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Commentary Free access | 10.1172/JCI124583
1Guangzhou Institutes of Biomedicine and Health,
2CAS Key Laboratory of Regenerative Biology, Guangzhou, China.
3Guangdong Provincial Key Laboratory of Stem Cell and Regenerative Medicine,
4Guangzhou Regenerative Medicine and Health, Guangdong Laboratory, Guangzhou, China.
Address correspondence to: Duanqing Pei, Guangzhou Institutes of Biomedicine and Health, CAS, No. 190, KaiYuan Road, Science Park, Guangzhou, Guangdong 510530, China. Phone: 86.20.32015231; Email: pei_duanqing@gibh.ac.cn.
Find articles by Wang, T. in: JCI | PubMed | Google Scholar
1Guangzhou Institutes of Biomedicine and Health,
2CAS Key Laboratory of Regenerative Biology, Guangzhou, China.
3Guangdong Provincial Key Laboratory of Stem Cell and Regenerative Medicine,
4Guangzhou Regenerative Medicine and Health, Guangdong Laboratory, Guangzhou, China.
Address correspondence to: Duanqing Pei, Guangzhou Institutes of Biomedicine and Health, CAS, No. 190, KaiYuan Road, Science Park, Guangzhou, Guangdong 510530, China. Phone: 86.20.32015231; Email: pei_duanqing@gibh.ac.cn.
Find articles by Pei, D. in: JCI | PubMed | Google Scholar
Published November 26, 2018 - More info
The loss of insulin-secreting β cells is characteristic among type I and type II diabetes. Stimulating proliferation to expand sources of β cells for transplantation remains a challenge because adult β cells do not proliferate readily. The cell cycle inhibitor p57 has been shown to control cell division in human β cells. Expression of p57 is regulated by the DNA methylation status of the imprinting control region 2 (ICR2), which is commonly hypomethylated in Beckwith-Wiedemann syndrome patients who exhibit massive β cell proliferation. We hypothesized that targeted demethylation of the ICR2 using a transcription activator–like effector protein fused to the catalytic domain of TET1 (ICR2-TET1) would repress p57 expression and promote cell proliferation. We report here that overexpression of ICR2-TET1 in human fibroblasts reduces p57 expression levels and increases proliferation. Furthermore, human islets overexpressing ICR2-TET1 exhibit repression of p57 with concomitant upregulation of Ki-67 while maintaining glucose-sensing functionality. When transplanted into diabetic, immunodeficient mice, the epigenetically edited islets show increased β cell replication compared with control islets. These findings demonstrate that epigenetic editing is a promising tool for inducing β cell proliferation, which may one day alleviate the scarcity of transplantable β cells for the treatment of diabetes.
Kristy Ou, Ming Yu, Nicholas G. Moss, Yue J. Wang, Amber W. Wang, Son C. Nguyen, Connie Jiang, Eseye Feleke, Vasumathi Kameswaran, Eric F. Joyce, Ali Naji, Benjamin Glaser, Dana Avrahami, Klaus H. Kaestner
Insulin-secreting β cell loss or dysfunction is a feature of both type 1 and type 2 diabetes. Strategies to restore β cell mass are limited, as sources of healthy islets are scarce and mature β cells are not readily expanded in vitro. In this issue of the JCI, Ou et al. report that mature β cell expansion can be induced in situ through epigenetic editing of regulatory elements in pancreatic tissue. Specifically, hypomethylation at imprinting control region 2 (ICR2) in human islets promoted β cell expansion. Importantly, transplantation of these epigenetically edited islets into diabetic mice reduced blood glucose levels. Together, these results support further evaluation of this strategy for restoring β cell mass in patients with diabetes.
Cell replication and identity are strictly controlled through multiple layers of mechanisms within tissues to maintain tissue homeostasis. In some cases, expansion of functional mature cells is needed to replace damaged cells in tissues. For type I or severe forms of type II diabetes, replenishment of malfunctioning β cells with functional β cells via islet transfer surgery has potential to confer long-term control of blood glucose levels. Unfortunately, there are few sources of healthy islet donors; therefore, additional strategies to restore β cell function are needed.
Beckwith-Wiedemann syndrome is an overgrowth disorder that features an excessive β cell mass, and the DNA hypomethylation status of imprinting control region 2 (ICR2) has been linked to the massive β cell expansion in these patients (1). This observation implies that manipulation of ICR2 has potential to modulate the expansion of mature β cells. In this issue, Ou et al. tested this hypothesis and used a TALE-TET1 fusion protein to target and demethylate ICR2 (2). TALE-TET1–induced hypomethylation of ICR2 consequently resulted in reentry of mature β cells into the cell cycle, thereby expanding the population. Moreover, transplantation of TALE-TET1–expressing islets into immunodeficient diabetic mice restored insulin secretion to a level capable of reducing blood glucose.
The reactivation method used by Ou et al. is quite unique compared with cell transplantation (2), in which exogenous functional cells are transplanted into the liver or abdomen. Once injected, the transplanted cells are faced with harsh microenvironmental challenges that lead to poor survival of the donor cells and little restoration of β cell function. Moreover, transplanted cells are at risk of being converted into a pathological phenotype, perhaps via interactions with locally secreted factors. Thus, reactivation of mature β cells in situ can avoid the myriad problems mentioned above.
Promoter hypomethylation usually results in high levels of expression of the regulated genes (3–5); however, TALE-TET1–mediated demethylation of ICR2 resulted in substantial suppression of p57. Although Ou and colleagues did not explore the underlying mechanisms of p57 suppression, several potential mechanisms could be further evaluated (2). For example, the issue can be examined from the standpoint of interactions between the ICR2 and other regulatory regions of p57 in a 3-dimensional context. Hypomethylation may disrupt ICR2-involved DNA-DNA/DNA-lncRNA interactions that influence p57 expression. Also, it is possible that ICR2 hypomethylation impairs/enables binding of critical factors and that this impairment/enhancement leads to repression of p57. More work is needed to uncover how ICR2 methylation regulates p57 expression, as understanding the underlying mechanisms may be useful for precisely manipulating p57 expression and β cell proliferation.
In addition to p57, other cell cycle inhibitors, such as p16, may be targets for increasing β cell proliferation (6). Therefore, it would be interesting to determine if epigenetic repression of p16 expression also promotes expansion of mature β cell populations in vivo. Alternatively, epigenetic editing methods could be applied to activate transcription factors to reprogram α cells into β cells in vivo. Indeed, as proof of principle, recent studies have demonstrated the conversion of α cells into β cells in vivo (7, 8). Further research is needed to determine whether or not CRISPR fusion proteins can be used to reprogram α cells in vivo.
In a broader sense, epigenetic modification of regulatory elements may provide a versatile platform to engineer cell fate in a variety of tissues in the field of regenerative medicine. For example, epigenetic targeting of DNA elements is critical for somatic cell reprogramming (9, 10), and the study by Ou et al. identifies a promising way to change cell fates with the use of synthetic tools (2). From this viewpoint, studies across different fields have already accumulated large data sets of epigenetic modifications, including histone, DNA, and RNA modifications, that are part of the epigenetic fingerprint associated with different cell statuses. Based on these data sets, it is reasonable to hypothesize that cell identities and/or physiological phenotypes are associated with these epigenetic characteristics. Thus, it is possible to engineer cell fate changes with fusion proteins between TALE or CRISPR and epigenetic enzymes or other proteins to modify these regions, and thereby modulate the expression of cell fate–associated genes. Similarly, as cancer cells harbor aberrant DNA methylation patterns or other epigenetic modifications (11, 12), a CRISPR-TET or CRISPR-X fusion protein could be designed to target single or multiple regions to modify epigenetic status and reprogram cancer cell fate. Compared with methods that introduce genes directly into cells, epigenetic editing can avoid risks of random insertion of exogenous genes into the genome; moreover, epigenetic editing provides much more flexible and precise control of target gene expression.
With the advancement of nanotechnology and/or other related delivery strategies, epigenetic targeting has potential to be expanded for many future applications in the field of regenerative medicine.
This work is supported by the Science and Technology Planning Project of Guangdong Province, China (2017B030314056).
Address correspondence to: Duanqing Pei, Guangzhou Institutes of Biomedicine and Health, CAS, No. 190, KaiYuan Road, Science Park, Guangzhou, Guangdong 510530, China. Phone: 86.20.32015231; Email: pei_duanqing@gibh.ac.cn.
Conflict of interest: The authors have declared that no conflict of interest exists.
Reference information: J Clin Invest. 2019;129(1):51–52. https://doi.org/10.1172/JCI124583.
See the related article at Targeted demethylation at the CDKN1C/p57 locus induces human β cell replication.