Atypical expression of circadian clock genes in denervated mouse skeletal muscle

The central circadian clock in the suprachiasmatic nucleus of the hypothalamus synchronizes peripheral clocks through neural and humoral signals in most mammalian tissues. Here, we analyzed the effects of unilateral sciatic denervation on the expression of circadian clock- and clock-controlled genes in the gastrocnemius muscles of mice twice per day on days 0, 3, 7, 9, 11 and 14 after denervation and six times on each of days 7 and 28 after denervation to assess the regulation mechanism of the circadian clock in skeletal muscle. Sciatic denervation did not affect systemic circadian rhythms since core body temperature (Day 7), corticosterone secretion (Days 7 and 28), and hepatic clock gene expression remained intact (Days 7 and 28). Expression levels of most circadian clock-related genes such as <i>Arntl, Per1, Rora, Nr1d1</i> and <i>Dbp</i> were reduced in accordance with the extent of muscle atrophy, although circadian <i>Per2</i> expression was significantly augmented (Day 28). Cosinor analysis revealed that the circadian expression of <i>Arntl</i> (Days 7 and 28) and <i>Dbp</i> (Day 28) was phase advanced in denervated muscle. The mRNA expression of <i>Clock</i> was significantly increased in denervated muscle on Day 3 when the severe atrophy was absent, and it was not affected by atrophic progression for 28 days. Sciatic denervation did not affect the expression of these genes in the contralateral muscle (Days 7 and 28), suggesting that humoral changes were not involved in denervation-induced muscle clock disruption. We then analyzed genome-wide gene expression using microarrays to determine the effects of disrupting the molecular clock in muscle on circadian rhythms at Day 7. Among 478 circadian genes, 313 lost rhythmicity in the denervated muscles. These denervation-sensitive genes included the lipid metabolism-related genes, <i>Nrip1, Bbs1, Ptgis, Acot1, Scd2, Hpgd, Insig1, Dhcr24, Ldlr</i> and <i>Mboat1</i>. Our findings revealed that sciatic denervation disrupts the circadian expression of clock and clock-controlled genes either directly or indirectly via muscle atrophy in the gastrocnemius muscles of mice in a gene-specific manner.