bims-pideca Biomed News
on Class IA PI3K signalling in development and cancer
Issue of 2022–08–07
fifteen papers selected by
Ralitsa Radostinova Madsen, University College London
  1. PFKFB4 interacts with ICMT and activates RAS/AKT signaling-dependent cell migration in melanoma.
  2. Loss of PTEN Expression, PIK3CA Mutations, and Breast Cancer Survival in the Nurses' Health Studies.
  3. Interactions between mTORC2 core subunits Rictor and mSin1 dictate selective and context-dependent phosphorylation of substrate kinases SGK1 and Akt.
  4. MAP3K4 promotes fetal and placental growth by controlling the receptor tyrosine kinases IGF1R/IR and Akt signaling pathway†.
  5. Exome sequencing reveals a distinct somatic genomic landscape in breast cancer from women with germline PTEN variants.
  6. Nucleotide imbalance decouples cell growth from cell proliferation.
  7. Looking closely at overgrowth: Constitutional mosaicism in PTEN hamartoma tumor syndrome.
  8. Convergence of Signaling Pathways in Mediating Actions of Leucine and IGF-1 on mTORC1 in L6 Myoblasts.
  9. Inhibition of polyploidization in Pten-deficient livers reduces steatosis.
  10. Afadin couples RAS GTPases to the polarity rheostat Scribble.
  11. Triple-negative breast cancer metastasis involves complex epithelial-mesenchymal transition dynamics and requires vimentin.
  12. Cross-species identification of cancer resistance-associated genes that may mediate human cancer risk.
  13. A robust and tunable system for targeted cell ablation in developing embryos.
  14. Dual inhibition of MAPK and PI3K/AKT pathways enhances maturation of human iPSC-derived cardiomyocytes.
  15. Unexpected role for IGF-1 in starvation: Maintenance of blood glucose.
  1. Life Sci Alliance. 2022 Dec;pii: e202201377. [Epub ahead of print]5(12):
    PFKFB4 interacts with ICMT and activates RAS/AKT signaling-dependent cell migration in melanoma.
    Méghane Sittewelle, Vincent Kappès, Chenxi Zhou, Déborah Lécuyer, Anne H Monsoro-Burq.
      Cell migration is a complex process, tightly regulated during embryonic development and abnormally activated during cancer metastasis. RAS-dependent signaling is a major nexus controlling essential cell parameters including proliferation, survival, and migration, utilizing downstream effectors such as the PI3K/AKT signaling pathway. In melanoma, oncogenic mutations frequently enhance RAS, PI3K/AKT, or MAP kinase signaling and trigger other cancer hallmarks among which the activation of metabolism regulators. PFKFB4 is one of these critical regulators of glycolysis and of the Warburg effect. Here, however, we explore a novel function of PFKFB4 in melanoma cell migration. We find that PFKFB4 interacts with ICMT, a posttranslational modifier of RAS. PFKFB4 promotes ICMT/RAS interaction, controls RAS localization at the plasma membrane, activates AKT signaling and enhances cell migration. We thus provide evidence of a novel and glycolysis-independent function of PFKFB4 in human cancer cells. This unconventional activity links the metabolic regulator PFKFB4 to RAS-AKT signaling and impacts melanoma cell migration.
    DOI:  https://doi.org/10.26508/lsa.202201377
  2. Cancer Epidemiol Biomarkers Prev. 2022 Aug 01. pii: EPI-22-0672. [Epub ahead of print]
    Loss of PTEN Expression, PIK3CA Mutations, and Breast Cancer Survival in the Nurses' Health Studies.
    Tengteng Wang, Yujing J Heng, Gabrielle M Baker, Vanessa C Bret-Mounet, Liza M Quintana, Lisa Frueh, Susan E Hankinson, Michelle D Holmes, Wendy Y Chen, Walter C Willett, Bernard Rosner, Rulla M Tamimi, A Heather Eliassen.
       BACKGROUND: The relationships between PTEN loss and/or PIK3CA mutation and breast cancer prognosis remain controversial. We aim to examine the associations in large epidemiological cohorts.
    METHODS: We followed women with invasive breast cancer from the Nurses' Health Studies with available data on tumor PTEN expression (n=4,111) and PIK3CA mutation (n=2,930). PTEN expression was evaluated by immunohistochemistry and digitally scored (0-100%). Pyrosequencing of six hotspot mutations of PIK3CA was performed.
    RESULTS: We found loss of PTEN expression (≤10%) occurred in 17% of cases, and PIK3CA mutations were detected in 11% of cases. After adjusting for clinical and lifestyle factors, PTEN loss was not associated with worse breast cancer-specific mortality among all samples (hazard ratio (HR) =0.85; 95% confidence intervals (CI)=0.71-1.03) or among estrogen receptor (ER)-positive tumors (HR =0.99; 95%CI=0.79-1.24). However, among ER-negative tumors, PTEN loss was associated with lower breast cancer-specific mortality (HR =0.68; 95%CI=0.48-0.95). PIK3CA mutation was not strongly associated with breast cancer-specific mortality (HR =0.89; 95%CI=0.67-1.17). Compared with tumors without PTEN loss and without PIK3CA mutation, those with alterations (n=540) were not at higher risk (HR =1.07; 95%CI=0.86-1.34). However, women with both PTEN loss and PIK3CA mutation (n=38) were at an increased risk of breast cancer-specific mortality (HR =1.65; 95%CI=0.83-3.26).
    CONCLUSIONS: In this large epidemiologic study, the PTEN-mortality association was more pronounced for ER-negative tumors, and the joint PTEN loss and PIK3CA mutation may be associated with worse prognosis.
    IMPACT: Further studies with a larger sample of ER-negative tumors are needed to replicate our findings and elucidate underlying mechanisms.
    DOI:  https://doi.org/10.1158/1055-9965.EPI-22-0672
  3. J Biol Chem. 2022 Aug 01. pii: S0021-9258(22)00730-X. [Epub ahead of print] 102288
    Interactions between mTORC2 core subunits Rictor and mSin1 dictate selective and context-dependent phosphorylation of substrate kinases SGK1 and Akt.
    Zanlin Yu, Junliang Chen, Enzo Takagi, Feng Wang, Bidisha Saha, Xi Liu, Lydia-Marie Joubert, Catherine E Gleason, Mingliang Jin, Chengmin Li, Carlos Nowotny, David Agard, Yifan Cheng, David Pearce.
      Mechanistic target of rapamycin complex 2 (mTORC2) is a multi-subunit kinase complex, central to multiple essential signaling pathways. Two core subunits, Rictor and mSin1, distinguish it from the related mTORC1 and support context-dependent phosphorylation of its substrates. mTORC2 structures have been determined previously, however, important questions remain, particularly regarding the structural determinants mediating substrate specificity and context-dependent activity. Here, we used cryo-EM to obtain high-resolution structures of the human mTORC2 apo-complex in the presence of substrates Akt and SGK1. Using functional assays, we then tested predictions suggested by substrate-induced structural changes in mTORC2. For the first time, we visualized in the apo-state the side chain interactions between Rictor and mTOR that sterically occlude recruitment of mTORC1 substrates and confer resistance to the mTORC1 inhibitor rapamycin. Also in the apo-state, we observed that mSin1 formed extensive contacts with Rictor via a pair of short α-helices nestled between two Rictor helical repeat clusters, as well as by an extended strand that makes multiple weak contacts with Rictor helical cluster 1. In co-complex structures, we found that SGK1, but not Akt, markedly altered the conformation of the mSin1 N-terminal extended strand, disrupting multiple weak interactions while inducing a large rotation of mSin1 residue Arg-83, which then interacts with a patch of negatively charged residues within Rictor. Finally, we demonstrate mutation of Arg-83 to Ala selectively disrupts mTORC2-dependent phosphorylation of SGK1, but not of Akt, supporting context-dependent substrate selection. These findings provide new structural and functional insights into mTORC2 specificity and context-dependent activity.
    DOI:  https://doi.org/10.1016/j.jbc.2022.102288
  4. J Biol Chem. 2022 Jul 31. pii: S0021-9258(22)00752-9. [Epub ahead of print] 102310
    MAP3K4 promotes fetal and placental growth by controlling the receptor tyrosine kinases IGF1R/IR and Akt signaling pathway†.
    Charles H Perry, Nathan A Mullins, Razan B A Sweileh, Noha A M Shendy, Patrick A Roberto, Amber L Broadhurst, Hannah A Nelson, Gustavo A Miranda-Carboni, Amy N Abell.
      Disruption of fetal growth results in severe consequences to human health, including increased fetal and neonatal morbidity and mortality, as well as potential lifelong health problems. Molecular mechanisms promoting fetal growth represent potential therapeutic strategies to treat and/or prevent fetal growth restriction (FGR). Here we identify a previously unknown role for the mitogen-activated protein kinase kinase kinase 4 (MAP3K4) in promoting fetal and placental growth. We demonstrate inactivation of MAP3K4 kinase activity causes FGR due in part to placental insufficiency. Significantly, MAP3K4 kinase-inactive mice display highly penetrant lethality prior to weaning and persistent growth reduction of surviving adults. Additionally, we elucidate molecular mechanisms by which MAP3K4 promotes growth through the control of the insulin-like growth factor 1 receptor (IGF1R), insulin receptor (IR), and Akt signaling pathway. Specifically, MAP3K4 kinase inactivation in trophoblast stem (TS) cells results in reduced IGF1R and IR expression and decreased Akt activation. We observe these changes in TS cells also occur in differentiated trophoblasts created through in vitro differentiation of cultured TS cells and in vivo in placental tissues formed by TS cells. Furthermore, we show that MAP3K4 controls this pathway by promoting Igf1r transcript expression in TS cells through activation of CREB binding protein (CBP). In the MAP3K4 kinase-inactive TS cells, Igf1r transcripts are repressed due to reduced CBP activity and increased histone deacetylase 6 (HDAC6) expression and activity. Together, these data demonstrate a critical role for MAP3K4 in promoting fetal and placental growth by controlling the activity of the IGF1R/IR and Akt signaling pathway.
    Keywords:  Akt/PKB; MAP3K4; fetal growth restriction; insulin receptor; insulin-like growth factor; insulin-like growth factor receptor; placenta; protein kinase
    DOI:  https://doi.org/10.1016/j.jbc.2022.102310
  5. Am J Hum Genet. 2022 Aug 04. pii: S0002-9297(22)00309-3. [Epub ahead of print]109(8): 1520-1533
    Exome sequencing reveals a distinct somatic genomic landscape in breast cancer from women with germline PTEN variants.
    Takae Brewer, Lamis Yehia, Peter Bazeley, Charis Eng.
      Germline PTEN variants (PTEN hamartoma tumor syndrome [PHTS]) confer up to 85% lifetime risk of female breast cancer (BC). BCs arising in PHTS are clinically distinct from sporadic BCs, including younger age of onset, multifocality, and an increased risk of second primary BCs. Yet, there is no previous investigation into the underlying genomic landscape of this entity. We sought to address the hypothesis that BCs arising in PHTS have a distinct genomic landscape compared to sporadic counterparts. We performed and analyzed exome sequencing data from 44 women with germline PTEN variants who developed BCs. The control cohort comprised of 497 women with sporadic BCs from The Cancer Genome Atlas (TCGA) dataset. We demonstrate that PHTS-derived BCs have a distinct somatic mutational landscape compared to the sporadic counterparts, namely second somatic hits in PTEN, distinct mutational signatures, and increased genomic instability. The PHTS group had a significantly higher frequency of somatic PTEN variants compared to TCGA (22.7% versus 5.6%; odds ratio [OR] 4.93; 95% confidence interval [CI] 2.21 to 10.98; p < 0.001) and a lower mutational frequency in PIK3CA (22.7% versus 33.4%; OR 0.59; 95% CI 0.28 to 1.22; p = 0.15). Somatic variants in PTEN and PIK3CA were mutually exclusive in PHTS (p = 0.01) but not in TCGA. Our findings have important implications for the personalized management of PTEN-related BCs, especially in the context of more accessible genetic testing.
    Keywords:  PTEN; PTEN hamartoma tumor syndrome; breast cancer; exome seqeuncing; tumor profiling; tumor suppressor gene
    DOI:  https://doi.org/10.1016/j.ajhg.2022.07.005
  6. Nat Cell Biol. 2022 Aug 04.
    Nucleotide imbalance decouples cell growth from cell proliferation.
    Frances F Diehl, Teemu P Miettinen, Ryan Elbashir, Christopher S Nabel, Alicia M Darnell, Brian T Do, Scott R Manalis, Caroline A Lewis, Matthew G Vander Heiden.
      Nucleotide metabolism supports RNA synthesis and DNA replication to enable cell growth and division. Nucleotide depletion can inhibit cell growth and proliferation, but how cells sense and respond to changes in the relative levels of individual nucleotides is unclear. Moreover, the nucleotide requirement for biomass production changes over the course of the cell cycle, and how cells coordinate differential nucleotide demands with cell cycle progression is not well understood. Here we find that excess levels of individual nucleotides can inhibit proliferation by disrupting the relative levels of nucleotide bases needed for DNA replication and impeding DNA replication. The resulting purine and pyrimidine imbalances are not sensed by canonical growth regulatory pathways like mTORC1, Akt and AMPK signalling cascades, causing excessive cell growth despite inhibited proliferation. Instead, cells rely on replication stress signalling to survive during, and recover from, nucleotide imbalance during S phase. We find that ATR-dependent replication stress signalling is activated during unperturbed S phases and promotes nucleotide availability to support DNA replication. Together, these data reveal that imbalanced nucleotide levels are not detected until S phase, rendering cells reliant on replication stress signalling to cope with this metabolic problem and disrupting the coordination of cell growth and division.
    DOI:  https://doi.org/10.1038/s41556-022-00965-1
  7. Clin Genet. 2022 Aug 03.
    Looking closely at overgrowth: Constitutional mosaicism in PTEN hamartoma tumor syndrome.
    Haley Newman, Jessica M Long, Kristin Zelley, Sarah Baldino, Marilyn M Li, Kara N Maxwell, Suzanne P MacFarland.
      
    DOI:  https://doi.org/10.1111/cge.14202
  8. Am J Physiol Cell Physiol. 2022 Aug 01.
    Convergence of Signaling Pathways in Mediating Actions of Leucine and IGF-1 on mTORC1 in L6 Myoblasts.
    Paul A Roberson, Leonard S Jefferson, Scot R Kimball.
      Leucine and Insulin-like Growth Factor-1 (IGF-1) are important regulators of protein synthesis in skeletal muscle. The mechanistic target of rapamycin complex 1 (mTORC1) is of particular importance in their mechanism of action. In the present study, pathways through which leucine and IGF-1 converge to mediate activation of mTORC1 were examined in L6 myoblasts that were deprived of leucine and serum followed by readdition of either leucine or IGF-1. Compared to leucine- and serum-deprived myoblasts, IGF-1, but not leucine, promoted phosphorylation of Protein Kinase B (AKT), Tuberous Sclerosis Complex 2 (TSC2), and the autophosphorylation site on mTOR (S2481) and also stimulated mTOR kinase activity in mTOR immunoprecipitated samples. Both leucine and IGF-1 promoted phosphorylation of mTOR on S2448. The association of mTOR with the Regulatory Associated Protein of mTOR (Raptor) was altered by IGF-1 treatment and trended (p=0.065) to be altered by leucine treatment. Alterations in the association of mTOR with Raptor were proportional to changes in phosphorylation of the mTOR substrates, eIF4E-Binding Protein 1 (4E-BP1) and Ribosomal Protein S6 Kinase-β1 (p70S6K1). Surprisingly, leucine, but not IGF-1, stimulated protein synthesis suggesting a unique role for nutrients in regulating protein synthesis. Overall, the results are consistent with a model whereby IGF-1 stimulates phosphorylation of 4E-BP1 and p70S6K1 in L6 myoblasts through an AKT-TSC2-mTORC1 signaling pathway that also involves changes in the interaction between mTOR and Raptor. In contrast, leucine signaling to mTOR results in alterations in certain mTOR phosphorylation sites, the interaction between mTOR and Raptor, and stimulates protein synthesis.
    Keywords:  Cellular Signaling; Metabolism; Protein Synthesis; Skeletal Muscle
    DOI:  https://doi.org/10.1152/ajpcell.00183.2022
  9. Liver Int. 2022 Aug 04.
    Inhibition of polyploidization in Pten-deficient livers reduces steatosis.
    Eva Moreno, Augustine B Matondo, Laura Bongiovanni, Chris H A van de Lest, Martijn R Molenaar, Mathilda J M Toussaint, Saskia C van Essen, Martin Houweling, J Bernd Helms, Bart Westendorp, Alain de Bruin.
      The tumor suppressor PTEN is a negative regulator of the PI3K/AKT signaling pathway. Liver-specific deletion of Pten in mice results in the hyper-activation PI3K/AKT signaling accompanied with enhanced genome duplication (polyploidization), marked lipid accumulation (steatosis) and formation of hepatocellular carcinomas. However, it is unknown whether polyploidization in this model has an impact on the development of steatosis and the progression towards liver cancer. Here, we used a liver-specific conditional knockout approach to delete Pten in combination with deletion of E2f7/8, known key inducers of polyploidization. As expected, Pten deletion caused severe steatosis and liver tumors accompanied by enhanced polyploidization. Additional deletion of E2f7/8 inhibited polyploidization, alleviated Pten-induced steatosis without affecting lipid species composition and accelerated liver tumor progression. Global transcriptomic analysis showed that inhibition of polyploidization in Pten-deficient livers resulted in reduced expression of genes involved in energy metabolism, including PPAR-gamma signaling. However, we find no evidence that deregulated genes in Pten-deficient livers are direct transcriptional targets of E2F7/8, supporting that reduction in steatosis and progression towards liver cancer are likely consequences of inhibiting polyploidization. Lastly, flow cytometry and image analysis on isolated primary wildtype mouse hepatocytes provided further support that polyploid cells can accumulate more lipid droplets than diploid hepatocytes. Collectively, we show that polyploidization promotes steatosis and function as an important barrier against liver tumor progression in Pten-deficient livers.
    Keywords:  Atypical E2Fs; Conditional knockout mice; Hepatocellular Carcinoma; Non-alcoholic fatty liver disease; PTEN; Polyploidization; Steatosis
    DOI:  https://doi.org/10.1111/liv.15384
  10. Nat Commun. 2022 Aug 05. 13(1): 4562
    Afadin couples RAS GTPases to the polarity rheostat Scribble.
    Marilyn Goudreault, Valérie Gagné, Chang Hwa Jo, Swati Singh, Ryan C Killoran, Anne-Claude Gingras, Matthew J Smith.
      AFDN/Afadin is required for establishment and maintenance of cell-cell contacts and is a unique effector of RAS GTPases. The biological consequences of RAS complex with AFDN are unknown. We used proximity-based proteomics to generate an interaction map for two isoforms of AFDN, identifying the polarity protein SCRIB/Scribble as the top hit. We reveal that the first PDZ domain of SCRIB and the AFDN FHA domain mediate a direct but non-canonical interaction between these important adhesion and polarity proteins. Further, the dual RA domains of AFDN have broad specificity for RAS and RAP GTPases, and KRAS co-localizes with AFDN and promotes AFDN-SCRIB complex formation. Knockout of AFDN or SCRIB in epithelial cells disrupts MAPK and PI3K activation kinetics and inhibits motility in a growth factor-dependent manner. These data have important implications for understanding why cells with activated RAS have reduced cell contacts and polarity defects and implicate AFDN as a genuine RAS effector.
    DOI:  https://doi.org/10.1038/s41467-022-32335-8
  11. Sci Transl Med. 2022 Aug 03. 14(656): eabn7571
    Triple-negative breast cancer metastasis involves complex epithelial-mesenchymal transition dynamics and requires vimentin.
    Eloïse M Grasset, Matthew Dunworth, Gaurav Sharma, Melanie Loth, Joseph Tandurella, Ashley Cimino-Mathews, Melissa Gentz, Sydney Bracht, Meagan Haynes, Elana J Fertig, Andrew J Ewald.
      Triple-negative breast cancer (TNBC) is an aggressive subtype associated with early metastatic recurrence and worse patient outcomes. TNBC tumors express molecular markers of the epithelial-mesenchymal transition (EMT), but its requirement during spontaneous TNBC metastasis in vivo remains incompletely understood. We demonstrated that spontaneous TNBC tumors from a genetically engineered mouse model (GEMM), multiple patient-derived xenografts, and archival patient samples exhibited large populations in vivo of hybrid E/M cells that lead invasion ex vivo while expressing both epithelial and mesenchymal characteristics. The mesenchymal marker vimentin promoted invasion and repressed metastatic outgrowth. We next tested the requirement for five EMT transcription factors and observed distinct patterns of utilization during invasion and colony formation. These differences suggested a sequential activation of multiple EMT molecular programs during the metastatic cascade. Consistent with this model, our longitudinal single-cell RNA analysis detected three different EMT-related molecular patterns. We observed cancer cells progressing from epithelial to hybrid E/M and strongly mesenchymal patterns during invasion and from epithelial to a hybrid E/M pattern during colony formation. We next investigated the relative epithelial versus mesenchymal state of cancer cells in both GEMM and patient metastases. In both contexts, we observed heterogeneity between and within metastases in the same individual. We observed a complex spectrum of epithelial, hybrid E/M, and mesenchymal cell states within metastases, suggesting that there are multiple successful molecular strategies for distant organ colonization. Together, our results demonstrate an important and complex role for EMT programs during TNBC metastasis.
    DOI:  https://doi.org/10.1126/scitranslmed.abn7571
  12. Sci Adv. 2022 Aug 05. 8(31): eabj7176
    Cross-species identification of cancer resistance-associated genes that may mediate human cancer risk.
    Nishanth Ulhas Nair, Kuoyuan Cheng, Lamis Naddaf, Elad Sharon, Lipika R Pal, Padma S Rajagopal, Irene Unterman, Kenneth Aldape, Sridhar Hannenhalli, Chi-Ping Day, Yuval Tabach, Eytan Ruppin.
      Cancer is a predominant disease across animals. We applied a comparative genomics approach to systematically characterize genes whose conservation levels correlate positively (PC) or negatively (NC) with cancer resistance estimates across 193 vertebrates. Pathway analysis reveals that NC genes are enriched for metabolic functions and PC genes in cell cycle regulation, DNA repair, and immune response, pointing to their corresponding roles in mediating cancer risk. We find that PC genes are less tolerant to loss-of-function (LoF) mutations, are enriched in cancer driver genes, and are associated with germline mutations that increase human cancer risk. Their relevance to cancer risk is further supported via the analysis of mouse functional genomics and cancer mortality of zoo mammals' data. In sum, our study describes a cross-species genomic analysis pointing to candidate genes that may mediate human cancer risk.
    DOI:  https://doi.org/10.1126/sciadv.abj7176
  13. Dev Cell. 2022 Jul 31. pii: S1534-5807(22)00497-X. [Epub ahead of print]
    A robust and tunable system for targeted cell ablation in developing embryos.
    Zahra Labbaf, Kleio Petratou, Laura Ermlich, Wilko Backer, Katsiaryna Tarbashevich, Michal Reichman-Fried, Stefan Luschnig, Stefan Schulte-Merker, Erez Raz.
      Cell ablation is a key method in the research fields of developmental biology, tissue regeneration, and tissue homeostasis. Eliminating specific cell populations allows for characterizing interactions that control cell differentiation, death, behavior, and spatial organization of cells. Current methodologies for inducing cell death suffer from relatively slow kinetics, making them unsuitable for analyzing rapid events and following primary and immediate consequences of the ablation. To address this, we developed a cell-ablation system that is based on bacterial toxin/anti-toxin proteins and enables rapid and cell-autonomous elimination of specific cell types and organs in zebrafish embryos. A unique feature of this system is that it uses an anti-toxin, which allows for controlling the degree and timing of ablation and the resulting phenotypes. The transgenic zebrafish generated in this work represent a highly efficient tool for cell ablation, and this approach is applicable to other model organisms as demonstrated here for Drosophila.
    Keywords:  cell ablation; neuron; notochord; organogenesis; regeneration; tissue ablation; toxin; vasculature; zebrafish
    DOI:  https://doi.org/10.1016/j.devcel.2022.07.008
  14. Stem Cell Reports. 2022 Jul 19. pii: S2213-6711(22)00362-9. [Epub ahead of print]
    Dual inhibition of MAPK and PI3K/AKT pathways enhances maturation of human iPSC-derived cardiomyocytes.
    Bayardo I Garay, Sophie Givens, Phablo Abreu, Man Liu, Doğacan Yücel, June Baik, Noah Stanis, Taylor M Rothermel, Alessandro Magli, Juan E Abrahante, Natalya A Goloviznina, Hossam A N Soliman, Neha R Dhoke, Michael Kyba, Patrick W Alford, Samuel C Dudley, Jop H van Berlo, Brenda Ogle, Rita R C Perlingeiro.
      Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) provide great opportunities for mechanistic dissection of human cardiac pathophysiology; however, hiPSC-CMs remain immature relative to the adult heart. To identify novel signaling pathways driving the maturation process during heart development, we analyzed published transcriptional and epigenetic datasets from hiPSC-CMs and prenatal and postnatal human hearts. These analyses revealed that several components of the MAPK and PI3K-AKT pathways are downregulated in the postnatal heart. Here, we show that dual inhibition of these pathways for only 5 days significantly enhances the maturation of day 30 hiPSC-CMs in many domains: hypertrophy, multinucleation, metabolism, T-tubule density, calcium handling, and electrophysiology, many equivalent to day 60 hiPSC-CMs. These data indicate that the MAPK/PI3K/AKT pathways are involved in cardiomyocyte maturation and provide proof of concept for the manipulation of key signaling pathways for optimal hiPSC-CM maturation, a critical aspect of faithful in vitro modeling of cardiac pathologies and subsequent drug discovery.
    Keywords:  MAPK; PI3K-AKT; calcium handling; cardiomyocyte; electrophysiology; inhibitors; maturation; multinucleation; pluripotent stem cells
    DOI:  https://doi.org/10.1016/j.stemcr.2022.07.003
  15. Proc Natl Acad Sci U S A. 2022 Aug 09. 119(32): e2208855119
    Unexpected role for IGF-1 in starvation: Maintenance of blood glucose.
    Fei Fang, Joseph L Goldstein, Xuanming Shi, Guosheng Liang, Michael S Brown.
      Wild-type (WT) mice maintain viable levels of blood glucose even when adipose stores are depleted by 6 d of 60% calorie restriction followed by a 23-h fast (hereafter designated as "starved" mice). Survival depends on ghrelin, an octanoylated peptide hormone. Mice that lack ghrelin suffer lethal hypoglycemia when subjected to the same starvation regimen. Ghrelin is known to stimulate secretion of growth hormone (GH), which in turn stimulates secretion of IGF-1 (insulin-like growth factor-1). In the current study, we found that starved ghrelin-deficient mice had a 90% reduction in plasma IGF-1 when compared with starved WT mice. Injection of IGF-1 in starved ghrelin-deficient mice caused a twofold increase in glucose production and raised blood glucose to levels seen in starved WT mice. Increased glucose production was accompanied by increases in plasma glycerol, fatty acids and ketone bodies, and hepatic triglycerides. All of these increases were abolished when the mice were treated with atglistatin, an inhibitor of adipose tissue triglyceride lipase. We conclude that IGF-1 stimulates adipose tissue lipolysis in starved mice and that this lipolysis supplies energy and substrates that restore hepatic gluconeogenesis. This action of IGF-1 in starved mice is in contrast to its known action in inhibiting adipose tissue lipase in fed mice. Surprisingly, the ghrelin-dependent maintenance of plasma IGF-1 in starved mice was not mediated by GH. Direct injection of GH into starved ghrelin-deficient mice failed to increase plasma IGF-1. These data call attention to an unsuspected role of IGF-1 in the adaptation to starvation.
    Keywords:  IGF-1; adipose tissue lipolysis; ghrelin-deficient mice; growth hormone-releasing hormone; hypoglycemia
    DOI:  https://doi.org/10.1073/pnas.2208855119
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