Loss of LMOD1 impairs smooth muscle cytocontractility and causes megacystis microcolon intestinal hypoperistalsis syndrome in humans and mice

Abstract

Megacystis microcolon intestinal hypoperistalsis syndrome (MMIHS) is a congenital visceral myopathy characterized by severe dilation of the urinary bladder and defective intestinal motility. The genetic basis of MMIHS has been ascribed to spontaneous and autosomal dominant mutations in actin gamma 2 (ACTG2), a smooth muscle contractile gene. However, evidence suggesting a recessive origin of the disease also exists. Using combined homozygosity mapping and whole exome sequencing, a genetically isolated family was found to carry a premature termination codon in Leiomodin1 (LMOD1), a gene preferentially expressed in vascular and visceral smooth muscle cells. Parents heterozygous for the mutation exhibited no abnormalities, but a child homozygous for the premature termination codon displayed symptoms consistent with MMIHS. We used CRISPR-Cas9 (CRISPR-associated protein) genome editing of Lmod1 to generate a similar premature termination codon. Mice homozygous for the mutation showed loss of LMOD1 protein and pathology consistent with MMIHS, including late gestation expansion of the bladder, hydronephrosis, and rapid demise after parturition. Loss of LMOD1 resulted in a reduction of filamentous actin, elongated cytoskeletal dense bodies, and impaired intestinal smooth muscle contractility. These results define LMOD1 as a disease gene for MMIHS and suggest its role in establishing normal smooth muscle cytoskeletal–contractile coupling.

Tropomodulins and Leiomodins: Actin Pointed End Caps and Nucleators in Muscles

“…Patients with mutations in the LMOD1 gene leading to the absence of Lmod1, and a Lmod1À/À mouse model, develop megacystis microcolon intestinal hypoperistalsis syndrome, caused by hypocontractility of bladder and intestinal smooth muscle that leads to functional obstruction of the urinary bladder and intestine (Table 1) (21). MMIHS appears to be a congenital disease due to defective smooth muscle contractility, because sporadic mutations in smooth muscle actin ACTG2 are among the most frequent causes of this syndrome (91), and at least one patient with a nonsense mutation in smooth muscle myosin MYH11 has also been reported (92).…”

“…MMIHS appears to be a congenital disease due to defective smooth muscle contractility, because sporadic mutations in smooth muscle actin ACTG2 are among the most frequent causes of this syndrome (91), and at least one patient with a nonsense mutation in smooth muscle myosin MYH11 has also been reported (92). Although Lmod1 is abundant in both vascular and visceral smooth muscles (21,(25)(26)(27), Lmod1À/À mice exhibit pathological thinning and compaction of visceral (stomach, bladder, intestine), but surprisingly, not vascular (aorta, esophagus) smooth muscles (21). siRNA knockdown of Lmod1 in isolated intestinal smooth muscle cells results in decreased contractility, indicating that functional defects in vivo are intrinsic to smooth muscle cells.…”

“…Interest in this family of proteins has increased dramatically, owing to recent discoveries linking the expression of Lmod2 and Lmod3, respectively, to dilated cardiomyopathy (11,12) and nemaline myopathy (13,14,(16)(17)(18). Lmod1, on the other hand, has been linked to autoimmune disorders (19,20), and a recent study finds that its deficiency impairs smooth muscle cytocontractility and causes megacystis microcolon intestinal hypoperistalsis syndrome (MMIHS) in humans and mice (21).…”

Recurrent arginine substitutions in the ACTG2 gene are the primary driver of disease burden and severity in visceral myopathy

“…Autosomal recessive forms of MMIHS are caused by biallelic loss‐of‐function variants in other proteins involved in actin–myosin interactions: MYH11 (myosin‐heavy chain; Gauthier et al, ), MYLK (myosin‐light chain kinase; Halim, Brosens, et al, ), LMOD1 (leiomodin 1, an actin‐binding protein expressed primarily in vascular and visceral smooth muscle; Halim, Wilson, et al, ) and MYL9 (regulatory myosin‐light chain; Moreno et al, ). Other genes that are implicated in intestinal hypoperistalsis, but usually with other distinguishing phenotypic features include genes causing mitochondrial disorders ( TYMP and POLG ); EDNRB, EDN3 , and SOX10 associated with Waardenburg syndrome with Hirschsprung disease; SGOL1 , RAD21 , FLNA , and L1CAM .…”

Cardiac leiomodin2 binds to the sides of actin filaments and regulates the ATPase activity of myosin

“…Lmods are expressed in different muscle tissues [3]. Lmod1 can be found in smooth muscle [4, 5] and was recently reported as a megacyst microcolon intestinal hypoperistaltis syndrome (MMIHS) disease gene in humans and mice [6]. Transcripts encoding the LMOD2 gene are present in fetal and adult heart and also in adult skeletal muscle [7–9].…”