Unexpected dependence of RyR1 splice variant expression in human lower limb muscles on fiber-type composition

Abstract

The skeletal muscle ryanodine receptor Ca(2+) release channel (RyR1), essential for excitation-contraction (EC) coupling, demonstrates a known developmentally regulated alternative splicing in the ASI region. We now find unexpectedly that the expression of the splice variants is closely related to fiber type in adult human lower limb muscles. We examined the distribution of myosin heavy chain isoforms and ASI splice variants in gluteus minimus, gluteus medius and vastus medialis from patients aged 45 to 85 years. There was a strong positive correlation between ASI(+)RyR1 and the percentage of type 2 fibers in the muscles (r = 0.725), and a correspondingly strong negative correlation between the percentages of ASI(+)RyR1 and percentage of type 1 fibers. When the type 2 fiber data were separated into type 2X and type 2A, the correlation with ASI(+)RyR1 was stronger in type 2X fibers (r = 0.781) than in type 2A fibers (r = 0.461). There was no significant correlation between age and either fiber-type composition or ASI(+)RyR1/ASI(-)RyR1 ratio. The results suggest that the reduced expression of ASI(-)RyR1 during development may reflect a reduction in type 1 fibers during development. Preferential expression of ASI(-) RyR1, having a higher gain of in Ca(2+) release during EC coupling than ASI(+)RyR1, may compensate for the reduced terminal cisternae volume, fewer junctional contacts and reduced charge movement in type 1 fibers.

A coding and non-coding transcriptomic perspective on the genomics of human metabolic disease

“…( B ) We utilized three clinical cohorts ( n = 282), with varying ranges of chronological age, to examine which ncRNAs were related to insulin sensitivity (IS). Eighty-six long ncRNA associated with IS, the majority (43) being either antisense or lncRNA (Figure 2B, See Supplemental data S3). The vast majority of these were also expressed in adipose and pancreatic cells ( in vitro beta cells, Supplemental data S3) indicating they could influence insulin biology across multiple organs.…”

“…We examined the impact of sexual dimorphism on muscle gene expression, as this has not been reliably assessed before, and found 650 genes with sexual dimorphic gene expression (1%FDR, n = 89 per sex, Supplemental data S9) and this included 15% of the CORE-IS genes. Interestingly, the expression of a type II muscle fiber-type splice-variant (from the RYR1 gene) was lower expressed in women (Supplemental data S9); however, this prototype muscle fiber-type biomarker (43) did not correlate with IS. Thus, with our global transcriptomic methods, a modest relationship between sex, IS and muscle gene expression is detectable; potentially reflecting small differences in fiber-type composition, along with environmental factors, and this may contribute to differences in T2DM risk and disease progression between the genders (122).…”

“…In the present analysis, each probe-set was based on ENSEMBL ENST definitions, and R Bioconductor packages (42) were used to update, assemble and summarize the expression data. We also included an exon specific probe-set, based on a recent observation that the RYR1 gene has one additional variant, which lacks a short 15 bp exon (ENSE00002436759), that correlated with a structural feature of muscle (‘fiber' type) (43). …”

Core skeletal muscle ryanodine receptor calcium release complex

“…47 Mass spectroscopy data confirms a binding site for β 1a within aa3201-3661 (Casarotto, Huber, Dulhunty, unpublished). This region contains the ASI residues, A 3481 GDAQ 3485 that are variably spliced depending on development and fibre-type, 48,49 and impact on the amplitude of the voltage-activated Ca 2+ transient. 50 In addition, the polybasic residues (K 3495 KKRRDGR 3502 ) influence β 1a binding to RyR1 and depolarisation-dependent Ca 2+ release.…”