association between Apolipoprotein E genotype and functional outcome in acute ischemic stroke.

This study aims to determine whether APOE alleles would affect the functional outcome in acute ischemic stroke (AIS) and whether the relationship between inflammation and stroke-related disability varies according to APOE genotypes. We retrospectively collected the demographic and clinical data of AIS patients within one week of symptom-onset through medical records review. The primary outcome was dependence or death, defined as modified Rankin scale (mRS) score of 2-6, which was assessed at 3 months. Among 1929 enrolled patients, the prevalence of APOE ε4 carriers was 17.73% (342/1929). There were 394 AIS patients (394/1929, 20.43%) showed poor function outcome of 90-day mRS (2-6), of whom 147 (147/342, 42.98%) were APOE ε4 carriers and 247 (247/1587, 15.56%) were non-ε4 carriers. There was a significant increased probability of poor functional outcome after AIS among APOE ε4 carriers versus non-ε4 carriers (adjusted-OR 4.62, 95% CI 3.51 to 6.09, P < 0.001). Among ε4 carriers, high neutrophil-to-lymphocyte ratio (NLR) was significantly associated with stroke-related disability (Ptrend = 0.035); however, no significant association was observed among non-ε4 carriers. Our study showed that the APOE ε4 carriers had worse functional outcome after AIS as compared with non-ε4 carriers. APOE genotype may modify the relationship between NLR and 3-month stroke outcome.

ACSS3 in brown fat drives propionate catabolism and its deficiency leads to autophagy and systemic metabolic dysfunction.

Propionate is a gut microbial metabolite that has been reported to have controversial effects on metabolic health. Here we show that propionate is activated by acyl-CoA synthetase short-chain family member 3 (ACSS3), located on the mitochondrial inner membrane in brown adipocytes. Knockout of Acss3 gene (Acss3-/- ) in mice reduces brown adipose tissue (BAT) mass but increases white adipose tissue (WAT) mass, leading to glucose intolerance and insulin resistance that are exacerbated by high-fat diet (HFD). Intriguingly, Acss3-/- or HFD feeding significantly elevates propionate levels in BAT and serum, and propionate supplementation induces autophagy in cultured brown and white adipocytes. The elevated levels of propionate in Acss3-/- mice similarly drive adipocyte autophagy, and pharmacological inhibition of autophagy using hydroxychloroquine ameliorates obesity, hepatic steatosis and insulin resistance of the Acss3-/- mice. These results establish ACSS3 as the key enzyme for propionate metabolism and demonstrate that accumulation of propionate promotes obesity and Type 2 diabetes through triggering adipocyte autophagy.

Lipid droplet dynamics regulate adult muscle stem cell fate.

The lipid droplet (LD) is a central hub for fatty acid metabolism in cells. Here we define the dynamics and explore the role of LDs in skeletal muscle satellite cells (SCs), a stem cell population responsible for muscle regeneration. In newly divided SCs, LDs are unequally distributed in sister cells exhibiting asymmetric cell fates, as the LDLow cell self-renews while the LDHigh cell commits to differentiation. When transplanted into regenerating muscles, LDLow cells outperform LDHigh cells in self-renewal and regeneration in vivo. Pharmacological inhibition of LD biogenesis or genetic inhibition of LD catabolism through knockout of Pnpla2 (encoding ATGL, the rate-limiting enzyme for lipolysis) disrupts cell fate homeostasis and impairs the regenerative capacity of SCs. Dysfunction of Pnpla2-null SCs is associated with energy insufficiency and oxidative stress that can be partially rescued by antioxidant (N-acetylcysteine) treatment. These results establish a direct link between LD dynamics and stem cell fate determination.

Labeling and analyzing lipid droplets in mouse muscle stem cells.

Lipid droplets are emerging as an important and dynamic organelle whose metabolism controls stem cell behavior. Here we present a comprehensive protocol to visualize and quantify these organelles in mouse muscle satellite cells (MuSCs). This protocol includes steps for BODIPY/LipidSpot610 staining of freshly isolated MuSCs, in vitro cultured myoblasts, and single myofibers to label lipid droplets and subsequent analysis and quantification of fluorescence signals. This protocol can be modified to stain lipid droplets in other cell types of interest. For complete details on the use and execution of this protocol, please refer to Yue et al. (2022).1.

LETMD1 is required for mitochondrial structure and thermogenic function of brown adipocytes.

Obesity and metabolic disorders caused by energy surplus pose an increasing concern within the global population. Brown adipose tissue (BAT) dissipates energy through mitochondrial non-shivering thermogenesis, thus representing a powerful agent against obesity. Here we explore the novel role of a mitochondrial outer membrane protein, LETM1-domain containing 1 (LETMD1), in BAT. We generated a knockout (Letmd1KO ) mouse model and analyzed BAT morphology, function and gene expression under various physiological conditions. While the Letmd1KO mice are born normally and have normal morphology and body weight, they lose multilocular brown adipocytes completely and have diminished mitochondrial abundance, DNA copy number, cristae structure, and thermogenic gene expression in the intrascapular BAT, associated with elevated reactive oxidative stress. In consequence, the Letmd1KO mice fail to maintain body temperature in response to acute cold exposure without food and become hypothermic within 4 h. Although the cold-exposed Letmd1KO mice can maintain body temperature in the presence of food, they cannot upregulate expression of uncoupling protein 1 (UCP1) and convert white to beige adipocytes, nor can they respond to adrenergic stimulation. These results demonstrate that LETMD1 is essential for mitochondrial structure and function, and thermogenesis of brown adipocytes.

Reduced electron transport chain complex I protein abundance and function in Mfn2-deficient myogenic progenitors lead to oxidative stress and mitochondria swelling.

Mitochondrial remodeling through fusion and fission is crucial for progenitor cell differentiation but its role in myogenesis is poorly understood. Here, we characterized the function of mitofusin 2 (Mfn2), a mitochondrial outer membrane protein critical for mitochondrial fusion, in muscle progenitor cells (myoblasts). Mfn2 expression is upregulated during myoblast differentiation in vitro and muscle regeneration in vivo. Targeted deletion of Mfn2 gene in myoblasts (Mfn2MKO ) increases oxygen-consumption rates (OCR) associated with the maximal respiration and spare respiratory capacity, and increased levels of reactive oxygen species (ROS). Skeletal muscles of Mfn2MKO mice exhibit robust mitochondrial swelling with normal mitochondrial DNA content. Additionally, mitochondria isolated from Mfn2MKO muscles have reduced OCR at basal state and for complex I respiration, associated with decreased levels of complex I proteins NDUFB8 (NADH ubiquinone oxidoreductase subunit B8) and NDUFS3 (NADH ubiquinone oxidoreductase subunit S3). However, Mfn2MKO has no obvious effects on myoblast differentiation, muscle development and function, and muscle regeneration. These results demonstrate a novel role of Mfn2 in regulating mitochondrial complex I protein abundance and respiratory functions in myogenic progenitors and myofibers.

The Relative Contribution of Plasma Homocysteine Levels vs. Traditional Risk Factors to the First Stroke: A Nested Case-Control Study in Rural China.

BACKGROUND: Approximately 75% of Chinese hypertensive patients have elevated homocysteine (Hcy). Its implication in risk assessment and prevention of the first stroke remains an important clinical and public health question. METHODS: This study was based on a community cohort recruited from 2016 to 2018 in the rural China. To maximize cost efficiency, we used a nested case-control design, including 3,533 first stroke cases and 3,533 controls matched for age ±1 years, sex, and village. Individual associations of tHcy and traditional risk factors with the first stroke were examined, and their population-attributable risks (PARs) were estimated. RESULTS: There was a significant dose-response association between first stroke and total Hcy (tHcy) levels, with adjusted odds ratios of 1.11 (95% CI: 0.97, 1.26) for tHcy 10-15 µmol/L and 1.44 (1.22, 1.69) for tHcy ≥ 15 µmol/L, all compared to tHcy < 10 µmol/L. A similar trend was found for ischemic and hemorrhagic stroke. tHcy and systolic blood pressure (SBP) were independently and additively associated with the risk of first stroke (tHcy: 1.06 [1.02, 1.1]; SBP: 1.13 [1.1, 1.16]; P-interaction, 0.889). Among the ten main risk factors examined, the top two contributors to the first stroke were SBP and tHcy, with PARs of 25.73 and 11.24%, respectively. CONCLUSIONS: Elevated tHcy is the second most important contributor and acts additively with SBP to increase the risk of the first stroke. This finding underscores the importance of screening and treating elevated tHcy along with traditional risk factors to further reduce the burden of the first stroke in the high-risk populations.

Prognosis of Neurological Improvement in Inpatient Acute Ischemic Stroke Survivors: A Propensity Score Matching Analysis.

OBJECTIVES: Stroke has become a national concern in China. Early prediction of stroke benefits patients and aids medical professionals in clinical decision making and rehabilitation plans to improve successful outcomes. To identify prediction factors influencing short-term outcomes in patients with acute ischemic stroke (AIS). MATERIALS AND METHODS: This was a hospital-based prospective observational study. Recovery of neurological improvement was represented by a percent reduction in the National Institutes of Health Stroke Scale (NIHSS) at discharge. We performed propensity score matching (PSM) to balance the NIHSS at admission and compared NIHSS scores before and after matching with PSM criteria. Finally, we assessed the prognosis of neurological improvement and patient-related variables. RESULTS: In the matched cohort, 92 pairs were matched by NIHSS admission after PSM. Modified Barthel Index, modified Rankin scale, NIHSS on admission, hypertension, sleep time, and Montreal Cognitive Assessment (MoCA) were statistically different between the two groups (P<0.05) before matching. Multivariable analysis identified two factors independently associated with neurological improvement: diabetes (P=0.030; adjusted odds ratio, 2.129; 95% confidence interval [CI] 1.078-4.026) and MoCA (P<0.001; adjusted odds ratio, 5.385; 95% CI 2.278-12.730). CONCLUSION: Consistent with previous studies, diabetes affected the short-term outcomes of AIS, while cognitive impairment had a negative effect on long-term AIS prognosis.Diabetes and early cognitive impairment have adverse effects on short-term prognosis after AIS.

Phosphatase orphan 1 inhibits myoblast proliferation and promotes myogenic differentiation.

Myogenesis includes sequential stages of progenitor cell proliferation, myogenic commitment and differentiation, myocyte fusion, and myotube maturation. Different stages of myogenesis are orchestrated and regulated by myogenic regulatory factors and various downstream cellular signaling. Here we identify phosphatase orphan 1 (Phospho1) as a new player in myogenesis. During activation, proliferation, and differentiation of quiescent satellite cells, the expression of Phospho1 gradually increases. Overexpression of Phospho1 inhibits myoblast proliferation but promotes their differentiation and fusion. Conversely, knockdown of Phospho1 accelerates myoblast proliferation but impairs myotube formation. Moreover, knockdown of Phospho1 decreases the OXPHO protein levels and mitochondria density, whereas overexpression of Phospho1 upregulates OXPHO protein levels and promotes mitochondrial oxygen consumption. Finally, we show that Phospho1 expression is controlled by myogenin, which binds to the promoter of Phospho1 to regulate its transcription. These results indicate a key role of Phospho1 in regulating myogenic differentiation and mitochondrial function.

Effects of Nurse-Led Support Via WeChat, a Smartphone Application, for Breast Cancer Patients After Surgery: A Quasi-Experimental Study.

Background: Women with breast cancer (BC) commonly experience physical and psychosocial symptoms after surgery. Web- and smartphone-based support can significantly improve women's symptoms and quality of life. Social care applications (apps) are widely used in China, but there are few studies on their effectiveness BC support. This study aimed to examine the effects of nurse-led support on the social care app WeChat® (Tencent Holdings Limited, Shenzhen, China) in BC patients after surgery. Methods: A quasi-experimental study was conducted between June 2015 and August 2015. Sixty patients with BC (30 in the intervention group, 30 in the control group) were enrolled. Subjects in the intervention group participated in a WeChat-based support program (WSP) led by nurses, while subjects in the control group received a follow-up by telephone. Subjects in both groups were evaluated at the time of discharge and at 1, 3, and 6 months of follow-up. Physical well-being status, psychology status, and social support were evaluated. Results: There were no differences between intervention and control patients at baseline. Physical well-being (p < 0.001), anxiety (p < 0.001), depression (p < 0.001), and support from outside of family (p = 0.037) were significantly better in the intervention group than in the control group after 6 months. The intervention group showed that physical well-being (p = 0.036), anxiety (p < 0.001), and depression (p < 0.001) were significantly different from baseline to 6 months of follow-up. Conclusion: WSP assisted with nurse-led support and had physical, psychological, and social benefits for patients after surgery for BC.

Laparoscopic colorectal cancer surgery reduces the adverse impacts of sarcopenia on postoperative outcomes: a propensity score-matched analysis.

BACKGROUND: Sarcopenia is a negative predictor for postoperative recovery. This study was performed to evaluate the short-term outcomes of laparoscopic surgery in colorectal cancer patients with sarcopenia. METHODS: We conducted a study of patients who underwent curative surgeries for colorectal cancer in two centers from July 2014 to July 2018. In order to reduce selection bias, we conducted a propensity score matching analysis. Preoperative characteristics including age, gender, anemia, body mass index, hypoalbuminemia, America society of anesthesiology scores, epidural anesthesia, operative procedure, stoma, tumor location, and combined resection were incorporated in the model, and produced 58 matched pairs. The third lumbar skeletal muscle mass, handgrip strength, and 6 m usual gait speed were measured to define sarcopenia. Short-term outcomes were compared between the two groups. RESULTS: In a total of 1136 patients, 272 had sarcopenia diagnosed, and 227 were further analyzed in this study. Among them, 108 patients underwent laparoscopic colorectal surgery and 119 underwent open colorectal surgery. In the matched cohort, the clinical characteristics of the two groups were well matched. The laparoscopic group had significantly reduced overall complications (15.5% vs. 36.2%, P = 0.016) and shorter postoperative hospital stays (10.5 vs. 14, P = 0.027). Subgroup analysis of postoperative complications showed that the incidence of surgical complications (P = 0.032) was lower in the laparoscopic group. Hospitalization costs (P = 0.071) and 30-day readmissions (P = 0.215) were similar between the two groups. CONCLUSION: Laparoscopic surgery for colorectal cancer is a safe and feasible option with better short-term outcomes in patients with sarcopenia.

Methyltransferase-like 21c methylates and stabilizes the heat shock protein Hspa8 in type I myofibers in mice.

Protein methyltransferases mediate posttranslational modifications of both histone and nonhistone proteins. Whereas histone methylation is well-known to regulate gene expression, the biological significance of nonhistone methylation is poorly understood. Methyltransferase-like 21c (Mettl21c) is a newly classified nonhistone lysine methyltransferase whose in vivo function has remained elusive. Using a Mettl21cLacZ knockin mouse model, we show here that Mettl21c expression is absent during myogenesis and restricted to mature type I (slow) myofibers in the muscle. Using co-immunoprecipitation, MS, and methylation assays, we demonstrate that Mettl21c trimethylates heat shock protein 8 (Hspa8) at Lys-561 to enhance its stability. As such, Mettl21c knockout reduced Hspa8 trimethylation and protein levels in slow muscles, and Mettl21c overexpression in myoblasts increased Hspa8 trimethylation and protein levels. We further show that Mettl21c-mediated stabilization of Hspa8 enhances its function in chaperone-mediated autophagy, leading to degradation of client proteins such as the transcription factors myocyte enhancer factor 2A (Mef2A) and Mef2D. In contrast, Mettl21c knockout increased Mef2 protein levels in slow muscles. These results identify Hspa8 as a Mettl21c substrate and reveal that nonhistone methylation has a physiological function in protein stabilization.

Methyltransferase-like 21e inhibits 26S proteasome activity to facilitate hypertrophy of type IIb myofibers.

Skeletal muscles contain heterogeneous myofibers that are different in size and contractile speed, with type IIb myofiber being the largest and fastest. Here, we identify methyltransferase-like 21e (Mettl21e), a member of newly classified nonhistone methyltransferases, as a gene enriched in type IIb myofibers. The expression of Mettl21e was strikingly up-regulated in hypertrophic muscles and during myogenic differentiation in vitro and in vivo. Knockdown (KD) of Mettl21e led to atrophy of cultured myotubes, and targeted mutation of Mettl21e in mice reduced the size of IIb myofibers without affecting the composition of myofiber types. Mass spectrometry and methyltransferase assay revealed that Mettl21e methylated valosin-containing protein (Vcp/p97), a key component of the ubiquitin-proteasome system. KD or knockout of Mettl21e resulted in elevated 26S proteasome activity, and inhibition of proteasome activity prevented atrophy of Mettl21e KD myotubes. These results demonstrate that Mettl21e functions to maintain myofiber size through inhibiting proteasome-mediated protein degradation.-Wang, C., Zhang, B., Ratliff, A. C., Arrington, J., Chen, J., Xiong, Y., Yue, F., Nie, Y., Hu, K., Jin, W., Tao, W. A., Hrycyna, C. A., Sun, X., Kuang, S. Methyltransferase-like 21e inhibits 26S proteasome activity to facilitate hypertrophy of type IIb myofibers.

Transdifferentiation of Muscle Satellite Cells to Adipose Cells Using CRISPR/Cas9-Mediated Targeting of MyoD.

Brown adipocytes dissipate energy through non-shivering thermogenesis mediated by UCP1 protein, hence representing a powerful target to overcome obesity due to energy surplus. However, brown adipocytes are scarce in adult humans, especially in obese subjects, urging the development of novel strategies to boost the number of these thermogenic adipocytes from a therapeutical perspective. In this regard, transdifferentiation of myoblasts into brown adipocytes represents a promising approach. Here, we describe a method that we have recently developed to transdifferentiate myoblasts into brown adipocytes through CRISPR/Cas9-medidated targeting of MyoD, the master myogenic regulatory factor.