{"id":{"repo_id":"edinburgh","oai_identifier":"oai:era.ed.ac.uk:1842/43343"},"canonical_url":"https://search.dev.ndltd.org/etd/edinburgh/oai:era.ed.ac.uk:1842/43343","repository":{"repo_id":"edinburgh","name":"University of Edinburgh","base_url":"https://era.ed.ac.uk/server/oai/request"},"display":{"title":"PTEN regulates the BMI1-mediated self-renewal of long-term hematopoietic stem cells in developmental and stress conditions","abstract":"In the hematopoietic system, self-renewing long-term hematopoietic stem cells (LT-HSCs) maintain stem cell pools and differentiate into hematopoietic progeny. In addition to its critical role in the daily production of blood cells, LT-HSCs are able to resist the threats posed by various types of stress. However, our understanding of LT-HSCs under stress is still limited. It has been observed in our laboratory that the deletion of Pten in the LT-HSCs of VE-cadherin-cre+;Ptenfl/fl mice does not lead to the loss of HSC self-renewal, raising the possibility that PTEN-mediated self-renewal regulation may be more complicated than previously reported. To understand the molecular regulation of HSC homeostasis, I crossed Bmi1GFP/+ knock-in reporter mice, in which the intact Bmi1 promoter drives the transcription of the GFP transgene instead of the self-renewal regulator gene Bmi1, with Pten-deficient mice (Vav-icre+;CD2-C3+;Ptenfl/fl, or vCPΔ/Δ) to generate vCBPΔ/Δ (vCPΔ/Δ;Bmi1GFP/+) mice. The intact GFP signals in vCBPΔ/Δ mice, which represent the expression of Bmi1, indicated that the transcription of Bmi1 was not affected by PTEN loss. However, vCBPΔ/Δ mice surprisingly suffered from the exhaustion of LT-HSCs and eventually died between 2 and 4 months after birth, which was reminiscent of the HSC defects in Bmi1-/- mice. The similar phenotypes between vCBPΔ/Δ mice and Bmi1-/- mice raised the possibility that PTEN plays an important role in the protein stability of BMI1 and the BMI1-mediated self-renewal of LT-HSCs. To understand the role of PTEN in the regulation of BMI1, the protein levels of BMI1 in vCBPΔ/Δ LT-HSCs were measured by protein-flow analysis. Indeed, the BMI1 protein in vCBPΔ/Δ LT-HSCs was decreased by more than 50%. In contrast, the protein levels of BMI1 in vCPΔ/Δ and Bmi1GFP/+ mice, where the HSC pools remained normal, were slightly reduced by less than 50%. Consistently, the stem cell exhaustion marker p16Ink4a, which is typically repressed by BMI1, was strikingly upregulated in vCBPΔ/Δ LT-HSCs. These observations indicate that the protein levels of BMI1 are critical for the expression of p16Ink4a and the BMI1-mediated self-renewal regulation. At the molecular level, the loss of PTEN or its phosphatase function led to the activation of the stress-responsive kinase p38α MAPK. The activated p38α phosphorylated BMI1 at T275, which resulted in the degradation of BMI1. However, the T275 phosphorylation of BMI1 was suppressed by the phosphatase-independent function of PTEN. The T275A mutant of BMI1, which was unable to be phosphorylated by p38α, rescued the protein levels of BMI1 and the HSC pool in vCBPΔ/Δ mice. These molecular and genetic findings suggest that the T275 phosphorylation of BMI1 is associated with its protein stability and self-renewal regulation. To investigate the molecular regulation of BMI1 by PTEN and p38α under stress, an X-ray irradiation murine model was employed. The 3 Gy irradiation led to a decrease in the BMI1 protein levels in response to irradiation, which was accompanied by the increased reactive oxygen species at 14 days post-irradiation. The irradiated HSCs with increased ROS exhibited compromised self-renewal activity in serial transplantation assays. Conversely, HSCs with the Bmi1T275A mutation rescued the self-renewal ability of irradiated HSCs in those serial transplantation assays. These observations highlight the BMI1 T275 as a critical checkpoint in HSCs in response to stress. Taken together, the regulators p38α, PTEN and BMI1 form a new circuit to regulate HSC self-renewal in developmental and stress conditions. PTEN and p38α play an essential role in regulating the protein levels of BMI1 and the self-renewal of HSCs via the BMI1 T275. The T275 locus in BMI1 is a critical checkpoint in response to stress.","abstract_html":"In the hematopoietic system, self-renewing long-term hematopoietic stem cells (LT-HSCs) maintain stem cell pools and differentiate into hematopoietic progeny. In addition to its critical role in the daily production of blood cells, LT-HSCs are able to resist the threats posed by various types of stress. However, our understanding of LT-HSCs under stress is still limited. It has been observed in our laboratory that the deletion of Pten in the LT-HSCs of VE-cadherin-cre+;Ptenfl/fl mice does not lead to the loss of HSC self-renewal, raising the possibility that PTEN-mediated self-renewal regulation may be more complicated than previously reported. To understand the molecular regulation of HSC homeostasis, I crossed Bmi1GFP/+ knock-in reporter mice, in which the intact Bmi1 promoter drives the transcription of the GFP transgene instead of the self-renewal regulator gene Bmi1, with Pten-deficient mice (Vav-icre+;CD2-C3+;Ptenfl/fl, or vCPΔ/Δ) to generate vCBPΔ/Δ (vCPΔ/Δ;Bmi1GFP/+) mice. The intact GFP signals in vCBPΔ/Δ mice, which represent the expression of Bmi1, indicated that the transcription of Bmi1 was not affected by PTEN loss. However, vCBPΔ/Δ mice surprisingly suffered from the exhaustion of LT-HSCs and eventually died between 2 and 4 months after birth, which was reminiscent of the HSC defects in Bmi1-/- mice. The similar phenotypes between vCBPΔ/Δ mice and Bmi1-/- mice raised the possibility that PTEN plays an important role in the protein stability of BMI1 and the BMI1-mediated self-renewal of LT-HSCs. To understand the role of PTEN in the regulation of BMI1, the protein levels of BMI1 in vCBPΔ/Δ LT-HSCs were measured by protein-flow analysis. Indeed, the BMI1 protein in vCBPΔ/Δ LT-HSCs was decreased by more than 50%. In contrast, the protein levels of BMI1 in vCPΔ/Δ and Bmi1GFP/+ mice, where the HSC pools remained normal, were slightly reduced by less than 50%. Consistently, the stem cell exhaustion marker p16Ink4a, which is typically repressed by BMI1, was strikingly upregulated in vCBPΔ/Δ LT-HSCs. These observations indicate that the protein levels of BMI1 are critical for the expression of p16Ink4a and the BMI1-mediated self-renewal regulation. At the molecular level, the loss of PTEN or its phosphatase function led to the activation of the stress-responsive kinase p38α MAPK. The activated p38α phosphorylated BMI1 at T275, which resulted in the degradation of BMI1. However, the T275 phosphorylation of BMI1 was suppressed by the phosphatase-independent function of PTEN. The T275A mutant of BMI1, which was unable to be phosphorylated by p38α, rescued the protein levels of BMI1 and the HSC pool in vCBPΔ/Δ mice. These molecular and genetic findings suggest that the T275 phosphorylation of BMI1 is associated with its protein stability and self-renewal regulation. To investigate the molecular regulation of BMI1 by PTEN and p38α under stress, an X-ray irradiation murine model was employed. The 3 Gy irradiation led to a decrease in the BMI1 protein levels in response to irradiation, which was accompanied by the increased reactive oxygen species at 14 days post-irradiation. The irradiated HSCs with increased ROS exhibited compromised self-renewal activity in serial transplantation assays. Conversely, HSCs with the Bmi1T275A mutation rescued the self-renewal ability of irradiated HSCs in those serial transplantation assays. These observations highlight the BMI1 T275 as a critical checkpoint in HSCs in response to stress. Taken together, the regulators p38α, PTEN and BMI1 form a new circuit to regulate HSC self-renewal in developmental and stress conditions. PTEN and p38α play an essential role in regulating the protein levels of BMI1 and the self-renewal of HSCs via the BMI1 T275. The T275 locus in BMI1 is a critical checkpoint in response to stress.","abstract_has_math":false,"creators":["Zheng, Wen"],"institution":"The University of Edinburgh","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Guo, Wei","Sloan, Richard","Welburn, Susan"],"committee_chairs":[],"committee_members":[],"year":2025,"date_issued":"2025-04-03","date_published":"2025-04-03","updated_at":"2026-07-24T02:14:22Z","subjects":["PTEN","BMI1","Self-renewal","Hematopoietic stem cells (HSCs)","Stress conditions"],"languages":["en"],"rights":[],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://dx.doi.org/10.7488/era/5881"],"render_values":[{"text":"http://dx.doi.org/10.7488/era/5881","href":"http://dx.doi.org/10.7488/era/5881","code":true}]}]},"links":{"outbound_url":"https://hdl.handle.net/1842/43343","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Guo, Wei","Sloan, Richard","Welburn, Susan"]},{"key":"dc:creator","label":"Author","values":["Zheng, Wen"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2025-04-03T10:11:22Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2025-04-03T10:11:22Z"]},{"key":"dc:date.issued","label":"Date","values":["2025-04-03"]},{"key":"dc:publisher","label":"Institution","values":["The University of Edinburgh"]},{"key":"dc:type","label":"Dc Type","values":["Thesis or Dissertation"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Doctoral"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["PhD Doctor of Philosophy"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["PTEN","BMI1","Self-renewal","Hematopoietic stem cells (HSCs)","Stress conditions"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/1842/43343","http://dx.doi.org/10.7488/era/5881"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["In the hematopoietic system, self-renewing long-term hematopoietic stem cells (LT-HSCs) maintain stem cell pools and differentiate into hematopoietic progeny. In addition to its critical role in the daily production of blood cells, LT-HSCs are able to resist the threats posed by various types of stress. However, our understanding of LT-HSCs under stress is still limited. It has been observed in our laboratory that the deletion of Pten in the LT-HSCs of VE-cadherin-cre+;Ptenfl/fl mice does not lead to the loss of HSC self-renewal, raising the possibility that PTEN-mediated self-renewal regulation may be more complicated than previously reported. To understand the molecular regulation of HSC homeostasis, I crossed Bmi1GFP/+ knock-in reporter mice, in which the intact Bmi1 promoter drives the transcription of the GFP transgene instead of the self-renewal regulator gene Bmi1, with Pten-deficient mice (Vav-icre+;CD2-C3+;Ptenfl/fl, or vCPΔ/Δ) to generate vCBPΔ/Δ (vCPΔ/Δ;Bmi1GFP/+) mice. The intact GFP signals in vCBPΔ/Δ mice, which represent the expression of Bmi1, indicated that the transcription of Bmi1 was not affected by PTEN loss. However, vCBPΔ/Δ mice surprisingly suffered from the exhaustion of LT-HSCs and eventually died between 2 and 4 months after birth, which was reminiscent of the HSC defects in Bmi1-/- mice. The similar phenotypes between vCBPΔ/Δ mice and Bmi1-/- mice raised the possibility that PTEN plays an important role in the protein stability of BMI1 and the BMI1-mediated self-renewal of LT-HSCs. To understand the role of PTEN in the regulation of BMI1, the protein levels of BMI1 in vCBPΔ/Δ LT-HSCs were measured by protein-flow analysis. Indeed, the BMI1 protein in vCBPΔ/Δ LT-HSCs was decreased by more than 50%. In contrast, the protein levels of BMI1 in vCPΔ/Δ and Bmi1GFP/+ mice, where the HSC pools remained normal, were slightly reduced by less than 50%. Consistently, the stem cell exhaustion marker p16Ink4a, which is typically repressed by BMI1, was strikingly upregulated in vCBPΔ/Δ LT-HSCs. These observations indicate that the protein levels of BMI1 are critical for the expression of p16Ink4a and the BMI1-mediated self-renewal regulation. At the molecular level, the loss of PTEN or its phosphatase function led to the activation of the stress-responsive kinase p38α MAPK. The activated p38α phosphorylated BMI1 at T275, which resulted in the degradation of BMI1. However, the T275 phosphorylation of BMI1 was suppressed by the phosphatase-independent function of PTEN. The T275A mutant of BMI1, which was unable to be phosphorylated by p38α, rescued the protein levels of BMI1 and the HSC pool in vCBPΔ/Δ mice. These molecular and genetic findings suggest that the T275 phosphorylation of BMI1 is associated with its protein stability and self-renewal regulation. To investigate the molecular regulation of BMI1 by PTEN and p38α under stress, an X-ray irradiation murine model was employed. The 3 Gy irradiation led to a decrease in the BMI1 protein levels in response to irradiation, which was accompanied by the increased reactive oxygen species at 14 days post-irradiation. The irradiated HSCs with increased ROS exhibited compromised self-renewal activity in serial transplantation assays. Conversely, HSCs with the Bmi1T275A mutation rescued the self-renewal ability of irradiated HSCs in those serial transplantation assays. These observations highlight the BMI1 T275 as a critical checkpoint in HSCs in response to stress. Taken together, the regulators p38α, PTEN and BMI1 form a new circuit to regulate HSC self-renewal in developmental and stress conditions. PTEN and p38α play an essential role in regulating the protein levels of BMI1 and the self-renewal of HSCs via the BMI1 T275. The T275 locus in BMI1 is a critical checkpoint in response to stress."]},{"key":"dc:title","label":"Title","values":["PTEN regulates the BMI1-mediated self-renewal of long-term hematopoietic stem cells in developmental and stress conditions"]}]}],"canonical_facts":{"dc:contributor.advisor":["Guo, Wei","Sloan, Richard","Welburn, Susan"],"dc:creator":["Zheng, Wen"],"dc:date.accessioned":["2025-04-03T10:11:22Z"],"dc:date.available":["2025-04-03T10:11:22Z"],"dc:date.issued":["2025-04-03"],"dc:description.abstract":["In the hematopoietic system, self-renewing long-term hematopoietic stem cells (LT-HSCs) maintain stem cell pools and differentiate into hematopoietic progeny. In addition to its critical role in the daily production of blood cells, LT-HSCs are able to resist the threats posed by various types of stress. However, our understanding of LT-HSCs under stress is still limited. It has been observed in our laboratory that the deletion of Pten in the LT-HSCs of VE-cadherin-cre+;Ptenfl/fl mice does not lead to the loss of HSC self-renewal, raising the possibility that PTEN-mediated self-renewal regulation may be more complicated than previously reported. To understand the molecular regulation of HSC homeostasis, I crossed Bmi1GFP/+ knock-in reporter mice, in which the intact Bmi1 promoter drives the transcription of the GFP transgene instead of the self-renewal regulator gene Bmi1, with Pten-deficient mice (Vav-icre+;CD2-C3+;Ptenfl/fl, or vCPΔ/Δ) to generate vCBPΔ/Δ (vCPΔ/Δ;Bmi1GFP/+) mice. The intact GFP signals in vCBPΔ/Δ mice, which represent the expression of Bmi1, indicated that the transcription of Bmi1 was not affected by PTEN loss. However, vCBPΔ/Δ mice surprisingly suffered from the exhaustion of LT-HSCs and eventually died between 2 and 4 months after birth, which was reminiscent of the HSC defects in Bmi1-/- mice. The similar phenotypes between vCBPΔ/Δ mice and Bmi1-/- mice raised the possibility that PTEN plays an important role in the protein stability of BMI1 and the BMI1-mediated self-renewal of LT-HSCs. To understand the role of PTEN in the regulation of BMI1, the protein levels of BMI1 in vCBPΔ/Δ LT-HSCs were measured by protein-flow analysis. Indeed, the BMI1 protein in vCBPΔ/Δ LT-HSCs was decreased by more than 50%. In contrast, the protein levels of BMI1 in vCPΔ/Δ and Bmi1GFP/+ mice, where the HSC pools remained normal, were slightly reduced by less than 50%. Consistently, the stem cell exhaustion marker p16Ink4a, which is typically repressed by BMI1, was strikingly upregulated in vCBPΔ/Δ LT-HSCs. These observations indicate that the protein levels of BMI1 are critical for the expression of p16Ink4a and the BMI1-mediated self-renewal regulation. At the molecular level, the loss of PTEN or its phosphatase function led to the activation of the stress-responsive kinase p38α MAPK. The activated p38α phosphorylated BMI1 at T275, which resulted in the degradation of BMI1. However, the T275 phosphorylation of BMI1 was suppressed by the phosphatase-independent function of PTEN. The T275A mutant of BMI1, which was unable to be phosphorylated by p38α, rescued the protein levels of BMI1 and the HSC pool in vCBPΔ/Δ mice. These molecular and genetic findings suggest that the T275 phosphorylation of BMI1 is associated with its protein stability and self-renewal regulation. To investigate the molecular regulation of BMI1 by PTEN and p38α under stress, an X-ray irradiation murine model was employed. The 3 Gy irradiation led to a decrease in the BMI1 protein levels in response to irradiation, which was accompanied by the increased reactive oxygen species at 14 days post-irradiation. The irradiated HSCs with increased ROS exhibited compromised self-renewal activity in serial transplantation assays. Conversely, HSCs with the Bmi1T275A mutation rescued the self-renewal ability of irradiated HSCs in those serial transplantation assays. These observations highlight the BMI1 T275 as a critical checkpoint in HSCs in response to stress. Taken together, the regulators p38α, PTEN and BMI1 form a new circuit to regulate HSC self-renewal in developmental and stress conditions. PTEN and p38α play an essential role in regulating the protein levels of BMI1 and the self-renewal of HSCs via the BMI1 T275. The T275 locus in BMI1 is a critical checkpoint in response to stress."],"dc:identifier.uri":["https://hdl.handle.net/1842/43343","http://dx.doi.org/10.7488/era/5881"],"dc:language.iso":["en"],"dc:publisher":["The University of Edinburgh"],"dc:subject":["PTEN","BMI1","Self-renewal","Hematopoietic stem cells (HSCs)","Stress conditions"],"dc:title":["PTEN regulates the BMI1-mediated self-renewal of long-term hematopoietic stem cells in developmental and stress conditions"],"dc:type":["Thesis or Dissertation"],"dc:type.qualificationlevel":["Doctoral"],"dc:type.qualificationname":["PhD Doctor of Philosophy"]},"updated_at":"2026-07-24T02:14:22Z"}