Tensin 2-deficient nephropathy: mechanosensitive nephropathy, genetic susceptibility.

Tensin 2 (TNS2), a focal adhesion protein, is considered to anchor focal adhesion proteins to β integrin as an integrin adaptor protein and/or serve as a scaffold to facilitate the interactions of these proteins. In the kidney, TNS2 localizes to the basolateral surface of glomerular epithelial cells, i.e., podocytes. Loss of TNS2 leads to the development of glomerular basement membrane lesions and abnormal accumulation of extracellular matrix in maturing glomeruli during the early postnatal stages. It subsequently results in podocyte foot process effacement, eventually leading to glomerulosclerosis. Histopathological features of the affected glomeruli in the middle stage of the disease include expansion of the mesangial matrix without mesangial cell proliferation. In this review, we provide an overview of TNS2-deficient nephropathy and discuss the potential mechanism underlying this mechanosensitive nephropathy, which may be applicable to other glomerulonephropathies, such as CD151-deficient nephropathy and Alport syndrome. The onset of TNS2-deficient nephropathy strictly depends on the genetic background, indicating the presence of critical modifier genes. A better understanding of molecular mechanisms of mechanosensitive nephropathy may open new avenues for the management of patients with glomerulonephropathies.

Introduction

Tensin 2 (TNS2, also known as TENC1 or C1-TEN) and its family members, including tensin 1 (TNS1), tensin 3 (TNS3), and tensin 4 (TNS4), are focal adhesion proteins present in mammals [1, 2]. Focal adhesion proteins are multiprotein complexes consisting of the membrane receptors integrins as pivotal components. They connect the extracellular matrix (ECM) and cytoskeleton [3, 4]. Among focal adhesions, multiple reciprocal protein interactions (such as binding of cofactors or ligands, phosphorylation, and mechanical tension) orchestrate the signal transductions that regulate various cellular events, such as cytoskeletal rearrangement, cell proliferation, cell migration, cell death, cell differentiation, and gene expression [5,6,7,8,9]. A characteristic feature of the TNS protein structure is C-terminal tandem Src homology 2 (SH2)–phosphotyrosine-binding (PTB) domains, which allow TNS proteins to bind to membrane lipids, including phosphatidylinositol (3,4,5)-triphosphate (PIP3) [10,11,12], the cytoplasmic tails of β integrins [13,14,15,16], and other focal adhesion proteins, such as p130Cas (also known as BCAR1), focal adhesion kinase (FAK, also known as PTK2) [17, 18], integrin-linked kinase (ILK) [18], and deleted in liver cancer 1 (DLC1) [19,20,21,22]. These binding potentials indicate that TNS proteins can anchor focal adhesion proteins to β integrin as integrin adaptor proteins and/or serve as a scaffold to facilitate the interactions of these proteins. As expected, similar to other focal adhesion proteins, TNS deficits can perturb focal adhesion interactions or the regulation of integrin-mediated cellular physiology, such as adhesion, migration, and proliferation, and can have severe pathological effects [1, 2]. In the case of human diseases, genetic associations of focal adhesion genes have been most prevalently identified in cancers, followed by cardiovascular diseases [23]. For example, compared with healthy tissues, TNS2 was found to be downregulated in colorectal cancer (CRC) tissues [24]. Knockdown of TNS2 increased the proliferation and migration of CRC cell lines with high TNS2 expression, whereas overexpression of mouse Tns2 decreased the proliferation and migration of CRC cell lines with low TNS2 expression [25]. TNS2 deficiency was found to promote polyp formation in Apc mice, a model of human familial adenomatous polyposis [25].

Overview of TNS2-deficient Nephropathy

In 2018, whole-exome sequencing and high-throughput exon sequencing for multiple cases with nephrotic syndrome revealed missense mutations in TNS2 as recessive causative mutations for nephropathy [26]. A Tns2 nonsense mutation (c.1546_1553del, p.Ser516Alafs*19, designated Tns2), which acts as the equivalent of a null allele, was identified as the recessive causative mutation for proteinuria in an ICGN mouse, a model of chronic kidney disease (CKD), by quantitative trait locus (QTL) analysis and subsequent nucleotide sequencing [27]. This genetic liability was evidenced by the phenotype of the genetically modified mouse: it carried a nonsense mutation in TNS2 that resulted in the partial loss of SH2–PTB domains [28].

TNS2 localization in the kidney

According to a microarray dataset of diverse cell types and tissues from adult mice (BioGPS accession number MOE430) [29], Tns2 mRNA is predominantly expressed in the lungs, followed by the heart, kidney, liver, adipose tissues, skeletal muscles, and diverse gland tissues. At the translational level, TNS2 is predominantly expressed in the glomerulus, according to the Human Protein Atlas (http://www.proteinatlas.org) [30]. The glomerulus, which is a spheroid capillary tuft located in the renal cortex, is the first segment of the nephron, where primary urine is produced by filtering the blood. It contains three cell types: glomerular endothelial cells, glomerular stromal cells (called mesangial cells), and glomerular epithelial cells (called podocytes). Podocytes are highly differentiated cells that have thick arms, major processes, and numerous subsequent projections or foot processes [31]. The glomerular basement membrane (GBM) is a specialized ECM that forms the capillary wall, while offering an epithelial basement membrane to podocytes (Fig. 1). The interdigitated foot processes of podocytes completely overlay the GBM and form membrane-like intercellular junctions, known as slit diaphragms [31]. In the glomeruli, TNS2 expression seems to be specific for podocytes (according to the Human Protein Atlas) [27, 32], but there is conflicting evidence regarding its expression in the mesangial cells [33]. TNS2 localizes to the basolateral surface of podocytes [32], where ECM receptors, including integrins, connect the GBM.

Fig. 1.

Transmission electron microscopic image of the glomerulus from an adult mouse. Glomerular endothelial cells (Endo) are specialized fenestrated cells that line the capillaries. The glomerular basement membrane (GBM) serves as a structural scaffold for the capillaries. Mesangial cells (Me) also support the capillaries. Podocytes (Pod) reside in Bowman’s space, and their interdigitated foot processes (FP) cover the epithelial side of the GBM.

Pathology

In Tns2-null mutant mice, no significant lesions have been reported in the perinatal kidney containing mature and immature glomeruli, the development stages of which can be morphologically classified as follows: S-shaped body, capillary loop, and maturing [32]. However, Tns2-null mutant glomeruli have been reported to form more numerous and larger GBM outpockets projecting toward the epithelial side in the maturation stage than wild-type glomeruli. These outpockets expand in the mutant glomeruli after birth, whereas they disappear in wild-type mature glomeruli [32, 34]. In the early postnatal stage, Tns2-null mutant mice have been reported to develop GBM lesions, forming a thick, multilayered pattern (known as lamellation) and a basket weave pattern (known as splitting), in addition to nonphysiological outpocketing [32, 34,35,36]. This abnormal ECM accumulation is followed by podocyte foot process alteration with the disappearance of the slit diaphragm, called effacement, which corresponds to a defect in glomerular filtration, resulting in proteinuria [34, 37, 38]. In contrast, glomerular endothelial cells exhibit normal development. Abnormal GBM materials are considered to be secreted from podocytes and not from endothelial cells [34]. Histopathological features of the affected glomeruli in the middle stage of the disease include expansion of the mesangial matrix without mesangial cell proliferation [35, 37, 39, 40]. This accumulation of mesangial matrix is thought to be caused by the phenotypic change in mesangial cells, which is accompanied by an increase in the expression of α-smooth muscle actin (α-SMA), and is slightly abrogated by prednisolone treatment [37]. The phenotypic change in mesangial cells may be induced by abnormal GBM materials because the formation of GBM lesions is followed by the appearance of α-SMA-positive mesangial cells. At the terminal stage, mesangial expansion progresses to the extent that it obliterates the glomerular capillaries, resulting in podocytopenia and glomerulosclerosis [35, 38]. After disruption of the glomerular filtration barrier, affected mice can develop tubulointerstitial injury, renal fibrosis, and eventually, end-stage renal disease, in accordance with the CKD progression pattern [40,41,42].

In humans, the severity of glomerular injury in patients with missense mutations in TNS2 probably varies according to the genetic background. In one study, three patients were diagnosed with minimal change nephrotic syndrome (MCNS), one was diagnosed with diffuse mesangial sclerosis (DMS), and one was diagnosed with focal segmental glomerulosclerosis (FSGS) [26]. This genetic susceptibility is discussed in a later section.

Potential Mechanism Underlying TNS2-deficient Nephropathy

The involvement of TNS2 in integrin signaling in podocytes is supported by its binding to integrin β1 in glomeruli [43] and by its localization in podocytes in vivo and in podocyte cell lines, which display a basolateral and peripheral dotted distribution pattern typical of a focal adhesion protein [26, 32, 44]. Furthermore, loss of the SH2–PTB domains in TNS2 impairs its ability to localize to focal adhesions and leads to the formation of glomerular lesions similar to those formed in Tns2-null mutant mice [44]. On the other hand, loss of the endogenous enzymatic activity of the protein tyrosine phosphatase (PTP) domain in TNS2, which catalyzes the dephosphorylation of phosphotyrosyl proteins, does not contribute to TNS2-deficient nephropathy [44]. These results indicate that the impairment of the TNS2-binding action of focal adhesions is the cause of TNS2-deficient nephropathy. As the binding potentials of the SH2–PTB domains indicate that TNS2 functions as an integrin adaptor protein and/or serves as a scaffold for other focal adhesion proteins, as mentioned above, an attractive hypothesis is that TNS2 deficiency perturbs multiple focal adhesion protein interactions that orchestrate the integrin signal transductions related to podocyte homeostasis. Podocyte-specific defects in either integrins (α3, β1) or integrin-binding molecules, such as CD151, ILK, and talin1, have been reported to result in nephrotic syndrome in murine models [45,46,47,48,49].

Adenovirus-mediated TNS2 overexpression also induces podocyte dysfunction in a manner that depends on PTP activity [50]. Overexpression of TNS2, which is observed in the glomeruli in diabetic nephropathy (DN) models, activates the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway in podocytes through its PTP activity toward nephrin, a principal podocyte slit diaphragm component [50]. This mTORC1 activation is associated with podocyte dysfunction in DN [51, 52].

Mechanosensitive nephropathy

Interestingly, in Tns2-null mutant mice, the glomeruli located in the inner renal cortex have been reported to exhibit only mild GBM thickening, while those located in the outer renal cortex have been reported to exhibit rapidly progressive lesions after birth [32]. This difference has been attributed to the difference in developmental maturity of the glomeruli at birth. At birth, the glomeruli located in the outer renal cortex are still maturing, while those in the inner renal cortex are already mature without obvious lesions [32]. These findings indicate that TNS2 deficiency impacts podocyte development ex utero but not in utero. The biomechanical stress on podocytes substantially differs between these two conditions. Fetal kidneys are characterized by very low blood flow and high vascular resistance. After birth, glomerular hydraulic pressure rapidly rises because of a sharp decrease in renal vascular resistance, followed by an increase in intrarenal blood flow [53].

Cells can sense and respond to the biophysical properties of the extracellular milieu through integrin-based adhesion, including focal adhesion, via a process called mechanotransduction. Mechanical force allosterically alters the conformations of mechanosensitive proteins, including integrins, within adhesions to elicit biochemical signals that regulate cellular mechanics and gene expression levels [54,55,56]. These mechanical transmissions are influenced by the resting tension level inside the cell, which is built by the cytoskeletal network [57]. Assuming that TNS2 plays a role in mechanotransduction in podocytes, it is not surprising that the impact of TNS2 deficiency differs depending on the maturity of podocytes, which are highly differentiated cells with an intricate cytoskeletal architecture. ECM remodeling is a major target for mechanoresponsive pathways [54, 58]. In general, mechanical stress facilitates FAK activation [59,60,61,62]. In TNS2-deficient nephropathy, abnormal accumulation of ECM in the GBM is the first abnormality observed in the early postnatal stage, as mentioned above. In addition, FAK activation in glomeruli is one of the molecular characteristics of its pathology [43, 63]. These findings suggest that TNS2 confers mechanical robustness to podocytes; in other words, it elevates the threshold for mechanosensitivity.

The idea that impaired mechanical adjustment of podocytes to biomechanical stress can lead to podocyte alteration is supported by the phenotype of podocyte-specific talin 1-knockout mice [45]. Talin 1 is a mechanosensitive protein that directly links integrins to the actin cytoskeleton [64, 65]. Similar to TNS2, loss of talin 1 in podocytes leads to GBM splitting and thickening, foot process effacement, and mesangial expansion (without mesangial cell proliferation) after birth [45]. Similar pathological features have been commonly reported in mice with podocyte-specific deletion of CD151 [47, 66]. CD151 interacts with laminin-binding integrins (such as integrin α3β1), and involved in the cellular mechanics [67, 68]. In contrast, podocyte-specific deletion of either subunit of integrin α3β1, which is a major type in podocytes [69], leads to prenatal or perinatal foot process effacement, followed by postnatal GBM thickening; however, it does not lead to obvious mesangial expansion [46, 47]. The absence of CD151 reduces the ability of integrin α3β1 to bind to laminin α5β2γ1 [70], a major ligand for integrin α3β1 and a core component of the GBM [71, 72]. Intraglomerular pressure markedly influences the glomerular pathology in CD151-knockout mice [73]. TNS2 deficiency also reduces the adhesion of primary cultured podocytes to laminins [32]. As ECM–integrin binding is bidirectionally involved in mechanotransduction [54, 56, 74], it is reasonable that defects in laminin binding are linked to mechanical stress in podocytes. These data indicate that at least two levels of regulation are involved in integrin-mediated podocyte homeostasis: mechanotransduction (including laminin binding) and differentiation. Laminin β2 chain deficiency itself causes Pierson syndrome, characterized by congenital nephrotic syndrome with DMS, in addition to distinct ocular abnormalities [75, 76]. Mice with a mutation in the laminin β2 chain have been reported to exhibit proteinuria before foot process effacement, likely due to increased GBM permeability [77, 78]. Subsequent foot process effacement is considered to be caused by the exposure of podocytes to high plasma protein concentrations [77].

The GBM is composed of four major components: laminin, collagen IV, heparan sulfate proteoglycan, and nidogen [71, 72]. Laminin α5β2γ1 trimers, a major isoform of GBM laminin, are secreted by both podocytes and endothelial cells [79]. They polymerize to form separate networks at each edge of the GBM [80]. Unlike other collagens, collagen IV is detected only in the basement membrane and consists of six genetically distinct α-chains, designated α1(IV) to α6(IV). The chains assemble into only three types of heterotrimers: α1α1α2(IV), α3α4α5(IV), and α5α5α6(IV) [81]. The GBM contains two distinct collagen IV networks. It mainly contains α3α4α5(IV) and marginally contains α1α1α2(IV) [82]. The collagen α3α4α5(IV) network is solely formed by podocytes [83] and is present at the center of the GBM, whereas the α1α1α2(IV) network is localized on the endothelial side of the GBM [80, 82]. Mutations in genes encoding α3(IV), α4(IV), or α5(IV) result in defects in the assembly of the collagen α3α4α5(IV) network and cause Alport syndrome, characterized by glomerulonephropathy and deafness [84, 85]. In Alport syndrome, the collagen α1α1α2(IV) network expands toward the podocyte side of the GBM [80, 82]. Experimental data suggest at least two levels of regulation are involved in the initiation of Alport syndrome: stimulation of collagen receptors (primarily integrin α1β1) by the compensated expansion of the collagen α1α1α2(IV) network [86,87,88] and biomechanical strain associated with abnormalities in the GBM [89,90,91] (reviewed by Funk, Lin, and Miner [92] and Chew and Lennon [93]). Either form of stimulation can induce a phenotypic change in podocytes, including the expression of genes associated with the ECM and matrix metallopeptidases (MMPs). Ectopic laminin α2 accumulation is observed in the affected GBM in patients and animals with Alport syndrome [94, 95] and is considered to be a key initiator of the pathologies [96]. This deposition of laminin α2 promotes the invasion of mesangial cells into the glomerular capillaries [96] and elevates the expression of MMPs, such as MMP-10 and MMP-12, via FAK activation [95]. Both MMP-10 and MMP-12 play a critical role in the progression of Alport syndrome [97, 98]. In particular, MMP-10 is upregulated in the podocytes of various murine models and patients with nephrotic syndromes, including DN, FSGS, and IgA nephropathy (IgAN), and is considered to be a key mediator of foot process effacement [97]. The upregulation of MMP-10 has also been reported in the podocytes of CD151-knockout mice [99] and Tns2-null mutant mice (our unpublished data). Experimental data suggest that MMP-10 leads to podocyte injury through the proteolytic degradation of the podocyte tight junction protein zonula occludens-1 (ZO-1) [97]. On the other hand, MMP-12 can activate other MMPs (such as MMP-2 and MMP-3) through the proteolytic process [100]. To our knowledge, although there is no direct evidence that MMP-12 can activate MMP-10, based on the similarity between the protein structures of MMP-3 and MMP-10 [101], MMP-12 seems to have the ability to directly activate MMP-10. Ultimately, variations in the pathologies of glomerular injury leading to foot process effacement can be attributed to differences in pathways for upregulating MMP-10.

In this respect, laminin α2 deposition in the glomeruli is a characteristic of Alport syndrome but is usually undetectable in other human CKDs, such as DN, MCNS, FSGS, IgAN, membranoproliferative glomerulonephritis type I, and membranous nephropathy [94]. In addition, FAK activation is not common in glomerulonephropathy [102]. Interestingly, both alterations are also observed in CD151-knockout mice [95, 96] and Tns2-null mutant mice [32, 43]. Furthermore, similar to Alport mice, Tns2-null mutant mice show MMP-12 upregulation in podocytes [103]. These data indicate that the laminin α2/FAK/MMP-12/MMP-10 pathway is common in these nephropathies. Based on the abovementioned hypothesis, this occurs because these nephropathies share a common mechanism wherein biomechanical stress in podocytes induces ectopic laminin α2 accumulation (Fig. 2). Histopathologically, TNS2-deficient nephropathy resembles Alport syndrome, except for mesangial cell proliferation. In Alport syndrome, mesangial expansion is accompanied by mesangial cell proliferation [106]. This dissimilarity can be attributed to collagen α1α1α2(IV)-mediated signaling unique to Alport syndrome.

Fig. 2.

A hypothetical model in which mechanical stress leads to foot process effacement in mechanosensitive nephropathy. (1) Loss of integrin-binding focal adhesion proteins, such as tensin 2 (TNS2), CD151, and talin 1, elevates the mechanosensitivity of podocytes. (2) Intraglomerular hydraulic pressure results in biomechanical strain in podocytes. The level of intraglomerular hydraulic pressure is elevated at birth or in the case of hypertension. (3) Highly mechanosensitive podocytes respond to biomechanical strain and trigger abnormal mechanotransduction, resulting in the ectopic expression of the extracellular matrix (ECM) and subsequently causing glomerular basement membrane (GBM) thickening. (4) Accumulated laminin α2 triggers integrin signaling, resulting in an increase in the expression of MMPs, such as matrix metallopeptidase (MMP)-10 and MMP-12, via focal adhesion kinase (FAK) activation. (5) MMP-12 is autolytically processed into an activated form [104, 105]. (6) Active MMP-12 directly activates MMP-10. (7) Active MMP-10 degrades the podocyte tight junction protein zonula occludens-1 (ZO-1), leading to foot process effacement.

Genetic Susceptibility to TNS2-deficient Nephropathy

Tns2-null mutant mice develop glomerular disease in a strain-dependent manner. TNS2 deficiency induces GBM lesions and podocyte foot process effacement and subsequently causes glomerular and tubulointerstitial injuries in the ICGN (the original strain possessing the Tns2 mutation), FVB/N (FVB), and DBA/2J (D2) strains [27, 63, 107]; however, it causes only modest GBM thickening in the C57BL/6J (B6) and 129/SvJcl strains [43, 108, 109]. The MSM strain is unaffected by TNS2 deficiency [27]. Similar strain-dependent disparities have been reported in CD151-deficient nephropathy [66, 110, 111]. Interestingly, similar to TNS2 deficiency, CD151 deficiency induces glomerular injuries in an FVB genetic background but not in a B6 genetic background [66]. In Alport syndrome, the rates of progression vary depending on the murine strains. Although Alport mice with a B6 genetic background develop progressive glomerular disease, the progression is slower than that in other strains [112,113,114,115]. These strain-dependent disparities strongly indicate the presence of modifier genes. In addition, a B6 genetic background is almost completely resistant to TNS2- or CD151-deficient nephropathy but is partially resistant to Alport syndrome. Therefore, based on the abovementioned hypothesis, these modifier genes are likely involved in biomechanical stress-mediated laminin α2 deposition in the glomeruli.

Modifier genes

QTL and congenic analyses using resistant B6 and susceptible ICGN mice previously revealed a modifier locus associated with glomerular injury caused by TNS2 deficiency, designated Tpir, on chromosome 2 [116, 117]. Introduction of the B6 allele of Tpir into ICGN mice can alleviate glomerular injury and albuminuria. However, the degree of improvement has been reported to be inferior to that noted in a B6 genetic background itself, wherein no podocyte alteration occurs [116]. This result indicates that Tpir is a minor modifier gene and is not involved in the fundamental step of the pathogenesis. This finding can be attributed to the fact that this genetic analysis focused on the severity of CKD and evaluated the traits related to the late phase of CKD, such as tubulointerstitial injury and renal anemia [117]. The histopathological glomerular injury score optimized for TNS2-deficient nephropathy, characterized by mesangial expansion, is a quantitative trait associated with Tpir. Symptoms of early glomerular injury, such as GBM thickening, can be evaluated using this glomerular injury score; however, in the later phase, the extent of mesangial expansion usually accounts for the largest part in this quantitative assessment. Mesangial expansion eventually disrupts the glomerular structure, and its extent generally correlates with the glomerular filtration rate (GFR) [118]. Therefore, Tpir may modify mesangial expansion. To determine the major modifier genes involved in the fundamental step of the pathogenesis, a genome-wide linkage analysis of Tns2-deficient backcrosses with resistant B6 and susceptible FVB genetic backgrounds was performed in a previous study [119]. In this genetic analysis, N2 backcross mice were phenotyped by assessing the urinary albumin level corresponding to their foot process effacement and not by assessing the amount of urinary albumin excreted, which can be modified by various factors. A marker–trait association test detected significant and suggestive modifier loci designated Tpir2 and Tpir1 were detected on chromosomes 10 and 2, respectively [119]. As the peak marker of Tpir1 is included in Tpir (57.65–78.72 cM), Tpir1 is considered to be identical to Tpir.

Tpir2

Tpir2 is a major modifier locus that may influence the fundamental step of the pathogenesis in TNS2-deficient nephropathy. Notably, the genetic loci associated with urinary albumin excretion in patients with essential hypertension (human 12q23.2 and 19p13.3) [120] reside within the syntenic regions of Tpir2 [119]. From the point of view of cellular mechanics, situations in which podocytes are subjected to biomechanical stress may be common between hypertension and TNS2 deficiency. Hypertension hydraulically loads mechanical strain on podocytes, whereas TNS2 deficiency may make podocytes susceptible to mechanical stress. Amino acid sequence variations between FVB and B6 in the proximity of the peak marker of Tpir2 are shown in Table 1. Here, we focus on the candidate gene Stab2, which resides in proximity to Pah, the peak marker of the human genetic locus for proteinuria in patients with hypertension [120]. Stab2 encodes the primary scavenger receptor for systemic hyaluronan (also known as hyaluronic acid, HA) [122]. STAB2 dysfunction results in a large increase in circulating HA [123, 124]. Although no data are available regarding the metabolism of HA in FVB mice, interestingly, susceptible D2 mice exhibit 10 times higher concentrations of plasma HA than B6 or 129S6 mice because of the ectopic expression of Stab2 triggered by an intracisternal A particle element [125, 126]. Furthermore, TNS2 deficiency can be dominantly inherited in STAB2-knockout mice with an FVB genetic background (our unpublished data). These data suggest that an increased level of systemic HA strongly modifies TNS2-deficient nephropathy; however, whether Stab2 is a causative gene for Tpir2 remains unknown. The biological functions of HA have been studied in nephrological research on inflammation and fibrosis (reviewed by Kaul et al. [127]). However, the direct effects of HA on podocytes remain unknown. On the other hand, pulmonary artery smooth muscle cells have been reported to exhibit changes in terms of cell stiffness, cell proliferation, and cell motility when exposed to HA fragments [128]. Thus, HA has the potential to alter the cellular mechanics of podocytes.

Table 1.

Amino acid sequence variations between FVB/N (FVB) and C57BL/6J (B6) in the proximity of the peak marker of Tpir2 (10:76.0–88.7 Mbp)

Chr	Position (bp)	SNP	B6	FVB	Gene	Transcript	Change type	Mutation
10	81643563	rs255887930	T	TGCAGAGGCGGAG	Ankrd24	NM_027480	Inframe indel	A786_E789dup
10	82226062	rs29382863	A	T	Zfp938	NM_001105557	Non-synonymous	D241E
10	82226120	rs29331622	C	T	Zfp938	NM_001105557	Non-synonymous	C222Y
10	82282677	rs29383954	T	C	LOC102635990	XM_006514360	Non-synonymous	K4833R
10	82284600	rs47061592	G	C	LOC102635990	XM_006514360	Non-synonymous	S4192C
10	82284880	rs47781362	T	C	LOC102635990	XM_006514360	Non-synonymous	I4099V
10	82285470	rs251725877	TCAG	T	LOC102635990	XM_006514360	Inframe indel	T3901_E3902delinsK
10	82285510	rs29340367	A	G	LOC102635990	XM_006514360	Non-synonymous	S3889P
10	82287454	rs29350159	C	T	LOC102635990	XM_006514360	Non-synonymous	A3241T
10	82289581	rs29327471	T	C	LOC102635990	XM_006514360	Non-synonymous	T2532A
10	82289593	rs29349975	T	C	LOC102635990	XM_006514360	Non-synonymous	I2528V
10	82290994	rs224869780	T	TTGTCAT	LOC102635990	XM_006514360	Inframe indel	S2060_F2061insMT
10	82291375	rs29339242	T	C	LOC102635990	XM_006514360	Non-synonymous	M1934V
10	82292155	rs50412724	G	A	LOC102635990	XM_006514360	Non-synonymous	P1674S
10	82293640	rs29348544	A	T	LOC102635990	XM_006514360	Non-synonymous	S1179T
10	82294805	rs29337081	T	G	LOC102635990	XM_006514360	Non-synonymous	R790S
10	82295226	rs29370034	C	T	LOC102635990	XM_006514360	Non-synonymous	R650K
10	82295391	rs29328221	C	T	LOC102635990	XM_006514360	Non-synonymous	R595K
10	82492194	rs47627276	G	T	Gm1553	NM_001255990	Non-synonymous	L60M
10	82638847	rs49510163	A	C	Tdg	NM_011561	Non-synonymous	E33A
10	82638847	rs49510163	A	C	Tdg	NM_172552	Non-synonymous	E57A
10	82647345	rs47249452	G	A	Tdg	NM_011561	Non-synonymous	A293T
10	82647347	rs49056941	G	C	Tdg	NM_011561	Non-synonymous
10	82647345	rs47249452	G	A	Tdg	NM_172552	Non-synonymous	A317T
10	82647347	rs49056941	G	C	Tdg	NM_172552	Non-synonymous
10	82648610	rs47946519	G	A	Tdg	NM_011561	Non-synonymous	A362T
10	82648610	rs47946519	G	A	Tdg	NM_172552	Non-synonymous	A386T
10	82648616	rs47182293	A	G	Tdg	NM_011561	Non-synonymous	S364G
10	82648616	rs47182293	A	G	Tdg	NM_172552	Non-synonymous	S388G
10	82670307	rs29334621	T	C	Glt8d2	NM_029102	Non-synonymous	H30R
10	83508124	rs13480674	A	G	Aldh1l2	NM_153543	Non-synonymous	Y476H
10	85388329	rs29382636	T	C	Btbd11	NM_028709	Non-synonymous	V334A
10	86294645	rs264253067	AA	-	Syn3	NM_001164495	Frameshift	F238Yfs*14
10	86467097	rs30199006	C	T	Syn3	NM_001164495	Non-synonymous	G65S
10	86467097	rs30199006	C	T	Syn3	NM_013722	Non-synonymous	G65S
10	86539954	rs265230719	C	A	Gm6729	NM_001384224	Non-synonymous	A461S
10	86539981	rs387036780	G	C	Gm6729	NM_001384224	Non-synonymous	L452V
10	86541308	rs259617967	T	G	Gm6729	NM_001384224	Non-synonymous	R9S
10	86541328	rs216762171	T	G	Gm6729	NM_001384224	Non-synonymous	S3R
10	86655945	rs220212569	A	T	Gm5174	NM_001384216	Non-synonymous	S3C
10	86656626	rs30217026	T	A	Gm5174	NM_001384216	Non-synonymous	Y230N
10	86656805	rs29377958	G	T	Gm5174	NM_001384216	Non-synonymous	E289D
10	86656930	rs386949678	T	C	Gm5174	NM_001384216	Non-synonymous	V331A
10	86657064	rs387395855	C	T	Gm5174	NM_001384216	Non-synonymous	L376F
10	86691704	rs250907279	G	C	Hsp90b1	NM_011631	Non-synonymous	D769E
10	86731086	rs30231257	G	A	Ttc41	NM_001003910, NM_153595	Non-synonymous	A539T
10	86776504	rs6412755	G	C	Ttc41	NM_001003910	Non-synonymous	A1214P
10	86776652	rs6152391	T	C	Ttc41	NM_001003910	Non-synonymous	L1263P
10	86776664	rs6152415	T	C	Ttc41	NM_001003910	Non-synonymous	V1267A
10	86779206	rs231797092	T	G	Nt5dc3	NM_175331	Non-synonymous	S33A
10	86779267	rs216734988	G	A	Nt5dc3	NM_175331	Non-synonymous	S53N
10	86848120	rs253335427	C	T	Stab2	NM_138673	Non-synonymous	V2392I
10	86850628	rs252154668	C	T	Stab2	NM_138673	Non-synonymous	D2313N
10	86850851	rs249686084	A	C	Stab2	NM_138673	Non-synonymous	I2276M
10	86858183	rs30231575	T	C	Stab2	NM_138673	Non-synonymous	M2065V
10	86865017	rs30230495	C	T	Stab2	NM_138673	Non-synonymous	R1917K
10	86872653	rs30236399	C	T	Stab2	NM_138673	Non-synonymous	V1683M
10	86872728	rs30236402	T	C	Stab2	NM_138673	Non-synonymous	K1658E
10	86873894	rs30238216	T	C	Stab2	NM_138673	Non-synonymous	Q1629R
10	86897981	rs211832720	T	C	Stab2	NM_138673	Non-synonymous	I1326V
10	86905631	rs29367139	T	C	Stab2	NM_138673	Non-synonymous	Q1208R
10	86933327	rs30245789	C	T	Stab2	NM_138673	Non-synonymous	S921N
10	86938052	rs30245017	A	G	Stab2	NM_138673	Non-synonymous	I805T
10	86969772	rs30243498	T	C	Stab2	NM_138673	Non-synonymous	K237E
10	86979990	rs30242264	C	T	Stab2	NM_138673	Non-synonymous	R151H
10	87165105	rs30247300	C	T	1700113H08Rik	NM_029685	Non-synonymous	T53M
10	87225901	rs30252317	T	A	1700113H08Rik	NM_029685	Non-synonymous	M71K
10	87226012	rs214268401	C	T	1700113H08Rik	NM_029685	Non-synonymous	S108L
10	88091308	rs49617371	G	A	Pmch	NM_029971	Non-synonymous	V58I
10	88093169	rs48863032	C	T	Parpbp	NM_029249	Non-synonymous	V470I
10	88133128	rs29314114	T	G	Parpbp	NM_029249	Non-synonymous	E152A
10	88245799	rs387426886	G	A	Washc3	NM_026070	Non-synonymous	V182I
10	88245799	rs387426886	G	A	Washc3	NM_001122960	Non-synonymous	V181I

Single nucleotide polymorphism (SNP) and indel data are from the Mouse Phenome Database (RRIDSCR_003212) [121]. Position data are based on Mus musculus genome assembly GRCm38 (mm10). Chr, chromosome.

Conclusion

TNS2-deficient nephropathy resembles podocyte-specific CD151- or talin 1-deficient nephropathy in that its pathology is characterized by early postnatal GBM thickening, foot process effacement, and mesangial expansion. These three integrin-binding focal adhesion proteins do not seem to be involved in podocyte differentiation; however, they seem to be involved in podocyte mechanics. A deficiency of either molecule may elevate the mechanosensitivity of podocytes, which can give rise to abnormal mechanotransduction in response to normal biomechanical strain. A similar mechanism seems to partially underlie Alport syndrome. Indeed, these nephropathies share common molecular pathologies, such as laminin α2 deposition and FAK activation in the glomeruli, which are not commonly observed in other glomerulonephropathies. Finally, we postulate that TNS2 deficiency promotes mechanical stress-induced activation of the laminin α2/FAK/MMP-12/MMP-10 axis and that MMP-10 activation eventually leads to podocyte foot process effacement. The strict strain-dependent onset of TNS2-deficient nephropathy may be attributed to modifier genes that can alter podocyte mechanics.