# Selective disruption of microtubule formation at the nuclear envelope impairs the bone resorption capacity of osteoclasts

## TL;DR

This study shows that microtubules forming at the nuclear envelope are crucial for osteoclasts to resorb bone, and disrupting them reduces this activity.

## Contribution

The study reveals a conserved role of AKAP6 and nesprin-1 in NE-MTOC formation during osteoclast differentiation.

## Key findings

- AKAP6 and nesprin-1 are upregulated during osteoclast differentiation, indicating a role in NE-MTOC assembly.
- Depletion of AKAP6 impairs NE-derived microtubules without affecting centrosomal ones, reducing podosome formation and bone resorption.
- NE-MTOC activity is essential for osteoclast function, highlighting its distinct role from centrosomal MTOCs.

## Abstract

Microtubule organization plays a central role in cell differentiation, orchestrating essential processes such as cell polarization, mechanotransduction, organelle positioning and intracellular transport. A hallmark of many differentiated cells is the transition from a centrosomal to a non-centrosomal microtubule-organizing center (MTOC). Here, we demonstrate that both centrosomal and nuclear envelope (NE)-associated MTOCs coexist in osteoclasts. We show that the key players for NE-MTOC formation, the AKAP6 and nesprin-1 (SYNE1) isoforms AKAP6β and nesprin-1α, previously considered muscle specific, are upregulated during osteoclast differentiation, suggesting a conserved role in NE-MTOC assembly across cell types. Targeted depletion of AKAP6 in RAW264.7-derived osteoclasts led to the displacement of the Golgi and MTOC-associated proteins PCM1, pericentrin and CDK5RAP2 from the NE, while their centrosomal localization remained intact. This selectively impaired microtubule nucleation from the NE without disrupting centrosomal microtubule activity, enabling a functional dissection of the two MTOCs. Loss of NE-MTOC activity, through AKAP6 depletion, impaired podosome formation and significantly reduced bone resorption capacity, highlighting the distinct and essential role of NE-derived microtubules in osteoclast function.

Summary: AKAP6-anchored microtubules emanating from the nuclear envelope play an important role in podosome formation. Interfering with AKAP6 function allows modulation of bone resorption activity.