The Middle Part of the Plucked Hair Follicle Outer Root Sheath Is Identified as an Area Rich in Lineage-Specific Stem Cell Markers

Hair follicle outer root sheath (ORS) is a putative source of stem cells with therapeutic capacity. ORS contains several multipotent stem cell populations, primarily in the distal compartment of the bulge region. However, the bulge is routinely obtained using invasive isolation methods, which require human scalp tissue ex vivo. Non-invasive sampling has been standardized by means of the plucking procedure, enabling to reproducibly obtain the mid-ORS part. The mid-ORS shows potential for giving rise to multiple stem cell populations in vitro. To demonstrate the phenotypic features of distal, middle, and proximal ORS parts, gene and protein expression profiles were studied in physically separated portions. The mid-part of the ORS showed a comparable or higher NGFR, nestin/NES, CD34, CD73, CD44, CD133, CK5, PAX3, MITF, and PMEL expression on both protein and gene levels, when compared to the distal ORS part. Distinct subpopulations of cells exhibiting small and round morphology were characterized with flow cytometry as simultaneously expressing CD73/CD271, CD49f/CD105, nestin, and not CK10. Potentially, these distinct subpopulations can give rise to cultured neuroectodermal and mesenchymal stem cell populations in vitro. In conclusion, the mid part of the ORS holds the potential for yielding multiple stem cells, in particular mesenchymal stem cells.

Nonhistone Proteins HMGB1 and HMGB2 Differentially Modulate the Response of Human Embryonic Stem Cells and the Progenitor Cells to the Anticancer Drug Etoposide

HMGB1 and HMGB2 proteins are abundantly expressed in human embryonic stem cells (hESCs) and hESC-derived progenitor cells (neuroectodermal cells, hNECs), though their functional roles in pluripotency and the mechanisms underlying their differentiation in response to the anticancer drug etoposide remain to be elucidated. Here, we show that HMGB1 and/or HMGB2 knockdown (KD) by shRNA in hESCs did not affect the cell stemness/pluripotency regardless of etoposide treatments, while in hESC-derived neuroectodermal cells, treatment resulted in differential effects on cell survival and the generation of rosette structures. The objective of this work was to determine whether HMGB1/2 proteins could modulate the sensitivity of hESCs and hESC-derived progenitor cells (hNECs) to etoposide. We observed that HMGB1 KD knockdown (KD) and, to a lesser extent, HMGB2 KD enhanced the sensitivity of hESCs to etoposide. Enhanced accumulation of 53BP1 on telomeres was detected by confocal microscopy in both untreated and etoposide-treated HMGB1 KD hESCs and hNECs, indicating that the loss of HMGB1 could destabilize telomeres. On the other hand, decreased accumulation of 53BP1 on telomeres in etoposide-treated HMGB2 KD hESCs (but not in HMGB2 KD hNECs) suggested that the loss of HMGB2 promoted the stability of telomeres. Etoposide treatment of hESCs resulted in a significant enhancement of telomerase activity, with the highest increase observed in the HMGB2 KD cells. Interestingly, no changes in telomerase activity were found in etoposide-treated control hNECs, but HMGB2 KD (unlike HMGB1 KD) markedly decreased telomerase activity in these cells. Changes in telomerase activity in the etoposide-treated HMGB2 KD hESCs or hNECs coincided with the appearance of DNA damage markers and could already be observed before the onset of apoptosis. Collectively, we have demonstrated that HMGB1 or HMGB2 differentially modulate the impact of etoposide treatment on human embryonic stem cells and their progenitor cells, suggesting possible strategies for the enhancement of the efficacy of this anticancer drug.

HMGB2 is a negative regulator of telomerase activity in human embryonic stem and progenitor cells

High-mobility group box (HMGB)1 and HMGB2 proteins are the subject of intensive research because of their involvement in DNA replication, repair, transcription, differentiation, proliferation, cell signaling, inflammation, and tumor migration. Using inducible, stably transfected human embryonic stem cells (hESCs) capable of the short hairpin RNA-mediated knockdown (KD) of HMGB1 and HMGB2, we provide evidence that deregulation of HMGB1 or HMGB2 expression in hESCs and their differentiated derivatives (neuroectodermal cells) results in distinct modulation of telomere homeostasis. Whereas HMGB1 enhances telomerase activity, HMGB2 acts as a negative regulator of telomerase activity in the cell. Stimulation of telomerase activity in the HMGB2-deficient cells may be related to activation of the PI3K/protein kinase B/ glycogen synthase kinase-3β/β-catenin signaling pathways by HMGB1, augmented TERT/telomerase RNA subunit transcription, and possibly also because of changes in telomeric repeat-containing RNA (TERRA) and TERRA-polyA⁺ transcription. The impact of HMGB1/2 KD on telomerase transcriptional regulation observed in neuroectodermal cells is partially masked in hESCs by their pluripotent state. Our findings on differential roles of HMGB1 and HMGB2 proteins in regulation of telomerase activity may suggest another possible outcome of HMGB1 targeting in cells, which is currently a promising approach aiming at increasing the anticancer activity of cytotoxic agents.-Kučírek, M., Bagherpoor, A. J., Jaroš, J., Hampl, A., Štros, M. HMGB2 is a negative regulator of telomerase activity in human embryonic stem and progenitor cells.

Properties of Human Embryonic Stem Cells and Their Differentiated Derivatives Depend on Nonhistone DNA-Binding HMGB1 and HMGB2 Proteins

HMGB1 and HMGB2 proteins have been implicated in numerous cellular processes, including proliferation, differentiation, apoptosis, and tumor growth. It is unknown whether they are involved in regulating the typical functions of pluripotent human embryonic stem cells (hESCs) and/or those of the differentiated derivatives of hESCs. Using inducible, stably transfected hESCs capable of shRNA-mediated knockdown of HMGB1 and HMGB2, we provide evidence that downregulation of HMGB1 and/or HMGB2 in undifferentiated hESCs does not affect the stemness of cells and induces only minor changes to the proliferation rate, cell-cycle profile, and apoptosis. After differentiation is induced, however, the downregulation of those proteins has important effects on proliferation, apoptosis, telomerase activity, and the efficiency of differentiation toward the neuroectodermal lineage. Furthermore, those processes are affected only when one, but not both, of the two proteins is downregulated; the knockdown of both HMGB1 and HMGB2 results in a normal phenotype. Those results advance our knowledge of regulation of hESC and human neuroectodermal cell differentiation and illustrate the distinct roles of HMGB1 and HMGB2 during early human development.