Transgenic inhibition of interleukin-6 trans-signaling does not prevent skeletal pathologies in mucolipidosis type II mice

Lena Marie Westermann,Michael Amling,Christoph Garbers,Giorgia Di Lorenzo,Stefan Rose-John,Thorsten Schinke,Tatyana Danyukova,Gretl Hendrickx,Anke Baranowsky,Jamie Soul,Sandra Pohl,Jean-Marc Schwartz

doi:10.1038/s41598-021-82802-3

Abstract

Severe skeletal alterations are common symptoms in patients with mucolipidosis type II (MLII), a rare lysosomal storage disorder of childhood. We have previously reported that progressive bone loss in a mouse model for MLII is caused by an increased number of bone-resorbing osteoclasts, which is accompanied by elevated expression of the cytokine interleukin-6 (IL-6) in the bone microenvironment. In the present study we addressed the question, if pharmacological blockade of IL-6 can prevent the low bone mass phenotype of MLII mice. Since the cellular IL-6 response can be mediated by either the membrane-bound (classic signaling) or the soluble IL-6 receptor (trans-signaling), we first performed cell culture assays and found that both pathways can increase osteoclastogenesis. We then crossed MLII mice with transgenic mice expressing the recombinant soluble fusion protein sgp130Fc, which represents a natural inhibitor of IL-6 trans-signaling. By undecalcified histology and bone-specific histomorphometry we found that high circulating sgp130Fc levels do not affect skeletal growth or remodeling in wild-type mice. Most importantly, blockade of IL-6 trans-signaling did neither reduce osteoclastogenesis, nor increase bone mass in MLII mice. Therefore, our data clearly demonstrate that the bone phenotype of MLII mice cannot be corrected by blocking the IL-6 trans-signaling.

Highlights

The maintenance of healthy skeletal structure and function during development, growth and adulthood is achieved by resorption of aged bone by osteoclasts and formation of new bone by osteoblasts
Since the expression of IL-6 was strongly increased in primary cultured mucolipidosis type II (MLII) o steoblasts[29], we hypothesized that the osteoporotic phenotype in MLII is mainly caused by excessive osteoclastogenesis, which is potentially induced by osteoblast-derived IL-6
Since lysosomal storage accumulation was more pronounced in mature MLII o steoblasts[30], we aimed to assess genome-wide transcriptional differences between wild-type and MLII osteoblasts, which were cultured for 25 days to reach an osteocyte-like state of terminal differentiation[31]

Summary

Introduction

The maintenance of healthy skeletal structure and function during development, growth and adulthood is achieved by resorption of aged bone by osteoclasts and formation of new bone by osteoblasts. RANKL binds to its receptor RANK, which is expressed on the surface of osteoclast precursors, and subsequently activates a variety of downstream signaling pathways required for the formation and maturation of o steoclasts[6]. Based on the finding that IL-6 promotes osteoclast formation only in the presence of sIL-6R10,16, IL-6 seems to stimulate osteoclastogenesis via the trans-signaling pathway. It has been proposed that IL-6 modulates osteoclastogenesis induced by RANKL-producing osteoblasts[16,22,23] It remains controversial which target cells are stimulated by IL-6 and which role IL-6 plays in basal and pathological bone resorption. Since the expression of IL-6 was strongly increased in primary cultured MLII o steoblasts[29], we hypothesized that the osteoporotic phenotype in MLII is mainly caused by excessive osteoclastogenesis, which is potentially induced by osteoblast-derived IL-6

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Conclusion