Clearance of p16Ink4a-positive cells in a mouse transgenic model does not change β-cell mass and has limited effects on their proliferative capacity

Abstract

Type 2 diabetes is partly characterized by decreased β-cell mass and function which have been linked to cellular senescence. Despite a low basal proliferative rate of adult β-cells, they can respond to growth stimuli, but this proliferative capacity decreases with age and correlates with increased expression of senescence effector, p16 Ink4a . We hypothesized that selective deletion of p16 Ink4a -positive cells would enhance the proliferative capacity of the remaining β-cells due to the elimination of the local senescence-associated secretory phenotype (SASP). We aimed to investigate the effects of p16 Ink4a -positive cell removal on the mass and proliferative capacity of remaining β-cells using INK-ATTAC mice as a transgenic model of senolysis. Clearance of p16 Ink4a positive subpopulation was tested in mice of different ages, males and females, and with two different insulin resistance models: high-fat diet (HFD) and insulin receptor antagonist (S961). Clearance of p16 Ink4a -positive cells did not affect the overall β-cell mass. β-cell proliferative capacity negatively correlated with cellular senescence load and clearance of p16 Ink4a positive cells in 1-year-old HFD mice improved β-cell function and increased proliferative capacity in a subset of animals. Single-cell sequencing revealed that the targeted p16 Ink4a subpopulation of β-cells is non-proliferative and non-SASP producing whereas additional senescent subpopulations remained contributing to continued local SASP secretion. In conclusion, deletion of p16 Ink4a cells did not negatively impact beta-cell mass and blood glucose under basal and HFD conditions and proliferation was restored in a subset of HFD mice opening further therapeutic targets in the treatment of diabetes.

Pancreatic β-cell senescence in diabetes: mechanisms, markers and therapies

“…Replicating this observation in a culture model, DNA damage-induced senescence in islets from healthy donors leads to stable activation of p21 Cip1 but not p16 Ink4a ( 1 , 34 , 35 ) and more recently p21 Cip1 expression was confirmed in β-cells in this model ( 36 ). Additional evidence for distinctions between p21 Cip1 and p16 Ink4a in senescent β-cells was recently shown with the INK-ATTAC mouse model, which revealed that ablation of p16 Ink4a -expressing β-cells left a remaining senescent β-cell population expressing SASP factor genes ( 96 ). In future work, it will be important to investigate the molecular features that distinguish p16 Ink4a -expressing β-cells from p21 Cip1 -expressing β-cells in the context of T1D and T2D mouse models and human islets.…”

“…Removal of senescent cells using this mouse model on adult HFD mice (7-8 months) or mice with insulin resistance induced by S961 treatment, mitigates glucose intolerance, restores insulin sensitivity concomitant with a reduction in the markers of proinflammatory senescent β-cells in mouse islets ( 2 ). More recent work on this model indicates that although it leads to ablation of p16 Ink4a -expressing senescent β-cells, overall β-cell mass and replication are not affected ( 96 ). Similarly, populations of p21 Cip1 -expressing senescent β-cells with SASP are were not affected by genetic deletion of p16 Ink4a -expressing senescent β-cells ( 96 ).…”

“…More recent work on this model indicates that although it leads to ablation of p16 Ink4a -expressing senescent β-cells, overall β-cell mass and replication are not affected ( 96 ). Similarly, populations of p21 Cip1 -expressing senescent β-cells with SASP are were not affected by genetic deletion of p16 Ink4a -expressing senescent β-cells ( 96 ). Whereas genetic tools have recently been developed to target p21 Cip1 -expressing senescent cells in mice ( 94 , 128 ), it will be of great interest to apply these to interrogate the roles of p21 High senescent β-cells in various diabetes models.…”

Interaction between Autophagy and Senescence in Pancreatic Beta Cells

“…A detail to be considered in pancreatic β-cells is the effect clearing senescent cells would have on beta cell mass. In the specific setting of beta cells, we recently showed that deletion of p16 Ink4a cells in a transgenic mouse model resulted in limited effects of proliferation and no changes in beta cell mass [ 142 ]. Targeting senescence is a promising strategy in many age-related diseases.…”