Rewiring the niche: sympathetic neuropathy drives malignant niche transformation

Sympathetic activity is correlated with satellite cell aging and myogenesis via β2-adrenoceptor

Background and objective

Sympathetic activity plays an important role in the proliferation and differentiation of stem cells, and it changes over time, thereby exerting differential effects on various stem cell types. Aging causes sympathetic hyperactivity in aged tissues and blunts sympathetic nerves regulation, and sympathetic abnormalities play a role in aging-related diseases. Currently, the effect of sympathetic activity on skeletal muscle stem cells, namely satellite cells (SCs), is unclear. This study aimed to investigate the effects of skeletal muscle sympathetic activity on SC aging and skeletal muscle repair.

Materials and methods

To evaluate skeletal muscle and fibrotic areas, numbers of SCs and myonuclei per muscle fiber, β2-adrenoceptor (β2-ADR) expression, muscle repair, and sympathetic innervation in skeletal muscle, aged mice, young mice that underwent chemical sympathectomy (CS) were utilized. Mice with a tibialis anterior muscle injury were treated by barium chloride (BaCl₂) and clenbuterol (CLB) in vivo. SCs or C2C12 cells were differentiated into myotubes and treated with or without CLB. Immunofluorescence, western blot, sirius red, and hematoxylin–eosin were used to evaluate SCs, myogenic repair and differentiation.

Results

The number of SCs, sympathetic activity, and reparability of muscle injury in aged mice were significantly decreased, compared with those in young mice. The above characteristics of young mice that underwent CS were similar to those of aged mice. While CLB promoted the repair of muscle injury in aged and CS mice and ameliorated the reduction in the SC number and sympathetic activity, the effects of CLB on the SCs and sympathetic nerves in young mice were not significant. CLB inhibited the myogenic differentiation of C2C12 cells in vitro. We further found that NF-κB and ERK1/2 signaling pathways were activated during myogenic differentiation, and this process could be inhibited by CLB.

Conclusion

Normal sympathetic activity promoted the stemness of SCs to thereby maintain a steady state. It also could maintain total and self-renewing number of SCs and maintain a quiescent state, which was correlated with skeletal SCs via β2-ADR. Normal sympathetic activity was also beneficial for the myogenic repair of injured skeletal muscle.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02571-8.

High fat diet increases melanoma cell growth in the bone marrow by inducing osteopontin and interleukin 6

The impact of metabolic stress induced by obesity on the bone marrow melanoma niche is largely unknown. Here we employed diet induced obese mice model, where mice received high-fat (HFD) or normal diet (ND) for 6 weeks before challenge with B16F10 melanoma cells. Tumor size, bone loss and osteoclasts numbers were assessed histologically in the tibial bones. For defining the molecular pathway, osteopontin knock-out mice, interleukin 6 neutralizing antibody or Janus kinase 2 inhibition were carried out in the same model. Mechanistic studies such as adipocyte-melanoma co-cultures for defining adipocyte induced changes of tumor cell proliferation and expression profiles were also performed. As results, HFD enhanced melanoma burden in bone by increasing tumor area and osteoclast numbers. This process was associated with higher numbers of bone marrow adipocytes expressing IL-6 in direct vicinity to tumor cells. Inhibition of IL-6 or of downstream JAK2 blocked HFD-induced tumor progression. Furthermore, the phenotypic changes of melanoma cells triggered macrophage and osteoclast accumulation accompanied by increased osteopontin expression. Osteopontin triggered osteoclastogenesis and also exerted a positive feedback loop to tumor cells, which was abrogated in its absence. Metabolic stress by HFD promotes melanoma growth in the bone marrow by an increase in bone marrow adipocytes and IL-6-JAK2-osteopontin mediated activation of tumor cells and osteoclast differentiation.

Neuropathy correlated with imbalanced Foxp3/IL-17 in bone marrow microenvironment of patients with acute myeloid leukemia

Bone marrow (BM) neural tissues are important components of bone marrow microenvironment and play important roles in normal hematopoiesis. Neuropathy of BM can cause immunological alteration in hematopoietic microenvironment. It also can induce the impairment of normal hematopoiesis and promote the development of hematologic diseases. In the present study, we determined the expression levels and clinical significances of nerve-related molecules [nestin, tyrosine hydroxylase (TH), Glial Fibrillary Acidic protein (GFAP) and S100B] and T helper-related molecules (IL-17, Foxp3) in BM of AML patients and controls by immunohistochemical analysis and RT-PCR. Our results showed that the positive rates and expression levels of nestin, TH, GFAP and IL-17 were significantly decreased while Foxp3 and the ratio of Foxp3/IL-17 were statistically elevated in BM of AML patients. We found that there were significantly positive correlations between nestin with TH and IL-17 in BM of AML patients. We also observed significantly negative correlations between nestin with TH and Foxp3/IL-17 ratio. Moreover, the expression of nestin was positively correlated with the overall survival of AML patients. Our study suggests that neuropathy together with imbalanced T helper immunology in bone marrow might play important roles in AML.

Leukemia Stem Cells Microenvironment

The dynamic interactions between leukemic cells and bone marrow (BM) cells in the leukemia BM microenvironment regulate leukemia stem cell (LSC) properties including localization, self-renewal, differentiation, and proliferation. Recent research of normal and leukemia BM microenvironments has revealed several key components of specific niches that provide a sanctuary where subpopulations of leukemia cells evade chemotherapy-induced death and acquire a drug-resistant phenotype, as well as the molecular pathways critical for microenvironment/leukemia interactions. Although the biology of LSCs shares many similarities with that of normal hematopoietic stem cells (HSCs), LSCs are able to outcompete HSCs and hijack BM niches. Increasing evidence indicates that these niches fuel the growth of leukemia cells and contribute to therapeutic resistance and the metastatic potential of leukemia cells by shielding LSCs. Not only "microenvironment-induced oncogenesis," but also a "malignancy-induced microenvironment" have been proposed. In this chapter, the key components and regulation of BM niches in leukemic BM is described. In addition, metabolic changes in LSCs, which are currently a subject of intense investigation, will also be discussed to understand LSC survival.

Role of Microenvironment in Resistance to Therapy in AML

As part of the dynamic interactions between leukemic cells and cells of the bone marrow microenvironment, specific niches provide a sanctuary where subpopulations of leukemic cells evade chemotherapy-induced death and acquire a drug-resistant phenotype. This review focuses on the cellular and molecular biology of the leukemia stem cell (LSC) niche and of microenvironment/leukemia interactions. Key emerging therapeutic targets include chemokine receptors, adhesion molecules, the sympathetic nervous system, and hypoxia-related proteins, as well as the genetic and epigenetic abnormalities of the leukemia-associated stroma. The complex interplay between LSCs and microenvironment components provides a rationale for appropriately tailored molecular therapies designed to improve outcomes in leukemia. Further understanding of the contribution of the bone marrow niche to the process of leukemogenesis may provide new targets that allow destruction of LSCs without adversely affecting normal stem cell self-renewal.