Both T- and K-kininogens increase in the serum of old rats but by different mechanisms

The natural course of hereditary angioedema in a Chinese cohort

Background

Hereditary angioedema (HAE) is a rare disease with potential life-threatening risks. To study the natural course of HAE under therapy-free conditions throughout patient life is essential for practitioners and patients to avoid possible risk factors and guide treatment.

Objectives

Describe the natural course of HAE and explore possible risk factors, providing new clues for guiding clinical prevention and treatment.

Methods

A web-based survey was conducted in 103 Chinese patients with type 1 HAE. Disease progression at different age stages was provided by each participant. The data for exploring the natural course of HAE composed of two parts: one came from the participants who had never adopted any prophylactic drug for HAE; the other was from the patients with a history of medication, but only the periods before they got confirmed diagnosis and received medications were analyzed. The demographic characteristics, lifestyles, disease severity, and family history were also collected.

Results

Among 103 patients, 14 (13.6%) had their first HAE attack before 10 years old and 51 (49.5%) between 10 and 19. The disease worsened in 83.3% of the patients in their twenties. The proportion of patients with symptoms alleviated increased after the age of 30 years old, but the disease maintained relatively severe in most cases before 50. The participants also reported 233 members shared similar symptoms of angioedema in their family and 30 had died of laryngeal edema with the median death age of 46 years old. The disease severity was not observed to be affected significantly by gender, BMI, alcohol or smoking.

Conclusions

We summarized HAE progression patterns under therapy-free conditions, showing the natural course of HAE development along with aging. Long-term prophylaxis and symptomatic treatment are recommended for all HAE patients, especially young and middle-aged and might be adjusted depending on the disease progression.

Diminished acute phase response and increased hepatic inflammation of aged rats in response to intraperitoneal injection of lipopolysaccharide

Aging is associated with a deterioration of the acute phase response to inflammatory challenges. However, the nature of these defects remains poorly defined. We analyzed the hepatic inflammatory response after intraperitoneal administration of lipopolysaccharide (LPS) given to Fisher 344 rats aged 6, 15, and 22-23 months. Induction of the acute phase proteins (APPs), haptoglobin, alpha-1-acid glycoprotein, and T-kininogen was reduced and/or retarded with aging. Initial induction of interleukin-6 in aged rats was normal, but the later response was increased relative to younger counterparts. An exacerbated hepatic injury was observed in aged rats receiving LPS, as evidenced by the presence of multiple microabscesses in portal tracts, confluent necrosis, higher neutrophil accumulation, and elevated serum levels of alanine aminotransferase, relative to younger animals. Our results suggest that aged rats displayed a reduced expression of APPs and increased hepatic injury in response to the inflammatory insult.

T-kininogen: a biomarker of aging in Fisher 344 rats with possible implications for the immune response

T-kininogen (T-KG) is a reliable biomarker of aging in male Sprague-Dawley rats. Here we confirm, in a longitudinal study, a similar behavior in Fisher 344 rats of both sexes. In males, the increase in serum levels of T-KG follows an exponential curve, whereas in females the increase is best fitted by a linear curve. In both genders, dietary restriction delays the increase in T-KG. We have previously shown that T-KG inhibits T lymphocyte proliferation. Here we show that serum T-KG levels correlate negatively with the ability of splenocytes (most likely B cells) to proliferate in response to lipopolysaccharide. A similar correlation was not observed with other markers of inflammation, including alpha1-acid glycoprotein (AGP), haptoglobin, or interleukin-10. We conclude that the increase in serum T-KG represents a useful biomarker of aging in Fisher 344, and it correlates with decreased lymphocyte proliferation with age, although a cause-effect relationship has not been established.

T-kininogen, a cystatin-like molecule, inhibits ERK-dependent lymphocyte proliferation

Plasma levels of kininogens increase with age in both rats and humans. Kininogens are inhibitors of cysteine proteinases, and filarial cysteine proteinase inhibitors (cystatins) reduce the proliferation of T cells. We evaluated whether T-kininogen (T-KG) might mimic this effect, and here we present data indicating that exposure of either rat splenocytes or Jurkat cells to purified T-KG results in inhibition of both ERK activation and [(3)H]-thymidine incorporation, both basal and in response to ConA or PHA. Interestingly, T-KG did not impair [(3)H]-thymidine incorporation in response to IL-2, which requires primarily the activation of the JNK and Jak/STAT pathways. These effects were neither the consequence of increased cell death, nor required the activity of kinin receptors. Furthermore, when T cell receptor proximal events were bypassed by the use of PMA plus Calcium ionophore, T-KG no longer inhibited ERK activation, suggesting that inhibition occurs upstream of these events, possibly at the level of membrane associated signal transduction molecules. We conclude that, like filarial cystatins, T-KG inhibits ERK-dependent T cell proliferation, and these observations suggest a possible role for T-KG in immunosenescence.

Increased Kinin Levels and Decreased Responsiveness to Kinins During Aging

Kinins are vasoactive peptides released from precursors called kininogens, and serum levels of both T- and K-kininogens increase dramatically as rats age. Kinin release is tightly regulated, and here we show that serum kinin levels also increase with age, from 63 +/- 16 nmol/L in young Fisher 344 rats to 398 +/- 102 nmol/L in old animals. Both K- and T-kininogens contribute sequentially to this increase, with the increase in middle-aged animals being driven primarily by K-kininogen, whereas the further augmentation in older rats occurs by increasing T-kininogen. By measuring ERK activation, we show that aorta endothelial cells from old animals are hyporesponsive to exogenous bradykinin. However, if serum kinin levels are experimentally decreased by lipopolysaccharide treatment, then the endothelial response to bradykinin is re-established. These results indicate that serum levels of kinins increase with age, whereas the responsiveness of target cells to kinins is reduced in these same animals.

T-kininogen can either induce or inhibit proliferation in Balb/c 3T3 fibroblasts, depending on the route of administration

T-kininogen (T-KG) is a precursor of T-kinin, the most abundant kinin in rat serum, and also acts as a strong and specific cysteine proteinase inhibitor. Its expression is strongly induced during aging in rats, and expression of T-KG in Balb/c 3T3 fibroblasts results in inhibition of cell proliferation. However, T-KG is a serum protein produced primarily in the liver, and thus, most cells are only exposed to the protein from the outside. To test the effect of T-KG on fibroblasts exposed to exogenous T-KG, we purified the protein from the serum of K-kininogen-deficient Katholiek rats. In contrast to the results obtained by transfection, exposure of Balb/c 3T3 fibroblasts to exogenously added T-KG leads to a dose-dependent increase in [3H]-thymidine incorporation. This response does not require kinin receptors, but it is clearly mediated by activation of the ERK pathway. As a control, we repeated the transfection experiments, using a different promoter. The results are consistent with our published data showing that, under these circumstances, T-KG inhibits cell proliferation. We conclude that T-KG exerts opposite effects on fibroblast proliferation, depending exclusively on the way that it is administered to the cells (transfection versus exogenous addition).

Replicative senescence: a critical review

Human cells in culture have a limited proliferative capacity. After a period of vigorous proliferation, the rate of cell division declines and a number of changes occur in the cells including increases in size, in secondary lysosomes and residual bodies, nuclear changes and a number of changes in gene expression which provide biomarkers for senescence. Although human cells in culture have been used for over 40 years as models for understanding the cellular basis of aging, the relationship of replicative senescence to aging of the organism is still not clear. In this review, we discuss replicative senescence in the light of current information on signal transduction and mitogenesis, cell stress, apoptosis, telomere changes and finally we discuss replicative senescence as a model of aging in vivo.

T-kininogen inhibits fibroblast proliferation in the G(1) phase of the cell cycle

By using synthetic protease inhibitors, several investigators have demonstrated that cysteine proteinases are required for cell proliferation. Kininogens are potent and specific physiological inhibitors of cysteine proteinases. We have used several mouse fibroblast-derived cell lines that express biologically active T-kininogen under the control of the mouse metallothionein promoter to test its effect on cell proliferation. Our results indicate that expression of T-kininogen results in diminished proliferative capacity, as measured by reduced cell numbers, both in logarithmically growing cultures and in G(0) cells induced to proliferate in response to serum. Furthermore, both fluorescence-activated cell sorting (FACS) analysis and incorporation of radioactive precursors into DNA suggest that the cells are unable to progress from G(0) through the S phase of the cell cycle in response to serum stimulation. However, we find that T-kininogen-expressing cell lines are still capable of responding to growth factors present in the serum, both by activating the ERK pathway and by expressing early genes, such as c-Fos and c-Jun. Thus, our results suggest that inhibition of cysteine proteinases by T-kininogen leads to inhibition of cell proliferation between the G(1) and S phases of the cell cycle.

T-kininogen is a biomarker of senescence in rats

We have previously reported on the identification of T-kininogen (T-KG) as a gene whose expression is increased during senescence in male Sprague-Dawley (S-D) rats. Serum T-KG levels increase 2.5-4 months before the time of death for any given animal, irrespective of the actual age of the animal at the time of this event. Furthermore, dietary restriction (DR) delays, but does not prevent, the increase in serum T-KG levels. In the present study, we have assessed whether or not the age-related increase in T-KG is a common feature of senescence in other strains of rat. We have analyzed hepatic T-KG mRNA levels in male Fischer 344 rats (F344), as well as in male and female (Fischer 344 x Brown Norway)F1 rats (F1). In both of these strains, we observed a dramatic increase in hepatic T-KG mRNA levels when male rats approach senescence. The mRNA levels behave similarly in F1 and S-D rats, in that the increase occurs late in life, and it is either repressed or delayed by DR. In contrast, the increase in T-KG mRNA levels in F344 rats occurs earlier in life, and is not significantly affected by DR. Young female F1 rats fed ad libitum (AL) show a statistically significant (P = 0.0009) 2.6-fold higher level of T-KG mRNA, as compared to their male counterparts. Thus, while we still observe an age-related increase in this parameter in both AL and DR female F1 rats, the difference is statistically significant (P = 0.0001) only in DR animals. We conclude that the increase in T-KG gene expression is a common feature of senescence and that, at least in males of these commonly used rat strains, T-KG can be used as a reliable biomarker of aging. Since the increase in T-KG gene expression does not appear to correlate with inflammatory processes, and since different strains of animals succumb to different pathologies, these results further suggest that the increase in T-KG expression might be related to the process of aging per se, rather than to any given age-related pathology.

T-kininogen present in the liver of old rats is biologically active and readily forms complexes with endogenous cysteine proteinases

We have previously reported an increase in T-kininogen mRNA levels in the liver of ageing Sprague-Dawley rats. T-Kininogen functions both as a precursor to the vasoactive peptide T-kinin, and as a potent and specific inhibitor of cysteine proteinases. Under normal physiological conditions, the majority of cysteine proteinases are found intracellularly and we have shown that a significant proportion of T-kininogen also accumulates intracellularly in the liver of old rats. Therefore, our aim was to determine whether or not this T-kininogen is biologically active as an inhibitor of cysteine proteases. Titration of whole liver extracts indicates that old rats do indeed contain a 4-fold higher level of cysteine proteinase inhibitory activity than younger counterparts. Using gel permeation chromatography in conjunction with an enzyme inhibitor assay, we show that this difference is mainly due to the presence of a low level of free biologically active T-kininogen. However, Western blot analysis of the gel permeation chromatography fractions demonstrate that most of the intrahepatic T-kininogen is found as enzyme-inhibitor complexes. Alkaline inactivation of the cysteine proteinase component of these complexes leads to the release of biologically competent free T-kininogen. These findings are discussed with regard to the possible mechanisms responsible for the accumulation of T-kininogen within the aged rat liver.

Zidovudine potentiates local and systemic inflammatory responses in the rat

The effect of chronic treatment with zidovudine (AZT) on the inflammatory response was examined in the rat. AZT was administered orally for 36 days. On day 35, inflammation was induced by hindpaw injection of 1% carrageenan lambda. Paw edema over a 24-hour period was used as a marker of the local inflammatory reaction. On day 36, quantification of immunoreactive T-kininogen and alpha 1-inhibitor-3 in liver and serum was used to assess the systemic inflammatory response. Albumin was selected as a protein whose concentration is modified only slightly or not at all during the acute-phase response. Animals treated with AZT transiently exhibited significantly greater (18%) paw edema 3 hours after carrageenan injection. AZT treatment alone induced a 1.8-fold increase in serum T-kininogen concentration, but it had no effect on albumin and alpha 1-inhibitor-3. In rats with inflamed paws, AZT administration led to a significant increase in liver (3.4-fold) and serum (1.8-fold) immunoreactive T-kininogen content. Dot blot analysis of total RNA isolated from liver correlated with the protein measurements. Our results indicate that chronic treatment with AZT potentiates the nonspecific local and the systemic inflammatory responses in the rat.