Introduction: An important explanation for the occurrence of Myelodysplastic syndrome (MDS) in the elderly is related to hematopoietic stem-cell (HSC) senescence. Recent studies have identified aging-related alterations in mesenchymal stromal cells in MDS. During the aging process, the different HSC subtypes lose the ability to differentiate into lymphoid and myeloid precursor cells, causing a breakdown in the immune system balance. This process exposes HSC to important genotoxic factors and may induce genetic or epigenetic alterations because exposure to these factors increases the risk of hematological malignancies. A new biomarker for cancer is Klotho (α and β subtypes), which has been identified as an anti-aging gene that extended the lifespan in murine models when it was overexpressed. Several studies have demonstrated that αKlotho (KL) deficiency causes development of aging features, including increased proliferation, reduction in tumor cell apoptosis, and disruption of HSC development. Some studies have established an association between low expression of KL and risks of cancer (i.e. lymphoma) by inducing cell apoptosis, inhibiting tumor growth, and causing a decrease in insulin-like growth factor 1 receptor (IGF-1R) activation. In parallel to these studies, a recent study reported that KL downregulation was associated with the occurrence of anemia, the main clinical feature of MDS, in cancer patients. However, the expression profile of KL and βKlotho (KLB) genes in the bone marrow (BM) of healthy patients with different ages and the way in which the genes modulate the pathogenesis of MDS in the elderly are unknown.
Methods: Total BM cell samples from 62 de novo MDS patients with a mean age of 66 ± 16 years old (10 MDS with single lineage dysplasia, 14 MDS with ring sideroblasts, 27 MDS with multilineage dysplasia, and 11 MDS with excess blasts based on World Health Organization's (WHO) 2016 classification) and from eleven healthy volunteer individuals were collected with informed consents. Healthy patients were stratified into young (n=6; mean 25 ± 6 years old) and elderly (n=5; mean 64 ± 9 years old) individuals. Pre-developed TaqMan gene expression assays for KL (Hs00934627_m1) and KLB (Hs00545621_m1) were used to quantify mRNA expression. Each sample was performed in duplicate, and the expression ratios were calculated using the 2−ΔCq method.
Results: Our results demonstrate that the KL gene was expressed in the BM samples from all experimental groups. High KL expression was identified in MDS patients when compared to young (p <0.001) and elderly (p <0.001) controls (Figure 1A). In MDS, KL was downregulated in male patients (p=0.042) (Figure 1B), neutropenic MDS cases (p=0.003) (Figure 1C), MDS patients with transfusion dependence (p=0.001) (Figure 1D), and MDS with an excess of blasts (p=0.038) (Figure 1D), representing more aggressive diseases. A multiple regression was performed in order to predict KL expression from gender, absolute neutrophil count (ANC), transfusion dependence, and WHO 2016 classification. These variables significantly predicted KL expression (F [4, 27] = 3.396; p=0.023; r2=0.335). Transfusion dependence (p=0.027) and WHO 2016 classification (p=0.049) variables significantly added to the prediction. The KLB gene was only expressed in a total of 8/62 MDS patients. The feature that stood out in these patients was the presence of dyserythropoiesis (62.5%). No control sample expressed the KLB gene.
Conclusions: Our results demonstrated an important expression profile of KL and KLB in BM of healthy young and old individuals and/or in MDS patients for the first time in contrast to a previous study in which it was demonstrated that human BM induces a negligible expression of these genes. Based on absence of differences between controls, our data showed that KL expression not was associated with the MDS pathogenesis-related senescence process, but its lower expression contributed to the poor prognostic MDS features, probably due to its high potential for affecting HSC number, function, and erythropoiesis. Additionally, low KLB expression in MDS patients with dyserythropoiesis suggests a compensatory response of the bone marrow environment to hematopoietic development block via clonal expansion, especially in the erythroid lineage. These approaches may define KL and KLB as new pathological markers of poor prognosis in MDS and improve future potential therapies.
No relevant conflicts of interest to declare.
This feature is available to Subscribers Only
Sign In or Create an Account Close Modal