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Oval cell proliferation in p16INK4a expressing mouse liver is triggered by chronic growth stimuli.

Ueberham E, Lindner R, Kamprad M, Hiemann R, Hilger N, Woithe B, Mahn D, Cross M, Sack U, Gebhardt R, Arendt T, Ueberham U - J. Cell. Mol. Med. (2007)

Bottom Line: Terminal differentiation requires molecules also involved in aging such as the cell cycle inhibitor p16(INK4a).Like other organs, the adult liver represents a quiescent organ with terminal differentiated cells, hepatocytes and cholangiocytes.However, under conditions which prevent mitotic activation of hepatocytes, regeneration can occur instead from facultative hepatic stem cells.For therapeutic application a non-toxic activation of this stem cell compartment is required.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biochemistry, University of Leipzig, Medical Faculty, Leipzig, Germany.

ABSTRACT
Terminal differentiation requires molecules also involved in aging such as the cell cycle inhibitor p16(INK4a). Like other organs, the adult liver represents a quiescent organ with terminal differentiated cells, hepatocytes and cholangiocytes. These cells retain the ability to proliferate in response to liver injury or reduction of liver mass. However, under conditions which prevent mitotic activation of hepatocytes, regeneration can occur instead from facultative hepatic stem cells.For therapeutic application a non-toxic activation of this stem cell compartment is required. We have established transgenic mice with conditional overexpression of the cell cycle inhibitor p16(INK4a) in hepatocytes and have provoked and examined oval cell activation in adult liver in response to a range of proliferative stimuli. We could show that the liver specific expression of p16(INK4a) leads to a faster differentiation of hepatocytes and an activation of oval cells already in postnatal mice without negative consequences on liver function.

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Mitotic figures inmouse liver sections after partial hepatectomy. (A) Sections of mouse livers of induced ptetp16INK4aTALAP-2 mice (A, C) and control mice (B, D) were stained with the anti-p16INK4a antibody (C-20, yellowish-brown colour) 72 hrs (A, B) and 14 days (C, D) after PH. Mitotic figures were identified by chromosomes visible as tangled, dark-staining threads (arrows).Number of mitotic figures in p16INK4a expressing and non-expressing livers was similar 72 hrs after PH, but differed significantly 14 days after PH (with control mice having no but p16INK4a expressing mice displaying some mitotic figures 14 days after PH (C)). Only in p16INK4a expressing mice abnormal mitotic figures like triphasic spindles were observed. Bar represents 50 μm.
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fig06: Mitotic figures inmouse liver sections after partial hepatectomy. (A) Sections of mouse livers of induced ptetp16INK4aTALAP-2 mice (A, C) and control mice (B, D) were stained with the anti-p16INK4a antibody (C-20, yellowish-brown colour) 72 hrs (A, B) and 14 days (C, D) after PH. Mitotic figures were identified by chromosomes visible as tangled, dark-staining threads (arrows).Number of mitotic figures in p16INK4a expressing and non-expressing livers was similar 72 hrs after PH, but differed significantly 14 days after PH (with control mice having no but p16INK4a expressing mice displaying some mitotic figures 14 days after PH (C)). Only in p16INK4a expressing mice abnormal mitotic figures like triphasic spindles were observed. Bar represents 50 μm.

Mentions: (PH) firstly described by Higgins and Anderson [37] is the strongest known stimulus for liver regeneration, with a two-third PH recruiting almost all hepatocytes into cycle within 48 hrs [17], so that an average of less than two doublings is sufficient to restore hepatocyte numbers. As expected, a 2/3 hepatectomy of control mice resulted in rapid activation of hepatocytes and the regeneration of 100% over 14 days. Interestingly, the mitotic index (MI) of hepatocytes in mice expressing p16INK4a was slightly higher than that in the controls from 48 hrs after PH, equal in both groups 72 hrs after PH, but significantly increased in livers of induced mice 14 days after PH (p16INK4a expressing mice display a MI of 9.9 per 50 mm2 and controls show 1 per 50 mm2). The mitotic figures, few of them visible as triphasic spindles, were restricted to cells which showed no detectable p16INK4a staining (Fig. 6). Bearing in mind the reduced regenerative capacity in these animals, it seems likely that these cells undergo either a retarded mitosis or most probably a prolonged proliferative response compensating for the low frequency of recruitable (non-expressing) hepatocytes similar as shown in the telomerase knock-out model [38]. This proliferation of p16INK4a non-expressing hepatocytes was obviously sufficient to restore liver mass after the unique proliferative stimulus by PH. Livers of induced mice werechecked up on oval cell proliferation at several time points (48 hrs, 3, 4, 6, 7, 12 and 14 days after PH) but never a recruitment of facultative stem cell compartment was observed (data not shown).


Oval cell proliferation in p16INK4a expressing mouse liver is triggered by chronic growth stimuli.

Ueberham E, Lindner R, Kamprad M, Hiemann R, Hilger N, Woithe B, Mahn D, Cross M, Sack U, Gebhardt R, Arendt T, Ueberham U - J. Cell. Mol. Med. (2007)

Mitotic figures inmouse liver sections after partial hepatectomy. (A) Sections of mouse livers of induced ptetp16INK4aTALAP-2 mice (A, C) and control mice (B, D) were stained with the anti-p16INK4a antibody (C-20, yellowish-brown colour) 72 hrs (A, B) and 14 days (C, D) after PH. Mitotic figures were identified by chromosomes visible as tangled, dark-staining threads (arrows).Number of mitotic figures in p16INK4a expressing and non-expressing livers was similar 72 hrs after PH, but differed significantly 14 days after PH (with control mice having no but p16INK4a expressing mice displaying some mitotic figures 14 days after PH (C)). Only in p16INK4a expressing mice abnormal mitotic figures like triphasic spindles were observed. Bar represents 50 μm.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3822548&req=5

fig06: Mitotic figures inmouse liver sections after partial hepatectomy. (A) Sections of mouse livers of induced ptetp16INK4aTALAP-2 mice (A, C) and control mice (B, D) were stained with the anti-p16INK4a antibody (C-20, yellowish-brown colour) 72 hrs (A, B) and 14 days (C, D) after PH. Mitotic figures were identified by chromosomes visible as tangled, dark-staining threads (arrows).Number of mitotic figures in p16INK4a expressing and non-expressing livers was similar 72 hrs after PH, but differed significantly 14 days after PH (with control mice having no but p16INK4a expressing mice displaying some mitotic figures 14 days after PH (C)). Only in p16INK4a expressing mice abnormal mitotic figures like triphasic spindles were observed. Bar represents 50 μm.
Mentions: (PH) firstly described by Higgins and Anderson [37] is the strongest known stimulus for liver regeneration, with a two-third PH recruiting almost all hepatocytes into cycle within 48 hrs [17], so that an average of less than two doublings is sufficient to restore hepatocyte numbers. As expected, a 2/3 hepatectomy of control mice resulted in rapid activation of hepatocytes and the regeneration of 100% over 14 days. Interestingly, the mitotic index (MI) of hepatocytes in mice expressing p16INK4a was slightly higher than that in the controls from 48 hrs after PH, equal in both groups 72 hrs after PH, but significantly increased in livers of induced mice 14 days after PH (p16INK4a expressing mice display a MI of 9.9 per 50 mm2 and controls show 1 per 50 mm2). The mitotic figures, few of them visible as triphasic spindles, were restricted to cells which showed no detectable p16INK4a staining (Fig. 6). Bearing in mind the reduced regenerative capacity in these animals, it seems likely that these cells undergo either a retarded mitosis or most probably a prolonged proliferative response compensating for the low frequency of recruitable (non-expressing) hepatocytes similar as shown in the telomerase knock-out model [38]. This proliferation of p16INK4a non-expressing hepatocytes was obviously sufficient to restore liver mass after the unique proliferative stimulus by PH. Livers of induced mice werechecked up on oval cell proliferation at several time points (48 hrs, 3, 4, 6, 7, 12 and 14 days after PH) but never a recruitment of facultative stem cell compartment was observed (data not shown).

Bottom Line: Terminal differentiation requires molecules also involved in aging such as the cell cycle inhibitor p16(INK4a).Like other organs, the adult liver represents a quiescent organ with terminal differentiated cells, hepatocytes and cholangiocytes.However, under conditions which prevent mitotic activation of hepatocytes, regeneration can occur instead from facultative hepatic stem cells.For therapeutic application a non-toxic activation of this stem cell compartment is required.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biochemistry, University of Leipzig, Medical Faculty, Leipzig, Germany.

ABSTRACT
Terminal differentiation requires molecules also involved in aging such as the cell cycle inhibitor p16(INK4a). Like other organs, the adult liver represents a quiescent organ with terminal differentiated cells, hepatocytes and cholangiocytes. These cells retain the ability to proliferate in response to liver injury or reduction of liver mass. However, under conditions which prevent mitotic activation of hepatocytes, regeneration can occur instead from facultative hepatic stem cells.For therapeutic application a non-toxic activation of this stem cell compartment is required. We have established transgenic mice with conditional overexpression of the cell cycle inhibitor p16(INK4a) in hepatocytes and have provoked and examined oval cell activation in adult liver in response to a range of proliferative stimuli. We could show that the liver specific expression of p16(INK4a) leads to a faster differentiation of hepatocytes and an activation of oval cells already in postnatal mice without negative consequences on liver function.

Show MeSH
Related in: MedlinePlus