The compensatory proliferation of insulin-producing β cells is critical to maintaining glucose homeostasis at the early stage of type 2 diabetes. Failure of β cells to proliferate results in hyperglycemia and insulin dependence in patients. To understand the effect of the interplay between β cell compensation and lipid metabolism upon obesity and peripheral insulin resistance, we eliminated LDL receptor–related protein 1 (LRP1), a pleiotropic mediator of cholesterol, insulin, energy metabolism, and other cellular processes, in β cells. Upon high-fat diet exposure, LRP1 ablation significantly impaired insulin secretion and proliferation of β cells. The diminished insulin signaling was partly contributed to by the hypersensitivity to glucose-induced, Ca2+-dependent activation of Erk and the mTORC1 effector p85 S6K1. Surprisingly, in LRP1-deficient islets, lipotoxic sphingolipids were mitigated by improved lipid metabolism, mediated at least in part by the master transcriptional regulator PPARγ2. Acute overexpression of PPARγ2 in β cells impaired insulin signaling and insulin secretion. Elimination of Apbb2, a functional regulator of LRP1 cytoplasmic domain, also impaired β cell function in a similar fashion. In summary, our results uncover the double-edged effects of intracellular lipid metabolism on β cell function and viability in obesity and type 2 diabetes and highlight LRP1 as an essential regulator of these processes.
Risheng Ye, Ruth Gordillo, Mengle Shao, Toshiharu Onodera, Zhe Chen, Shiuhwei Chen, Xiaoli Lin, Jeffrey A. SoRelle, Xiaohong Li, Miao Tang, Mark P. Keller, Regina Kuliawat, Alan D. Attie, Rana K. Gupta, William L. Holland, Bruce Beutler, Joachim Herz, Philipp E. Scherer
Major histocompatibility (MHC) class II molecules are strongly associated with many autoimmune disorders. In type 1 diabetes, the DQ8 molecule is common, confers significant disease risk and is involved in disease pathogenesis. We hypothesized blocking DQ8 antigen presentation would provide therapeutic benefit by preventing recognition of self-peptides by pathogenic T cells. We used the crystal structure of DQ8 to select drug-like small molecules predicted to bind structural pockets in the MHC antigen-binding cleft. A limited number of the predicted compounds inhibited DQ8 antigen presentation in vitro with one compound preventing insulin autoantibody production and delaying diabetes onset in an animal model of spontaneous autoimmune diabetes. An existing drug of similar structure, methyldopa, specifically blocked DQ8 in recent-onset patients with type 1 diabetes along with reducing inflammatory T cell responses toward insulin, highlighting the relevance of blocking disease-specific MHC class II antigen presentation to treat autoimmunity.
David A. Ostrov, Aimon Alkanani, Kristen A. McDaniel, Stephanie Case, Erin E. Baschal, Laura Pyle, Samuel Ellis, Bernadette Pöllinger, Katherine J. Seidl, Viral N. Shah, Satish K. Garg, Mark A. Atkinson, Peter A. Gottlieb, Aaron W. Michels
BACKGROUND. Amongst non-diabetic individuals, mild glucose decrements alter brain activity in regions linked to reward, motivation and executive control. Whether these effects differ in T1DM patients with and without hypoglycemia awareness remains unclear. METHODS. 42 individuals (13 healthy control subjects (HC), 16 T1DM individuals with hypoglycemia awareness (T1DM-Aware) and 13 T1DM individuals with hypoglycemia unawareness (T1DM-Unaware)) underwent BOLD fMRI brain imaging during a 2-step hyperinsulinemic euglycemic (90 mg/dl)-hypoglycemic (60 mg/dl) clamp for assessment of neural responses to mild hypoglycemia. RESULTS. Mild hypoglycemia in HC altered activity in the caudate, insula, prefrontal cortex, and angular gyrus, whereas T1DM-Aware subjects showed no caudate and insula changes, but showed altered activation patterns in the prefrontal cortex and angular gyrus. Most strikingly, in direct contrast to HC and T1DM-Aware subjects, T1DM-Unaware subjects failed to show any hypoglycemia-induced changes in brain activity. These findings were also associated with blunted hormonal counterregulatory responses and hypoglycemia symptoms scores during mild hypoglycemia. CONCLUSION. In T1DM, and in particular T1DM-Unaware patients, there is a progressive blunting of brain responses in cortico-striatal and fronto-parietal neurocircuits in response to mild-moderate hypoglycemia. These findings have implications for understanding why individuals with impaired hypoglycemia awareness fail to respond appropriately to falling blood glucose levels. FUNDING. This study was supported in part by grants from the NIH R01DK020495 and P30 DK045735 (Sherwin), K23DK109284 (Hwang), K08AA023545 (Seo), the Yale Center for Clinical Investigation supported by the Clinical Translational Science Award (UL1 RR024139).
Janice Jin Hwang, Lisa Parikh, Cheryl Lacadie, Dongju Seo, Wai Lam, Muhammad Hamza, Christian Schmidt, Feng Dai, Anne-Sophie Sejling, Renata Belfort-DeAguiar, R. Todd Constable, Rajita Sinha, Robert Sherwin
An increase in hepatic glucose production (HGP) is a key feature of type 2 diabetes. Excessive signaling through hepatic Gs–linked glucagon receptors critically contributes to pathologically elevated HGP. Here, we tested the hypothesis that this metabolic impairment can be counteracted by enhancing hepatic Gi signaling. Specifically, we used a chemogenetic approach to selectively activate Gi-type G proteins in mouse hepatocytes in vivo. Unexpectedly, activation of hepatic Gi signaling triggered a pronounced increase in HGP and severely impaired glucose homeostasis. Moreover, increased Gi signaling stimulated glucose release in human hepatocytes. A lack of functional Gi-type G proteins in hepatocytes reduced blood glucose levels and protected mice against the metabolic deficits caused by the consumption of a high-fat diet. Additionally, we delineated a signaling cascade that links hepatic Gi signaling to ROS production, JNK activation, and a subsequent increase in HGP. Taken together, our data support the concept that drugs able to block hepatic Gi–coupled GPCRs may prove beneficial as antidiabetic drugs.
Mario Rossi, Lu Zhu, Sara M. McMillin, Sai Prasad Pydi, Shanu Jain, Lei Wang, Yinghong Cui, Regina J. Lee, Amanda H. Cohen, Hideaki Kaneto, Morris J. Birnbaum, Yanling Ma, Yaron Rotman, Jie Liu, Travis J. Cyphert, Toren Finkel, Owen P. McGuinness, Jürgen Wess
Histone protein modifications control fate determination during normal development and dedifferentiation during disease. Here, we set out to determine the extent to which dynamic changes to histones affect the differentiated phenotype of ordinarily quiescent adult glomerular podocytes. To do this, we examined the consequences of shifting the balance of the repressive histone H3 lysine 27 trimethylation (H3K27me3) mark in podocytes. Adriamycin nephrotoxicity and subtotal nephrectomy (SNx) studies indicated that deletion of the histone methylating enzyme EZH2 from podocytes decreased H3K27me3 levels and sensitized mice to glomerular disease. H3K27me3 was enriched at the promoter region of the Notch ligand Jag1 in podocytes, and derepression of Jag1 by EZH2 inhibition or knockdown facilitated podocyte dedifferentiation. Conversely, inhibition of the Jumonji C domain–containing demethylases Jmjd3 and UTX increased the H3K27me3 content of podocytes and attenuated glomerular disease in adriamycin nephrotoxicity, SNx, and diabetes. Podocytes in glomeruli from humans with focal segmental glomerulosclerosis or diabetic nephropathy exhibited diminished H3K27me3 and heightened UTX content. Analogous to human disease, inhibition of Jmjd3 and UTX abated nephropathy progression in mice with established glomerular injury and reduced H3K27me3 levels. Together, these findings indicate that ostensibly stable chromatin modifications can be dynamically regulated in quiescent cells and that epigenetic reprogramming can improve outcomes in glomerular disease by repressing the reactivation of developmental pathways.
Syamantak Majumder, Karina Thieme, Sri N. Batchu, Tamadher A. Alghamdi, Bridgit B. Bowskill, M. Golam Kabir, Youan Liu, Suzanne L. Advani, Kathryn E. White, Laurette Geldenhuys, Karthik K. Tennankore, Penelope Poyah, Ferhan S. Siddiqi, Andrew Advani
The discovery, characterization, and clinical development of glucagon-like-peptide-1 (GLP-1) spans more than 30 years and includes contributions from multiple investigators, science recognized by the 2017 Harrington Award Prize for Innovation in Medicine. Herein, we provide perspectives on the historical events and key experimental findings establishing the biology of GLP-1 as an insulin-stimulating glucoregulatory hormone. Important attributes of GLP-1 action and enteroendocrine science are reviewed, with emphasis on mechanistic advances and clinical proof-of-concept studies. The discovery that GLP-2 promotes mucosal growth in the intestine is described, and key findings from both preclinical studies and the GLP-2 clinical development program for short bowel syndrome (SBS) are reviewed. Finally, we summarize recent progress in GLP biology, highlighting emerging concepts and scientific insights with translational relevance.
Daniel J. Drucker, Joel F. Habener, Jens Juul Holst
Glucagon plays a major role in the regulation of glucose homeostasis during fed and fasting states. However, the mechanisms responsible for the regulation of pancreatic α cell mass and function are not completely understood. In the current study, we identified mTOR complex 1 (mTORC1) as a major regulator of α cell mass and glucagon secretion. Using mice with tissue-specific deletion of the mTORC1 regulator Raptor in α cells (αRaptorKO), we showed that mTORC1 signaling is dispensable for α cell development, but essential for α cell maturation during the transition from a milk-based diet to a chow-based diet after weaning. Moreover, inhibition of mTORC1 signaling in αRaptorKO mice and in WT animals exposed to chronic rapamycin administration decreased glucagon content and glucagon secretion. In αRaptorKO mice, impaired glucagon secretion occurred in response to different secretagogues and was mediated by alterations in KATP channel subunit expression and activity. Additionally, our data identify the mTORC1/FoxA2 axis as a link between mTORC1 and transcriptional regulation of key genes responsible for α cell function. Thus, our results reveal a potential function of mTORC1 in nutrient-dependent regulation of glucagon secretion and identify a role for mTORC1 in controlling α cell–mass maintenance.
Nadejda Bozadjieva, Manuel Blandino-Rosano, Jennifer Chase, Xiao-Qing Dai, Kelsey Cummings, Jennifer Gimeno, Danielle Dean, Alvin C. Powers, George K. Gittes, Markus A. Rüegg, Michael N. Hall, Patrick E. MacDonald, Ernesto Bernal-Mizrachi
Deficiency in Krüppel-like zinc finger transcription factor GLI-similar 3 (GLIS3) in humans is associated with the development of congenital hypothyroidism. However, the functions of GLIS3 in the thyroid gland and the mechanism by which GLIS3 dysfunction causes hypothyroidism are unknown. In the current study, we demonstrate that GLIS3 acts downstream of thyroid-stimulating hormone (TSH) and TSH receptor (TSHR) and is indispensable for TSH/TSHR-mediated proliferation of thyroid follicular cells and biosynthesis of thyroid hormone. Using ChIP-Seq and promoter analysis, we demonstrate that GLIS3 is critical for the transcriptional activation of several genes required for thyroid hormone biosynthesis, including the iodide transporters Nis and Pds, both of which showed enhanced GLIS3 binding at their promoters. The repression of cell proliferation of GLIS3-deficient thyroid follicular cells was due to the inhibition of TSH-mediated activation of the mTOR complex 1/ribosomal protein S6 (mTORC1/RPS6) pathway as well as the reduced expression of several cell division–related genes regulated directly by GLIS3. Consequently, GLIS3 deficiency in a murine model prevented the development of goiter as well as the induction of inflammatory and fibrotic genes during chronic elevation of circulating TSH. Our study identifies GLIS3 as a key regulator of TSH/TSHR-mediated thyroid hormone biosynthesis and proliferation of thyroid follicular cells and uncovers a mechanism by which GLIS3 deficiency causes neonatal hypothyroidism and prevents goiter development.
Hong Soon Kang, Dhirendra Kumar, Grace Liao, Kristin Lichti-Kaiser, Kevin Gerrish, Xiao-Hui Liao, Samuel Refetoff, Raja Jothi, Anton M. Jetten
Although peptides are safe and useful as therapeutics, they are often easily degraded or metabolized. Dampening the clearance system for peptide ligands is a promising strategy for increasing the efficacy of peptide therapies. Natriuretic peptide receptor B (NPR-B) and its naturally occurring ligand, C-type natriuretic peptide (CNP), are potent stimulators of endochondral bone growth, and activating the CNP/NPR-B system is expected to be a powerful strategy for treating impaired skeletal growth. CNP is cleared by natriuretic peptide clearance receptor (NPR-C); therefore, we investigated the effect of reducing the rate of CNP clearance on skeletal growth by limiting the interaction between CNP and NPR-C. Specifically, we generated transgenic mice with increased circulating levels of osteocrin (OSTN) protein, a natural NPR-C ligand without natriuretic activity, and observed a dose-dependent skeletal overgrowth phenotype in these animals. Skeletal overgrowth in OSTN-transgenic mice was diminished in either CNP- or NPR-C–depleted backgrounds, confirming that CNP and NPR-C are indispensable for the bone growth–stimulating effect of OSTN. Interestingly, double-transgenic mice of CNP and OSTN had even higher levels of circulating CNP and additional increases in bone length, as compared with mice with elevated CNP alone. Together, these results support OSTN administration as an adjuvant agent for CNP therapy and provide a potential therapeutic approach for diseases with impaired skeletal growth.
Yugo Kanai, Akihiro Yasoda, Keita P. Mori, Haruko Watanabe-Takano, Chiaki Nagai-Okatani, Yui Yamashita, Keisho Hirota, Yohei Ueda, Ichiro Yamauchi, Eri Kondo, Shigeki Yamanaka, Yoriko Sakane, Kazumasa Nakao, Toshihito Fujii, Hideki Yokoi, Naoto Minamino, Masashi Mukoyama, Naoki Mochizuki, Nobuya Inagaki
Inadequate pancreatic β cell function underlies type 1 and type 2 diabetes mellitus. Strategies to expand functional cells have focused on discovering and controlling mechanisms that limit the proliferation of human β cells. Here, we developed an engraftment strategy to examine age-associated human islet cell replication competence and reveal mechanisms underlying age-dependent decline of β cell proliferation in human islets. We found that exendin-4 (Ex-4), an agonist of the glucagon-like peptide 1 receptor (GLP-1R), stimulates human β cell proliferation in juvenile but not adult islets. This age-dependent responsiveness does not reflect loss of GLP-1R signaling in adult islets, since Ex-4 treatment stimulated insulin secretion by both juvenile and adult human β cells. We show that the mitogenic effect of Ex-4 requires calcineurin/nuclear factor of activated T cells (NFAT) signaling. In juvenile islets, Ex-4 induced expression of calcineurin/NFAT signaling components as well as target genes for proliferation-promoting factors, including NFATC1, FOXM1, and CCNA1. By contrast, expression of these factors in adult islet β cells was not affected by Ex-4 exposure. These studies reveal age-dependent signaling mechanisms regulating human β cell proliferation, and identify elements that could be adapted for therapeutic expansion of human β cells.
Chunhua Dai, Yan Hang, Alena Shostak, Greg Poffenberger, Nathaniel Hart, Nripesh Prasad, Neil Phillips, Shawn E. Levy, Dale L. Greiner, Leonard D. Shultz, Rita Bottino, Seung K. Kim, Alvin C. Powers