Key Points

I-mfa is a multifunctional cytosolic protein and its function in kidney is unknown.The major finding in the present study was that I-mfa promoted glomerular filtration rate in both male and female mice.I-mfa suppressed contractile function of both human and mouse glomerular mesangial cells by decreasing TRPC1 channel protein abundance.

Background

Inhibitor of MyoD family A (I-mfa) is a cytosolic protein. Its function in the kidney is unknown. The aim of this study was to examine the regulatory role of I-mfa on GFR.

Methods

GFR was measured by transdermal measurement of fluorescein isothiocyanate–sinitrin clearance in conscious wild-type (WT) and I-mfa knockout (KO) mice. Cell contractility was assessed in a single human or mouse mesangial cell. Single-cell RNA sequence, Western blot, and Ca2+ imaging were used to evaluate the effects of I-mfa on transient receptor potential canonical (TRPCs) at messenger, protein, and functional levels in mesangial cells.

Results

In KO mice, GFR was significantly lower than that in WT mice. In WT mice, knocking down I-mfa selectively in mesangial cells using targeted nanoparticle/small interfering RNA delivery system significantly decreased GFR. In human mesangial cells, overexpression of I-mfa significantly blunted the angiotensin II (Ang II)-stimulated contraction, and knockdown of I-mfa significantly enhanced the contractile response. Consistently, the Ang II–induced contraction was significantly augmented in primary mesangial cells isolated from KO mice. The exaggerated response was restored by reintroducing I-mfa. Furthermore, single-cell RNA sequence showed an increase in trpc1 messenger, and Western blot showed an increase in TRPC1 protein abundance in I-mfa KO mouse mesangial cells. TRPC1 protein abundance was decreased in human embryonic kidney cells overexpressing I-mfa. Ca2+ imaging experiments showed that downregulation of I-mfa significantly enhanced Ang II–stimulated Ca2+ entry in human mesangial cells. Finally, TRPC1 inhibitor Pico145 significantly blunted Ang II–induced mesangial cell contraction.

Conclusions

I-mfa positively regulated GFR by decreasing mesangial cell contractile function through inhibition of TRPC1-mediated Ca2+ signaling.