Survey of senescent cell markers with age in human tissues

Abstract

Cellular senescence, triggered by sublethal damage, is characterized by indefinite growth arrest, altered gene expression patterns, and a senescence-associated secretory phenotype. While the accumulation of senescent cells during aging decreases tissue function and promotes many age-related diseases, at present there is no universal marker to detect senescent cells in tissues. Cyclin-dependent kinase inhibitors 2A (p16/CDKN2A) and 1A (p21/CDKN1A) can identify senescent cells, but few studies have examined the numbers of cells expressing these markers in different organs as a function of age. Here, we investigated systematically p16- and p21-positive cells in tissue arrays designed to include normal organs from persons across a broad spectrum of ages. Increased numbers of p21-positive and p16-positive cells with donor age were found in skin (epidermis), pancreas, and kidney, while p16-expressing cells increased in brain cortex, liver, spleen and intestine (colon), and p21-expressing cells increased in skin (dermis). The numbers of cells expressing p16 or p21 in lung did not change with age, and muscle did not appear to have p21- or p16-positive cells. In summary, different organs display different levels of the senescent proteins p16 and p21 as a function of age across the human life span.

Keywords: aging; p16; p21; senescence in tissues.

Figure 1

Pancreas. (A, B) Cells expressing p16 (A) or p21 (B) were identified by IHC staining in exocrine regions of the pancreas of Young, Middle-aged, and Old donors. (C, D) Cells expressing p16 (C) or p21 (D) were identified by IHC staining in the endocrine regions of the pancreas from Young, Middle-aged, and Old donors. Graphs represent the quantification (%) of p16-positive (A, C) and p21-positive (B, D) cells from 5 tissue cores from independent donors per organ and age group; data represent the means ±SD from 5 different donors. p values were determined by one-way ANOVA with Tukey adjustments for multiple comparisons where appropriate. **, p < 0.01; *, p < 0.05.

Figure 2

Skin. (A, B) Cells expressing p16 (A) or p21 (B) were identified by IHC staining in the epidermis of Young, Middle-aged, and Old donors. (C, D) Cells expressing p16 (C) or p21 (D) were identified by IHC staining in the dermis from Young, Middle-aged, and Old donors. Graphs represent the quantification (%) of p16-positive (A) and p21-positive (B, D) cells from 5 tissue cores from independent donors per organ and age group; data represent the means ±SD from 5 different donors. p values were determined by one-way ANOVA with Tukey adjustments for multiple comparisons where appropriate. **, p < 0.01; *, p < 0.05.

Figure 3

Kidney. (A, B) Cells expressing p16 (A) or p21 (B) were identified by IHC staining in the renal cortex of kidney of Young, Middle-aged, and Old donors. (C) Decreased magnification images showing p16-positive cells in the Bowman capsule of Old donors. Graphs represent the quantification (%) of p16-positive (A) and p21-positive (B) cells from 5 tissue cores from independent donors per organ and age group; data represent the means ±SD from 5 different donors. p values were determined by one-way ANOVA with Tukey adjustments for multiple comparisons where appropriate. **, p < 0.01; *, p < 0.05.

Figure 4

Liver. Cells expressing p16 (A) or p21 (B) were identified by IHC staining in the liver of Young, Middle-aged, and Old donors. Graphs represent the quantification (%) of p16-positive (A) and p21-positive (B) cells from 5 tissue cores from independent donors per organ and age group; data represent the means ±SD from 5 different donors. p values were determined by one-way ANOVA with Tukey adjustments for multiple comparisons where appropriate. **, p < 0.01; *, p < 0.05.

Figure 5

Intestine (colon). (A, B) Cells expressing p16 (A) or p21 (B) were identified by IHC staining in the colon of Young, Middle-aged, and Old donors. (C) p16-expressing cells in colon shown at lower magnification (20x). Graphs represent the quantification (%) of p16-positive (A) and p21-positive (B) cells from 5 tissue cores from independent donors per organ and age group; data represent the means ±SD from 5 different donors. p values were determined by one-way ANOVA with Tukey adjustments for multiple comparisons where appropriate. *, p < 0.05.

Figure 6

Spleen. Cells expressing p16 (A) or p21 (B) were identified by IHC staining in the spleen of Young, Middle-aged, and Old donors. Graph represents the quantification (%) of p16-positive cells from 5 tissue cores from independent donors per organ and age group; data represent the means ±SD from 5 different donors. p values were determined by one-way ANOVA with Tukey adjustments for multiple comparisons where appropriate. *, p < 0.05.

Figure 7

Brain cortex. Cells expressing p16 (A) or p21 (B) were identified by IHC staining in the brain cortex from Young, Middle-aged, and Old donors. Graph represents the quantification (%) of p16-positive cells from 5 tissue cores from independent donors per organ and age group; data represent the means ±SD from 5 different donors. p values were determined by one-way ANOVA with Tukey adjustments for multiple comparisons where appropriate. *, p < 0.05.

Figure 8

Lung. Cells expressing p16 (A) or p21 (B) were identified by IHC staining in the lung from Young, Middle-aged, and Old donors. Graph represents the quantification (%) of p16-positive cells (A) and p21-positive cells (B) from 5 tissue cores from independent donors per organ and age group; data represent the means ±SD from 5 different donors.

Figure 9

Muscle. IHC analysis to detect cells expressing p16 (A) or p21 (B) in skeletal muscle of Young, Middle-aged, and Old donors. IHC analysis to detect cells expressing p16 (C) or p21 (D) in cardiac muscle of Young, Middle-aged, and Old donors. These proteins were undetectable in these muscle biopsies (5 cores per organ and age group).