Contractile apparatus in CNS capillary pericytes

SIGNIFICANCE: Whether or not capillary pericytes contribute to blood flow regulation in the brain and retina has long been debated. This was partly caused by failure of detecting the contractile protein [Formula: see text]-smooth muscle actin ([Formula: see text]-SMA) in capillary pericytes. AIM: The aim of this review is to summarize recent developments in detecting [Formula: see text]-SMA and contractility in capillary pericytes and the relevant literature on the biology of actin filaments. RESULTS: Evidence suggests that for visualization of the small amounts of [Formula: see text]-SMA in downstream mid-capillary pericytes, actin depolymerization must be prevented during tissue processing. Actin filaments turnover is mainly based on de/re-polymerization rather than transcription of the monomeric form, hence, small amounts of [Formula: see text]-SMA mRNA may evade detection by transcriptomic studies. Similarly, transgenic mice expressing fluorescent reporters under the [Formula: see text]-SMA promoter may yield low fluorescence due to limited transcriptional activity in mid-capillary pericytes. Recent studies show that pericytes including mid-capillary ones express several actin isoforms and myosin heavy chain type 11, the partner of [Formula: see text]-SMA in mediating contraction. Emerging evidence also suggests that actin polymerization in pericytes may have a role in regulating the tone of downstream capillaries. CONCLUSIONS: With guidance of actin biology, innovative labeling and imaging techniques can reveal the molecular machinery of contraction in pericytes.