Journal Club: Identification of CD74+CD14+ macrophage subpopulation that increase in both noise-induced and age-related sensorineural hearing loss model.

on

Today's journal article

Wu MY, Chen AH, Li LQ, Yi Y, Xiong Q, Chen KT, Cai ZM, Lei WB, Xiong GX, Fang SB. Single-cell RNA sequencing analysis of mouse cochlea identifies a novel proinflammatory CD74+CD14+ macrophage subset in mice with age-related and noise-induced hearing loss. 

Why I picked this article

Immune activity in the cochlea is increasingly linked to both age‑related hearing loss (ARHL) and noise‑induced hearing loss (NIHL). Macrophages are resident immune cells that patrol tissues, clear debris, and signal to nearby cells; in the cochlea, they are found around the spiral ganglion, stria vascularis, and sensory epithelium. When they shift into a proinflammatory state, they can help respond to injury but may also harm nearby neurons if the response persists. 

This research uses single‑cell RNA sequencing (scRNA‑seq) to map the immune landscape and identifies a subset of unique macrophage populations that look primed for inflammation.

Some of the research findings

Animal model:
  • Male C57BL/6 mice
  • Noise exposure: broadband noise exposure (2 to 20 kHz) at a sound pressure level (SPL) of 120 dB for 2 h.
  • Experimental groups: 
    • Control
    • 3-days post-exposure
    • 7-days post-exposure 
    • Ageing model: 10-months old 
Data analysis: 
  • Data was downloaded GSA: CRA004814 (National Genomics Data Center, China National Center for Bioinformation/Beijing Institute of Genomics, Chinese Academy of Sciences)
  • Clustering analyses showed a different mix of immune cells between the age-related sensorineural hearing loss model and the noise-induced hearing loss model. 
  • Within the noise-induced hearing loss model, the immune cell makeup was very different between the spiral ganglion neuron area and the lateral wall. 
  • Researchers have identified that the CD74+/CD14+ population of macrophages were increased in both the ageing sensorineural hearing loss model and the noise-induced sensorineural hearing loss model consistently. 
Flow cytometry analysis: 
  • Control, ageing mice and noise-exposed animal cochleae were extracted and analysed by flow cytometry for CD74+/CD14+ population. 
  • In brief, the dissected cochlear tissues were placed in a digestion solution (Stemcell, USA), at 37 ◦C for 30 min, filtered through a 70-μm cell strainer (BD Falcon, USA), centrifuged at 500 g at 4 ◦C for 10 min and stained with: F4/80-FITC, CD74-AF647, and CD14-PE (BioLegend, USA).
  • The percentage of CD74+/CD14+ population was increased with ageing (10-month-old) compared to 1-month-old mice cochlea. 
  • The percentage of CD74+/CD14+ population was increased 3 day after noise exposure.
Other findings: 
  • With immunohistochemistry, they showed that CD74+ labelling and CD14 labelling were increased in the basilar membrane. They overlapped/were closely associated with Iba1 labelling, the marker for macrophages. 
  • Transcriptome signatures point to proinflammatory pathways and chemotaxis programs in this subset.
  • Bioinformatic analysis suggests cross-talk between these macrophages and spiral ganglion neurons. 

Haruna's takeaway

Macrophages are a very exciting population of cells.... even for non-scientists, the name "macrophage", the large size and alien-like shape, make them feel like a very special creature of their own right. 

Takeaway from this research for me, I guess, was the heterogeneity of immune cells, including macrophages and how dynamic that heterogeneity may be under insult. I have to say I found some of the graphical representations this research publication a little hard to understand, or perhaps there is too much indirect evidence that suggests certain pathways, but hard to appreciate what those really mean. The initial single-cell RNAseq data and following that by flow cytometry to confirm the RNAseq data is a very nice complementary approach that I will rember. 

 ------- 

This is Haruna's 72/100 of the 100-day challenge to post a science blog article every day! I love inner ear biology & cochlear physiology.