- Email: [email protected]
FISHing for β Cells
Developmental Cell
Previews FISHing for b Cells Laura I. Hudish,1 David S. Lorberbaum,1 and Lori Sussel1,* 1Barbara Davis Center for Diabetes, University of Colorado Anschutz Medical Center, Aurora, CO 80045, USA *Correspondence: [email protected] https://doi.org/10.1016/j.devcel.2018.12.007
b cell heterogeneity has emerged as an important contributor to islet function, with potential implications for diabetes. Using an optimized smFISH technique in intact islets, Farack et al. (2018) identify in the islet core an endocrine cell population of ‘‘extreme’’ b cells with distinct molecular properties. Diabetes mellitus is a complex disease caused by the dysfunction and ultimate loss of the insulin-producing b cells that reside in the pancreatic islets of Langerhans. With the recent discovery of islet cell plasticity and b cell heterogeneity (reviewed in Gutie´rrez et al., 2017), the composition of the b cell population has become central to how we think about b cell function and the development of diabetes. Instead of a fixed and homogeneous b cell population, single-cell technologies have revealed transcriptionally and functionally distinct b cell subsets (Wang et al., 2016; Dorrell et al., 2016). However, most studies thus far have captured the molecular and functional characteristics of dissociated b cells, neglecting the contributions of cell-cell connections and overall islet structure (Benninger and Hodson, 2018). In this issue of Developmental Cell, Farack et al. (2018) use an optimized single-molecule transcript imaging technique to examine b cell heterogeneity in the intact islet. Using this approach, the authors identify a unique b cell population termed ‘‘extreme’’ b cells that is located within the islet core. The extreme b cells are characterized by a distinctive intracellular polarization pattern, higher pro-insulin and ribosomal RNA content, and less mature insulin protein (Figure 1). Based on these characteristics, Farack et al. (2018) hypothesize that the extreme b cells may have a higher basal insulin secretion rate compared to non-extreme cells; however, the exact function of these cells remains to be explored. These data are consistent with another recent study that employed a modified small molecule (sm)FISH technique called fliFISH to identify within the core of the islet a subpopulation of b cells that express more Ins2 and Nkx2.2 mRNA compared to b cells located at the islet
periphery (Cui et al., 2018). Both studies support the findings in earlier functional studies that more-mature b cells were located centrally in the islet, whereas less-mature b cells were found at the periphery (Stefan et al., 1987). Farack et al. (2018) took their analysis further to determine whether the extreme b cells represented several recently described specialized b cell populations (Johnston et al., 2016; van der Meulen et al., 2017). However, characterization of the extreme b cells for the expression of several b cells markers, including Pdx1, Ucn3, and the glucose transporter Slc2a2, suggested that extreme cells are distinct from previously characterized hub and virgin cell populations. To determine whether the extreme b cells contribute to the overall function of the islet and whether they are affected by disease, Farack et al. (2018) also examined whether insulin resistance in diabetic Leprdb/db (db/db) mice affected the balance between extreme and non-extreme cells. The authors observed that the larger islets in db/db mice had significantly more extreme cells than healthy islets. This observation suggests that either the extreme cells have higher proliferative capacity that could favor their expansion, or the non-extreme cells convert to the extreme phenotype. Which of these alternatives underlies the extreme cell expansion is not yet clear. In a recent study, Bader et al. (2016) identified Flattop as a marker that distinguished proliferationcompetent versus functionally mature b cells in mouse islets (Bader et al., 2016); however, Flattop expression was not characterized in the extreme b cell population. Altogether, Farack et al. (2018) identify and describe a b cell population with distinct molecular features and a robust adaptive response to insulin resistance. Additional studies will be needed to
define the functional differences between extreme and non-extreme cells, including assessment of parameters such as proliferative capacity, calcium signaling, and/ or islet connectivity. It will also be interesting to follow these cells during disease onset and progression. It is well appreciated that b cells have the unique ability to adapt to abrupt glycemic changes by altering insulin production. The identification of these heterogeneous subsets of b cells within the islet suggests that rather than a single b cell altering its function in response to glycemic fluctuations, adjustment in the relative ratios of different b cell populations may be responsible for optimal responses to changing metabolic states. Although the smFISH analysis from Farack et al. (2018) and the fliFISH technique mentioned above (Cui et al., 2018) were applied to mouse tissues, similar in situ single-molecule techniques could be a valuable resource to characterize human islets. Dorrell et al. (2016) identified four antigenically diverse human b cell populations (b1–4) with unique characteristics. Each population showed distinct gene expression profiles and insulin secretion capabilities, with the lowest basal insulin secretion properties associated with the most abundant b1 population and highest insulin secretion capabilities found in the rarest b4 population. It would be interesting to determine whether the extreme b cells described by Farack et al. (2018) were phenotypically similar to the b4 population, especially since Dorrell et al. (2016) observed a significant increase in the b4 population in the islets of individuals with type 2 diabetes, analogous to the observed increase in extreme b cells in the db/db mice. The recent findings regarding b cell heterogeneity represent exciting new concepts in islet biology and raise many
Developmental Cell 48, January 7, 2019 ª 2018 Elsevier Inc. 7
Developmental Cell
Previews
Figure 1. Characterization of Extreme Beta Cells Extreme beta cells (described by Farack et al., 2018) are found in rosettes near the interior of the pancreatic islet. Compared to non-extreme beta cells, extreme cells have increased levels of insulin mRNA concentrated in the apical region of the cell, increased proinsulin content, and less processed insulin. Under diabetic stress (Leprdb/db), the number of extreme beta cells increases. Future studies will be needed to fully characterize the function and molecular properties of this cell type.
interesting questions for future studies. For example, are extreme b cells more susceptible to exhaustion and death? Is this extreme state a permanent or transient state that all mature cells can transition through? When are extreme b cells specified, and are they more or less proliferative than non-extreme b cells? When do these cells arise, and how long do they persist within the islet? Do extreme subpopulations of cells exist in the non-b endocrine populations? Finally, are these extreme b cells present in human islets, and do they change during disease progression? The discovery and characterization of extreme b cells in the Farack et al. (2018) study provide important information about the b cell populations present within an islet and begin to assess how their presence is impacted by disease. This study and others like it demonstrate the power of emerging technologies to
8 Developmental Cell 48, January 7, 2019
further our understanding of islet cell function and disease development. REFERENCES Bader, E., Migliorini, A., Gegg, M., Moruzzi, N., Gerdes, J., Roscioni, S.S., Bakhti, M., Brandl, E., Irmler, M., Beckers, J., et al. (2016). Identification of proliferative and mature b-cells in the islets of Langerhans. Nature 535, 430–434. Benninger, R.K.P., and Hodson, D.J. (2018). New understanding of b-cell heterogeneity and in situ islet function. Diabetes 67, 537–547. Cui, Y., Hu, D., Markillie, L.M., Chrisler, W.B., Gaffrey, M.J., Ansong, C., Sussel, L., and Orr, G. (2018). Fluctuation localization imaging-based fluorescence in situ hybridization (fliFISH) for accurate detection and counting of RNA copies in single cells. Nucleic Acids Res. 46, e7. Dorrell, C., Schug, J., Canaday, P.S., Russ, H.A., Tarlow, B.D., Grompe, M.T., Horton, T., Hebrok, M., Streeter, P.R., Kaestner, K.H., and Grompe, M. (2016). Human islets contain four distinct subtypes of b cells. Nat. Commun. 7, 11756. Farack, L., Golan, M., Egozi, A., Dezorella, N., Bahar Halpern, K., Ben-Moshe, S., Garzilli, I.,
To´th, B., Roitman, L., Krizhanovsky, V., and Itzkovitz, S. (2018). Transcriptional heterogeneity of beta cells in the intact pancreas. Dev. Cell 48, this issue, 115–125. Gutie´rrez, G.D., Gromada, J., and Sussel, L. (2017). Heterogeneity of the pancreatic beta cell. Front. Genet. 8, 22. Johnston, N.R., Mitchell, R.K., Haythorne, E., Pessoa, M.P., Semplici, F., Ferrer, J., Piemonti, L., Marchetti, P., Bugliani, M., Bosco, D., et al. (2016). Beta cell hubs dictate pancreatic islet responses to glucose. Cell Metab. 24, 389–401. Stefan, Y., Meda, P., Neufeld, M., and Orci, L. (1987). Stimulation of insulin secretion reveals heterogeneity of pancreatic B cells in vivo. J. Clin. Invest. 80, 175–183. van der Meulen, T., Mawla, A.M., DiGruccio, M.R., Adams, M.W., Nies, V., Do´lleman, S., Liu, S., Ackermann, A.M., Ca´ceres, E., Hunter, A.E., et al. (2017). Virgin beta cells persist throughout life at a neogenic niche within pancreatic islets. Cell Metab. 25, 911–926.e6. Wang, Y.J., Schug, J., Won, K.-J., Liu, C., Naji, A., Avrahami, D., Golson, M.L., and Kaestner, K.H. (2016). Single-cell transcriptomics of the human endocrine pancreas. Diabetes 65, 3028–3038.
Previews FISHing for b Cells Laura I. Hudish,1 David S. Lorberbaum,1 and Lori Sussel1,* 1Barbara Davis Center for Diabetes, University of Colorado Anschutz Medical Center, Aurora, CO 80045, USA *Correspondence: [email protected] https://doi.org/10.1016/j.devcel.2018.12.007
b cell heterogeneity has emerged as an important contributor to islet function, with potential implications for diabetes. Using an optimized smFISH technique in intact islets, Farack et al. (2018) identify in the islet core an endocrine cell population of ‘‘extreme’’ b cells with distinct molecular properties. Diabetes mellitus is a complex disease caused by the dysfunction and ultimate loss of the insulin-producing b cells that reside in the pancreatic islets of Langerhans. With the recent discovery of islet cell plasticity and b cell heterogeneity (reviewed in Gutie´rrez et al., 2017), the composition of the b cell population has become central to how we think about b cell function and the development of diabetes. Instead of a fixed and homogeneous b cell population, single-cell technologies have revealed transcriptionally and functionally distinct b cell subsets (Wang et al., 2016; Dorrell et al., 2016). However, most studies thus far have captured the molecular and functional characteristics of dissociated b cells, neglecting the contributions of cell-cell connections and overall islet structure (Benninger and Hodson, 2018). In this issue of Developmental Cell, Farack et al. (2018) use an optimized single-molecule transcript imaging technique to examine b cell heterogeneity in the intact islet. Using this approach, the authors identify a unique b cell population termed ‘‘extreme’’ b cells that is located within the islet core. The extreme b cells are characterized by a distinctive intracellular polarization pattern, higher pro-insulin and ribosomal RNA content, and less mature insulin protein (Figure 1). Based on these characteristics, Farack et al. (2018) hypothesize that the extreme b cells may have a higher basal insulin secretion rate compared to non-extreme cells; however, the exact function of these cells remains to be explored. These data are consistent with another recent study that employed a modified small molecule (sm)FISH technique called fliFISH to identify within the core of the islet a subpopulation of b cells that express more Ins2 and Nkx2.2 mRNA compared to b cells located at the islet
periphery (Cui et al., 2018). Both studies support the findings in earlier functional studies that more-mature b cells were located centrally in the islet, whereas less-mature b cells were found at the periphery (Stefan et al., 1987). Farack et al. (2018) took their analysis further to determine whether the extreme b cells represented several recently described specialized b cell populations (Johnston et al., 2016; van der Meulen et al., 2017). However, characterization of the extreme b cells for the expression of several b cells markers, including Pdx1, Ucn3, and the glucose transporter Slc2a2, suggested that extreme cells are distinct from previously characterized hub and virgin cell populations. To determine whether the extreme b cells contribute to the overall function of the islet and whether they are affected by disease, Farack et al. (2018) also examined whether insulin resistance in diabetic Leprdb/db (db/db) mice affected the balance between extreme and non-extreme cells. The authors observed that the larger islets in db/db mice had significantly more extreme cells than healthy islets. This observation suggests that either the extreme cells have higher proliferative capacity that could favor their expansion, or the non-extreme cells convert to the extreme phenotype. Which of these alternatives underlies the extreme cell expansion is not yet clear. In a recent study, Bader et al. (2016) identified Flattop as a marker that distinguished proliferationcompetent versus functionally mature b cells in mouse islets (Bader et al., 2016); however, Flattop expression was not characterized in the extreme b cell population. Altogether, Farack et al. (2018) identify and describe a b cell population with distinct molecular features and a robust adaptive response to insulin resistance. Additional studies will be needed to
define the functional differences between extreme and non-extreme cells, including assessment of parameters such as proliferative capacity, calcium signaling, and/ or islet connectivity. It will also be interesting to follow these cells during disease onset and progression. It is well appreciated that b cells have the unique ability to adapt to abrupt glycemic changes by altering insulin production. The identification of these heterogeneous subsets of b cells within the islet suggests that rather than a single b cell altering its function in response to glycemic fluctuations, adjustment in the relative ratios of different b cell populations may be responsible for optimal responses to changing metabolic states. Although the smFISH analysis from Farack et al. (2018) and the fliFISH technique mentioned above (Cui et al., 2018) were applied to mouse tissues, similar in situ single-molecule techniques could be a valuable resource to characterize human islets. Dorrell et al. (2016) identified four antigenically diverse human b cell populations (b1–4) with unique characteristics. Each population showed distinct gene expression profiles and insulin secretion capabilities, with the lowest basal insulin secretion properties associated with the most abundant b1 population and highest insulin secretion capabilities found in the rarest b4 population. It would be interesting to determine whether the extreme b cells described by Farack et al. (2018) were phenotypically similar to the b4 population, especially since Dorrell et al. (2016) observed a significant increase in the b4 population in the islets of individuals with type 2 diabetes, analogous to the observed increase in extreme b cells in the db/db mice. The recent findings regarding b cell heterogeneity represent exciting new concepts in islet biology and raise many
Developmental Cell 48, January 7, 2019 ª 2018 Elsevier Inc. 7
Developmental Cell
Previews
Figure 1. Characterization of Extreme Beta Cells Extreme beta cells (described by Farack et al., 2018) are found in rosettes near the interior of the pancreatic islet. Compared to non-extreme beta cells, extreme cells have increased levels of insulin mRNA concentrated in the apical region of the cell, increased proinsulin content, and less processed insulin. Under diabetic stress (Leprdb/db), the number of extreme beta cells increases. Future studies will be needed to fully characterize the function and molecular properties of this cell type.
interesting questions for future studies. For example, are extreme b cells more susceptible to exhaustion and death? Is this extreme state a permanent or transient state that all mature cells can transition through? When are extreme b cells specified, and are they more or less proliferative than non-extreme b cells? When do these cells arise, and how long do they persist within the islet? Do extreme subpopulations of cells exist in the non-b endocrine populations? Finally, are these extreme b cells present in human islets, and do they change during disease progression? The discovery and characterization of extreme b cells in the Farack et al. (2018) study provide important information about the b cell populations present within an islet and begin to assess how their presence is impacted by disease. This study and others like it demonstrate the power of emerging technologies to
8 Developmental Cell 48, January 7, 2019
further our understanding of islet cell function and disease development. REFERENCES Bader, E., Migliorini, A., Gegg, M., Moruzzi, N., Gerdes, J., Roscioni, S.S., Bakhti, M., Brandl, E., Irmler, M., Beckers, J., et al. (2016). Identification of proliferative and mature b-cells in the islets of Langerhans. Nature 535, 430–434. Benninger, R.K.P., and Hodson, D.J. (2018). New understanding of b-cell heterogeneity and in situ islet function. Diabetes 67, 537–547. Cui, Y., Hu, D., Markillie, L.M., Chrisler, W.B., Gaffrey, M.J., Ansong, C., Sussel, L., and Orr, G. (2018). Fluctuation localization imaging-based fluorescence in situ hybridization (fliFISH) for accurate detection and counting of RNA copies in single cells. Nucleic Acids Res. 46, e7. Dorrell, C., Schug, J., Canaday, P.S., Russ, H.A., Tarlow, B.D., Grompe, M.T., Horton, T., Hebrok, M., Streeter, P.R., Kaestner, K.H., and Grompe, M. (2016). Human islets contain four distinct subtypes of b cells. Nat. Commun. 7, 11756. Farack, L., Golan, M., Egozi, A., Dezorella, N., Bahar Halpern, K., Ben-Moshe, S., Garzilli, I.,
To´th, B., Roitman, L., Krizhanovsky, V., and Itzkovitz, S. (2018). Transcriptional heterogeneity of beta cells in the intact pancreas. Dev. Cell 48, this issue, 115–125. Gutie´rrez, G.D., Gromada, J., and Sussel, L. (2017). Heterogeneity of the pancreatic beta cell. Front. Genet. 8, 22. Johnston, N.R., Mitchell, R.K., Haythorne, E., Pessoa, M.P., Semplici, F., Ferrer, J., Piemonti, L., Marchetti, P., Bugliani, M., Bosco, D., et al. (2016). Beta cell hubs dictate pancreatic islet responses to glucose. Cell Metab. 24, 389–401. Stefan, Y., Meda, P., Neufeld, M., and Orci, L. (1987). Stimulation of insulin secretion reveals heterogeneity of pancreatic B cells in vivo. J. Clin. Invest. 80, 175–183. van der Meulen, T., Mawla, A.M., DiGruccio, M.R., Adams, M.W., Nies, V., Do´lleman, S., Liu, S., Ackermann, A.M., Ca´ceres, E., Hunter, A.E., et al. (2017). Virgin beta cells persist throughout life at a neogenic niche within pancreatic islets. Cell Metab. 25, 911–926.e6. Wang, Y.J., Schug, J., Won, K.-J., Liu, C., Naji, A., Avrahami, D., Golson, M.L., and Kaestner, K.H. (2016). Single-cell transcriptomics of the human endocrine pancreas. Diabetes 65, 3028–3038.