Minocycline protects against microgliopathy in a Csf1r haplo-insufficient mouse model of adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP)
Authors: Li Xin , Hu Banglian , Guan Xiaoyan , Wang Ziwei , Zhou Yuhang , Sun Hao , Zhang Xian , Li Yanfang , Huang Xiaohua , Zhao Yingjun , Wang Xin , Xu Huaxi , Zhang Yun-Wu , Wang Zhanxiang , Zheng Honghua 
Published: May 2023

Abstract
Background
Mutations in colony-stimulating factor 1 receptor (CSF1R) are known to cause adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP), which has been recently demonstrated as a primary microgliopathy characterized by cognitive impairment. Although the molecular mechanism underlying CSF1R-mediated microgliopathy remains unclear, therapeutic strategies have generally targeted modulation of microglial function. In particular, the microglial inhibitor, minocycline, has been shown to attenuate learning and memory deficits in several neurodegenerative diseases. The objectives of this study were to investigate the pathogenic mechanisms underlying ALSP and to explore the therapeutic effects of minocycline in an in vivo model of ALSP. We hypothesized that inhibiting microglial activation via minocycline could reverse the behavior and pathological defects in ALSP model mice.

Methods
We generated a Csf1r haploinsufficiency mouse model of ALSP using CRISPR/Cas9 genome editing and conducted electrophysiological recordings of long-term potentiation (LTP) and behavioral tests to validate the recapitulation of clinical ALSP characteristics in 8- to 11-month-old mice. RNA-sequencing was used to explore enriched gene expression in the molecular pathogenesis of ALSP. Microglial activation was assessed by immunofluorescent detection of Iba1 and CD68 in brain sections of male ALSP mice and pro-inflammatory activation and phagocytosis were assessed in Csf1r+/− microglia. Therapeutic effects were assessed by behavioral tests, histological analysis, and morphological examination after four weeks of intraperitoneal injection with minocycline or vehicle control in Csf1r+/− mice and wild-type control littermates.

Results
We found that synaptic function was reduced in LTP recordings of neurons in the hippocampal CA1 region, while behavioral tests showed impaired spatial and cognitive memory specifically in male Csf1r+/− mice. Increased activation, pro-inflammatory cytokine production, and enhanced phagocytic capacity were also observed in Csf1r+/− microglia. Treatment with minocycline could suppress the activation of Csf1r+/− microglia both in vitro and in vivo. Notably, the behavioral and pathological deficits in Csf1r+/− mice were partially rescued by minocycline administration, potentially due to inhibition of microglial inflammation and phagocytosis in Csf1r+/− mice.

Conclusions
Our study shows that CSF1R deficiency results in aberrant microglial activation, characterized by a pro-inflammatory phenotype and enhanced phagocytosis of myelin. Our results also indicate that microglial inhibition by minocycline can ameliorate behavioral impairment and ALSP pathogenesis in CSF1R-deficient male mice, suggesting a potential therapeutic target for CSF1R-related leukoencephalopathy. Collectively, these data support that minocycline confers protective effects against CSF1R-related microgliopathy in male ALSP model mice.