Protein Tyrosine Phosphatase-N13 Promotes Myofibroblast Resistance to Apoptosis in Idiopathic Pulmonary Fibrosis

RATIONALE

Idiopathic pulmonary fibrosis (IPF) is a progressive, fibrotic interstitial lung disease characterized by (myo)fibroblast accumulation and collagen deposition. Resistance to Fas-induced apoptosis is thought to facilitate (myo)fibroblast persistence in fibrotic lung tissues by poorly understood mechanisms.

OBJECTIVES

To test the hypothesis that PTPN13 (protein tyrosine phosphatase-N13) is expressed by IPF lung (myo)fibroblasts, promotes their resistance to Fas-induced apoptosis, and contributes to the development of pulmonary fibrosis.

METHODS

PTPN13 was localized in lung tissues from patients with IPF and control subjects by immunohistochemical staining. Inhibition of PTPN13 function in primary IPF and normal lung (myo)fibroblasts was accomplished by: 1) downregulation with TNF-α (tumor necrosis factor-α)/IFN-γ, 2) siRNA knockdown, or 3) a cell-permeable Fas/PTPN13 interaction inhibitory peptide. The role of PTPN13 in the development of pulmonary fibrosis was assessed in mice with genetic deficiency of PTP-BL, the murine ortholog of PTPN13.

MEASUREMENTS AND MAIN RESULTS

PTPN13 was constitutively expressed by (myo)fibroblasts in the fibroblastic foci of patients with IPF. Human lung (myo)fibroblasts, which are resistant to Fas-induced apoptosis, basally expressed PTPN13 in vitro. TNF-α/IFN-γ or siRNA-mediated PTPN13 downregulation and peptide-mediated inhibition of the Fas/PTPN13 interaction in human lung (myo)fibroblasts promoted Fas-induced apoptosis. Bleomycin-challenged PTP-BL-/- mice, while developing inflammatory lung injury, exhibited reduced pulmonary fibrosis compared with wild-type mice.

CONCLUSIONS

These findings suggest that PTPN13 mediates the resistance of human lung (myo)fibroblasts to Fas-induced apoptosis and promotes pulmonary fibrosis in mice. Our results suggest that strategies aimed at interfering with PTPN13 expression or function may represent a novel strategy to reduce fibrosis in IPF.

High resolution computed tomography pattern of usual interstitial pneumonia in rheumatoid arthritis-associated interstitial lung disease: Relationship to survival

PURPOSE

Interstitial lung disease is a common extra-articular manifestation of rheumatoid arthritis (RA-ILD) and is associated with significant morbidity and mortality. However, limited data exist regarding predictors of mortality. We sought to examine the prognostic value of the high-resolution computed tomography (HRCT) patterns in patients with RA-ILD.

MATERIALS AND METHODS

RA-ILD patients with HRCT patterns of usual interstitial pneumonia (UIP) or nonspecific interstitial pneumonia (NSIP) were identified among a longitudinal cohort of individuals evaluated at National Jewish Health. A total of 158 subjects were included in the study. For each subject, the earliest available HRCT was reviewed independently by two expert thoracic radiologists blinded to clinical data. HRCT patterns were classified as demonstrating definite UIP, possible UIP, or NSIP. Kaplan-Meier curves were generated and survival was compared among the three patterns using a log rank test for trend.

RESULTS

One hundred subjects (63%) had HRCT findings classified as definite UIP, 23 (15%) as possible UIP and 35 (22%) as NSIP. No difference in survival was seen between subjects with definite UIP versus those with possible UIP. The combined group of subjects with either definite- or possible UIP had significantly worse survival than those with NSIP (log-rank p = 0.03).

CONCLUSIONS

In patients with RA-ILD, patients with either definite UIP or possible UIP have equally poor survival when compared to those with an NSIP pattern.

Tumor necrosis factor-α accelerates the resolution of established pulmonary fibrosis in mice by targeting profibrotic lung macrophages

Idiopathic pulmonary fibrosis (IPF) is a relentless, fibrotic parenchymal lung disease in which alternatively programmed macrophages produce profibrotic molecules that promote myofibroblast survival and collagen synthesis. Effective therapies to treat patients with IPF are lacking, and conventional therapy may be harmful. We tested the hypothesis that therapeutic lung delivery of the proinflammatory cytokine tumor necrosis factor (TNF)-α into wild-type fibrotic mice would reduce the profibrotic milieu and accelerate the resolution of established pulmonary fibrosis. Fibrosis was assessed in bleomycin-instilled wild-type and TNF-α(-/-) mice by measuring hydroxyproline levels, static compliance, and Masson's trichrome staining. Macrophage infiltration and programming status was assessed by flow cytometry of enzymatically digested lung and in situ immunostaining. Pulmonary delivery of TNF-α to wild-type mice with established pulmonary fibrosis was found to reduce their fibrotic burden, to improve lung function and architecture, and to reduce the number and programming status of profibrotic alternatively programmed macrophages. In contrast, fibrosis and alternative macrophage programming were prolonged in bleomycin-instilled TNF-α(-/-) mice. To address the role of the reduced numbers of alternatively programmed macrophages in the TNF-α-induced resolution of established pulmonary fibrosis, we conditionally depleted macrophages in MAFIA (MAcrophage Fas-Induced Apoptosis) mice. Conditional macrophage depletion phenocopied the resolution of established pulmonary fibrosis observed after therapeutic TNF-α delivery. Taken together, our results show for the first time that TNF-α is involved in the resolution of established pulmonary fibrosis via a mechanism involving reduced numbers and programming status of profibrotic macrophages. We speculate that pulmonary delivery of TNF-α or augmenting its signaling pathway represent a novel therapeutic strategy to resolve established pulmonary fibrosis.

Testosterone is protective in the sexually dimorphic development of arthritis and lung disease in SKG mice

OBJECTIVE

Rheumatoid arthritis (RA) is a sexually dimorphic inflammatory autoimmune disease with both articular and extraarticular disease manifestations, including RA-associated interstitial lung disease. Low levels of testosterone have been linked to disease severity in men with RA, and supplemental testosterone has been shown to improve RA symptoms in both postmenopausal women and men with low levels of testosterone. The mechanisms by which sex and sex steroids affect the immune system and autoimmunity are poorly understood. The purpose of this study was to examine the protective effects of testicular-derived sex hormones on the development of joint and lung disease in an autoimmune mouse model.

METHODS

Arthritis prevalence and severity were assessed in orchiectomized, sham-orchiectomized, and intact male SKG mice as well as in female SKG mice over a 12-week period after intraperitoneal injection of zymosan. Lung tissues were evaluated by quantifying cellular accumulation in bronchoalveolar lavage fluid, collagen levels, and histologic changes. An antigen microarray was used to evaluate autoantibody generation under each experimental condition.

RESULTS

Female SKG mice developed arthritis and lung disease at increased prevalence and severity as compared to intact male mice. The absence of testosterone after orchiectomy led to increased arthritis, lung disease, and autoantibody generation in orchiectomized male mice as compared to intact male mice.

CONCLUSION

SKG mice represent an authentic sexually dimorphic mouse model of both the joint and lung disease seen in humans with RA. Testosterone protects against the development of joint and lung disease in male SKG mice.

A novel model of rheumatoid arthritis-associated interstitial lung disease in SKG mice

Rheumatoid arthritis-associated interstitial lung disease (RA-ILD) is associated with increased mortality in up to 10% of patients with rheumatoid arthritis. Lung exposure to cigarette smoke has been implicated in disease development. Little is known about the mechanisms underlying the development of RA-ILD, in part due to the lack of an appropriate mouse model. The objectives of this study were (i) to test the suitability of SKG mice as a model of cellular and fibrotic interstitial pneumonia in the setting of autoimmune arthritis, and (ii) to determine the role of lung injury in the development of arthritis in SKG mice. Lung tissues were evaluated in arthritic SKG mice by quantifying cell accumulation in bronchoalveolar lavage, static compliance, collagen levels, and infiltrating cell phenotypes by flow cytometry and histology. Lung injury was induced by exposure to cigarette smoke or bleomycin. Arthritic SKG mice developed a patchy cellular and fibrotic interstitial pneumonia associated with reduced static compliance, increased collagen levels, and accumulation of inflammatory cells. Infiltrating cells comprised CD4+ T cells, B cells, macrophages, and neutrophils. Chronic exposure to cigarette smoke or initiation of lung injury with bleomycin did not cause arthritis. The pattern of lung disease suggests that arthritic SKG mice represent an authentic model of nonspecific interstitial pneumonia in RA-ILD patients. The lack of arthritis development after cigarette smoke or lung injury suggests that a model where breaches in immunologic tolerance are induced by lung inflammation and injury alone may be overly simplistic.

Age and sex dimorphisms contribute to the severity of bleomycin-induced lung injury and fibrosis

Fibrotic interstitial pneumonias are more prevalent in males of advancing age, although little is known about the underlying mechanisms. To evaluate the contributions of age and sex to the development of pulmonary fibrosis, we intratracheally instilled young (8-12 wk) and aged (52-54 wk) male and female mice with bleomycin and assessed the development and severity of fibrotic lung disease by measurements of lung collagen levels, static compliance, leukocyte infiltration, and stereological quantification of fibrotic areas in histological sections. We also quantified proinflammatory and profibrotic chemokine and cytokine levels in the bronchoalveolar lavage fluid. Aged male mice developed more severe lung disease, indicated by increased mortality, increased collagen deposition, and neutrophilic alveolitis compared with aged female mice or young mice of either sex. Aged male mice also exhibited increased levels of transforming growth factor-β, IL-17A, and CXCL1 in their bronchoalveolar lavage fluid. Young male mice developed a more fibrotic disease after bleomycin instillation compared with female mice, regardless of age. There was no difference in fibrosis between young and aged female mice. Taken together, these findings suggest that the variables of advanced age and male sex contribute to the severity of pulmonary fibrosis in this model. Our findings also emphasize the importance of stratifying experimental groups on the basis of age and sex in experimental and epidemiological studies of this nature.

Increased cell surface Fas expression is necessary and sufficient to sensitize lung fibroblasts to Fas ligation-induced apoptosis: implications for fibroblast accumulation in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is associated with the accumulation of collagen-secreting fibroblasts and myofibroblasts in the lung parenchyma. Many mechanisms contribute to their accumulation, including resistance to apoptosis. In previous work, we showed that exposure to the proinflammatory cytokines TNF-α and IFN-γ reverses the resistance of lung fibroblasts to apoptosis. In this study, we investigate the underlying mechanisms. Based on an interrogation of the transcriptomes of unstimulated and TNF-α- and IFN-γ-stimulated primary lung fibroblasts and the lung fibroblast cell line MRC5, we show that among Fas-signaling pathway molecules, Fas expression was increased ∼6-fold in an NF-κB- and p38(mapk)-dependent fashion. Prevention of the increase in Fas expression using Fas small interfering RNAs blocked the ability of TNF-α and IFN-γ to sensitize fibroblasts to Fas ligation-induced apoptosis, whereas enforced adenovirus-mediated Fas overexpression was sufficient to overcome basal resistance to Fas-induced apoptosis. Examination of lung tissues from IPF patients revealed low to absent staining of Fas in fibroblastic cells of fibroblast foci. Collectively, these findings suggest that increased expression of Fas is necessary and sufficient to overcome the resistance of lung fibroblasts to Fas-induced apoptosis. Our findings also suggest that approaches aimed at increasing Fas expression by lung fibroblasts and myofibroblasts may be therapeutically relevant in IPF.

Atypical Internal Yellowing of Papaya Fruit in Hawaii Caused by Enterobacter sakazakii

Internal yellowing (IY) caused by Enterobacter cloacae and characterized by yellow discolored tissue surrounding the papaya (Carica papaya L.) seed cavity, diffuse margins, and the presence of a distinctly rotten odor was first reported in 1987 (3). Here we report the formation of atypical internal yellowing (AIY) in ripe papaya caused by the bacterium Enterobacter sakazakii. In surveys conducted from 2006 to 2007, 'Kapoho Solo' papayas grown in the Puna District of Hawaii Island were obtained from various packinghouses. After incubation at 27°C, the papayas were bisected and examined for symptoms of IY. Among papayas that were asymptomatic for IY, a dull, greenish yellow discoloration of the flesh with a distinct margin extending from the seed cavity into the pericarp was noted, along with a pungent odor. These symptoms occurred in 5 of the 500 fruit surveyed and bacterial populations were 10² to 10³ CFU/g. Discolored tissue was aseptically excised, weighed, macerated, serially diluted in sterile distilled water (SDW), and plated onto modified peptone yeast extract medium (PT-M4) (4). The plates were incubated at 30°C for 24 to 48 h until single colonies were evident. After 48 h, colonies on PT-M4 were orange-red, convex and circular, and surrounded by a somewhat opaque 1-mm margin. After single colony purification, five strains were obtained. The strains, inoculated into oxidation/fermentation-glucose tubes and API 20E strips (bioMerieux, Inc., Durham, NC) incubated at 30°C, were shown to be facultative anaerobes and identified as E. sakazakii with a 98.4% certainty. Colonies plated onto tryptic soy agar (TSA) and incubated for 72 h at 25°C produced yellow pigmentation, indicative of E. sakazakii. Amplification by PCR with E. sakazakii-specific primers (2) yielded a 929-bp fragment, which was absent with E. cloacae and Pseudomonas aeruginosa template DNA. To confirm pathogenicity, cell suspensions at 10⁹ CFU/ml of putative E. sakazakii strains RK07-05, RK07-06, and RK07-07 and E. cloacae (3) were inoculated by injection (0.5 ml per site) into one-third-ripe 'Kapoho Solo' papayas (six fruit per strain, inoculated at duplicate sites) and incubated at 27°C for 4 days. Control sites were injected with 0.5 ml of SDW. Fruit inoculation experiments were repeated. E. cloacae-inoculated sites produced typical IY as previously described (3), while the sites inoculated with the three E. sakazakii strains produced greenish yellow tissue (26% mean incidence), symptomatic of AIY. Control sites did not produce IY or AIY. Koch's postulates were fulfilled, and the identification of reisolated bacterial strains was confirmed with API 20E, PCR, and pigment production on TSA. Although less prevalent (1% incidence) than the typical IY produced by E. cloacae (3), E. sakazakii has the potential to affect quality and food safety of fresh and processed papaya products. E. sakazakii has been implicated in a severe form of neonatal meningitis, sepsis, and necrotizing enterocolitis (1). Research into the transmission and infection of papaya of this cross-domain pathogen merits further study. References: (1) D. H. Adamson. Clin. Microbiol. Newsl. 3:19, 1981. (2) A. Lehner et al. BMC Microbiol. 4:43, 2004. (3) K. A. Nishijima et al. Plant Dis. 71:1029, 1987. (4) K. A. Nishijima et al. Plant Dis. 88:1318, 2004.