Loss of Nkx3.1 expression in bacterial prostatitis: a potential link between inflammation and neoplasia

Abstract

NKX3.1 is a homeodomain protein that functions as a dosage sensitive prostate-specific transcription factor. Diminished NKX3.1 expression is associated with prostate epithelial cell proliferation in vitro and with increasing Gleason grade in patient samples. Mouse Nkx3.1 also functions as a negative regulator of prostate cell growth in prostate cancer models. Identifying biological and environmental factors that modulate NKX3.1 accumulation is therefore central to efforts aimed at elucidating prostate growth control mechanisms. To determine the effect of inflammation on Nxk3.1 accumulation, bacterial prostatitis was induced by intraurethral inoculation of a uropathogenic E. coli strain in mice. Nkx3.1 expression was profoundly reduced in infected prostate lobes and correlated with increased expression of a proliferation marker. Androgen receptor levels were also reduced in concert with Nkx3.1, and a marked increase in the basal cell marker p63 was observed. Analyses of the inflammatory infiltrate revealed a classic acute inflammatory response that attained characteristics of a chronic state within fourteen days postinoculation. Comparison of the four prostate lobes revealed clear differences in the extent of inflammation. These data demonstrate that acute inflammation in response to a bacterial agent in the prostate is associated with a significant diminution in the level of a key regulator of prostate cell proliferation. These observations provide a plausible mechanism whereby prostate inflammation may establish a local environment conducive to epithelial cell growth.

Figure 1

Histopathological analysis of individual prostate lobes from CP9-infected mice at five, 10, and 14 days postinoculation. A–C: Anterior prostate (AP). A: Day five AP showing heavily infiltrated glandular lumen and a multilayered ductal epithelium. Note the complete loss of papillary infoldings within the ductal epithelium. B: Day 10 AP exhibiting hyperchromatic and multilayered epithelium. Note the marked fibrosis within the stromal layer. C: Day 14 AP with a thickened fibromuscular sheath surrounding a recovered duct. Note the newly generated cribriform architecture. D–F: Dorsal prostate (DP). Note the juxtaposition of inflamed and noninflamed ducts in all three panels. D: Day five DP. E: Day 10 DP with a slightly disorganized multilayered epithelium. F: Day 14 DP exhibiting severe glandular and periglandular inflammation. Note the distended duct and hyperchromatic nuclear appearance. G–I: Lateral prostate (LP). G: Day five LP with no apparent inflammation. A few mononuclear inflammatory cells appear in stroma and around the blood capillary. H: Day 10 LP exhibiting an involved duct with mild glandular infiltrate and extensive epithelial multilayering. Note the markedly thickened stromal layer. I: Day 14 LP. Note the slightly thickened stroma and the scattered inflammatory infiltrate in the absence of any apparent glandular inflammation. J–L: Ventral prostate (VP). J: Day five VP. K: Day 10 VP exhibiting dense periglandular infiltrate with disorganized and multilayered ductal epithelia. L: Day 14 VP. Note the increase in newly formed stromal capillaries. Original magnifications: ×400 (A–E, G–L); ×100 (F). H&E staining.

Figure 2

Nkx3.1 expression in CP9-infected anterior prostate. A: Day 14 anterior prostate. Note the juxtaposition of inflamed and noninflamed ducts. H&E, ×100. B: Section adjacent to that shown in A, stained with anti-Nkx3.1 antibody. Note the marked reduction in Nkx3.1 staining from the inflamed duct, whereas noninflamed duct shows normal Nkx3.1 expression. Immunoperoxidase, ×100. C: Day 14 anterior prostate. Note the absence of glandular infiltrate and the newly generated cribriform architecture. H&E ×400. D: Section adjacent to that shown in C, stained with anti-Nkx3.1 antibody. Nkx3.1 staining is almost uniformly restored, although it remains absent from a subset of epithelial cells closest to the lumen. Immunoperoxidase, ×400.

Figure 3

AR, Ki-67, and p63 expression in control and CP9-infected anterior prostate at day 14. A: Anterior prostate. Note the juxtaposition of an inflamed and noninflamed duct. B: Section adjacent to that shown in A, stained with anti-AR antibody. Note the reduced AR staining from the inflamed duct. Noninflamed duct shows normal AR expression. C: Ki-67 immunostaining in control section from anterior prostate demonstrating a very low proliferative index in the normal prostate. D: Day 14 infected anterior prostate showing a marked increase in Ki-67 nuclear staining. E: Nuclear p63 immunostaining in the basal epithelial layer in normal prostate. Note the slender and slightly angular morphology of basal nuclei. F: Increased expression of p63 in a basally-located layer of cells lining the infected duct. Note the change in nuclear morphology from that seen in E and the appearance of scattered p63-positive cells closer to the lumen. H&E (A) ×400. Immunoperoxidase (B–F) ×400.

Figure 4

Immunohistochemical characterization of the inflammatory infiltrate in bacterially-induced prostatitis. A: Anterior prostate section from CP9-infected mice at day 14 stained with the macrophage marker F4/80. Note the dense stromal and periglandular macrophage infiltration. B: High-power image of boxed region indicated in A demonstrating intraepithelial macrophage infiltration. C: A nearby section to that shown in A, stained with the T-cell marker CD3. D: High-power image of boxed region indicated in C demonstrating stromal and intraepithelial T-cell presence. Immunoperoxidase (A–D). Original magnifications: ×100 (A, C), ×400 (B, D).