Absence Of Histidine Dipeptides Does Not Affect Muscle Contractile Proprieties: Study With Carns1 Knockout Rats

Abstract

Carnosine and anserine are a histidine-containing dipeptides (HCDs) abundantly expressed in the skeletal muscle. Although several properties have been ascribed to HCDs (e.g., H+ buffering and Ca2+ handling), it remains unknown whether it is relevant for muscle contractility in vivo. PURPOSE: To investigate the impact of the absence of HCDs on muscle contractile properties assessed in vivo. METHODS: We developed a novel CARNS1 knockout (KO) rat strain using the CRISPR/Cas9 technology to generate rats that are fully devoid of HCDs, and thus examine its role on muscle function. Male wild-type (WT) and KO rats (4 months-old) were used. We examined whether CARNS1 KO impacted: i) exercise tolerance in a progressive maximal treadmill exercise test; ii) the in vitro muscle buffering capacity using the titration method; iii) force generation, contractile properties and tolerance to fatigue using the in situ assessment of the tibialis anterioris function evoked by electrical stimulation of the sciatic nerve. Data are presented as mean ± SD. Fatigue test were analysed with mixed models. For all other variables, Welch’s two-sample t-tests for unequal sample sizes were used to compare the groups (RStudio v.4.0.0). RESULTS: Exercise tolerance was similar between KO and WT (KO: n = 6, WT: n = 4; p = 0.34). We next determined the in vitro buffering capacity of skeletal muscle extracts, which confirmed no effect of the absence of HCDs on muscle buffering capacity (n = 15 per group; p = 0.85). The absence of HCDs did not impact muscle resistance to fatigue (KO: n = 10, WT: n = 7; p = 0.37), peak force attained in single twitch and in maximal tetanic contractions, as well as time to peak force and half-relaxation time (KO: n = 10/WT: n = 7; all p > 0.05) (Table). CONCLUSION: HCDs absence did not affect exercise capacity, force generation, fatigability, and the in vitro buffering capacity, indicating that carnosine and anserine are not essential for pH regulation or muscle function. Supported by FAPESP and CAPES