Association Of Relative Telomere Length With Mortality in Patients With Chronic Kidney Disease

Contact: Audrey Hu Whatsapp/hp: 0086 13880143964 Email: audrey.hu@wecistanche.com

Results From The German Chronic Kidney Disease Study Support Association Of Relative Telomere Length With Mortality in A Large Cohort Of Patients With Moderate Chronic Kidney Disease

Keywords: chronic kidney disease, mortality, telomere length, kidney.

Introduction

Telomere length is known to be inversely associated with aging and has been proposed as a marker for aging-related diseases. Telomere attrition can be accelerated by oxidative stress and inflammation, both commonly present in patients with chronic kidney disease. Here, we investigated whether relative telomere length is associated with mortality in a large cohort of patients with chronic kidney disease stage G3 and A1-3 or G1-2 with overt proteinuria (A3) at enrollment. Relative telomere length was quantified in peripheral blood by a quantitative PCR method in 4,955 patients from the chronic kidney disease study, an ongoing prospective observational cohort. Complete four-year follow-up was available from 4,926 patients in whom we recorded 354 deaths. Relative telomere length was a strong and independent predictor of all-cause mortality. Each decrease of 0.1 relative telomere length unit was highly associated with a 14% increased risk of death (hazard ratio1.14 [95% confidence interval 1.06-1.22]) in a model adjusted for age, sex, baseline eGFR, urine albumin/creatinine ratio, diabetes mellitus, prevalent cardiovascular disease, LDL-cholesterol, HDL-cholesterol, smoking, body mass index, systolic and diastolic blood pressure, C-reactive protein and serum albumin. This translated to a 75% higher risk for those in the lowest compared to the highest quartile of relative telomere length. The association was mainly driven by 117 cardiovascular deaths (1.20 [1.05-1.35]) as well as 67 deaths due to infections (1.27 [1.07-1.50]). Thus, our findings support an association of shorter telomere length with all-cause mortality, cardiovascular mortality, and death due to infections in patients with moderate chronic kidney disease.

Telomeres are non-coding, repetitive nucleotide sequences (TTAGGG) ranging from 5 to 15 kilobase pairs in length that are located at the end of eukaryotic chromosomes¹. Their functions include protection of the DNA and maintenance of chromosomal integrity. Telomeres shorten at each cycle of cell division due to the incapacity of DNA polymerase to replicate the very ends of linear chromosomes.² Approximately 50–200 base pairs are lost during each cell division, and when a critical telomere length is reached, cells undergo replicative senescence or apoptosis. Consequently, telomere length has been proposed as a marker of biological age,³ and its predictive role in aging-related disease has been investigated in many epidemiologic studies.^4–6

Telomere attrition, accelerated by oxidative stress and inflammation, leads to cell senescence, which compromises the regeneration and functionality of vital organs, including the kidneys.⁷ In particular, it has been shown that chronic inflammation leads to lymphocyte telomere attrition, cell senescence, and finally impairment of the immune response.⁸ This T-cell dysfunction can contribute to increased susceptibility to kidney infections and injury.⁷

Chronic kidney disease is a complex disease, and its heritability has been estimated to be 30%–70%.^9–12 In past years, genome-wide association studies have identified many genetic loci associated with kidney function and chronic kidney disease.^13–17

However, index single nucleotide polymorphisms at the identified loci explain only a minor part of the heritability, and additional genetic contributors might be missing. To date, only a few small studies have investigated the association between telomere length and kidney disease. Some studies found that short telomere length correlates with impaired kidney function in the general population,^18,19 as well as in heart failure patients.²⁰ We recently described significantly shorter relative telomere length in patients with moderately severe chronic kidney disease who have prevalent cardiovascular disease (CVD),²¹ as well as an association with duration²² and progression of chronic kidney disease.²³ Patients who have reached kidney failure treated by hemodialysis are described as having reduced telomere length in comparison with healthy controls,^24–27 and reduced telomere length is inversely associated with mortality.²⁸ Only a few investigations have been conducted in non-dialysis-dependent kidney patients.^{21–23,29,30} To our knowledge, the current study is the first prospective study that investigates the association between leukocyte telomere length and causes of mortality in a large non-dialysis-dependent chronic kidney disease cohort.

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RESULTS

Baseline characteristics of the study population

telomere length was quantified in peripheral blood by a quantitative polymerase chain reaction method in 4955 patients from the German Chronic Kidney Disease study. A complete 4-year follow-up was available from 4926 patients. Baseline characteristics of these 4926 patients according to quartiles of the telomere length are provided in Table 1. Related telomere length ranged from a minimum of 0.40 to a maximum of 2.31 (Supplementary Figure S1), with a mean ± SD of 0.95 ±0.19 and a median of 0.92 (1st quartile ¼ 0.82; 3rd quartile ¼ 1.05). telomere length was negatively correlated with age (r ¼ –0.36, P < 0.001) and positively correlated with estimated glomerular filtration rate (eGFR; r ¼ 0.17, P < 0.001) and urine albumin–creatinine ratio (r ¼ 0.05, P < 0.001). When we adjusted telomere length for age and sex, we no longer observed a significant correlation with eGFR and urine albumin–creatinine ratio.

Prospective follow-up and mortality

A total of 354 deaths occurred during a median follow-up period of 4 years (1483 days). The causes of death were CVD including myocardial infarction, coronary heart disease, sudden cardiac death, congestive heart failure, pulmonary embolism, cardiac valve disease and ischemic stroke (117 patients, 33.1%), infections (67 patients, 18.9%), nonischemic cerebrovascular causes (9 patients, 2.5%), peripheral vascular disease (7 patients, 2.0%), kidney failure (8 patients, 2.3%), various other causes (103 patients, 29.1%) and unknown causes (43 patients, 12.1%). Cumulative incidence plots show that incidence of all-cause mortality (Figure 1a) increases with shorter Related telomere length, with the highest incidence with the lowest Related telomere length quartile. In the cumulative incidence function curves of cardiovascular (Figure 1b) and infection mortality (Figure 1c), the difference between quartiles was less pronounced, but the order of the quartiles was the same.

Results of Cox regression models applying different adjustments are provided in Table 2 and showed a significant association between shorter Related telomere length and the risk of all-cause mortality. Evaluated continuously, each decrease of 0.1 Related telomere length units was associated with a 16% increased risk of death in a model adjusted for age and sex (hazard ratio [HR], 1.16; 95% confidence interval [CI], 1.08–1.24; P ¼ 1.7e-05). The association remained significant after an extended adjustment for eGFR, urine albumin–creatinine ratio, diabetes mellitus, and prevalent cardiovascular disease (model 2: HR, 1.16; 95% CI, 1.08–1.24) as well the additional CVD risk factors low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, smoking, body mass index, systolic blood pressure, diastolic blood pressure, C-reactive protein, and serum albumin at baseline (model 3: HR, 1.14; 95% CI, 1.06–1.22; P ¼ 3.5e-04). Nonlinear P spline analyses are given in Figure 2 and revealed an almost linear association of Related telomere length with all-cause mortality. Patients with the shortest Related telomere length (1st quartile) had a 75% higher risk for all-cause mortality compared to those in the quartile with the longest Related telomere length (Supplementary Table S1, fully adjusted model: HR, 1.75; 95% CI, 1.22–2.50; P ¼ 0.0024).

Next, we analyzed what is driving the association of Related telomere length with all-cause mortality (Table 2). We evaluated the 2 most frequent specific causes of death and observed that each decrease of 0.1 Related telomere length units was associated with a 20% increased risk of CVD death in the fully adjusted model (HR, 1.20; 95% CI, 1.05–1.35; P ¼ 0.0052). Reduced Related telomere length was also significantly inversely associated with death due to infections. Each 0.1 unit decrease of Related telomere length was associated with a 1.27-fold higher risk for death due to infections (HR, 1.27; 95% CI, 1.07–1.50; P ¼ 0.0051). Looking at the estimates for the various quartiles in Supplementary Table S1 revealed for death due to infections that the estimates for each of the quartiles 1, 2, and 3 were similarly elevated compared to that for quartile 4. The analysis with other causes of death as well as unknown causes of death was obviously too heterogeneous and did not reveal any association with Related telomere length (data not shown).

The graph of the scaled Schoenfeld residuals and test on proportional hazard assumptions did not suggest any time-varying effects for Related telomere length on any of the investigated outcomes. The subdistribution HRs for both cardiovascular and infection death, reported in Supplementary Table S2, are only slightly attenuated compared to the cause-specific HRs.

We also evaluated whether the effect of Related telomere length on the 3 different outcomes differed between men and women and for patients with and without diabetes mellitus, but we did not detect a significant interaction for these variables, or forage (all P values of interaction >0.1 in the fully adjusted models).

Given that we recently observed a U-shaped association between the duration of chronic kidney disease and Related telomere length,²² we performed a sensitivity analysis additionally adjusting for the duration of chronic kidney disease at baseline is defined as less than 6 months, between 6 months and 5 years, and more than 5 years. This additional adjustment resulted in only marginal changes of the HRs obtained for all 3 endpoints (Supplementary Table S3).

DISCUSSION

The results of this study showed a significant association of Related telomere length with all-cause mortality in a non-dialysis-dependent chronic kidney disease cohort. Shorter Related telomere length was associated with a higher risk of mortality independently from kidney function and traditional CVD risk factors. This association was driven by death due to CVD as well as death due to infections.

Association with all-cause mortality

Prior studies,^5,6,31–35 with few exceptions,^36,37 have demonstrated a negative association between Related telomere length and all-cause mortality in the general population. The largest study so far (n ¼ 64,637) was performed by Rode et al., with an adjusted HR for mortality of 1.40 for the decile with the shortest versus the decile with the longest Related telomere length.³⁵ In accordance with these results, our study showed with each decrease of 0.1 Related telomere length units a 14% higher risk for all-cause mortality, which translates to a 75% higher risk for those in the lowest compared to the highest quartile of Related telomere length. To our knowledge, only Carrero et al.²⁸ have investigated the relationship between Related telomere length and mortality risk in chronic kidney disease patients. They studied 175 patients with end-stage kidney disease treated by hemodialysis, of whom 70 died during a median of 31 months of observation. The authors observed that telomere length independently predicted patient survival after additional adjustment for age, sex, and inflammation. The current study extends these observations to the much larger group of individuals with chronic kidney disease who do not require dialysis.

Association with CVD mortality

No studies have investigated the association of Related telomere length with CVD mortality in chronic kidney disease patients so far, although this is the major cause of death in these patients. Depending on the investigated ethnicity and on the data adjustment models, some, but not all, studies in the general population reported an association between low Related telomere length and CVD outcomes.^33,38–41 Strong support for a causal association came from a Mendelian randomization study in which genetic variants associated with shorter Related telomere length were found to be associated with ischemic heart disease.⁴⁰ In the present study, we identified a significant association of Related telomere length with cardiovascular deaths, with a 20% higher risk with each decrease of Related telomere length by 0.1 units, or a 75% higher risk for those patients in the quartile with the shortest telomere length compared to the quartile with the longest telomere lengths. This finding is in line with our earlier report of an association with prevalent cardiovascular events in this patient population: each decrease of Related telomere length by 0.1 units was significantly associated with a 6% higher odds for prevalent CVD in a model adjusting for age, sex, current smoking, hypertension, diabetes status, low-density lipoprotein cholesterol, high-density

lipoprotein cholesterol, C-reactive protein, eGFR, and body mass index.21 The prospective follow-up in these patients in the present investigation revealed that especially the lowest quartile of telomere length was associated with a markedly increased risk, whereas the other 3 quartiles showed very similar estimates (Figure 1b).

Association with death due to infections

Although experimental evidence supports the role of cell senescence and short telomere length in impaired immune response, epidemiologic studies are sparse, especially in chronic kidney disease patients. Helby et al. conducted the largest (n ¼ 75,309) prospective population-based study investigating Related telomere length and the risk of hospitalization for infectious disease and the risk of infection-related death. During 7 years of follow-up, they observed a higher risk of any infections in the quartile with the shortest compared with the quartile with the longest Related telomere length.⁴² Previous studies with smaller sample sizes reported conflicting results.^32,43,44 Our findings in chronic kidney disease patients describe for the first time the association between short Related telomere length and a higher risk for death due to infections in this high-risk population.

Potential mechanism

The biological mechanism underlying the relationship between Related telomere length and mortality is still unclear. The association identified by our study does not elucidate whether Related telomere length shortening is causally related to cardiovascular disease and infections. However, a genome-wide association study followed by a genetic risk score analysis combining lead variants at 7 genetic loci showed an association of the alleles associated with shorter Related telomere length with increased risk of coronary artery disease. This finding provides possible support for a potential causal role of Related telomere length in CVD.^45,46 Furthermore, cellular senescence induced by telomere attrition could be a trigger of atherosclerosis as well arteriosclerosis. The accumulation of senescent cells in the vessel contributes to atherosclerotic plaque formation and media calcifications resulting in increased arterial stiffness as a dominant feature of uremic arterial disease.⁴⁷ Most of the studies have measured Related telomere length in the DNA from peripheral leukocytes. However, a close correlation has been shown between leukocyte and aortic wall tissue telomere length.⁴⁸ Therefore, cellular senescence could affect endothelial cells leading to dysfunction in the vascular wall and promoting the adhesion of immune cells, a primary event in atherosclerosis. Furthermore, short telomeres activate p⁵³ and autophagy in cardiac progenitor cells, destabilizing the balance of quiescence and proliferation toward differentiation and senescence, leading to an exhaustion of cardiac progenitor cells.⁴⁹ Telomere dysfunction has been shown to induce profound p⁵³-dependent repression of the master regulators of mitochondrial biogenesis and function, which leads to bioenergetic compromise due to impaired oxidative phosphorylation and adenosine triphosphate generation.^50,51

There are also several links between Related telomere length and infections. The loss of telomeres has been observed during T cell differentiation, ⁵² in chronic viral infections,⁵³ and with age.⁵⁴ Furthermore, short leukocyte telomere length has been reported as a risk factor in various immune-related diseases⁵⁵ and diabetes.⁵⁶ Leukocyte shorter telomere length causes cell senescence that is followed by a reduction of immune cell proliferative capacity. telomere length may also be involved in age-related declines in immune function related to insufficient response to vaccines and acute infections. ^57–59 A potential role of telomere length in infections is also supported by a recent genome-wide association study in a Chinese population. Dorjee and colleagues observed an association between a telomere length-reducing allele and death due to respiratory infection.60 Related telomere length attrition might be strongly triggered by the presence of elevated oxidative stress, a common condition in chronic kidney disease.⁶¹ Several in vitro and in vivo studies showed that oxidative stress accelerates telomere attrition.^62,63 Indeed, telomeres, with their high guanine content, are highly susceptible to oxidative damage,⁶⁴ and single-strand DNA breaks induced by oxidative stress could be an important factor for telomere shortening during DNA replication.⁶⁵

Strengths and limitations

Strengths of this investigation include the large sample size of a well-defined population with a median follow-up of 4 years with almost no loss to follow-up, homogeneity of the study population, and a centralized assessment of telomere length and outcome measures. The measurement of Related telomere length especially is of utmost importance because standardization between laboratories is not easy to accomplish and therefore the process should be performed in the same laboratory under exactly the same conditions in terms of protocol, reference gene, instrument, personnel,66, and DNA extraction procedure.⁶⁷

There are some limitations to this study. First, Related telomere length was measured in peripheral leukocytes. It is known that the rate of progression to senescence differs among lymphocyte subsets. ⁵⁹ Unfortunately, no data were available about blood cell type composition in the German Chronic Kidney Disease study and it was therefore not possible to investigate this aspect. Knowing Related telomere length from various kidney cell types would be of interest, but it is not possible to obtain in a large epidemiologic study as this would require tissue material from biopsies. The second limitation includes the observational design of the study, which does not allow for clarification of causality or biological mechanism. Third, the study recruited mainly chronic kidney disease patients in stage G3 or A3, and the findings might not be generalizable to other stages of chronic kidney disease. Fourth, the association with specific causes of death might have been limited by statistical power but was still present for the 2 specific main causes of death. Finally, although our analyses were adjusted for traditional cardiovascular risk factors as well as kidney function parameters, we cannot exclude the possibility of residual confounding by unknown or unmeasured

variables. However, it was very interesting to see that the age and sex-adjusted estimates of Related telomere length for various outcomes were very stable with further adjustment for the other variables, indicating that Related telomere length is relatively independent of other variables when data are adjusted for age and sex.

Conclusions

Short relative telomere length quantified from peripheral blood leukocytes was independently associated with all-cause mortality during 4 years of follow-up in patients with moderately severe chronic kidney disease. This association was driven by death due to CVD as well as death due to infections.

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The source is by Federica Fazzini, Claudia Lamina and etc.